In nbdkit-error-filter we need to parse parameters as probabilities. This is useful enough to add to nbdkit, since we will use it in another filter in future. --- docs/nbdkit-plugin.pod | 19 +++++++ plugins/python/nbdkit-python-plugin.pod | 6 ++ include/nbdkit-common.h | 2 + server/nbdkit.syms | 1 + server/public.c | 37 +++++++++++++ server/test-public.c | 73 +++++++++++++++++++++++++ plugins/ocaml/NBDKit.mli | 11 ++-- plugins/ocaml/NBDKit.ml | 2 + plugins/ocaml/bindings.c | 16 ++++++ plugins/python/modfunctions.c | 21 +++++++ tests/test-python-plugin.py | 12 ++++ tests/test_ocaml_plugin.ml | 1 + 12 files changed, 196 insertions(+), 5 deletions(-) diff --git a/docs/nbdkit-plugin.pod b/docs/nbdkit-plugin.pod index 860c5cecb..e8d30a98e 100644 --- a/docs/nbdkit-plugin.pod +++ b/docs/nbdkit-plugin.pod @@ -1433,6 +1433,25 @@ C<str> can be a string containing a case-insensitive form of various common toggle values. The function returns 0 or 1 if the parse was successful. If there was an error, it returns C<-1>. +=head2 Parsing probabilities + +Use the C<nbdkit_parse_probability> utility function to parse +probabilities. Common formats understood include: C<"0.1">, C<"10%"> +or C<"1:10">, which all mean a probability of 1 in 10. + + int nbdkit_parse_probability (const char *what, const char *str, + double *ret); + +The C<what> parameter is printed in error messages to provide context. +The C<str> parameter is the probability string. + +On success the function returns C<0> and sets C<*ret>. B<Note> that +the probability returned may be outside the range S<[ 0.0..1.0 ]>, for +example if C<str == "200%">. If you want to clamp the result you must +check that yourself. + +On error, nbdkit_error is called and C<-1> is returned. + =head2 Reading passwords The C<nbdkit_read_password> utility function can be used to read diff --git a/plugins/python/nbdkit-python-plugin.pod b/plugins/python/nbdkit-python-plugin.pod index e328cc2e0..0e55dcfcc 100644 --- a/plugins/python/nbdkit-python-plugin.pod +++ b/plugins/python/nbdkit-python-plugin.pod @@ -136,6 +136,12 @@ C<import errno>. Parse a string (such as "100M") into a size in bytes. Wraps the C<nbdkit_parse_size()> C function. +=head3 C<nbdkit.parse_probability(what, str)> + +Parse a string (such as "100%") into a probability, returning a +floating point number. Wraps the C<nbdkit_parse_probability()> C +function. + =head3 C<nbdkit.shutdown()> Request asynchronous server shutdown. diff --git a/include/nbdkit-common.h b/include/nbdkit-common.h index e070245b8..b44e77323 100644 --- a/include/nbdkit-common.h +++ b/include/nbdkit-common.h @@ -105,6 +105,8 @@ NBDKIT_EXTERN_DECL (void, nbdkit_vdebug, NBDKIT_EXTERN_DECL (char *, nbdkit_absolute_path, (const char *path)); NBDKIT_EXTERN_DECL (int64_t, nbdkit_parse_size, (const char *str)); +NBDKIT_EXTERN_DECL (int, nbdkit_parse_probability, + (const char *what, const char *str, double *r)); NBDKIT_EXTERN_DECL (int, nbdkit_parse_bool, (const char *str)); NBDKIT_EXTERN_DECL (int, nbdkit_parse_int, (const char *what, const char *str, int *r)); diff --git a/server/nbdkit.syms b/server/nbdkit.syms index 353ea2a98..c6480e43e 100644 --- a/server/nbdkit.syms +++ b/server/nbdkit.syms @@ -67,6 +67,7 @@ nbdkit_parse_int64_t; nbdkit_parse_int8_t; nbdkit_parse_int; + nbdkit_parse_probability; nbdkit_parse_size; nbdkit_parse_uint16_t; nbdkit_parse_uint32_t; diff --git a/server/public.c b/server/public.c index 71ea6779d..fe2b48c7c 100644 --- a/server/public.c +++ b/server/public.c @@ -421,6 +421,43 @@ nbdkit_parse_size (const char *str) return size * scale; } +NBDKIT_DLL_PUBLIC int +nbdkit_parse_probability (const char *what, const char *str, + double *retp) +{ + double d, d2; + char c; + int n; + + if (sscanf (str, "%lg%[:/]%lg%n", &d, &c, &d2, &n) == 3 && + strcmp (&str[n], "") == 0) { /* N:M or N/M */ + if (d == 0 && d2 == 0) /* 0/0 is OK */ + ; + else if (d2 == 0) /* N/0 is bad */ + goto bad_parse; + else + d /= d2; + } + else if (sscanf (str, "%lg%n", &d, &n) == 1) { + if (strcmp (&str[n], "%") == 0) /* percentage */ + d /= 100.0; + else if (strcmp (&str[n], "") == 0) /* probability */ + ; + else + goto bad_parse; + } + else + goto bad_parse; + + if (retp) + *retp = d; + return 0; + + bad_parse: + nbdkit_error ("%s: could not parse '%s'", what, str); + return -1; +} + /* Parse a string as a boolean, or return -1 after reporting the error. */ NBDKIT_DLL_PUBLIC int diff --git a/server/test-public.c b/server/test-public.c index 676411290..0d84abdd2 100644 --- a/server/test-public.c +++ b/server/test-public.c @@ -200,6 +200,78 @@ test_nbdkit_parse_size (void) return pass; } +static bool +test_nbdkit_parse_probability (void) +{ + size_t i; + bool pass = true; + struct pair { + const char *str; + int result; + double expected; + } tests[] = { + /* Bogus strings */ + { "", -1 }, + { "garbage", -1 }, + { "0garbage", -1 }, + { "1X", -1 }, + { "1%%", -1 }, + { "1:", -1 }, + { "1:1:1", -1 }, + { "1:0", -1 }, /* format is valid but divide by zero is not allowed */ + { "1/", -1 }, + { "1/2/3", -1 }, + + /* Numbers. */ + { "0", 0, 0 }, + { "1", 0, 1 }, + { "2", 0, 2 }, /* values outside [0..1] range are allowed */ + { "0.1", 0, 0.1 }, + { "0.5", 0, 0.5 }, + { "0.9", 0, 0.9 }, + { "1.0000", 0, 1 }, + + /* Percentages. */ + { "0%", 0, 0 }, + { "50%", 0, 0.5 }, + { "100%", 0, 1 }, + { "90.25%", 0, 0.9025 }, + + /* N in M */ + { "1:1000", 0, 0.001 }, + { "1/1000", 0, 0.001 }, + { "2:99", 0, 2.0/99 }, + { "2/99", 0, 2.0/99 }, + { "0:1000000", 0, 0 }, + }; + + for (i = 0; i < ARRAY_SIZE (tests); i++) { + int r; + double d; + + error_flagged = false; + r = nbdkit_parse_probability ("test", tests[i].str, &d); + if (r != tests[i].result) { + fprintf (stderr, + "Wrong return value for %s, got %d, expected %d\n", + tests[i].str, r, tests[i].result); + pass = false; + } + if (r == 0 && d != tests[i].expected) { + fprintf (stderr, + "Wrong result for %s, got %g, expected %g\n", + tests[i].str, d, tests[i].expected); + pass = false; + } + if ((r == -1) != error_flagged) { + fprintf (stderr, "Wrong error message handling for %s\n", tests[i].str); + pass = false; + } + } + + return pass; +} + static bool test_nbdkit_parse_ints (void) { @@ -503,6 +575,7 @@ main (int argc, char *argv[]) { bool pass = true; pass &= test_nbdkit_parse_size (); + pass &= test_nbdkit_parse_probability (); pass &= test_nbdkit_parse_ints (); pass &= test_nbdkit_read_password (); /* nbdkit_absolute_path and nbdkit_nanosleep not unit-tested here, but diff --git a/plugins/ocaml/NBDKit.mli b/plugins/ocaml/NBDKit.mli index 81447d07d..bc190f267 100644 --- a/plugins/ocaml/NBDKit.mli +++ b/plugins/ocaml/NBDKit.mli @@ -134,9 +134,9 @@ val register_plugin : into [EINVAL]. *) val set_error : Unix.error -> unit -(** Bindings for [nbdkit_parse_size], [nbdkit_parse_bool] and - [nbdkit_read_password]. See nbdkit-plugin(3) for information - about these functions. +(** Bindings for [nbdkit_parse_size], [nbdkit_parse_probability], + [nbdkit_parse_bool] and [nbdkit_read_password]. See + nbdkit-plugin(3) for information about these functions. On error these functions all raise [Invalid_argument]. The actual error is sent to the nbdkit error log and is not @@ -145,10 +145,11 @@ val set_error : Unix.error -> unit (* Note OCaml has functions already for parsing other integers, so * there is no need to bind them here. We only bind the functions * which have special abilities in nbdkit: [parse_size] can parse - * human sizes, [parse_bool] parses a range of nbdkit-specific - * boolean strings, and [read_password] suppresses echo. + * human sizes, [parse_probability] and [parse_bool] parses a range + * of nbdkit-specific strings, and [read_password] suppresses echo. *) val parse_size : string -> int64 +val parse_probability : string -> string -> float val parse_bool : string -> bool val read_password : string -> string diff --git a/plugins/ocaml/NBDKit.ml b/plugins/ocaml/NBDKit.ml index e1cf28c94..2d1696917 100644 --- a/plugins/ocaml/NBDKit.ml +++ b/plugins/ocaml/NBDKit.ml @@ -160,6 +160,8 @@ let register_plugin ~name (* Bindings to nbdkit server functions. *) external set_error : Unix.error -> unit = "ocaml_nbdkit_set_error" [@@noalloc] external parse_size : string -> int64 = "ocaml_nbdkit_parse_size" +external parse_probability : string -> string -> float = + "ocaml_nbdkit_parse_probability" external parse_bool : string -> bool = "ocaml_nbdkit_parse_bool" external read_password : string -> string = "ocaml_nbdkit_read_password" external realpath : string -> string = "ocaml_nbdkit_realpath" diff --git a/plugins/ocaml/bindings.c b/plugins/ocaml/bindings.c index f2c9ca07d..4885feac5 100644 --- a/plugins/ocaml/bindings.c +++ b/plugins/ocaml/bindings.c @@ -74,6 +74,22 @@ ocaml_nbdkit_parse_size (value strv) CAMLreturn (rv); } +NBDKIT_DLL_PUBLIC value +ocaml_nbdkit_parse_probability (value whatv, value strv) +{ + CAMLparam2 (whatv, strv); + CAMLlocal1 (dv); + int r; + double d; + + r = nbdkit_parse_probability (String_val (whatv), String_val (strv), &d); + if (r == -1) + caml_invalid_argument ("nbdkit_parse_probability"); + dv = caml_copy_double (d); + + CAMLreturn (dv); +} + NBDKIT_DLL_PUBLIC value ocaml_nbdkit_parse_bool (value strv) { diff --git a/plugins/python/modfunctions.c b/plugins/python/modfunctions.c index 479707e78..74bfd6f27 100644 --- a/plugins/python/modfunctions.c +++ b/plugins/python/modfunctions.c @@ -122,11 +122,32 @@ parse_size (PyObject *self, PyObject *args) return PyLong_FromSize_t ((size_t)size); } +/* nbdkit.parse_probability */ +static PyObject * +parse_probability (PyObject *self, PyObject *args) +{ + const char *what, *str; + double d; + + if (!PyArg_ParseTuple (args, "ss:parse_probability", &what, &str)) + return NULL; + + if (nbdkit_parse_probability (what, str, &d) == -1) { + PyErr_SetString (PyExc_ValueError, + "Unable to parse string as probability"); + return NULL; + } + + return PyFloat_FromDouble (d); +} + static PyMethodDef NbdkitMethods[] = { { "debug", debug, METH_VARARGS, "Print a debug message" }, { "export_name", export_name, METH_NOARGS, "Return the optional export name negotiated with the client" }, + { "parse_probability", parse_probability, METH_VARARGS, + "Parse probability strings into floating point number" }, { "parse_size", parse_size, METH_VARARGS, "Parse human-readable size strings into bytes" }, { "set_error", set_error, METH_VARARGS, diff --git a/tests/test-python-plugin.py b/tests/test-python-plugin.py index c3232a112..7f3a2c2e4 100644 --- a/tests/test-python-plugin.py +++ b/tests/test-python-plugin.py @@ -55,8 +55,20 @@ class TestAPI(unittest.TestCase): with self.assertRaises(ValueError): nbdkit.parse_size('foo') + def test_parse_probability(self): + self.assertEqual(nbdkit.parse_probability('test', '1:10'), 0.1) + self.assertEqual(nbdkit.parse_probability('test', '100%'), 1) + self.assertEqual(nbdkit.parse_probability('test', '0'), 0) + + with self.assertRaises(TypeError): + nbdkit.parse_probability('test', 17) + + with self.assertRaises(ValueError): + nbdkit.parse_probability('test', 'bar') + TestAPI().test_parse_size() +TestAPI().test_parse_probability() def config(k, v): diff --git a/tests/test_ocaml_plugin.ml b/tests/test_ocaml_plugin.ml index 8132de8f8..bf998d361 100644 --- a/tests/test_ocaml_plugin.ml +++ b/tests/test_ocaml_plugin.ml @@ -39,6 +39,7 @@ let sparse = Bytes.make nr_sectors '\000' (* sparseness bitmap *) (* Test parse_* functions. *) let () = assert (NBDKit.parse_size "1M" = Int64.of_int (1024*1024)); + assert (NBDKit.parse_probability "test parse probability" "1:10" = 0.1); assert (NBDKit.parse_bool "true" = true); assert (NBDKit.parse_bool "0" = false) -- 2.39.2

It takes a 64 bit integer and finds the next power of 2, eg. next_power_of_2 (510) => 512 (2^9) Taken from https://jameshfisher.com/2018/03/30/round-up-power-2/ with some fixes. --- common/include/ispowerof2.h | 9 +++++++++ common/include/test-ispowerof2.c | 14 ++++++++++++++ 2 files changed, 23 insertions(+) diff --git a/common/include/ispowerof2.h b/common/include/ispowerof2.h index f067caf07..57ebcc4fd 100644 --- a/common/include/ispowerof2.h +++ b/common/include/ispowerof2.h @@ -59,4 +59,13 @@ log_2_bits (unsigned long v) return SIZEOF_LONG*8 - __builtin_clzl (v) - 1; } +/* Round up to next power of 2. + * https://jameshfisher.com/2018/03/30/round-up-power-2/ + */ +static inline uint64_t +next_power_of_2 (uint64_t x) +{ + return x == 1 ? 1 : UINT64_C(1) << (64 - __builtin_clzll (x-1)); +} + #endif /* NBDKIT_ISPOWEROF2_H */ diff --git a/common/include/test-ispowerof2.c b/common/include/test-ispowerof2.c index 9620192f0..fe37c4a32 100644 --- a/common/include/test-ispowerof2.c +++ b/common/include/test-ispowerof2.c @@ -68,5 +68,19 @@ main (void) assert (log_2_bits (0x8000000000000000) == 63); #endif + /* Test next power of 2. */ + assert (next_power_of_2 (1) == 1); + assert (next_power_of_2 (3) == 4); + assert (next_power_of_2 (8) == 8); + assert (next_power_of_2 (9) == 16); + assert (next_power_of_2 (0xffff) == 0x10000); + assert (next_power_of_2 (0x10000) == 0x10000); + assert (next_power_of_2 (UINT64_C ( 0xffffffff)) == 0x100000000); + assert (next_power_of_2 (UINT64_C (0x100000000)) == 0x100000000); + assert (next_power_of_2 (UINT64_C (0x200000001)) == 0x400000000); + assert (next_power_of_2 (UINT64_C (0x6ffffffff)) == 0x800000000); + assert (next_power_of_2 (UINT64_C (0x700000001)) == 0x800000000); + assert (next_power_of_2 (UINT64_C (0x800000000)) == 0x800000000); + exit (EXIT_SUCCESS); } -- 2.39.2

On Tue, May 16, 2023 at 07:29:45AM -0500, Eric Blake wrote: Just a note here that the original code being copied [see link above] does not cast the 1 constant, and in fact does not work past 32 bits. I think it may be that the original code was tested on Windows which IIRC has 64 bit 'int'. Good point, will fix. Ditto. Thanks, Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v

Returns a fully allocated disk containing all 0xff (all ones), or another byte of your choice. --- plugins/data/nbdkit-data-plugin.pod | 1 + plugins/full/nbdkit-full-plugin.pod | 1 + plugins/null/nbdkit-null-plugin.pod | 1 + plugins/ones/nbdkit-ones-plugin.pod | 74 +++++++ plugins/pattern/nbdkit-pattern-plugin.pod | 4 +- plugins/random/nbdkit-random-plugin.pod | 1 + .../nbdkit-sparse-random-plugin.pod | 1 + plugins/zero/nbdkit-zero-plugin.pod | 1 + configure.ac | 2 + plugins/ones/Makefile.am | 70 +++++++ tests/Makefile.am | 4 + plugins/ones/ones.c | 191 ++++++++++++++++++ tests/test-ones.sh | 53 +++++ 13 files changed, 403 insertions(+), 1 deletion(-) diff --git a/plugins/data/nbdkit-data-plugin.pod b/plugins/data/nbdkit-data-plugin.pod index cec1af7f7..46daa859e 100644 --- a/plugins/data/nbdkit-data-plugin.pod +++ b/plugins/data/nbdkit-data-plugin.pod @@ -404,6 +404,7 @@ L<nbdkit-plugin(3)>, L<nbdkit-info-plugin(1)>, L<nbdkit-memory-plugin(1)>, L<nbdkit-null-plugin(1)>, +L<nbdkit-ones-plugin(1)>, L<nbdkit-partitioning-plugin(1)>, L<nbdkit-pattern-plugin(1)>, L<nbdkit-random-plugin(1)>, diff --git a/plugins/full/nbdkit-full-plugin.pod b/plugins/full/nbdkit-full-plugin.pod index 5664aa2da..18c86a327 100644 --- a/plugins/full/nbdkit-full-plugin.pod +++ b/plugins/full/nbdkit-full-plugin.pod @@ -65,6 +65,7 @@ L<nbdkit(1)>, L<nbdkit-plugin(3)>, L<nbdkit-error-filter(1)>, L<nbdkit-null-plugin(1)>, +L<nbdkit-ones-plugin(1)>, L<nbdkit-pattern-plugin(1)>, L<nbdkit-random-plugin(1)>. L<nbdkit-sparse-random-plugin(1)>, diff --git a/plugins/null/nbdkit-null-plugin.pod b/plugins/null/nbdkit-null-plugin.pod index 27fe68746..c71dc2c6f 100644 --- a/plugins/null/nbdkit-null-plugin.pod +++ b/plugins/null/nbdkit-null-plugin.pod @@ -55,6 +55,7 @@ C<nbdkit-null-plugin> first appeared in nbdkit 1.2. L<nbdkit(1)>, L<nbdkit-plugin(3)>, L<nbdkit-full-plugin(1)>, +L<nbdkit-ones-plugin(1)>, L<nbdkit-pattern-plugin(1)>, L<nbdkit-random-plugin(1)>. L<nbdkit-sparse-random-plugin(1)>, diff --git a/plugins/ones/nbdkit-ones-plugin.pod b/plugins/ones/nbdkit-ones-plugin.pod new file mode 100644 index 000000000..83137f608 --- /dev/null +++ b/plugins/ones/nbdkit-ones-plugin.pod @@ -0,0 +1,74 @@ +=head1 NAME + +nbdkit-ones-plugin - nbdkit plugin filled with repeated 0xff or other bytes + +=head1 SYNOPSIS + + nbdkit ones [[size=]SIZE] [byte=N] + +=head1 DESCRIPTION + +C<nbdkit-ones-plugin> is a plugin for L<nbdkit(1)>. Any read returns +a repeating pattern of C<0xff> (all ones) bytes, or another repeating +byte if you use the C<byte=>N parameter. Everything written to the +virtual device is discarded. + +Most NBD consumers will be very confused by this device. It is mainly +useful for testing. L<nbdkit-data-plugin(1)> can be used to create a +modifiable RAM disk initialized with fixed data. + +=head1 PARAMETERS + +=over 4 + +=item B<byte=>N + +Set the repeating byte to C<N>. The default is C<0xff> (all ones). + +=item [B<size=>]SIZE + +Specify the virtual size of the disk image. + +This parameter is optional. If omitted then a zero-sized device is +created. + +C<size=> is a magic config key and may be omitted in most cases. +See L<nbdkit(1)/Magic parameters>. + +=back + +=head1 FILES + +=over 4 + +=item F<$plugindir/nbdkit-ones-plugin.so> + +The plugin. + +Use C<nbdkit --dump-config> to find the location of C<$plugindir>. + +=back + +=head1 VERSION + +C<nbdkit-ones-plugin> first appeared in nbdkit 1.36. + +=head1 SEE ALSO + +L<nbdkit(1)>, +L<nbdkit-plugin(3)>, +L<nbdkit-data-plugin(1)>, +L<nbdkit-full-plugin(1)>, +L<nbdkit-null-plugin(1)>, +L<nbdkit-pattern-plugin(1)>, +L<nbdkit-random-plugin(1)>. +L<nbdkit-sparse-random-plugin(1)>, +L<nbdkit-zero-plugin(1)>. + +=head1 AUTHORS + +Richard W.M. Jones + +=head1 COPYRIGHT + +Copyright Red Hat diff --git a/plugins/pattern/nbdkit-pattern-plugin.pod b/plugins/pattern/nbdkit-pattern-plugin.pod index c5d4f0d36..f4ae324ed 100644 --- a/plugins/pattern/nbdkit-pattern-plugin.pod +++ b/plugins/pattern/nbdkit-pattern-plugin.pod @@ -11,7 +11,8 @@ nbdkit-pattern-plugin - plugin to serve a fixed pattern of data for testing C<nbdkit-pattern-plugin> is a plugin for L<nbdkit(1)> which serves a fixed pattern of data, read only. This is used for testing nbdkit filters and NBD clients. To create test disks filled with other -repeated patterns use L<nbdkit-data-plugin(1)> instead. +repeated patterns use L<nbdkit-data-plugin(1)> or +L<nbdkit-ones-plugin(1)> instead. The fixed pattern is the offset, as a 64 bit big endian integer, every 8 bytes. In hexadecimal this looks like: @@ -88,6 +89,7 @@ L<nbdkit-plugin(3)>, L<nbdkit-data-plugin(1)>, L<nbdkit-full-plugin(1)>, L<nbdkit-null-plugin(1)>, +L<nbdkit-ones-plugin(1)>, L<nbdkit-offset-filter(1)>, L<nbdkit-random-plugin(1)>, L<nbdkit-sparse-random-plugin(1)>, diff --git a/plugins/random/nbdkit-random-plugin.pod b/plugins/random/nbdkit-random-plugin.pod index 040d86bfc..0d6da8d5f 100644 --- a/plugins/random/nbdkit-random-plugin.pod +++ b/plugins/random/nbdkit-random-plugin.pod @@ -76,6 +76,7 @@ L<nbdkit-plugin(3)>, L<nbdkit-data-plugin(1)>, L<nbdkit-full-plugin(1)>, L<nbdkit-null-plugin(1)>, +L<nbdkit-ones-plugin(1)>, L<nbdkit-pattern-plugin(1)>, L<nbdkit-sparse-random-plugin(1)>, L<nbdkit-zero-plugin(1)>, diff --git a/plugins/sparse-random/nbdkit-sparse-random-plugin.pod b/plugins/sparse-random/nbdkit-sparse-random-plugin.pod index 03e98ee16..5636e76c4 100644 --- a/plugins/sparse-random/nbdkit-sparse-random-plugin.pod +++ b/plugins/sparse-random/nbdkit-sparse-random-plugin.pod @@ -110,6 +110,7 @@ L<nbdkit-plugin(3)>, L<nbdkit-data-plugin(1)>, L<nbdkit-full-plugin(1)>, L<nbdkit-null-plugin(1)>, +L<nbdkit-ones-plugin(1)>, L<nbdkit-pattern-plugin(1)>, L<nbdkit-random-plugin(1)>, L<nbdkit-zero-plugin(1)>, diff --git a/plugins/zero/nbdkit-zero-plugin.pod b/plugins/zero/nbdkit-zero-plugin.pod index 03544ad6e..2ac846027 100644 --- a/plugins/zero/nbdkit-zero-plugin.pod +++ b/plugins/zero/nbdkit-zero-plugin.pod @@ -37,6 +37,7 @@ L<nbdkit-plugin(3)>, L<nbdkit-data-plugin(1)>, L<nbdkit-full-plugin(1)>, L<nbdkit-null-plugin(1)>, +L<nbdkit-ones-plugin(1)>, L<nbdkit-pattern-plugin(1)>, L<nbdkit-random-plugin(1)>, L<nbdkit-sparse-random-plugin(1)>. diff --git a/configure.ac b/configure.ac index dafddcc29..310de7ac1 100644 --- a/configure.ac +++ b/configure.ac @@ -95,6 +95,7 @@ non_lang_plugins="\ nbd \ null \ ondemand \ + ones \ partitioning \ pattern \ random \ @@ -1500,6 +1501,7 @@ AC_CONFIG_FILES([Makefile plugins/null/Makefile plugins/ocaml/Makefile plugins/ondemand/Makefile + plugins/ones/Makefile plugins/partitioning/Makefile plugins/pattern/Makefile plugins/perl/Makefile diff --git a/plugins/ones/Makefile.am b/plugins/ones/Makefile.am new file mode 100644 index 000000000..9f8cbc4e2 --- /dev/null +++ b/plugins/ones/Makefile.am @@ -0,0 +1,70 @@ +# nbdkit +# Copyright Red Hat +# +# Redistribution and use in source and binary forms, with or without +# modification, are permitted provided that the following conditions are +# met: +# +# * Redistributions of source code must retain the above copyright +# notice, this list of conditions and the following disclaimer. +# +# * Redistributions in binary form must reproduce the above copyright +# notice, this list of conditions and the following disclaimer in the +# documentation and/or other materials provided with the distribution. +# +# * Neither the name of Red Hat nor the names of its contributors may be +# used to endorse or promote products derived from this software without +# specific prior written permission. +# +# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND +# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, +# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A +# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR +# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF +# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND +# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, +# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT +# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +# SUCH DAMAGE. + +include $(top_srcdir)/common-rules.mk + +EXTRA_DIST = nbdkit-ones-plugin.pod + +plugin_LTLIBRARIES = nbdkit-ones-plugin.la + +nbdkit_ones_plugin_la_SOURCES = \ + ones.c \ + $(top_srcdir)/include/nbdkit-plugin.h \ + $(NULL) + +nbdkit_ones_plugin_la_CPPFLAGS = \ + -I$(top_srcdir)/include \ + -I$(top_builddir)/include \ + $(NULL) +nbdkit_ones_plugin_la_CFLAGS = $(WARNINGS_CFLAGS) +nbdkit_ones_plugin_la_LIBADD = \ + $(IMPORT_LIBRARY_ON_WINDOWS) \ + $(NULL) +nbdkit_ones_plugin_la_LDFLAGS = \ + -module -avoid-version -shared $(NO_UNDEFINED_ON_WINDOWS) \ + $(NULL) +if USE_LINKER_SCRIPT +nbdkit_ones_plugin_la_LDFLAGS += \ + -Wl,--version-script=$(top_srcdir)/plugins/plugins.syms +endif + +if HAVE_POD + +man_MANS = nbdkit-ones-plugin.1 +CLEANFILES += $(man_MANS) + +nbdkit-ones-plugin.1: nbdkit-ones-plugin.pod \ + $(top_builddir)/podwrapper.pl + $(PODWRAPPER) --section=1 --man $@ \ + --html $(top_builddir)/html/$@.html \ + $< + +endif HAVE_POD diff --git a/tests/Makefile.am b/tests/Makefile.am index 3c8123f45..3ae13d660 100644 --- a/tests/Makefile.am +++ b/tests/Makefile.am @@ -955,6 +955,10 @@ EXTRA_DIST += \ test-ondemand-locking.sh \ $(NULL) +# ones plugin test. +TESTS += test-ones.sh +EXTRA_DIST += test-ones.sh + # partitioning plugin test. TESTS += \ test-partitioning1.sh \ diff --git a/plugins/ones/ones.c b/plugins/ones/ones.c new file mode 100644 index 000000000..2ff1ed028 --- /dev/null +++ b/plugins/ones/ones.c @@ -0,0 +1,191 @@ +/* nbdkit + * Copyright Red Hat + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions are + * met: + * + * * Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * + * * Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * * Neither the name of Red Hat nor the names of its contributors may be + * used to endorse or promote products derived from this software without + * specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, + * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A + * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR + * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF + * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND + * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, + * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT + * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + */ + +#include <config.h> + +#include <stdio.h> +#include <stdlib.h> +#include <stdint.h> +#include <string.h> +#include <errno.h> + +#define NBDKIT_API_VERSION 2 + +#include <nbdkit-plugin.h> + +/* The size of disk in bytes (initialized by size=<SIZE> parameter). */ +static int64_t size = 0; + +/* Repeating byte. */ +static uint8_t byte = 0xff; + +static int +ones_config (const char *key, const char *value) +{ + int64_t r; + + if (strcmp (key, "size") == 0) { + r = nbdkit_parse_size (value); + if (r == -1) + return -1; + size = r; + } + else if (strcmp (key, "byte") == 0) { + if (nbdkit_parse_uint8_t ("byte", value, &byte) == -1) + return -1; + } + else { + nbdkit_error ("unknown parameter '%s'", key); + return -1; + } + + return 0; +} + +#define ones_config_help \ + "byte=<BYTE> Repeating byte to use (default: 0xff).