"NBD_FLAG_CAN_MULTI_CONN: Indicates that the server operates entirely without cache, or that the cache it uses is shared among all connections to the given device. In particular, if this flag is present, then the effects of NBD_CMD_FLUSH and NBD_CMD_FLAG_FUA MUST be visible across all connections when the server sends its reply to that command to the client. In the absence of this flag, clients SHOULD NOT multiplex their commands over more than one connection to the export." This is implemented in nbdkit by a boolean function which plugins may implement if they believe they satisfy the requirements above. It can also be passed through or modified by filters. It defaults to false, which is the safe default. --- docs/nbdkit-filter.pod | 4 ++++ docs/nbdkit-plugin.pod | 20 ++++++++++++++++++++ docs/nbdkit-protocol.pod | 4 ++++ include/nbdkit-filter.h | 3 +++ include/nbdkit-plugin.h | 2 ++ server/internal.h | 1 + server/protocol.h | 1 + server/connections.c | 9 +++++++++ server/filters.c | 24 ++++++++++++++++++++++++ server/plugins.c | 17 +++++++++++++++++ tests/test-layers-filter.c | 10 ++++++++++ tests/test-layers-plugin.c | 8 ++++++++ tests/test-layers.c | 6 ++++++ 13 files changed, 109 insertions(+) diff --git a/docs/nbdkit-filter.pod b/docs/nbdkit-filter.pod index 1e1bf5d..4f27adb 100644 --- a/docs/nbdkit-filter.pod +++ b/docs/nbdkit-filter.pod @@ -354,6 +354,8 @@ calls. =head2 C<.can_fua> +=head2 C<.can_multi_conn> + int (*can_write) (struct nbdkit_next_ops *next_ops, void *nxdata, void *handle); int (*can_flush) (struct nbdkit_next_ops *next_ops, void *nxdata, @@ -367,6 +369,8 @@ calls. void *handle); int (*can_fua) (struct nbdkit_next_ops *next_ops, void *nxdata, void *handle); + int (*can_multi_conn) (struct nbdkit_next_ops *next_ops, void *nxdata, + void *handle); These intercept the corresponding plugin methods, and control feature bits advertised to the client. diff --git a/docs/nbdkit-plugin.pod b/docs/nbdkit-plugin.pod index cfa14b0..c72ea0d 100644 --- a/docs/nbdkit-plugin.pod +++ b/docs/nbdkit-plugin.pod @@ -586,6 +586,26 @@ handle FUA requests. If omitted, nbdkit checks whether C<.flush> exists, and behaves as if this function returns C<NBDKIT_FUA_NONE> or C<NBDKIT_FUA_EMULATE> as appropriate. +=head2 C<.can_multi_conn> + + int can_multi_conn (void *handle); + +This is called during the option negotiation phase to find out if the +plugin can handle multiple connections from a single client. + +Specifically it means that either the plugin does not cache requests +at all. Or if it does cache then the effects of a C<.flush> request +or setting C<NBDKIT_FLAG_FUA> on a request must be visible across all +connections to the plugin before the plugin replies to that request. + +If you use the Linux NBD client with the I<-C> option then this flag +is checked. + +If there is an error, C<.can_multi_conn> should call C<nbdkit_error> +with an error message and return C<-1>. + +This callback is not required. If omitted, then we return false. + =head2 C<.pread> int pread (void *handle, void *buf, uint32_t count, uint64_t offset, diff --git a/docs/nbdkit-protocol.pod b/docs/nbdkit-protocol.pod index d5ba00f..db7fcf9 100644 --- a/docs/nbdkit-protocol.pod +++ b/docs/nbdkit-protocol.pod @@ -116,6 +116,10 @@ Supported in nbdkit E<ge> 1.9.3. This protocol enhancement allows a client to inspect