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ec64b1ca08
qemu/block
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Hanna Reitz ec64b1ca08 block/qcow2: Keep auto_backing_file if possible 
qcow2_do_open() is used by qcow2_co_invalidate_cache(), i.e. may be run
on an image that has been opened before.  When reading the backing file
string from the image header, compare it against the existing
bs->backing_file, and update bs->auto_backing_file only if they differ.

auto_backing_file should ideally contain the filename the backing BDS
will actually have after opening, i.e. a post-bdrv_refresh_filename()
version of what is in the image header.  So for example, if the image
header reports the following backing file string:

    json:{"driver": "qcow2", "file": {
        "driver": "file", "filename": "/tmp/backing.qcow2"
    }}

Then auto_backing_file should contain simply "/tmp/backing.qcow2".

Because bdrv_refresh_filename() only works on existing BDSs, though, the
way how we get this auto_backing_file value is to have the format driver
set it to whatever is in the image header, and when the backing BDS is
opened based on that, we update it with the filename the backing BDS
actually got.

However, qcow2's qcow2_co_invalidate_cache() implementation breaks this
because it just resets auto_backing_file to whatever is in the image
file without opening a BDS based on it, so we never get
auto_backing_file back to the "refreshed" version, and in the example
above, it would stay "json:{...}".

Then, bs->backing->bs->filename will differ from bs->auto_backing_file,
making bdrv_backing_overridden(bs) return true, which will lead
bdrv_refresh_filename(bs) to generate a json:{} filename for bs, even
though that may not have been necessary.  This is reported in the issue
linked below.

Therefore, skip updating auto_backing_file if nothing has changed in the
image header since we last read it.

Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1117
Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220803144446.20723-2-hreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2022-09-30 18:43:44 +02:00
..
export block: Change blk_{pread,pwrite}() param order 2022-07-12 12:14:56 +02:00
monitor block: improve block_dirty_bitmap_merge(): don't allocate extra bitmap 2022-06-24 17:07:06 +02:00
accounting.c block: add missed block_acct_setup with new block device init procedure 2022-09-30 18:42:34 +02:00
aio_task.c block/aio_task: assert max_busy_tasks is greater than 0 2021-10-05 18:56:41 +02:00
amend.c block/amend: Keep strong reference to BDS 2022-03-04 18:18:26 +01:00
backup.c block: simplify handling of try to merge different sized bitmaps 2022-06-24 17:07:06 +02:00
blkdebug.c block: use int64_t instead of int in driver discard handlers 2021-09-29 13:46:32 -05:00
blklogwrites.c block: Change bdrv_{pread,pwrite,pwrite_sync}() param order 2022-07-12 12:14:55 +02:00
blkreplay.c block: use int64_t instead of int in driver discard handlers 2021-09-29 13:46:32 -05:00
blkverify.c Replace GCC_FMT_ATTR with G_GNUC_PRINTF 2022-03-22 14:40:51 +04:00
block-backend.c block: Remove remaining unused symbols in coroutines.h 2022-07-12 12:14:56 +02:00
block-copy.c block/block-copy: block_copy(): add timeout_ns parameter 2022-06-29 10:56:12 +03:00
block-gen.h scripts: add block-coroutine-wrapper.py 2020-10-05 10:59:06 +01:00
bochs.c block: Change bdrv_{pread,pwrite,pwrite_sync}() param order 2022-07-12 12:14:55 +02:00
cloop.c block: Make bdrv_{pread,pwrite}() return 0 on success 2022-07-12 12:14:55 +02:00
commit.c block: Change blk_{pread,pwrite}() param order 2022-07-12 12:14:56 +02:00
copy-before-write.c block/copy-before-write: implement cbw-timeout option 2022-06-29 10:56:12 +03:00
copy-before-write.h block/copy-before-write.h: global state API + assertions 2022-03-04 18:18:25 +01:00
copy-on-read.c block: use int64_t instead of int in driver discard handlers 2021-09-29 13:46:32 -05:00
copy-on-read.h Clean up ill-advised or unusual header guards 2022-05-11 16:50:01 +02:00
coroutines.h block: Remove remaining unused symbols in coroutines.h 2022-07-12 12:14:56 +02:00
create.c block_int-common.h: assertions in the callers of BlockDriver function pointers 2022-03-04 18:18:25 +01:00
crypto.c block: Change blk_{pread,pwrite}() param order 2022-07-12 12:14:56 +02:00
crypto.h nomaintainer: Fix Lesser GPL version number 2020-11-15 17:04:40 +01:00
curl.c block/curl.c: Check error return from curl_easy_setopt() 2022-03-07 09:19:20 +01:00
dirty-bitmap.c block: simplify handling of try to merge different sized bitmaps 2022-06-24 17:07:06 +02:00
dmg-bz2.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
dmg-lzfse.c block: Remove unused include 2020-11-09 15:44:21 +01:00
dmg.c block: Make bdrv_{pread,pwrite}() return 0 on success 2022-07-12 12:14:55 +02:00
dmg.h Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
file-posix.c block: use bdrv_is_sg() helper instead of raw bs->sg reading 2022-09-30 18:43:44 +02:00
file-win32.c block: use int64_t instead of uint64_t in driver write handlers 2021-09-29 13:46:31 -05:00
filter-compress.c block: use int64_t instead of int in driver discard handlers 2021-09-29 13:46:32 -05:00
gluster.c gluster: stop using .bdrv_needs_filename 2022-09-30 18:43:44 +02:00
io_uring.c block/io_uring: add missing include file 2022-08-02 11:01:24 +02:00
io.c block: make serializing requests functions 'void' 2022-09-30 18:43:44 +02:00
iscsi-opts.c modules: add block module annotations 2021-07-09 18:20:27 +02:00
iscsi.c block: use bdrv_is_sg() helper instead of raw bs->sg reading 2022-09-30 18:43:44 +02:00
linux-aio.c misc: fix commonly doubled up words 2022-08-01 11:58:02 +02:00
meson.build block: Implement blk_{pread,pwrite}() using generated_co_wrapper 2022-07-12 12:14:56 +02:00
mirror.c block: use 'unsigned' for in_flight field on driver state 2022-06-29 10:57:02 +03:00
nbd.c block: use 'unsigned' for in_flight field on driver state 2022-06-29 10:57:02 +03:00
nfs.c aio-posix: split poll check from ready handler 2022-01-12 17:09:39 +00:00
null.c block: use int64_t instead of uint64_t in driver write handlers 2021-09-29 13:46:31 -05:00
