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Alberto Garcia 3441ad4bc4 qcow2: Document and enforce the QCowL2Meta invariants 
The QCowL2Meta structure is used to store information about a part of
a write request that touches clusters that need changes in their L2
entries. This happens with newly-allocated clusters or subclusters.

This structure has changed a bit since it was first created and its
current documentation is not quite up-to-date.

A write request can span a region consisting of a combination of
clusters of different types, and qcow2_alloc_host_offset() can
repeatedly call handle_copied() and handle_alloc() to add more
clusters to the mix as long as they all are contiguous on the image
file.

Because of this a write request has a list of QCowL2Meta structures,
one for each part of the request that needs changes in the L2
metadata.

Each one of them spans nb_clusters and has two copy-on-write regions
located immediately before and after the middle region touched by that
part of the write request. Even when those regions themselves are
empty their offsets must be correct because they are used to know the
location of the middle region.

This was not always the case but it is not a problem anymore
because the only two places where QCowL2Meta structures are created
(calculate_l2_meta() and qcow2_co_truncate()) ensure that the
copy-on-write regions are correctly defined, and so do assertions like
the ones in perform_cow().

The conditional initialization of the 'written_to' variable is
therefore unnecessary and is removed by this patch.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20201007161323.4667-1-berto@igalia.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
2020-11-09 15:44:21 +01:00
..
export block/export: fix vhost-user-blk get_config() information leak 2020-11-03 16:39:05 -05:00
monitor block/export: Add block-export-del 2020-10-02 15:46:40 +02:00
accounting.c block: add empty account cookie type 2019-10-10 10:56:18 +02:00
aio_task.c block: introduce aio task pool 2019-10-10 10:56:17 +02:00
amend.c block/amend: Check whether the node exists 2020-07-27 12:37:25 +02:00
backup-top.c block: Inline bdrv_co_block_status_from_*() 2020-09-07 12:31:31 +02:00
backup-top.h block: introduce backup-top filter driver 2019-10-10 10:56:18 +02:00
backup.c backup: Deal with filters 2020-09-07 12:31:31 +02:00
blkdebug.c block/blkdebug: fix memory leak 2020-10-13 13:33:46 +02:00
blklogwrites.c block: Inline bdrv_co_block_status_from_*() 2020-09-07 12:31:31 +02:00
blkreplay.c block: Use bdrv_default_perms() 2020-05-18 19:05:25 +02:00
blkverify.c error: Eliminate error_propagate() with Coccinelle, part 2 2020-07-10 15:18:08 +02:00
block-backend.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
block-copy.c block-copy: Use CAF to find sync=top base 2020-09-07 12:31:31 +02:00
block-gen.h scripts: add block-coroutine-wrapper.py 2020-10-05 10:59:06 +01:00
bochs.c block: Use bdrv_default_perms() 2020-05-18 19:05:25 +02:00
cloop.c block: Use bdrv_default_perms() 2020-05-18 19:05:25 +02:00
commit.c block: Return depth level during bdrv_is_allocated_above 2020-10-30 15:21:23 -05:00
copy-on-read.c block: Inline bdrv_co_block_status_from_*() 2020-09-07 12:31:31 +02:00
coroutines.h block: Return depth level during bdrv_is_allocated_above 2020-10-30 15:21:23 -05:00
create.c block/create: Do not abort if a block driver is not available 2019-09-13 12:18:37 +02:00
crypto.c block/crypto: disallow write sharing by default 2020-07-21 10:49:02 +02:00
crypto.h block/crypto: implement the encryption key management 2020-07-06 08:49:28 +02:00
curl.c error: Eliminate error_propagate() with Coccinelle, part 1 2020-07-10 15:18:08 +02:00
dirty-bitmap.c block/dirty-bitmap: add bdrv_has_named_bitmaps helper 2020-05-28 13:15:22 -05:00
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: Use bdrv_default_perms() 2020-05-18 19:05:25 +02:00
dmg.h Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
file-posix.c block/file: switch to use qemu_open/qemu_create for improved errors 2020-09-16 10:33:48 +01:00
file-win32.c block/file: switch to use qemu_open/qemu_create for improved errors 2020-09-16 10:33:48 +01:00
filter-compress.c block: Inline bdrv_co_block_status_from_*() 2020-09-07 12:31:31 +02:00
gluster.c error: Reduce unnecessary error propagation 2020-07-10 15:18:08 +02:00