details about the export without actually connecting. +=item C<NBD_FLAG_CAN_MULTI_CONN> + +Supported in nbdkit E<ge> 1.9.10. + =item Structured Replies I<Not supported>. diff --git a/include/nbdkit-filter.h b/include/nbdkit-filter.h index 931d923..71c06c8 100644 --- a/include/nbdkit-filter.h +++ b/include/nbdkit-filter.h @@ -59,6 +59,7 @@ struct nbdkit_next_ops { int (*can_trim) (void *nxdata); int (*can_zero) (void *nxdata); int (*can_fua) (void *nxdata); + int (*can_multi_conn) (void *nxdata); int (*pread) (void *nxdata, void *buf, uint32_t count, uint64_t offset, uint32_t flags, int *err); @@ -121,6 +122,8 @@ struct nbdkit_filter { void *handle); int (*can_fua) (struct nbdkit_next_ops *next_ops, void *nxdata, void *handle); + int (*can_multi_conn) (struct nbdkit_next_ops *next_ops, void *nxdata, + void *handle); int (*pread) (struct nbdkit_next_ops *next_ops, void *nxdata, void *handle, void *buf, uint32_t count, uint64_t offset, diff --git a/include/nbdkit-plugin.h b/include/nbdkit-plugin.h index 31aa6c7..d43b2f5 100644 --- a/include/nbdkit-plugin.h +++ b/include/nbdkit-plugin.h @@ -123,6 +123,8 @@ struct nbdkit_plugin { #endif const char *magic_config_key; + + int (*can_multi_conn) (void *handle); }; extern void nbdkit_set_error (int err); diff --git a/server/internal.h b/server/internal.h index e5c91a9..1f237a5 100644 --- a/server/internal.h +++ b/server/internal.h @@ -212,6 +212,7 @@ struct backend { int (*can_trim) (struct backend *, struct connection *conn); int (*can_zero) (struct backend *, struct connection *conn); int (*can_fua) (struct backend *, struct connection *conn); + int (*can_multi_conn) (struct backend *, struct connection *conn); int (*pread) (struct backend *, struct connection *conn, void *buf, uint32_t count, uint64_t offset, uint32_t flags, int *err); diff --git a/server/protocol.h b/server/protocol.h index 6709ddc..003fc45 100644 --- a/server/protocol.h +++ b/server/protocol.h @@ -94,6 +94,7 @@ extern const char *name_of_nbd_flag (int); #define NBD_FLAG_ROTATIONAL (1 << 4) #define NBD_FLAG_SEND_TRIM (1 << 5) #define NBD_FLAG_SEND_WRITE_ZEROES (1 << 6) +#define NBD_FLAG_CAN_MULTI_CONN (1 << 8) /* NBD options (new style handshake only). */ extern const char *name_of_nbd_opt (int); diff --git a/server/connections.c b/server/connections.c index 0a89315..51d4912 100644 --- a/server/connections.c +++ b/server/connections.c @@ -84,6 +84,7 @@ struct connection { bool can_trim; bool can_zero; bool can_fua; + bool can_multi_conn; bool using_tls; int sockin, sockout; @@ -463,6 +464,14 @@ compute_eflags (struct connection *conn, uint16_t *flags) conn->is_rotational = true; } + fl = backend->can_multi_conn (backend, conn); + if (fl == -1) + return -1; + if (fl) { + eflags |= NBD_FLAG_CAN_MULTI_CONN; + conn->can_multi_conn = true; + } + *flags = eflags; return 0; } diff --git a/server/filters.c b/server/filters.c index d02e7fb..5b7abc4 100644 --- a/server/filters.c +++ b/server/filters.c @@ -316,6 +316,13 @@ next_can_fua (void *nxdata) return b_conn->b->can_fua (b_conn->b, b_conn->conn); } +static int +next_can_multi_conn (void *nxdata) +{ + struct b_conn *b_conn = nxdata; + return b_conn->b->can_multi_conn (b_conn->b, b_conn->conn); +} + static int next_pread (void *nxdata, void *buf, uint32_t count, uint64_t offset, uint32_t flags, int *err) @@ -365,6 +372,7 @@ static