nvme.c Replace qemu_real_host_page variables with inlined functions 2022-04-06 10:50:38 +02:00
parallels-ext.c block: Change bdrv_{pread,pwrite,pwrite_sync}() param order 2022-07-12 12:14:55 +02:00
parallels.c block/parallels: Fix buffer-based write call 2022-07-26 22:04:59 +03:00
parallels.h parallels: support bitmap extension for read-only mode 2021-03-08 14:56:55 +01:00
preallocate.c block: fix preallocate filter: don't do unaligned preallocate requests 2022-03-07 09:19:20 +01:00
progress_meter.c progressmeter: protect with a mutex 2021-06-25 14:24:24 +03:00
qapi-sysemu.c block: add 'force' parameter to 'blockdev-change-medium' command 2022-04-25 12:02:36 +02:00
qapi.c block: use GDateTime for formatting timestamp when dumping snapshot info 2021-06-14 13:28:50 +01:00
qcow2-bitmap.c block/qcow2-bitmap: Add missing cast to silent GCC error 2022-09-30 18:02:30 +02:00
qcow2-cache.c block: Change bdrv_{pread,pwrite,pwrite_sync}() param order 2022-07-12 12:14:55 +02:00
qcow2-cluster.c block: Change bdrv_{pread,pwrite,pwrite_sync}() param order 2022-07-12 12:14:55 +02:00
qcow2-refcount.c block: Change bdrv_{pread,pwrite,pwrite_sync}() param order 2022-07-12 12:14:55 +02:00
qcow2-snapshot.c block: Use bdrv_co_pwrite_sync() when caller is coroutine_fn 2022-07-12 12:14:56 +02:00
qcow2-threads.c qcow2: add zstd cluster compression 2020-05-13 14:20:31 +02:00
qcow2.c block/qcow2: Keep auto_backing_file if possible 2022-09-30 18:43:44 +02:00
qcow2.h Replace GCC_FMT_ATTR with G_GNUC_PRINTF 2022-03-22 14:40:51 +04:00
qcow.c block: Change blk_{pread,pwrite}() param order 2022-07-12 12:14:56 +02:00
qed-check.c block/qed: add missed coroutine_fn markers 2019-04-30 15:29:00 +02:00
qed-cluster.c qed: protect table cache with CoMutex 2017-07-17 11:34:11 +08:00
qed-l2-cache.c osdep: Move memalign-related functions to their own header 2022-03-07 13:16:49 +00:00
qed-table.c osdep: Move memalign-related functions to their own header 2022-03-07 13:16:49 +00:00
qed.c block: Change blk_{pread,pwrite}() param order 2022-07-12 12:14:56 +02:00
qed.h qed: Simplify backing reads 2020-07-06 10:34:14 +02:00
quorum.c osdep: Move memalign-related functions to their own header 2022-03-07 13:16:49 +00:00
raw-format.c block: use bdrv_is_sg() helper instead of raw bs->sg reading 2022-09-30 18:43:44 +02:00
rbd.c block/rbd: report a better error when namespace does not exist 2022-06-24 17:07:06 +02:00
replication.c job: @force parameter for job_cancel_sync() 2021-10-07 10:42:09 +02:00
reqlist.c block/reqlist: add reqlist_wait_all() 2022-03-07 09:33:30 +01:00
snapshot-access.c block: introduce snapshot-access block driver 2022-03-07 09:33:31 +01:00
snapshot.c include/block/snapshot: global state API + assertions 2022-03-04 18:18:25 +01:00
ssh.c Replace GCC_FMT_ATTR with G_GNUC_PRINTF 2022-03-22 14:40:51 +04:00
stream.c block/stream: Drain subtree around graph change 2022-03-29 16:30:55 +02:00
throttle-groups.c block/throttle-groups: throttle_group_co_io_limits_intercept(): 64bit bytes 2021-02-03 08:14:00 -06:00
throttle.c block: use int64_t instead of int in driver discard handlers 2021-09-29 13:46:32 -05:00
trace-events nbd: trace long NBD operations 2022-06-29 10:57:02 +03:00
trace.h trace: switch position of headers to what Meson requires 2020-08-21 06:18:24 -04:00
vdi.c block: Change blk_{pread,pwrite}() param order 2022-07-12 12:14:56 +02:00
vhdx-endian.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
vhdx-log.c block: Change bdrv_{pread,pwrite,pwrite_sync}() param order 2022-07-12 12:14:55 +02:00
vhdx.c block: Change blk_{pread,pwrite}() param order 2022-07-12 12:14:56 +02:00
vhdx.h block/vhdx: Use IEC binary prefixes for size constants 2019-04-30 15:29:00 +02:00
vmdk.c block: Change blk_{pread,pwrite}() param order 2022-07-12 12:14:56 +02:00
vpc.c block: Change blk_{pread,pwrite}() param order 2022-07-12 12:14:56 +02:00
vvfat.c block: Change bdrv_{pread,pwrite,pwrite_sync}() param order 2022-07-12 12:14:55 +02:00
win32-aio.c osdep: Move memalign-related functions to their own header 2022-03-07 13:16:49 +00:00
write-threshold.c write-threshold: deal with includes 2021-05-14 16:14:10 +02:00