\n" \ + "size=<SIZE> Size of the backing disk." + +/* Create the per-connection handle. */ +static void * +ones_open (int readonly) +{ + return NBDKIT_HANDLE_NOT_NEEDED; +} + +#define THREAD_MODEL NBDKIT_THREAD_MODEL_PARALLEL + +/* Get the disk size. */ +static int64_t +ones_get_size (void *handle) +{ + return size; +} + +/* Serves the same data over multiple connections. */ +static int +ones_can_multi_conn (void *handle) +{ + return 1; +} + +/* Cache. */ +static int +ones_can_cache (void *handle) +{ + /* Everything is already in memory, returning this without + * implementing .cache lets nbdkit do the correct no-op. + */ + return NBDKIT_CACHE_NATIVE; +} + +/* Read data. */ +static int +ones_pread (void *handle, void *buf, uint32_t count, uint64_t offset, + uint32_t flags) +{ + memset (buf, byte, count); + return 0; +} + +/* Write data. */ +static int +ones_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset, + uint32_t flags) +{ + /* nothing */ + return 0; +} + +/* Write zeroes. */ +static int +ones_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags) +{ + /* nothing */ + return 0; +} + +/* Flush is a no-op, so advertise native FUA support */ +static int +ones_can_fua (void *handle) +{ + return NBDKIT_FUA_NATIVE; +} + +/* Trim. */ +static int +ones_trim (void *handle, uint32_t count, uint64_t offset, uint32_t flags) +{ + /* nothing */ + return 0; +} + +/* Nothing is persistent, so flush is trivially supported */ +static int +ones_flush (void *handle, uint32_t flags) +{ + return 0; +} + +/* Extents. */ +static int +ones_extents (void *handle, uint32_t count, uint64_t offset, uint32_t flags, + struct nbdkit_extents *extents) +{ + /* Return a fully allocated data extent covering the entire disk. */ + return nbdkit_add_extent (extents, 0, size, 0); +} + +static struct nbdkit_plugin plugin = { + .name = "ones", + .version = PACKAGE_VERSION, + .config = ones_config, + .config_help = ones_config_help, + .magic_config_key = "size", + .open = ones_open, + .get_size = ones_get_size, + .can_multi_conn = ones_can_multi_conn, + .can_cache = ones_can_cache, + .pread = ones_pread, + .pwrite = ones_pwrite, + .zero = ones_zero, + .trim = ones_trim, + .can_fua = ones_can_fua, + .flush = ones_flush, + .extents = ones_extents, + /* In this plugin, errno is preserved properly along error return + * paths from failed system calls. + */ + .errno_is_preserved = 1, +}; + +NBDKIT_REGISTER_PLUGIN (plugin) diff --git a/tests/test-ones.sh b/tests/test-ones.sh new file mode 100755 index 000000000..1a2b22caf --- /dev/null +++ b/tests/test-ones.sh @@ -0,0 +1,53 @@ +#!/usr/bin/env bash +# nbdkit +# Copyright Red Hat +# +# Redistribution and use in source and binary forms, with or without +# modification, are permitted provided that the following conditions are +# met: +# +# * Redistributions of source code must retain the above copyright +# notice, this list of conditions and the following disclaimer. +# +# * Redistributions in binary form must reproduce the above copyright +# notice, this list of conditions and the following disclaimer in the +# documentation and/or other materials provided with the distribution. +# +# * Neither the name of Red Hat nor the names of its contributors may be +# used to endorse or promote products derived from this software without +# specific prior written permission. +# +# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND +# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, +# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A +# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR +# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF +# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND +# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, +# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT +# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +# SUCH DAMAGE. + +source ./functions.sh +set -e +set -x + +requires_plugin ones +requires_nbdsh_uri +requires_nbdinfo + +# Check the disk contains 0xff by default. +nbdkit -U - ones 1024 --run ' +nbdsh -u "$uri" -c "assert (h.pread(1024,0) == b\"\\xff\"*1024)" +' + +# Change the byte. +nbdkit -U - ones 1024 byte=0x5a --run ' +nbdsh -u "$uri" -c "assert (h.pread(1024,0) == b\"\\x5a\"*1024)" +' + +# Check the disk is fully allocated. +nbdkit -U - ones 1G --run 'nbdinfo --map "$uri"' | \ + grep -E '0[[:space:]]+1073741824[[:space:]]+0[[:space:]]+data' -- 2.39.2

This filter adds random data corruption when reading from the underlying plugin. --- filters/error/nbdkit-error-filter.pod | 4 + filters/evil/nbdkit-evil-filter.pod | 159 ++++++++++++ configure.ac | 2 + filters/evil/Makefile.am | 77 ++++++ tests/Makefile.am | 14 + filters/evil/evil.c | 353 ++++++++++++++++++++++++++ tests/test-evil-cosmic.sh | 76 ++++++ tests/test-evil-stuck-high-bits.sh | 86 +++++++ tests/test-evil-stuck-low-bits.sh | 79 ++++++ tests/test-evil-stuck-wires.sh | 85 +++++++ 10 files changed, 935 insertions(+) diff --git a/filters/error/nbdkit-error-filter.pod b/filters/error/nbdkit-error-filter.pod index 49f21d10a..91af7f713 100644 --- a/filters/error/nbdkit-error-filter.pod +++ b/filters/error/nbdkit-error-filter.pod @@ -25,6 +25,9 @@ All parameters are optional, but you should usually specify one of the C<error-rate> or C<error-*-rate> parameters, B<otherwise this filter will do nothing>. +L<nbdkit-evil-filter(1)> is a related filter that injects data +corruption instead of errors. + =head1 EXAMPLES Inject a low rate of errors randomly into the connection: @@ -162,6 +165,7 @@ C<nbdkit-error-filter> first appeared in nbdkit 1.6. =head1 SEE ALSO L<nbdkit(1)>, +L<nbdkit-evil-filter(1)>, L<nbdkit-file-plugin(1)>, L<nbdkit-full-plugin(1)>, L<nbdkit-retry-filter(1)>, diff --git a/filters/evil/nbdkit-evil-filter.pod b/filters/evil/nbdkit-evil-filter.pod new file mode 100644 index 000000000..5100117ab --- /dev/null +++ b/filters/evil/nbdkit-evil-filter.pod @@ -0,0 +1,159 @@ +=head1 NAME + +nbdkit-evil-filter - add random data corruption to reads + +=head1 SYNOPSIS + + nbdkit --filter=evil PLUGIN [PLUGIN-ARGS...] + evil=[cosmic-rays|stuck-bits|stuck-wires] + [evil-probability=PROB] [evil-stuck-probability=PROB] + [evil-seed=SEED] + +=head1 DESCRIPTION + +nbdkit-evil-filter is a Byzantine filter for L<nbdkit(1)> that +randomly corrupts data when reading from the underlying plugin. This +can be used for testing filesystem checksums. Note that it does not +change write operations, so the underlying plugin contains the correct +data. + +L<nbdkit-error-filter(1)> is a related filter that injects hard errors +into the NBD protocol. + +This filter has several modes, controlled using the C<evil=...