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Max Reitz 5e003f17ec block: Make bdrv_next() keep strong references 
On one hand, it is a good idea for bdrv_next() to return a strong
reference because ideally nearly every pointer should be refcounted.
This fixes intermittent failure of iotest 194.

On the other, it is absolutely necessary for bdrv_next() itself to keep
a strong reference to both the BB (in its first phase) and the BDS (at
least in the second phase) because when called the next time, it will
dereference those objects to get a link to the next one.  Therefore, it
needs these objects to stay around until then.  Just storing the pointer
to the next in the iterator is not really viable because that pointer
might become invalid as well.

Both arguments taken together means we should probably just invoke
bdrv_ref() and blk_ref() in bdrv_next().  This means we have to assert
that bdrv_next() is always called from the main loop, but that was
probably necessary already before this patch and judging from the
callers, it also looks to actually be the case.

Keeping these strong references means however that callers need to give
them up if they decide to abort the iteration early.  They can do so
through the new bdrv_next_cleanup() function.

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20171110172545.32609-1-mreitz@redhat.com
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
 		2017-11-17 18:21:31 +01:00
..
Makefile.objs block: add throttle block filter driver 2017-09-06 10:12:02 +02:00
accounting.c block: make accounting thread-safe 2017-06-16 07:55:00 +08:00
backup.c dirty-bitmap: Change bdrv_dirty_iter_next() to report byte offset 2017-10-06 16:28:58 +02:00
blkdebug.c block: Align block status requests 2017-10-26 14:45:57 +02:00
blkreplay.c block: change variable names in BlockDriverState 2017-06-26 14:54:46 +02:00
blkverify.c blkverify: Catch bs->exact_filename overflow 2017-06-26 14:54:46 +02:00
block-backend.c block: Make bdrv_next() keep strong references 2017-11-17 18:21:31 +01:00
bochs.c block: Deprecate bdrv_set_read_only() and users 2017-11-17 13:35:59 +01:00
cloop.c block: Deprecate bdrv_set_read_only() and users 2017-11-17 13:35:59 +01:00
commit.c commit: Remove overlay_bs 2017-10-06 16:28:58 +02:00
crypto.c block: support passthrough of BDRV_REQ_FUA in crypto driver 2017-10-06 16:30:47 +02:00
crypto.h qcow: convert QCow to use QCryptoBlock for encryption 2017-07-11 17:44:56 +02:00
curl.c curl: do not do aio_poll when waiting for a free CURLState 2017-05-16 10:34:50 -04:00
dirty-bitmap.c dirty-bitmap: Convert internal hbitmap size/granularity 2017-10-06 16:28:58 +02:00
dmg-bz2.c dmg: Move libbz2 code to dmg-bz2.so 2016-10-07 14:14:06 +02:00
dmg.c block: Deprecate bdrv_set_read_only() and users 2017-11-17 13:35:59 +01:00
dmg.h dmg: Move libbz2 code to dmg-bz2.so 2016-10-07 14:14:06 +02:00
file-posix.c file-posix: Clear out first sector in hdev_create 2017-09-26 14:46:23 +02:00
file-win32.c qapi: Change data type of the FOO_lookup generated for enum FOO 2017-09-04 13:09:13 +02:00
gluster.c qapi: Change data type of the FOO_lookup generated for enum FOO 2017-09-04 13:09:13 +02:00
io.c block: Guard against NULL bs->drv 2017-11-17 18:21:31 +01:00
iscsi-opts.c block/iscsi: statically link qemu_iscsi_opts 2017-01-27 18:07:58 +01:00
iscsi.c scsi: move block/scsi.h to include/scsi/constants.h 2017-09-19 14:09:31 +02:00
linux-aio.c block: explicitly acquire aiocontext in aio callbacks that need it 2017-02-21 11:39:39 +00:00
mirror.c block: Convert bdrv_get_block_status_above() to bytes 2017-10-26 14:45:57 +02:00
