7:26 a.m.
To avoid breaking existing plugins, Python plugins wishing to use
version 2 of the API must opt in by declaring:
API_VERSION = 2
(Plugins which do not do this are assumed to want API version 1).
---
plugins/python/example.py | 14 ++-
plugins/python/nbdkit-python-plugin.pod | 56 +++++++-----
plugins/python/python.c | 114 ++++++++++++++++++++----
tests/test.py | 20 +++--
4 files changed, 156 insertions(+), 48 deletions(-)
diff --git a/plugins/python/example.py b/plugins/python/example.py
index 60f9d7f..c85d2f8 100644
--- a/plugins/python/example.py
+++ b/plugins/python/example.py
@@ -34,6 +34,12 @@ import errno
disk = bytearray(1024 * 1024)
+# There are several variants of the API. nbdkit will call this
+# function first to determine which one you want to use. This is the
+# latest version at the time this example was written.
+API_VERSION = 2
+
+
# This just prints the extra command line parameters, but real plugins
# should parse them and reject any unknown parameters.
def config(key, value):
@@ -54,20 +60,20 @@ def get_size(h):
return len(disk)
-def pread(h, count, offset):
+def pread(h, count, offset, flags):
global disk
return disk[offset:offset+count]
-def pwrite(h, buf, offset):
+def pwrite(h, buf, offset, flags):
global disk
end = offset + len(buf)
disk[offset:end] = buf
-def zero(h, count, offset, may_trim):
+def zero(h, count, offset, flags):
global disk
- if may_trim:
+ if flags & nbdkit.FLAG_MAY_TRIM:
disk[offset:offset+count] = bytearray(count)
else:
nbdkit.set_error(errno.EOPNOTSUPP)
diff --git a/plugins/python/nbdkit-python-plugin.pod
b/plugins/python/nbdkit-python-plugin.pod
index e089bc9..f393e8f 100644
--- a/plugins/python/nbdkit-python-plugin.pod
+++ b/plugins/python/nbdkit-python-plugin.pod
@@ -82,6 +82,18 @@ I<--dump-plugin> option, eg:
python_version=3.7.0
python_pep_384_abi_version=3
+=head2 API versions
+
+The nbdkit API has evolved and new versions are released periodically.
+To ensure backwards compatibility plugins have to opt in to the new
+version. From Python you do this by declaring a constant in your
+module:
+
+ API_VERSION = 2
+
+(where 2 is the latest version at the time this documentation was
+written). All newly written Python modules must have this constant.
+
=head2 Executable script
If you want you can make the script executable and include a "shebang"
@@ -199,12 +211,12 @@ contents will be garbage collected.
(Required)
- def pread(h, count, offset):
+ def pread(h, count, offset, flags):
# construct a bytearray of length count bytes and return it
The body of your C<pread> function should construct a buffer of length
(at least) C<count> bytes. You should read C<count> bytes from the
-disk starting at C<offset>.
+disk starting at C<offset>. C<flags> is always 0.
NBD only supports whole reads, so your function should try to read
the whole region (perhaps requiring a loop). If the read fails or
@@ -215,13 +227,13 @@ C<nbdkit.set_error> first.
(Optional)
- def pwrite(h, buf, offset):
+ def pwrite(h, buf, offset, flags):
length = len (buf)
# no return value
The body of your C<pwrite> function should write the C<buf> string to
the disk. You should write C<count> bytes to the disk starting at
-C<offset>.
+C<offset>. C<flags> may contain C<nbdkit.FLAG_FUA>.
NBD only supports whole writes, so your function should try to
write the whole region (perhaps requiring a loop). If the write
@@ -232,11 +244,12 @@ fails or is partial, your function should throw an exception,
(Optional)
- def flush(h):
+ def flush(h, flags):
# no return value
The body of your C<flush> function should do a L<sync(2)> or
L<fdatasync(2)> or equivalent on the backing store.
+C<flags> is always 0.
If the flush fails, your function should throw an exception, optionally
using C<nbdkit.set_error> first.
@@ -245,32 +258,35 @@ using C<nbdkit.set_error> first.
(Optional)
- def trim(h, count, offset):
+ def trim(h, count, offset, flags):
# no return value
-The body of your C<trim> function should "punch a hole" in the
-backing store. If the trim fails, your function should throw an
-exception, optionally using C<nbdkit.set_error> first.
+The body of your C<trim> function should "punch a hole" in the backing
+store. C<flags> may contain C<nbdkit.FLAG_FUA>. If the trim fails,
+your function should throw an exception, optionally using
+C<nbdkit.set_error> first.
=item C<zero>
(Optional)
- def zero(h, count, offset, may_trim):
+ def zero(h, count, offset, flags):
# no return value
-The body of your C<zero> function should ensure that C<count> bytes
-of the disk, starting at C<offset>, will read back as zero. If
-C<may_trim> is true, the operation may be optimized as a trim as long
-as subsequent reads see zeroes.