> +parameter. These are: + +=over 4 + +=item C<evil=cosmic-rays> + +Bits are flipped at random when reading data. The probability that a +bit is flipped is controlled using the C<evil-probability> parameter, +defaulting to 1e-8 (on average 1 in every 100 million bits read is +flipped). + +=item C<evil=stuck-bits> + +This is the default mode. + +Fixed bits in the backing file are stuck randomly high or low. The +C<evil-probability> parameter controls the expected probability that a +particular bit is stuck, defaulting in this mode to 1e-8 (1 in 100 +million). C<evil-stuck-probability> controls the probability that a +stuck bit is read as its stuck value or its correct value, defaulting +to 100% (always read as a stuck bit). + +=item C<evil=stuck-wires> + +This is similar to C<stuck-bits> but instead of simulating bad backing +data, it simulates stuck wires along the data path (eg. in a +register). The difference is that when reading, the stuck bit always +happens at the same position in the packet of data being read, +regardless of where on the underlying disk it is being read from. +C<evil-probability> and controls the probability of a stuck wire, +defaulting in this mode to 1e-6 (1 in 1 million). +C<evil-stuck-probability> controls the probability that a stuck bit is +read as its stuck value or its correct value, defaulting to 100% +(always read as a stuck bit). + +=back + +=head1 EXAMPLES + +Add some stuck bits to the backing file at random: + + nbdkit --filter=evil file disk.img + +Cosmic rays will flip (on average) one in every 100 million bits +copied from the backing file over NBD: + + nbdkit --filter=evil file disk.img evil=cosmic-rays \ + --run 'nbdcopy $uri output.img' + +=head2 Extents + +Plugins can be sparse. This filter only corrupts bits in non-sparse +parts of the backing disk and it leaves sparse regions unchanged +(which is realistic behaviour). If you wish to use this filter to +corrupt sparse regions, then combine this filter with +L<nbdkit-noextents-filter(1)>. For example: + + nbdkit --filter=evil --filter=noextents memory 1G + +=head1 PARAMETERS + +=over 4 + +=item B<evil=cosmic-rays> + +=item B<evil=stuck-bits> + +=item B<evil=stuck-wires> + +Select the mode of evil. See the L</DESCRIPTION> above. The default +is C<stuck-bits>. + +=item B<evil-probability=>N + +=item B<evil-probability=>NB<:>M + +=item B<evil-probability=>NB<%> + +Set the probability for the mode. You can either use a floating point +number between 0 and 1, eg. C<evil-probability=0.001> or +C<evil-probability=1e-6>. Or you can write it as N in M, eg. +C<evil-probability=1:1000000> or C<evil-probability=3.33:100000>. Or +you can write this as a percentage, eg. C<evil-probability=1%>. + +The default probability depends on the mode. + +=item B<evil-seed=>SEED + +To make runs repeatable, use this to set a seed for the random number +generator. The default is to choose a seed at random. + +=item B<evil-stuck-probability=>N + +=item B<evil-stuck-probability=>NB<:>M + +=item B<evil-stuck-probability=>NB<%> + +For the "stuck-*" modes, the probability that when reading a stuck bit +you will read the stuck bit or the correct value. This defaults to 1 +(ie. 100%) which means the bit is always stuck. Setting it to 0.5 for +example will mean that half the time the bit appears stuck and half +the time you see the correct value. + +=back + +=head1 FILES + +=over 4 + +=item F<$filterdir/nbdkit-evil-filter.so> + +The filter. + +Use C<nbdkit --dump-config> to find the location of C<$filterdir>. + +=back + +=head1 VERSION + +C<nbdkit-pause-filter> first appeared in nbdkit 1.36. + +=head1 SEE ALSO + +L<nbdkit(1)>, +L<nbdkit-filter(3)>, +L<nbdkit-delay-filter(1)>, +L<nbdkit-noextents-filter(1)>, +L<nbdkit-error-filter(1)>. + +=head1 AUTHORS + +Richard W.M. Jones + +=head1 COPYRIGHT + +Copyright Red Hat diff --git a/configure.ac b/configure.ac index 310de7ac1..18431958a 100644 --- a/configure.ac +++ b/configure.ac @@ -124,6 +124,7 @@ filters="\ exportname \ ext2 \ extentlist \ + evil \ fua \ gzip \ ip \ @@ -1534,6 +1535,7 @@ AC_CONFIG_FILES([Makefile filters/exportname/Makefile filters/ext2/Makefile filters/extentlist/Makefile + filters/evil/Makefile filters/fua/Makefile filters/gzip/Makefile filters/ip/Makefile diff --git a/filters/evil/Makefile.am b/filters/evil/Makefile.am new file mode 100644 index 000000000..ac6337428 --- /dev/null +++ b/filters/evil/Makefile.am @@ -0,0 +1,77 @@ +# nbdkit +# Copyright Red Hat +# +# Redistribution and use in source and binary forms, with or without +# modification, are permitted provided that the following conditions are +# met: +# +# * Redistributions of source code must retain the above copyright +# notice, this list of conditions and the following disclaimer. +# +# * Redistributions in binary form must reproduce the above copyright +# notice, this list of conditions and the following disclaimer in the +# documentation and/or other materials provided with the distribution. +# +# * Neither the name of Red Hat nor the names of its contributors may be +# used to endorse or promote products derived from this software without +# specific prior written permission. +# +# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND +# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, +# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A +# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR +# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF +# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND +# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, +# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT +# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +# SUCH DAMAGE. + +include $(top_srcdir)/common-rules.mk + +EXTRA_DIST = nbdkit-evil-filter.pod + +# Relies on a Unix domain socket. +if !IS_WINDOWS + +filter_LTLIBRARIES = nbdkit-evil-filter.la + +nbdkit_evil_filter_la_SOURCES = \ + evil.c \ + $(top_srcdir)/include/nbdkit-filter.h \ + $(NULL) + +nbdkit_evil_filter_la_CPPFLAGS = \ + -I$(top_srcdir)/include \ + -I$(top_builddir)/include \ + -I$(top_srcdir)/common/include \ + -I$(top_srcdir)/common/utils \ + $(NULL) +nbdkit_evil_filter_la_CFLAGS = $(WARNINGS_CFLAGS) +nbdkit_evil_filter_la_LIBADD = \ + $(top_builddir)/common/utils/libutils.la \ + $(IMPORT_LIBRARY_ON_WINDOWS) \ + $(NULL) +nbdkit_evil_filter_la_LDFLAGS = \ + -module -avoid-version -shared $(NO_UNDEFINED_ON_WINDOWS) \ + $(NULL) +if USE_LINKER_SCRIPT +nbdkit_evil_filter_la_LDFLAGS += \ + -Wl,--version-script=$(top_srcdir)/filters/filters.syms +endif + +if HAVE_POD + +man_MANS = nbdkit-evil-filter.1 +CLEANFILES += $(man_MANS) + +nbdkit-evil-filter.1: nbdkit-evil-filter.pod \ + $(top_builddir)/podwrapper.pl + $(PODWRAPPER) --section=1 --man $@ \ + --html $(top_builddir)/html/$@.html \ + $< + +endif HAVE_POD +endif !IS_WINDOWS diff --git a/tests/Makefile.am b/tests/Makefile.am index 3ae13d660..ca4fc6b4e 100644 --- a/tests/Makefile.am +++ b/tests/Makefile.am @@ -1598,6 +1598,20 @@ EXTRA_DIST += \ test-error-triggered.sh \ $(NULL) +# evil filter test. +TESTS += \ + test-evil-cosmic.sh \ + test-evil-stuck-high-bits.sh \ + test-evil-stuck-low-bits.sh \ + test-evil-stuck-wires.sh \ + $(NULL) +EXTRA_DIST += \ + test-evil-cosmic.sh \ + test-evil-stuck-high-bits.sh \ + test-evil-stuck-low-bits.sh \ + test-evil-stuck-wires.sh \ + $(NULL) + # exitlast filter test. TESTS += test-exitlast.sh EXTRA_DIST += test-exitlast.sh diff --git a/filters/evil/evil.c b/filters/evil/evil.c new file mode 100644 index 000000000..e961f6861 --- /dev/null +++ b/filters/evil/evil.c @@ -0,0 +1,353 @@ +/* nbdkit + * Copyright Red Hat + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions are + * met: + * + * * Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * + * * Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * + * * Neither the name of Red Hat nor the names of its contributors may be + * used to endorse or promote products derived from this software without + * specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, + * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A + * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR + * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF + * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND + * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, + * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT + * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + */ + +#include <config.h> + +#include <stdio.h> +#include <stdlib.h> +#include <stdbool.h> +#include <stdint.h> +#include <inttypes.h> +#include <string.h> +#include <time.h> +#include <assert.h> + +#include <nbdkit-filter.h> + +#include "minmax.h" +#include "ispowerof2.h" +#include "random.h" + +enum mode { + COSMIC_RAYS, + STUCK_BITS, + STUCK_WIRES, +}; + +static enum mode evil_mode = STUCK_BITS; +static double evil_probability = -1; /* default depends on mode */ +static double evil_stuck_probability = 1.0; +static uint32_t evil_seed; + +static void +evil_load (void) +{ + evil_seed = time (NULL); +} + +static int +evil_config (nbdkit_next_config *next, nbdkit_backend *nxdata, + const char *key, const char *value) +{ + if (strcmp (key, "evil") == 0 || strcmp (key, "evil-mode") == 0) { + if (strcmp (value, "cosmic-rays") == 0 || + strcmp (value, "cosmic") == 0) { + evil_mode = COSMIC_RAYS; + return 0; + } + else if (strcmp (value, "stuck-bits") == 0 || + strcmp (value, "stuck-bit") == 0 || + strcmp (value, "stuck") == 0) { + evil_mode = STUCK_BITS; + return 0; + } + else if (strcmp (value, "stuck-wires") == 0 || + strcmp (value, "stuck-wire") == 0) { + evil_mode = STUCK_WIRES; + return 0; + } + else { + nbdkit_error ("evil: unknown mode: %s", value); + return -1; + } + } + else if (strcmp (key, "evil-probability") == 0) { + if (nbdkit_parse_probability ("evil-probability", value, + &evil_probability) == -1) + return -1; + if (evil_probability < 0 || evil_probability > 1) { + nbdkit_error ("%s: probability out of range, should be [0..1]", key); + return -1; + } + return 0; + } + else if (strcmp (key, "evil-stuck-probability") == 0) { + if (nbdkit_parse_probability ("evil-stuck-probability", value, + &evil_stuck_probability) == -1) + return -1; + if (evil_stuck_probability < 0 || evil_stuck_probability > 1) { + nbdkit_error ("%s: probability out of range, should be [0..1]", key); + return -1; + } + return 0; + } + else if (strcmp (key, "evil-seed") == 0) { + if (nbdkit_parse_uint32_t ("evil-seed", value, &evil_seed) == -1) + return -1; + return 0; + } + else + return next (nxdata, key, value); +} + +static int +evil_config_complete (nbdkit_next_config_complete *next, + nbdkit_backend *nxdata) +{ + if (evil_probability < 0) { + /* Choose default probability based on the chosen mode. */ + switch (evil_mode) { + case COSMIC_RAYS: + case STUCK_BITS: + evil_probability = 1e-8; + break; + case STUCK_WIRES: + evil_probability = 1e-6; + } + } + + return next (nxdata); +} + +#define evil_config_help \ + "evil=cosmic-rays|stuck-bits|stuck-wires\n" \ + " Set the mode (default: cosmic-rays).\n" \ + "evil-probability=PROB Probability of flipped or stuck bit.\n" \ + "evil-seed=SEED Random number seed.\n" \ + "evil-stuck-probability=PROB Probability of stuck bit being stuck." + +/* This is the heart of the algorithm, the function which corrupts + * the buffer after reading it from the plugin. + * + * The observation is that if we have a block of (eg) size 10^6 bits + * and our probability of finding a corrupt bit is (eg) 1/10^4, then + * we expect approximately 100 bits in the block to be corrupted. + * + * For stuck bits we want the corrupted bits to be the same on each + * access, either relative to the backing disk (STUCK_BITS) or to the + * request (STUCK_WIRES). + * + * Instead of creating an expensive bitmap ahead of time covering the + * whole disk, we can use the random number generator with a fixed + * seed derived from the offset of the start of the block. We can + * then choose a random number uniformly in the range [0..2*(1/P)] (in + * the example [0..2*10^4]) as the distance to the next corrupt bit. + * We jump forwards, corrupt that bit, and repeat until we reach + * the end of the block. + * + * "Corrupted" in this case can mean flipped by cosmic rays or stuck, + * depending on the filter mode. + * + * On average this will choose the right number of bits in the block. + * (Although their distribution will be suboptimal. In a uniform + * distribution it should be possible for two corrupted bits to be + * greater than 2*(1/P) apart, but the above algorithm would not do + * this. In practice this probably doesn't matter.) + * + * Note that "block" != "buffer", especially in the STUCK_BITS mode. + * We iterate over blocks as above, but only corrupt a bit when it + * happens to coincide with the buffer we have just read. + * + * We choose the block size adaptively so that at least 100 bits in + * the block will be corrupted. The block size must be a power of 2. + * The block size thus depends on the probability. + */ +enum corruption_type { FLIP, STUCK }; + +static uint64_t block_size; /* in bytes */ +static struct random_state state; /* only used for cosmic-rays */ + +static int +evil_thread_model (void) +{ + switch (evil_mode) { + case COSMIC_RAYS: + /* Because cosmic-rays uses the global random state we need to + * tighten the thread model. + */ + return NBDKIT_THREAD_MODEL_SERIALIZE_REQUESTS; + + case STUCK_BITS: + case STUCK_WIRES: + return NBDKIT_THREAD_MODEL_PARALLEL; + } + abort (); +} + +static int +evil_get_ready (int thread_model) +{ + switch (evil_mode) { + case COSMIC_RAYS: + xsrandom ((uint64_t) evil_seed, &state); + break; + + case STUCK_BITS: + case STUCK_WIRES: + ; + } + + /* Choose the block size based on the probability, so that at least + * 100 bits are expected to be corrupted in the block. Block size + * must be a power of 2. + */ + block_size = next_power_of_2 ((uint64_t) (100. / evil_probability)); + + return 0; +} + +static uint8_t +corrupt_one_bit (uint8_t byte, unsigned bit, + uint64_t rand, enum corruption_type ct) +{ + const unsigned mask = 1 << bit; + + switch (ct) { + case FLIP: + byte ^= mask; + break; + case STUCK: + rand &= 0xffffffff; + if (evil_stuck_probability * 0x100000000 > rand) { + if (rand & 1) /* stuck high or low? */ + byte |= mask; + else + byte &= ~mask; + } + } + return byte; +} + +static void +corrupt_buffer (uint8_t *buf, uint32_t count, uint64_t offset_in_block, + struct random_state *rs, enum corruption_type ct) +{ + if (evil_probability == 0) + /* No corruption, and avoids a divide by zero below. */ + return; + + uint64_t offs, intvl, i, rand; + const uint64_t dinvp = (uint64_t) (2.0 * (1.0 / evil_probability)); + + assert ((offset_in_block & ~(block_size-1)) == 0); + + /* Iterate over the whole block from the start. */ + for (offs = 0; offs < offset_in_block + count; ) { + /* Choose the length of the interval to the next corrupted bit, by + * picking a random number in [0..2*(1/P)]. + * + * Remember this is in bits! + */ + intvl = xrandom (rs) % dinvp; + + /* Consume one more random state. We may or may not use this. + * But we need to always consume two random states per iteration + * to make the output predictable. + */ + rand = xrandom (rs); + + /* Adjust offs to that byte. */ + offs += intvl / 8; + + /* If we have gone past the end of buffer, stop. */ + if (offs >= offset_in_block + count) break; + + /* If the current offs lies within the buffer, corrupt a bit. */ + if (offs >= offset_in_block) { + i = offs - offset_in_block; + assert (i < count); + buf[i] = corrupt_one_bit (buf[i], intvl & 7, rand, ct); + } + } +} + +/* Read data. */ +static int +evil_pread (nbdkit_next *next, + void *handle, void *buf, uint32_t count, uint64_t offset, + uint32_t flags, int *err) +{ + uint64_t seed, bstart, len; + struct random_state local_state; + + if (next->pread (next, buf, count, offset, flags, err) == -1) + return -1; + + switch (evil_mode) { + case COSMIC_RAYS: + /* Use the global random state because we want to flip bits at random. */ + corrupt_buffer (buf, count, 0, &state, FLIP); + break; + + case STUCK_BITS: + /* Split the request to align with blocks. */ + bstart = offset & ~(block_size-1); + while (count > 0) { + /* Set the seed so we corrupt the same bits relative to the offset. */ + seed = (int64_t) evil_seed + bstart; + xsrandom (seed, &local_state); + /* If the buffer straddles two blocks, shorten to just the part + * inside the first block. + */ + len = MIN (count, bstart + block_size - offset); + corrupt_buffer (buf, len, offset - bstart, &local_state, STUCK); + bstart += block_size; + offset += len; + buf += len; + count -= len; + } + break; + + case STUCK_WIRES: + /* Set the seed so we corrupt the same bits in every request. */ + seed = (int64_t) evil_seed; + xsrandom (seed, &local_state); + corrupt_buffer (buf, count, 0, &local_state, STUCK); + break; + } + + return 0; +} + +static struct nbdkit_filter filter = { + .name = "evil", + .longname = "nbdkit evil filter", + .load = evil_load, + .config = evil_config, + .config_complete = evil_config_complete, + .config_help = evil_config_help, + .thread_model = evil_thread_model, + .get_ready = evil_get_ready, + .pread = evil_pread, +}; + +NBDKIT_REGISTER_FILTER (filter) diff --git a/tests/test-evil-cosmic.sh b/tests/test-evil-cosmic.sh new file mode 100755 index 000000000..00f09ac7a --- /dev/null +++ b/tests/test-evil-cosmic.sh @@ -0,0 +1,76 @@ +#!