nbd-client.c nbd-client: Stricter enforcing of structured reply spec 2017-11-09 10:22:26 -06:00
nbd-client.h nbd: Minimal structured read for client 2017-10-30 21:48:41 +01:00
nbd.c nbd: Implement NBD_INFO_BLOCK_SIZE on client 2017-07-14 12:04:42 +02:00
nfs.c qapi: Mechanically convert FOO_lookup[...] to FOO_str(...) 2017-09-04 13:09:13 +02:00
null.c block/null: Remove 'filename' option 2017-08-08 15:19:16 +02:00
parallels.c block/parallels: add migration blocker 2017-11-14 18:06:26 +01:00
qapi.c block: Guard against NULL bs->drv 2017-11-17 18:21:31 +01:00
qcow.c block: convert qcrypto_block_encrypt|decrypt to take bytes offset 2017-10-06 16:30:47 +02:00
qcow2-bitmap.c qcow2: Switch store_bitmap_data() to byte-based iteration 2017-10-06 16:28:58 +02:00
qcow2-cache.c qcow2: Fix overly broad madvise() 2017-11-17 18:21:31 +01:00
qcow2-cluster.c qcow2: Unaligned zero cluster in handle_alloc() 2017-11-17 18:21:30 +01:00
qcow2-refcount.c qcow2: Add bounds check to get_refblock_offset() 2017-11-17 18:21:31 +01:00
qcow2-snapshot.c qcow2: Discard/zero clusters by byte count 2017-05-11 14:28:07 +02:00
qcow2.c qcow2: check_errors are fatal 2017-11-17 18:21:30 +01:00
qcow2.h qcow2: Add bounds check to get_refblock_offset() 2017-11-17 18:21:31 +01:00
qed-check.c qed: Use DIV_ROUND_UP 2016-06-07 18:19:24 +03:00
qed-cluster.c qed: protect table cache with CoMutex 2017-07-17 11:34:11 +08:00
qed-l2-cache.c qed: protect table cache with CoMutex 2017-07-17 11:34:11 +08:00
qed-table.c qed: protect table cache with CoMutex 2017-07-17 11:34:11 +08:00
qed.c block: rename bdrv_co_drain to bdrv_co_drain_begin 2017-10-13 12:38:41 +01:00
qed.h qed: protect table cache with CoMutex 2017-07-17 11:34:11 +08:00
quorum.c qapi: Change data type of the FOO_lookup generated for enum FOO 2017-09-04 13:09:13 +02:00
raw-format.c block: remove unused bdrv_media_changed 2017-09-04 18:31:13 +02:00
rbd.c block: Deprecate bdrv_set_read_only() and users 2017-11-17 13:35:59 +01:00
replication.c block: Guard against NULL bs->drv 2017-11-17 18:21:31 +01:00
sheepdog.c Merge QEMU I/O 2017/09/05 v2 2017-09-05 14:14:33 +01:00
snapshot.c block: Make bdrv_next() keep strong references 2017-11-17 18:21:31 +01:00
ssh.c util: remove the obsolete non-blocking connect 2017-09-05 13:21:58 +01:00
stream.c block: Make bdrv_is_allocated_above() byte-based 2017-07-10 13:18:07 +02:00
throttle-groups.c throttle-groups: forget timer and schedule next TGM on detach 2017-11-16 14:12:57 +00:00
throttle.c block/throttle.c: add bdrv_co_drain_begin/end callbacks 2017-10-13 12:38:41 +01:00
trace-events block: Make bdrv_round_to_clusters() signature more useful 2017-10-26 14:45:57 +02:00
vdi.c vdi: make it thread-safe 2017-07-17 11:28:15 +08:00
vhdx-endian.c vhdx: Use QEMU UUID API 2016-09-23 11:42:52 +08:00
vhdx-log.c vhdx: use QEMU_ALIGN_DOWN 2017-08-31 12:29:07 +02:00
vhdx.c block/vhdx.c: Don't blindly update the header 2017-11-14 18:06:25 +01:00
vhdx.h block: vhdx - update PAYLOAD_BLOCK_UNMAPPED value to match 1.00 spec 2014-12-12 15:42:22 +00:00
vmdk.c vmdk: Fix error handling/reporting of vmdk_check 2017-08-08 15:19:16 +02:00
vpc.c vpc: use DIV_ROUND_UP 2017-08-31 12:29:07 +02:00
vvfat.c block: Guard against NULL bs->drv 2017-11-17 18:21:31 +01:00
vxhs.c qobject: Use simpler QDict/QList scalar insertion macros 2017-05-09 09:13:51 +02:00
win32-aio.c block: explicitly acquire aiocontext in aio callbacks that need it 2017-02-21 11:39:39 +00:00
write-threshold.c block: use bdrv_add_before_write_notifier 2016-10-07 13:34:07 +02:00