qemu-e2k/block
Eric Blake 737d3f5244 nbd-client: Work around server BLOCK_STATUS misalignment at EOF
The NBD spec is clear that a server that advertises a minimum block
size should reply to NBD_CMD_BLOCK_STATUS with extents aligned
accordingly. However, we know that the qemu NBD server implementation
has had a corner-case bug where it is not compliant with the spec,
present since the introduction of NBD_CMD_BLOCK_STATUS in qemu 2.12
(and unlikely to be patched in time for 4.0). Namely, when qemu is
serving a file that is not a multiple of 512 bytes, it rounds the size
advertised over NBD up to the next sector boundary (someday, I'd like
to fix that to be byte-accurate, but it's a much bigger audit not
appropriate for this release); yet if the final sector contains data
prior to EOF, lseek(SEEK_HOLE) will point to the implicit hole
mid-sector which qemu then reported over NBD.

We are well within our rights to hang up on a server that can't follow
the spec, but it is more useful to try and keep the connection alive
in spite of the problem. Do so by tracing a message about the problem,
and then either truncating the request back to an aligned boundary (if
it covered more than the final sector) or widening it out to the full
boundary with a forced status of data (since truncating would result
in 0 bytes, but we have to make progress, and valid since data is a
default-safe answer). And in practice, since the problem only happens
on a sector that starts with data and ends with a hole, we are going
to want to read that full sector anyway (where qemu as the server
fills in the tail beyond EOF with appropriate NUL bytes).

Easy reproduction:
$ printf %1000d 1 > file
$ qemu-nbd -f raw -t file & pid=$!
$ qemu-img map --output=json -f raw nbd://localhost:10809
qemu-img: Could not read file metadata: Invalid argument
$ kill $pid

where the patched version instead succeeds with:
[{ "start": 0, "length": 1024, "depth": 0, "zero": false, "data": true}]