/usr/bin/env bash +# nbdkit +# Copyright Red Hat +# +# Redistribution and use in source and binary forms, with or without +# modification, are permitted provided that the following conditions are +# met: +# +# * Redistributions of source code must retain the above copyright +# notice, this list of conditions and the following disclaimer. +# +# * Redistributions in binary form must reproduce the above copyright +# notice, this list of conditions and the following disclaimer in the +# documentation and/or other materials provided with the distribution. +# +# * Neither the name of Red Hat nor the names of its contributors may be +# used to endorse or promote products derived from this software without +# specific prior written permission. +# +# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND +# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, +# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A +# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR +# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF +# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND +# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, +# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT +# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +# SUCH DAMAGE. + +# Test evil filter with cosmic rays. + +source ./functions.sh +set -e +set -x + +requires_plugin null +requires_filter evil +requires_filter noextents +requires nbdcopy --version + +# Make sure these are the coreutils versions to avoid surprises. +requires od --version +requires sort --version +requires uniq --version + +f="test-evil-cosmic.out" +rm -f $f +cleanup_fn rm -f $f + +# 80 million zero bits in the backing disk, and the filter will +# randomly flip (ie. set high) 1 in 800,000 bits, or about 100. + +# XXX Actually the number of set bits clusters around 80. There could +# be a mistake in my calculations or the interval algorithm we use +# might be biased. + +export f +nbdkit -U - null 10000000 \ + --filter=evil --filter=noextents \ + evil=cosmic-rays evil-probability=1/800000 \ + --run 'nbdcopy "$uri" $f' + +# This will give an approximate count of the number of set bits. + +zbytes="$( od -A n -w1 -v -t x1 < $f | sort | uniq -c | + $SED -n -E -e 's/([0-9]+)[[:space:]]+00[[:space:]]*$/\1/p' )" +nzbits=$(( 10000000 - zbytes )); # looks wrong but actually correct ... + +if [ $nzbits -lt 20 ] || [ $nzbits -gt 180 ]; then + echo "ERROR: $0: unexpected number of non-zero bits: $nzbits" + echo " (expecting about 100)" + exit 1 +fi diff --git a/tests/test-evil-stuck-high-bits.sh b/tests/test-evil-stuck-high-bits.sh new file mode 100755 index 000000000..8f6db2ea0 --- /dev/null +++ b/tests/test-evil-stuck-high-bits.sh @@ -0,0 +1,86 @@ +#!/usr/bin/env bash +# nbdkit +# Copyright Red Hat +# +# Redistribution and use in source and binary forms, with or without +# modification, are permitted provided that the following conditions are +# met: +# +# * Redistributions of source code must retain the above copyright +# notice, this list of conditions and the following disclaimer. +# +# * Redistributions in binary form must reproduce the above copyright +# notice, this list of conditions and the following disclaimer in the +# documentation and/or other materials provided with the distribution. +# +# * Neither the name of Red Hat nor the names of its contributors may be +# used to endorse or promote products derived from this software without +# specific prior written permission. +# +# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND +# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, +# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A +# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR +# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF +# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND +# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, +# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT +# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +# SUCH DAMAGE. + +# Test evil filter in the default mode ("stuck-bits"). + +source ./functions.sh +set -e +set -x + +requires_plugin null +requires_filter evil +requires_filter noextents +requires_nbdsh_uri + +sock=$(mktemp -u /tmp/nbdkit-test-sock.XXXXXX) +pidfile=evil-stuck-high-bits.pid +files="$sock $pidfile" +rm -f $files +cleanup_fn rm -f $files + +# Run nbdkit with the evil filter. +start_nbdkit -P $pidfile -U $sock \ + --filter=evil --filter=noextents \ + null 1G evil-probability=1/800000 + +# Since 1 in 800,000 bits are stuck (on average), for every 100,000 +# bytes that we read we expect about 1 stuck bit. Note however that +# bits are stuck randomly low or high, and against the null filter you +# cannot see a stuck low bit, so in fact we expect to see only 1 stuck +# bit per 200,000 bytes. +# +# There is a separate test for stuck low bits (test-evil-stuck-low-bits.sh). +# +# Also stuck bits should be consistent across reads. + +nbdsh -u "nbd+unix://?socket=$sock" \ + -c - <<EOF +def count_bits(buf): + r = 0 + for i in range(0, len(buf)-1): + if buf[i] != 0: + r += bin(buf[i]).count("1") + return r + +# Expect about 50 stuck-high bits. +buf = h.pread(10000000, 0) +bits = count_bits(buf) +print("stuck high bits: %d (expected 50)" % bits) +assert(bits > 20 and bits < 80) + +# If we read subsets they should match the contents of the buffer. +buf1 = h.pread(1000, 1000) +assert(buf1 == buf[1000:2000]) + +buf1 = h.pread(10000, 999) +assert(buf1 == buf[999:10999]) +EOF diff --git a/tests/test-evil-stuck-low-bits.sh b/tests/test-evil-stuck-low-bits.sh new file mode 100755 index 000000000..3b0a48af7 --- /dev/null +++ b/tests/test-evil-stuck-low-bits.sh @@ -0,0 +1,79 @@ +#!/usr/bin/env bash +# nbdkit +# Copyright Red Hat +# +# Redistribution and use in source and binary forms, with or without +# modification, are permitted provided that the following conditions are +# met: +# +# * Redistributions of source code must retain the above copyright +# notice, this list of conditions and the following disclaimer. +# +# * Redistributions in binary form must reproduce the above copyright +# notice, this list of conditions and the following disclaimer in the +# documentation and/or other materials provided with the distribution. +# +# * Neither the name of Red Hat nor the names of its contributors may be +# used to endorse or promote products derived from this software without +# specific prior written permission. +# +# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND +# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, +# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A +# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR +# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF +# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND +# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, +# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT +# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +# SUCH DAMAGE. + +# Test