struct nbdkit_next_ops next_ops = { .can_trim = next_can_trim, .can_zero = next_can_zero, .can_fua = next_can_fua, + .can_multi_conn = next_can_multi_conn, .pread = next_pread, .pwrite = next_pwrite, .flush = next_flush, @@ -518,6 +526,21 @@ filter_can_fua (struct backend *b, struct connection *conn) return f->backend.next->can_fua (f->backend.next, conn); } +static int +filter_can_multi_conn (struct backend *b, struct connection *conn) +{ + struct backend_filter *f = container_of (b, struct backend_filter, backend); + void *handle = connection_get_handle (conn, f->backend.i); + struct b_conn nxdata = { .b = f->backend.next, .conn = conn }; + + debug ("%s: can_multi_conn", f->name); + + if (f->filter.can_multi_conn) + return f->filter.can_multi_conn (&next_ops, &nxdata, handle); + else + return f->backend.next->can_multi_conn (f->backend.next, conn); +} + static int filter_pread (struct backend *b, struct connection *conn, void *buf, uint32_t count, uint64_t offset, @@ -645,6 +668,7 @@ static struct backend filter_functions = { .can_trim = filter_can_trim, .can_zero = filter_can_zero, .can_fua = filter_can_fua, + .can_multi_conn = filter_can_multi_conn, .pread = filter_pread, .pwrite = filter_pwrite, .flush = filter_flush, diff --git a/server/plugins.c b/server/plugins.c index cb0f411..bbde578 100644 --- a/server/plugins.c +++ b/server/plugins.c @@ -197,6 +197,7 @@ plugin_dump_fields (struct backend *b) HAS (flush); HAS (trim); HAS (zero); + HAS (can_multi_conn); #undef HAS /* Custom fields. */ @@ -414,6 +415,21 @@ plugin_can_fua (struct backend *b, struct connection *conn) return NBDKIT_FUA_NONE; } +static int +plugin_can_multi_conn (struct backend *b, struct connection *conn) +{ + struct backend_plugin *p = container_of (b, struct backend_plugin, backend); + + assert (connection_get_handle (conn, 0)); + + debug ("can_multi_conn"); + + if (p->plugin.can_multi_conn) + return p->plugin.can_multi_conn (connection_get_handle (conn, 0)); + else + return 0; /* assume false */ +} + /* Plugins and filters can call this to set the true errno, in cases * where !errno_is_preserved. */ @@ -656,6 +672,7 @@ static struct backend plugin_functions = { .can_trim = plugin_can_trim, .can_zero = plugin_can_zero, .can_fua = plugin_can_fua, + .can_multi_conn = plugin_can_multi_conn, .pread = plugin_pread, .pwrite = plugin_pwrite, .flush = plugin_flush, diff --git a/tests/test-layers-filter.c b/tests/test-layers-filter.c index c5a96e7..6da6ee6 100644 --- a/tests/test-layers-filter.c +++ b/tests/test-layers-filter.c @@ -167,6 +167,15 @@ test_layers_filter_can_fua (struct nbdkit_next_ops *next_ops, void *nxdata, return next_ops->can_fua (nxdata); } +static int +test_layers_filter_can_multi_conn (struct nbdkit_next_ops *next_ops, + void *nxdata, + void *handle) +{ + DEBUG_FUNCTION; + return next_ops->can_multi_conn (nxdata); +} + static int test_layers_filter_pread (struct nbdkit_next_ops *next_ops, void *nxdata, void *handle, void *buf, @@ -233,6 +242,7 @@ static struct nbdkit_filter filter = { .can_trim = test_layers_filter_can_trim, .can_zero = test_layers_filter_can_zero, .can_fua = test_layers_filter_can_fua, + .can_multi_conn = test_layers_filter_can_multi_conn, .pread = test_layers_filter_pread, .pwrite = test_layers_filter_pwrite, .flush = test_layers_filter_flush, diff --git a/tests/test-layers-plugin.c