io_uring.c io_uring: use io_uring_cq_ready() to check for ready cqes 2020-06-05 09:54:48 +01:00
io.c block: Return depth level during bdrv_is_allocated_above 2020-10-30 15:21:23 -05:00
iscsi-opts.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
iscsi.c qapi: Restrict query-uuid command to machine code 2020-09-29 15:41:35 +02:00
linux-aio.c misc: Replace zero-length arrays with flexible array member (automatic) 2020-03-16 22:07:42 +01:00
meson.build block/export: convert vhost-user-blk server to block export API 2020-10-23 13:42:16 +01:00
mirror.c block: Return depth level during bdrv_is_allocated_above 2020-10-30 15:21:23 -05:00
nbd.c nbd: Add 'qemu-nbd -A' to expose allocation depth 2020-10-30 15:22:00 -05:00
nfs.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
null.c block/null: Implement bdrv_get_allocated_file_size 2020-09-07 12:31:31 +02:00
nvme.c block/nvme: Add driver statistics for access alignment and hw errors 2020-10-23 13:42:16 +01:00
parallels.c error: Avoid error_propagate() after migrate_add_blocker() 2020-07-10 15:18:08 +02:00
parallels.h
qapi-sysemu.c block: Move system emulator QMP commands to block/qapi-sysemu.c 2020-03-06 17:15:38 +01:00
qapi.c migration: introduce icount field for snapshots 2020-10-06 08:34:49 +02:00
qcow2-bitmap.c qcow2: Use macros for the L1, refcount and bitmap table entry sizes 2020-09-15 11:05:12 +02:00
qcow2-cache.c core: replace getpagesize() with qemu_real_host_page_size 2019-10-26 15:38:06 +02:00
qcow2-cluster.c qcow2: Document and enforce the QCowL2Meta invariants 2020-11-09 15:44:21 +01:00
qcow2-refcount.c qcow2: Make qcow2_free_any_clusters() free only one cluster 2020-09-15 11:05:13 +02:00
qcow2-snapshot.c migration: introduce icount field for snapshots 2020-10-06 08:34:49 +02:00
qcow2-threads.c qcow2: add zstd cluster compression 2020-05-13 14:20:31 +02:00
qcow2.c qcow2: Document and enforce the QCowL2Meta invariants 2020-11-09 15:44:21 +01:00
qcow2.h qcow2: Document and enforce the QCowL2Meta invariants 2020-11-09 15:44:21 +01:00
qcow.c block/qcow: remove runtime opts 2020-09-15 11:05:13 +02:00
qed-check.c block/qed: add missed coroutine_fn markers 2019-04-30 15:29:00 +02:00
qed-cluster.c
qed-l2-cache.c
qed-table.c block/qed: add missed coroutine_fn markers 2019-04-30 15:29:00 +02:00
qed.c qapi: Smooth another visitor error checking pattern 2020-07-10 15:18:08 +02:00
qed.h qed: Simplify backing reads 2020-07-06 10:34:14 +02:00
quorum.c block/quorum.c: stable children names 2020-09-15 11:05:12 +02:00
raw-format.c error: Eliminate error_propagate() with Coccinelle, part 2 2020-07-10 15:18:08 +02:00
rbd.c block/rbd: add 'namespace' to qemu_rbd_strong_runtime_opts[] 2020-09-15 11:31:10 +02:00
replication.c error: Reduce unnecessary error propagation 2020-07-10 15:18:08 +02:00
sheepdog.c block: deprecate the sheepdog block driver 2020-10-15 16:06:28 +02:00
snapshot.c block/snapshot: Fix fallback 2020-09-07 12:31:31 +02:00
ssh.c qapi: Smooth another visitor error checking pattern 2020-07-10 15:18:08 +02:00
stream.c block: Return depth level during bdrv_is_allocated_above 2020-10-30 15:21:23 -05:00
throttle-groups.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
throttle.c qemu/atomic.h: rename atomic_ to qatomic_ 2020-09-23 16:07:44 +01:00
trace-events trace-events: Fix attribution of trace points to source 2020-09-09 17:17:58 +01:00
trace.h trace: switch position of headers to what Meson requires 2020-08-21 06:18:24 -04:00
vdi.c error: Avoid error_propagate() after migrate_add_blocker() 2020-07-10 15:18:08 +02:00
vhdx-endian.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
vhdx-log.c block: Add flags to bdrv(_co)_truncate() 2020-04-30 17:51:07 +02:00
vhdx.c block/vhdx: Support vhdx image only with 512 bytes logical sector size 2020-09-15 11:05:13 +02:00
vhdx.h block/vhdx: Use IEC binary prefixes for size constants 2019-04-30 15:29:00 +02:00
vmdk.c vmdk: fix maybe uninitialized warnings 2020-10-13 13:33:45 +02:00
vpc.c error: Avoid error_propagate() after migrate_add_blocker() 2020-07-10 15:18:08 +02:00
vvfat.c block/vvfat: Fix bad printf format specifiers 2020-11-03 16:24:56 +01:00
win32-aio.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
write-threshold.c qapi: Drop qapi_event_send_FOO()'s Error ** argument 2018-08-28 18:21:38 +02:00