evil filter in the default mode ("stuck-bits"). + +source ./functions.sh +set -e +set -x + +requires_plugin ones +requires_filter evil +requires_nbdsh_uri + +sock=$(mktemp -u /tmp/nbdkit-test-sock.XXXXXX) +pidfile=evil-stuck-low-bits.pid +files="$sock $pidfile" +rm -f $files +cleanup_fn rm -f $files + +# Run nbdkit with the evil filter. +start_nbdkit -P $pidfile -U $sock \ + --filter=evil \ + ones 1G evil-probability=1/800000 + +# See description in test-evil-stuck-high-bits.sh. This test uses the +# ones plugin to test for stuck low bits. The other parameters are +# the same. + +nbdsh -u "nbd+unix://?socket=$sock" \ + -c - <<EOF +def count_bits(buf): + r = 0 + for i in range(0, len(buf)-1): + if buf[i] != 0xff: + r += 8 - bin(buf[i]).count("1") + return r + +# Expect about 50 stuck-low bits. +buf = h.pread(10000000, 32*1024*1024) +bits = count_bits(buf) +print("stuck low bits: %d (expected 50)" % bits) +assert(bits > 20 and bits < 80) + +# If we read subsets they should match the contents of the buffer. +buf1 = h.pread(1000, 32*1024*1024 + 1000) +assert(buf1 == buf[1000:2000]) + +buf1 = h.pread(10000, 32*1024*1024 + 999) +assert(buf1 == buf[999:10999]) +EOF diff --git a/tests/test-evil-stuck-wires.sh b/tests/test-evil-stuck-wires.sh new file mode 100755 index 000000000..c79a009fc --- /dev/null +++ b/tests/test-evil-stuck-wires.sh @@ -0,0 +1,85 @@ +#!/usr/bin/env bash +# nbdkit +# Copyright Red Hat +# +# Redistribution and use in source and binary forms, with or without +# modification, are permitted provided that the following conditions are +# met: +# +# * Redistributions of source code must retain the above copyright +# notice, this list of conditions and the following disclaimer. +# +# * Redistributions in binary form must reproduce the above copyright +# notice, this list of conditions and the following disclaimer in the +# documentation and/or other materials provided with the distribution. +# +# * Neither the name of Red Hat nor the names of its contributors may be +# used to endorse or promote products derived from this software without +# specific prior written permission. +# +# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND +# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, +# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A +# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR +# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF +# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND +# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, +# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT +# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +# SUCH DAMAGE. + +# Test evil filter in stuck-wires mode. + +source ./functions.sh +set -e +set -x + +requires_plugin null +requires_filter evil +requires_filter noextents +requires_nbdsh_uri + +sock=$(mktemp -u /tmp/nbdkit-test-sock.XXXXXX) +pidfile=evil-stuck-wires.pid +files="$sock $pidfile" +rm -f $files +cleanup_fn rm -f $files + +# Run nbdkit with the evil filter. +start_nbdkit -P $pidfile -U $sock \ + --filter=evil --filter=noextents \ + null 1G evil=stuck-wires evil-probability=1/10000 + +# Reads from the filter should have 1:10,000 bits stuck high or low. +# However we don't see stuck low bits are we are always reading +# zeroes, so we only expect about 1:20,000 bits stuck high. +# +# If we read 10,000,000 bytes (80,000,000 bits) we would expect about +# 4000 stuck bits. +# +# No matter where we read from the pattern of stuck bits should be the +# same (stuck wires, not backing bits). + +nbdsh -u "nbd+unix://?socket=$sock" \ + -c - <<EOF +def count_bits(buf): + r = 0 + for i in range(0, len(buf)-1): + if buf[i] != 0: + r += bin(buf[i]).count("1") + return r + +buf1 = h.pread(10000000, 0) +bits = count_bits(buf1) +print("stuck high bits: %d (expected 4000)" % bits) +assert(bits > 3000 and bits < 5000) + +# These buffers should be identical. +buf2 = h.pread(10000000, 1024) +buf3 = h.pread(10000000, 32*1024*1024 - 9999) +assert(buf1 == buf2) +assert(buf1 == buf3) + +EOF -- 2.39.2

On 5/16/23 14:12, Richard W.M. Jones wrote: This is a binomial distribution (in the example, n=10^6, p=10^(-4)): https://en.wikipedia.org/wiki/Binomial_distribution The expected value is E = n*p = 10^2, so the comment looks correct in that regard. There is a different interpretation for "we expect" as well. Namely, the "mode" -- the most probable outcome, the number of corrupted bits we're most probably going to see. That's a different concept <https://en.wikipedia.org/wiki/Mode_(statistics)>;. However, per the WP article, for the binomial distribution, it is essentially the same. Namely, the WP article says, for this distribution, the mode M (an integer) is given uniquely by (n + 1) * p - 1 <= M < (n + 1) * p [1] if ((n + 1) * p) is *not* an integer, and the M1 and M2 (equally probable, integer) modes M1 = (n + 1) * p [2] M2 = (n + 1) * p - 1 [3] if ((n + 1) * p) *is* an integer. Now,if we distribute the multiplications over the addends (break the parens open), we get: n * p + p - 1 <= M < n * p + p [1] M1 = n * p + p [2] M2 = n * p + p - 1 [3] But for the binomial distribution, E = n * p, so we can substitute (also rewriting +(p-1) as -(1-p) in [1]): E - (1 - p) <= M < E + p [1] M1 = E + p [2] M2 = E + p - 1 [3] Using the values from the code comment: n = 1,000,000 p = 0.000,1 E = n * p = 100 (n + 1) * p = 100.000,1 --> not an integer, so [1] applies: E - (1 - p) <= M < E + p [1] 99.000,1 <= M < 100.000,1 Therefore the mode M is 100 -- it equals the expected value E, for the particular "n" and "p" values! In general, they need not be equal. (For example, the mode(s) are always integers, but E need not be:if we change n to 1,000,001 then E is 100.0001, which is clearly impossible to interpret as a number of corrupted bits. It's effectively an average, but never directly produced by the distribution as a value.) Either way, my point is that M, M1 and M2 (from [1], [2], [3]) are very close to E in the general case too, so the "we expect" language applies even when we interpret it as "mode", not as "expected value". Two points: (1) I figure the idea is that the "average distance" will be 1/p bits -- the expected value being (0 + 2*(1/p))/2 == 1/p -- so we expect this "average distance" to fit n/(1/p) = n*p times in the block size. This looks sane, but I'm unequipped to make any arguments about "expected value". According to wikipedia, this is the Irwin-Hall distribution <https://en.wikipedia.org/wiki/Irwin%E2%80%93Hall_distribution>;: "the sum of a number of independent random variables, each having a uniform distribution". The individual random variables need to follow continuous (not discrete) uniform distributions though, so I don't know if Irwin-Hall "applies" here at all. Wikipedia says that, as "n" increases -- that is, as we sample our underlying uniform U(0, 1) distribution more and more times, and add up the results --, the distribution of the sum (= the Irwin-Hall distribution) approximates a Normal distribution, with both the epxected value and the mode being (s/2), where "s" is the number of samples (variables) summed. I don't know what happens if we scale the underlying U(0, 1) distribution's domain by 2/p, so that it becomes U(0, 2/p). I guess we'd *hope* that the expected value of the sum scales similarly, to: E = s/2 * 2/p = s/p Because in that case, we coul wish for the expected value (and mode) of the sum of the jumps to match our block size, that is: E = s/p = n or put differently, s = n*p Meaning that we'd expect having to sum as many "samples", i.e. having to take as many "jumps", in the average case, as n*p is (= 100 jumps with our numbers). But this is entirely hand-waving; I don't know if this holds up at all! (2) I think the interval as written is off-by-one. The left hand side (0) should indeed be inclusive, but the RHS 2*(1/p) should be *excluded*. We're supposed to have 20,000 integers in the set, from 0 to 19,999 inclusive. Some explanation on this would be nice. Laszlo