b/tests/test-layers-plugin.c index 3befcc1..042ecc3 100644 --- a/tests/test-layers-plugin.c +++ b/tests/test-layers-plugin.c @@ -137,6 +137,13 @@ test_layers_plugin_can_fua (void *handle) return NBDKIT_FUA_NATIVE; } +static int +test_layers_plugin_can_multi_conn (void *handle) +{ + DEBUG_FUNCTION; + return 1; +} + static int test_layers_plugin_pread (void *handle, void *buf, uint32_t count, uint64_t offset, @@ -196,6 +203,7 @@ static struct nbdkit_plugin plugin = { .can_trim = test_layers_plugin_can_trim, .can_zero = test_layers_plugin_can_zero, .can_fua = test_layers_plugin_can_fua, + .can_multi_conn = test_layers_plugin_can_multi_conn, .pread = test_layers_plugin_pread, .pwrite = test_layers_plugin_pwrite, .flush = test_layers_plugin_flush, diff --git a/tests/test-layers.c b/tests/test-layers.c index 261b9c6..c8d15d2 100644 --- a/tests/test-layers.c +++ b/tests/test-layers.c @@ -349,6 +349,12 @@ main (int argc, char *argv[]) "filter1: test_layers_filter_is_rotational", "test_layers_plugin_is_rotational", NULL); + log_verify_seen_in_order + ("filter3: test_layers_filter_can_multi_conn", + "filter2: test_layers_filter_can_multi_conn", + "filter1: test_layers_filter_can_multi_conn", + "test_layers_plugin_can_multi_conn", + NULL); fprintf (stderr, "%s: protocol connected\n", program_name); -- 2.19.2

After examining each filter and where it appears that the filter implements a cache and does not properly consider consistency across clients for flush requests, force .can_multi_conn to return false. In fact I believe only one filter (blocksize) needs to be updated and all the other ones are safe. --- filters/blocksize/blocksize.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/filters/blocksize/blocksize.c b/filters/blocksize/blocksize.c index 34f58c9..9e0e713 100644 --- a/filters/blocksize/blocksize.c +++ b/filters/blocksize/blocksize.c @@ -164,6 +164,17 @@ blocksize_get_size (struct nbdkit_next_ops *next_ops, void *nxdata, return size == -1 ? size : size & ~(minblock - 1); } +static int +blocksize_can_multi_conn (struct nbdkit_next_ops *next_ops, void *nxdata, + void *handle) +{ + /* Although we are serializing all requests anyway so this likely + * doesn't make a difference, return false because the bounce buffer + * is not consistent for flush. + */ + return 0; +} + static int blocksize_pread (struct nbdkit_next_ops *next_ops, void *nxdata, void *handle, void *b, uint32_t count, uint64_t offs, @@ -370,6 +381,7 @@ static struct nbdkit_filter filter = { .config_help = blocksize_config_help, .prepare = blocksize_prepare, .get_size = blocksize_get_size, + .can_multi_conn = blocksize_can_multi_conn, .pread = blocksize_pread, .pwrite = blocksize_pwrite, .trim = blocksize_trim, -- 2.19.2

--- plugins/ocaml/ocaml.c | 25 +++++++++++++++++++++++++ plugins/ocaml/NBDKit.ml | 10 +++++++++- plugins/ocaml/NBDKit.mli | 2 ++ 3 files changed, 36 insertions(+), 1 deletion(-) diff --git a/plugins/ocaml/ocaml.c b/plugins/ocaml/ocaml.c index 7dd5e4e..a89ad08 100644 --- a/plugins/ocaml/ocaml.c +++ b/plugins/ocaml/ocaml.c @@ -111,6 +111,8 @@ static value flush_fn; static value trim_fn; static value zero_fn; +static value can_multi_conn_fn; + /* Wrapper functions that translate calls from C (ie. nbdkit) to OCaml. */ static void @@ -167,6 +169,8 @@ unload_wrapper (void) REMOVE (flush); REMOVE (trim); REMOVE (zero); + + REMOVE (can_multi_conn); } static int @@ -550,6 +554,25 @@ zero_wrapper (void *h, uint32_t count, uint64_t offset, uint32_t flags) CAMLreturnT (int, 0); } +static int +can_multi_conn_wrapper (void *h) +{ + CAMLparam0 (); + CAMLlocal1 (rv); + + caml_leave_blocking_section (); + + rv = caml_callback_exn (can_multi_conn_fn, *(value *) h); + if (Is_exception_result (rv)) { + nbdkit_error ("%s", caml_format_exception (Extract_exception (rv))); + caml_enter_blocking_section (); + CAMLreturnT (int, -1); + } + + caml_enter_blocking_section (); + CAMLreturnT (int, Bool_val (rv)); +} + value ocaml_nbdkit_set_thread_model (value modelv) { @@ -629,6 +652,8 @@ SET(flush) SET(trim) SET(zero) +SET(can_multi_conn) + /* NB: noalloc function. */ value ocaml_nbdkit_set_error (value nv) diff --git a/plugins/ocaml/NBDKit.ml b/plugins/ocaml/NBDKit.ml index 1937bc2..fdeecd3 100644 --- a/plugins/ocaml/NBDKit.ml +++ b/plugins/ocaml/NBDKit.ml @@ -71,6 +71,8 @@ type 'a plugin = { flush : ('a -> flags -> unit) option; trim : ('a -> int32 -> int64 -> flags -> unit) option; zero : ('a -> int32 -> int64 -> flags -> unit) option; + + can_multi_conn : ('a -> bool) option; } let default_callbacks = { @@ -106,6 +108,8 @@ let default_callbacks = { flush = None; trim = None; zero = None; + + can_multi_conn = None; } type thread_model = @@ -149,6 +153,8 @@ external set_flush : ('a -> flags -> unit) -> unit = "ocaml_nbdkit_set_flush" external set_trim : ('a -> int32 -> int64 -> flags -> unit) -> unit = "ocaml_nbdkit_set_trim" external set_zero : ('a -> int32 -> int64 -> flags -> unit) -> unit = "ocaml_nbdkit_set_zero" +external set_can_multi_conn : ('a -> bool) -> unit = "ocaml_nbdkit_set_can_multi_conn" + let may f = function None -> () | Some a -> f a let register_plugin thread_model plugin = @@ -203,7 +209,9 @@ let register_plugin thread_model plugin = may set_pwrite plugin.pwrite; may set_flush plugin.flush; may set_trim plugin.trim; - may set_zero plugin.zero + may set_zero plugin.zero; + + may set_can_multi_conn plugin.can_multi_conn external _set_error : int -> unit = "ocaml_nbdkit_set_error" "noalloc" diff --git a/plugins/ocaml/NBDKit.mli b/plugins/ocaml/NBDKit.mli index c0f9248..ec888ce 100644 --- a/plugins/ocaml/NBDKit.mli +++ b/plugins/ocaml/NBDKit.mli @@ -73,6 +73,8 @@ type 'a plugin = { flush : ('a -> flags -> unit) option; trim : ('a -> int32 -> int64 -> flags -> unit) option; zero : ('a -> int32 -> int64 -> flags -> unit) option; + + can_multi_conn : ('a -> bool) option; } (** The plugin fields and callbacks. ['a] is the handle type. *) -- 2.19.2

Upgrade this plugin to version 2 of the API. The main change is implementing FUA support. --- plugins/file/file.c | 62 ++++++++++++++++++++++++++++++--------------- 1 file changed, 42 insertions(+), 20 deletions(-) diff --git a/plugins/file/file.c b/plugins/file/file.c index 2a8c9b5..e564787 100644 --- a/plugins/file/file.c +++ b/plugins/file/file.c @@ -52,6 +52,8 @@ #include <linux/fs.h> /* For BLKZEROOUT */ #endif +#define NBDKIT_API_VERSION 2 + #include <nbdkit-plugin.h> #include "isaligned.h" @@ -263,9 +265,30 @@ file_can_trim (void *handle) #endif } +static int +file_can_fua (void *handle) +{ + return NBDKIT_FUA_NATIVE; +} + +/* Flush the file to disk. */ +static int +file_flush (void *handle, uint32_t flags) +{ + struct handle *h = handle; + + if (fdatasync (h->fd) == -1) { + nbdkit_error ("fdatasync: %m"); + return -1; + } + + return 0; +} + /* Read data from the file. */ static int -file_pread (void *handle, void *buf, uint32_t count, uint64_t offset) +file_pread (void *handle, void *buf, uint32_t count, uint64_t offset, + uint32_t flags) { struct handle *h = handle; @@ -289,7 +312,8 @@ file_pread (void *handle, void *buf, uint32_t count, uint64_t offset) /* Write data to the file. */ static int -file_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset) +file_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset, + uint32_t flags) { struct handle *h = handle; @@ -304,6 +328,9 @@ file_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset) offset += r; } + if (flags & NBDKIT_FLAG_FUA && file_flush (handle, 0) == -1) + return -1; + return 0; } @@ -323,20 +350,20 @@ do_fallocate(int fd, int mode, off_t offset, off_t len) /* Write zeroes to the file. */ static int -file_zero (void *handle, uint32_t count, uint64_t offset, int may_trim) +file_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags) { struct handle *h = handle; int r; #ifdef FALLOC_FL_PUNCH_HOLE - if (h->can_punch_hole && may_trim) { + if (h->can_punch_hole && (flags & NBDKIT_FLAG_MAY_TRIM)) { r = do_fallocate (h->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, offset, count); if (r == 0) { if (file_debug_zero) nbdkit_debug ("h->can_punch_hole && may_trim: " "zero succeeded using fallocate"); - return 0; + goto out; } if (errno != EOPNOTSUPP) { @@ -355,7 +382,7 @@ file_zero (void *handle, uint32_t count, uint64_t offset, int may_trim) if (file_debug_zero) nbdkit_debug ("h->can_zero-range: " "zero succeeded using fallocate"); - return 0; + goto out; } if (errno != EOPNOTSUPP) { @@ -380,7 +407,7 @@ file_zero (void *handle, uint32_t count, uint64_t offset, int may_trim) if (file_debug_zero) nbdkit_debug ("h->can_punch_hole && h->can_fallocate: " "zero succeeded using fallocate"); - return 0; + goto out; } if (errno != EOPNOTSUPP) { @@ -410,7 +437,7 @@ file_zero (void *handle, uint32_t count, uint64_t offset, int may_trim) if (file_debug_zero) nbdkit_debug ("h->can_zeroout && IS_ALIGNED: " "zero succeeded using BLKZEROOUT"); - return 0; + goto out; } if (errno != ENOTTY) { @@ -427,25 +454,16 @@ file_zero (void *handle, uint32_t count, uint64_t offset, int may_trim) nbdkit_debug ("zero falling back to writing"); errno = EOPNOTSUPP; return -1; -} -/* Flush the file to disk. */ -static int -file_flush (void *handle) -{ - struct handle *h = handle; - - if (fdatasync (h->fd) == -1) { - nbdkit_error ("fdatasync: %m"); + out: + if (flags & NBDKIT_FLAG_FUA && file_flush (handle, 0) == -1) return -1; - } - return 0; } /* Punch a hole in the file. */ static int -file_trim (void *handle, uint32_t count, uint64_t offset) +file_trim (void *handle, uint32_t count, uint64_t offset, uint32_t flags) { #ifdef FALLOC_FL_PUNCH_HOLE struct handle *h = handle; @@ -470,6 +488,9 @@ file_trim (void *handle, uint32_t count, uint64_t offset) } #endif + if (flags & NBDKIT_FLAG_FUA && file_flush (handle, 0) == -1) + return -1; + return 0; } @@ -487,6 +508,7 @@ static struct nbdkit_plugin plugin = { .close = file_close, .get_size = file_get_size, .can_trim = file_can_trim, + .can_fua = file_can_fua, .pread = file_pread, .pwrite = file_pwrite, .flush = file_flush, -- 2.19.2