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20190326171317.4036-1-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
2019-03-30 10:06:08 -05:00
..
accounting.c
backup.c block/backup: use qemu_iovec_init_buf 2019-02-22 09:42:13 +00:00
blkdebug.c block: Advertise BDRV_REQ_NO_FALLBACK in filter drivers 2019-03-26 11:37:51 +01:00
blklogwrites.c block: Purify .bdrv_refresh_filename() 2019-02-25 15:11:27 +01:00
blkreplay.c
blkverify.c block: Purify .bdrv_refresh_filename() 2019-02-25 15:11:27 +01:00
block-backend.c Block layer patches: 2019-02-26 19:04:47 +00:00
bochs.c avoid TABs in files that only contain a few 2019-01-11 15:46:56 +01:00
cloop.c
commit.c block: Freeze the backing chain for the duration of the commit job 2019-03-12 20:30:14 +01:00
copy-on-read.c block: Advertise BDRV_REQ_NO_FALLBACK in filter drivers 2019-03-26 11:37:51 +01:00
create.c
crypto.c block: Make bdrv_{copy_on_read,crypto_luks,replication} static 2019-03-19 15:49:29 +01:00
crypto.h
curl.c block/curl: Implement bdrv_refresh_filename() 2019-02-25 15:11:27 +01:00
dirty-bitmap.c bitmaps: Fix typo in function name 2019-03-12 12:05:49 -04:00
dmg-bz2.c
dmg-lzfse.c
dmg.c dmg: don't skip zero chunk 2019-01-04 11:15:09 +00:00
dmg.h
file-posix.c file-posix: Support BDRV_REQ_NO_FALLBACK for zero writes 2019-03-26 11:37:51 +01:00
file-win32.c avoid TABs in files that only contain a few 2019-01-11 15:46:56 +01:00
gluster.c gluster: the glfs_io_cbk callback function pointer adds pre/post stat args 2019-03-12 14:26:49 +01:00
io.c block: Add BDRV_REQ_NO_FALLBACK 2019-03-26 11:37:51 +01:00
iscsi-opts.c
iscsi.c block/iscsi: Restrict Linux-specific code 2019-03-11 16:33:49 +01:00
linux-aio.c avoid TABs in files that only contain a few 2019-01-11 15:46:56 +01:00
Makefile.objs
mirror.c block: Advertise BDRV_REQ_NO_FALLBACK in filter drivers 2019-03-26 11:37:51 +01:00
nbd-client.c nbd-client: Work around server BLOCK_STATUS misalignment at EOF 2019-03-30 10:06:08 -05:00
nbd-client.h nbd: Restrict connection_co reentrance 2019-02-25 15:03:19 +01:00
nbd.c block: Purify .bdrv_refresh_filename() 2019-02-25 15:11:27 +01:00
nfs.c block: Purify .bdrv_refresh_filename() 2019-02-25 15:11:27 +01:00
null.c block/null: Generate filename even with latency-ns 2019-02-25 15:11:27 +01:00
nvme.c block/nvme: Fix bdrv_refresh_filename() 2019-02-25 15:11:27 +01:00
parallels.c block/parallels: use QEMU_IOVEC_INIT_BUF 2019-02-22 09:42:13 +00:00
parallels.h
qapi.c qapi: drop x- from x-block-latency-histogram-set 2019-03-12 20:30:08 +01:00
qcow2-bitmap.c block/qcow2-bitmap: Allow resizes with persistent bitmaps 2019-03-12 14:57:38 -04:00
qcow2-cache.c qcow2: External file I/O 2019-03-08 12:26:46 +01:00
qcow2-cluster.c qcow2: Implement data-file-raw create option 2019-03-08 12:26:46 +01:00
qcow2-refcount.c qcow2: Support external data file in qemu-img check 2019-03-08 12:26:46 +01:00
qcow2-snapshot.c qcow2: Return error for snapshot operation with data file 2019-03-08 12:26:46 +01:00
qcow2.c qcow2: Fix data file error condition in qcow2_co_create() 2019-03-19 15:49:29 +01:00
qcow2.h block/qcow2-bitmap: Allow resizes with persistent bitmaps 2019-03-12 14:57:38 -04:00
qcow.c Block layer patches: 2019-02-26 19:04:47 +00:00
qed-check.c
qed-cluster.c
qed-l2-cache.c
qed-table.c block/qed: use qemu_iovec_init_buf 2019-02-22 09:42:13 +00:00
qed.c Block layer patches: 2019-02-26 19:04:47 +00:00
qed.h
quorum.c block: Purify .bdrv_refresh_filename() 2019-02-25 15:11:27 +01:00
raw-format.c block: Advertise BDRV_REQ_NO_FALLBACK in filter drivers 2019-03-26 11:37:51 +01:00
rbd.c block: Add strong_runtime_opts to BlockDriver 2019-02-25 15:11:27 +01:00
replication.c block: Make bdrv_{copy_on_read,crypto_luks,replication} static 2019-03-19 15:49:29 +01:00
sheepdog.c block: Add strong_runtime_opts to BlockDriver 2019-02-25 15:11:27 +01:00
snapshot.c block/snapshot: remove bdrv_snapshot_delete_by_id_or_name 2019-02-25 15:03:18 +01:00
ssh.c block: Add strong_runtime_opts to BlockDriver 2019-02-25 15:11:27 +01:00
stream.c block: Freeze the backing chain for the duration of the stream job 2019-03-12 20:30:14 +01:00
throttle-groups.c throttle-groups: fix restart coroutine iothread race 2019-01-24 10:02:28 +00:00
throttle.c block: Add strong_runtime_opts to BlockDriver 2019-02-25 15:11:27 +01:00
trace-events nbd: Tolerate some server non-compliance in NBD_CMD_BLOCK_STATUS 2019-03-30 10:06:08 -05:00
vdi.c block: Eliminate the S_1KiB, S_2KiB, ... macros 2019-02-01 13:46:45 +01:00
vhdx-endian.c
vhdx-log.c block: Use bdrv_refresh_filename() to pull 2019-02-25 15:11:25 +01:00
vhdx.c
vhdx.h qemu/queue.h: leave head structs anonymous unless necessary 2019-01-11 15:46:55 +01:00
vmdk.c vmdk: Support version=3 in VMDK descriptor files 2019-03-19 15:49:29 +01:00
vpc.c block: Add strong_runtime_opts to BlockDriver 2019-02-25 15:11:27 +01:00
vvfat.c block: Add strong_runtime_opts to BlockDriver 2019-02-25 15:11:27 +01:00
vxhs.c block: Add strong_runtime_opts to BlockDriver 2019-02-25 15:11:27 +01:00
win32-aio.c
write-threshold.c