qemu-e2k/docs/interop
Eric Blake 0a4795455c nbd: Prepare for NBD_CMD_FLAG_FAST_ZERO
Commit fe0480d6 and friends added BDRV_REQ_NO_FALLBACK as a way to
avoid wasting time on a preliminary write-zero request that will later
be rewritten by actual data, if it is known that the write-zero
request will use a slow fallback; but in doing so, could not optimize
for NBD.  The NBD specification is now considering an extension that
will allow passing on those semantics; this patch updates the new
protocol bits and 'qemu-nbd --list' output to recognize the bit, as
well as the new errno value possible when using the new flag; while
upcoming patches will improve the client to use the feature when
present, and the server to advertise support for it.

The NBD spec recommends (but not requires) that ENOTSUP be avoided for
all but failures of a fast zero (the only time it is mandatory to
avoid an ENOTSUP failure is when fast zero is supported but not
requested during write zeroes; the questionable use is for ENOTSUP to
other actions like a normal write request).  However, clients that get
an unexpected ENOTSUP will either already be treating it the same as
EINVAL, or may appreciate the extra bit of information.  We were
equally loose for returning EOVERFLOW in more situations than
recommended by the spec, so if it turns out to be a problem in
practice, a later patch can tighten handling for both error codes.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20190823143726.27062-3-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
[eblake: tweak commit message, also handle EOPNOTSUPP]
2019-09-05 16:03:13 -05:00
..
bitmaps.rst docs/bitmaps: use QMP lexer instead of json 2019-07-10 15:08:07 -04:00
conf.py docs: Provide separate conf.py for each manual we want 2019-03-07 14:26:46 +00:00
firmware.json qapi: Move query-target from misc.json to machine.json 2019-08-21 13:24:01 +02:00
index.rst vhost-user: add vhost_user_gpu_set_socket() 2019-05-29 06:29:07 +02:00
live-block-operations.rst Remove the deprecated -nodefconfig option 2018-08-31 09:52:46 +02:00
nbd.txt nbd: Prepare for NBD_CMD_FLAG_FAST_ZERO 2019-09-05 16:03:13 -05:00
parallels.txt
pr-helper.rst scsi: build qemu-pr-helper 2017-09-22 21:07:24 +02:00
prl-xml.txt docs/interop/prl-xml: description of Parallels Disk format 2018-01-22 14:02:33 +00:00
qcow2.txt docs/interop/qcow2: Improve bitmap flag in_use specification 2019-03-12 12:06:11 -04:00
qed_spec.txt
qemu-ga-ref.texi
qemu-qmp-ref.texi
qmp-intro.txt docs/interop/qmp: Improve OOB documentation 2018-07-03 23:09:31 +02:00
qmp-spec.txt docs: Update references to JSON RFC 2018-12-13 19:10:06 +01:00
vhost-user-gpu.rst vhost-user: add vhost_user_gpu_set_socket() 2019-05-29 06:29:07 +02:00
vhost-user.json docs/vhost-user.json: some firmware.json copy leftovers 2019-06-16 16:16:52 -04:00
vhost-user.rst docs: clarify multiqueue vs multiple virtqueues 2019-07-25 04:17:34 -04:00
vnc-ledstate-Pseudo-encoding.txt