+The body of your C<zero> function should ensure that C<count> bytes of
+the disk, starting at C<offset>, will read back as zero. C<flags> is
+a bitmask which may include C<nbdkit.FLAG_MAY_TRIM>,
+C<nbdkit.FLAG_FUA>, C<nbdkit.FLAG_FAST_ZERO>.
NBD only supports whole writes, so your function should try to
-write the whole region (perhaps requiring a loop). If the write
-fails or is partial, your function should throw an exception,
-optionally using C<nbdkit.set_error> first. In particular, if
-you would like to automatically fall back to C<pwrite> (perhaps
-because there is nothing to optimize if C<may_trim> is false),
-use C<nbdkit.set_error(errno.EOPNOTSUPP)>.
+write the whole region (perhaps requiring a loop).
+
+If the write fails or is partial, your function should throw an
+exception, optionally using C<nbdkit.set_error> first. In particular,
+if you would like to automatically fall back to C<pwrite> (perhaps
+because there is nothing to optimize if
+S<C<flags & nbdkit.FLAG_MAY_TRIM>> is false), use
+S<C<nbdkit.set_error (errno.EOPNOTSUPP)>>.
=back
diff --git a/plugins/python/python.c b/plugins/python/python.c
index 52eb752..66f9232 100644
--- a/plugins/python/python.c
+++ b/plugins/python/python.c
@@ -46,6 +46,8 @@
#define PY_SSIZE_T_CLEAN 1
#include <Python.h>
+#define NBDKIT_API_VERSION 2
+
#include <nbdkit-plugin.h>
#include "cleanup.h"
@@ -60,6 +62,7 @@
*/
static const char *script;
static PyObject *module;
+static int py_api_version = 1;
static int last_error;
@@ -285,9 +288,14 @@ py_dump_plugin (void)
PyObject *fn;
PyObject *r;
+ /* Python version and ABI. */
printf ("python_version=%s\n", PY_VERSION);
printf ("python_pep_384_abi_version=%d\n", PYTHON_ABI_VERSION);
+ /* Maximum nbdkit API version supported. */
+ printf ("nbdkit_python_maximum_api_version=%d\n", NBDKIT_API_VERSION);
+
+ /* If the script has a dump_plugin function, call it. */
if (script && callback_defined ("dump_plugin", &fn)) {
PyErr_Clear ();
@@ -297,6 +305,30 @@ py_dump_plugin (void)
}
}
+static int
+get_py_api_version (void)
+{
+ PyObject *obj;
+ long value;
+
+ obj = PyObject_GetAttrString (module, "API_VERSION");
+ if (obj == NULL)
+ return 1; /* Default to API version 1. */
+
+ value = PyLong_AsLong (obj);
+ Py_DECREF (obj);
+
+ if (value < 1 || value > NBDKIT_API_VERSION) {
+ nbdkit_error ("%s: API_VERSION requested unknown version: %ld. "
+ "This plugin supports API versions between 1 and %d.",
+ script, value, NBDKIT_API_VERSION);
+ return -1;
+ }
+
+ nbdkit_debug ("module requested API_VERSION %ld", value);
+ return (int) value;
+}
+
static int
py_config (const char *key, const char *value)
{
@@ -359,6 +391,11 @@ py_config (const char *key, const char *value)
"nbdkit requires these callbacks.", script);
return -1;
}
+
+ /* Get the API version. */
+ py_api_version = get_py_api_version ();
+ if (py_api_version == -1)
+ return -1;
}
else if (callback_defined ("config", &fn)) {
/* Other parameters are passed to the Python .config callback. */
@@ -469,8 +506,8 @@ py_get_size (void *handle)
}
static int
-py_pread (void *handle, void *buf,
- uint32_t count, uint64_t offset)
+py_pread (void *handle, void *buf, uint32_t count, uint64_t offset,
+ uint32_t flags)
{
PyObject *obj = handle;
PyObject *fn;
@@ -485,7 +522,15 @@ py_pread (void *handle, void *buf,
PyErr_Clear ();
- r = PyObject_CallFunction (fn, "OiL", obj, count, offset, NULL);
+ switch (py_api_version) {
+ case 1:
+ r = PyObject_CallFunction (fn, "OiL", obj, count, offset, NULL);
+ break;
+ case 2:
+ r = PyObject_CallFunction (fn, "OiLI", obj, count, offset, flags, NULL);
+ break;
+ default: abort ();
+ }
Py_DECREF (fn);
if (check_python_failure ("pread") == -1)
return ret;
@@ -515,8 +560,8 @@ out:
}
static int
-py_pwrite (void *handle, const void *buf,
- uint32_t count, uint64_t offset)
+py_pwrite (void *handle, const void *buf, uint32_t count, uint64_t offset,
+ uint32_t flags)
{
PyObject *obj = handle;
PyObject *fn;
@@ -525,9 +570,19 @@ py_pwrite (void *handle, const void *buf,
if (callback_defined ("pwrite", &fn)) {
PyErr_Clear ();
- r = PyObject_CallFunction (fn, "ONL", obj,
- PyByteArray_FromStringAndSize (buf, count),
- offset, NULL);
+ switch (py_api_version) {
+ case 1:
+ r = PyObject_CallFunction (fn, "ONL", obj,
+ PyByteArray_FromStringAndSize (buf, count),
+ offset, NULL);
+ break;
+ case 2:
+ r = PyObject_CallFunction (fn, "ONLI", obj,
+ PyByteArray_FromStringAndSize (buf, count),
+ offset, flags, NULL);
+ break;
+ default: abort ();
+ }
Py_DECREF (fn);
if (check_python_failure ("pwrite") == -1)
return -1;
@@ -542,7 +597,7 @@ py_pwrite (void *handle, const void *buf,
}
static int
-py_flush (void *handle)
+py_flush (void *handle, uint32_t flags)
{
PyObject *obj = handle;
PyObject *fn;
@@ -551,7 +606,15 @@ py_flush (void *handle)
if (callback_defined ("flush", &fn)) {
PyErr_Clear ();
- r = PyObject_CallFunctionObjArgs (fn, obj, NULL);
+ switch (py_api_version) {
+ case 1:
+ r = PyObject_CallFunctionObjArgs (fn, obj, NULL);
+ break;
+ case 2:
+ r = PyObject_CallFunction (fn, "OI", obj, flags, NULL);
+ break;
+ default: abort ();
+ }
Py_DECREF (fn);
if (check_python_failure ("flush") == -1)
return -1;
@@ -566,7 +629,7 @@ py_flush (void *handle)
}
static int
-py_trim (void *handle, uint32_t count, uint64_t offset)
+py_trim (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
{
PyObject *obj = handle;
PyObject *fn;
@@ -575,7 +638,15 @@ py_trim (void *handle, uint32_t count, uint64_t offset)
if (callback_defined ("trim", &fn)) {
PyErr_Clear ();
- r = PyObject_CallFunction (fn, "OiL", obj, count, offset, NULL);
+ switch (py_api_version) {
+ case 1:
+ r = PyObject_CallFunction (fn, "OiL", obj, count, offset, NULL);
+ break;
+ case 2:
+ r = PyObject_CallFunction (fn, "OiLI", obj, count, offset, flags, NULL);
+ break;
+ default: abort ();
+ }
Py_DECREF (fn);
if (check_python_failure ("trim") == -1)
return -1;
@@ -590,7 +661,7 @@ py_trim (void *handle, uint32_t count, uint64_t offset)
}
static int
-py_zero (void *handle, uint32_t count, uint64_t offset, int may_trim)
+py_zero (void *handle, uint32_t count, uint64_t offset, uint32_t flags)
{
PyObject *obj = handle;
PyObject *fn;
@@ -600,9 +671,20 @@ py_zero (void *handle, uint32_t count, uint64_t offset, int
may_trim)
PyErr_Clear ();
last_error = 0;
- r = PyObject_CallFunction (fn, "OiLO",
- obj, count, offset,
- may_trim ? Py_True : Py_False, NULL);
+ switch (py_api_version) {
+ case 1: {
+ int may_trim = flags & NBDKIT_FLAG_MAY_TRIM;
+ r = PyObject_CallFunction (fn, "OiLO",
+ obj, count, offset,
+ may_trim ? Py_True : Py_False, NULL);
+ break;
+ }
+ case 2:
+ r = PyObject_CallFunction (fn, "OiLI",
+ obj, count, offset, flags, NULL);
+ break;
+ default: abort ();
+ }
Py_DECREF (fn);
if (last_error == EOPNOTSUPP || last_error == ENOTSUP) {
/* When user requests this particular error, we want to
diff --git a/tests/test.py b/tests/test.py
index 9a2e947..ac80d96 100644
--- a/tests/test.py
+++ b/tests/test.py
@@ -3,6 +3,10 @@ import nbdkit
disk = bytearray(1024*1024)
+def api_version():
+ return 2
+
+
def config_complete():
print ("set_error = %r" % nbdkit.set_error)
@@ -32,25 +36,25 @@ def can_trim(h):
return True
-def pread(h, count, offset):
+def pread(h, count, offset, flags):
global disk
return disk[offset:offset+count]
-def pwrite(h, buf, offset):
+def pwrite(h, buf, offset, flags):
global disk
end = offset + len(buf)
disk[offset:end] = buf
-def zero(h, count, offset, may_trim=False):
- global disk
- disk[offset:offset+count] = bytearray(count)
+def flush(h, flags):
+ pass
-def flush(h):
+def trim(h, count, offset, flags):
pass
-def trim(h, count, offset):
- pass
+def zero(h, count, offset, flags):
+ global disk
+ disk[offset:offset+count] = bytearray(count)
--
2.23.0