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5bb0474778
bs->file and bs->backing are a kind of duplication of part of
bs->children. But very useful diplication, so let's not drop them at
all:)
We should manage bs->file and bs->backing in same place, where we
manage bs->children, to keep them in sync.
Moreover, generic io paths are unprepared to BdrvChild without a bs, so
it's double good to clear bs->file / bs->backing when we detach the
child.
Detach is simple: if we detach bs->file or bs->backing child, just
set corresponding field to NULL.
Attach is a bit more complicated. But we still can precisely detect
should we set one of bs->file / bs->backing or not:
- if role is BDRV_CHILD_COW, we definitely deal with bs->backing
- else, if role is BDRV_CHILD_FILTERED (it must be also
BDRV_CHILD_PRIMARY), it's a filtered child. Use
bs->drv->filtered_child_is_backing to chose the pointer field to
modify.
- else, if role is BDRV_CHILD_PRIMARY, we deal with bs->file
- in all other cases, it's neither bs->backing nor bs->file. It's some
other child and we shouldn't care
OK. This change brings one more good thing: we can (and should) get rid
of all indirect pointers in the block-graph-change transactions:
bdrv_attach_child_common() stores BdrvChild** into transaction to clear
it on abort.
bdrv_attach_child_common() has two callers: bdrv_attach_child_noperm()
just pass-through this feature, bdrv_root_attach_child() doesn't need
the feature.
Look at bdrv_attach_child_noperm() callers:
- bdrv_attach_child() doesn't need the feature
- bdrv_set_file_or_backing_noperm() uses the feature to manage
bs->file and bs->backing, we don't want it anymore
- bdrv_append() uses the feature to manage bs->backing, again we
don't want it anymore
So, we should drop this stuff! Great!
We could probably keep BdrvChild** argument to keep the int return
value, but it seems not worth the complexity.
Finally, we now set .file / .backing automatically in generic code and
want to restring setting them by hand outside of .attach/.detach.
So, this patch cleanups all remaining places where they were set.
To find such places I use:
git grep '\->file ='
git grep '\->backing ='
git grep '&.*\<backing\>'
git grep '&.*\<file\>'
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220726201134.924743-14-vsementsov@yandex-team.ru>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
133 lines
4.2 KiB
C
133 lines
4.2 KiB
C
/*
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* snapshot_access block driver
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*
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* Copyright (c) 2022 Virtuozzo International GmbH.
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*
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* Author:
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* Sementsov-Ogievskiy Vladimir <vsementsov@virtuozzo.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "qemu/osdep.h"
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#include "sysemu/block-backend.h"
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#include "qemu/cutils.h"
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#include "block/block_int.h"
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static coroutine_fn int
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snapshot_access_co_preadv_part(BlockDriverState *bs,
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int64_t offset, int64_t bytes,
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QEMUIOVector *qiov, size_t qiov_offset,
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BdrvRequestFlags flags)
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{
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if (flags) {
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return -ENOTSUP;
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}
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return bdrv_co_preadv_snapshot(bs->file, offset, bytes, qiov, qiov_offset);
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}
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static int coroutine_fn
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snapshot_access_co_block_status(BlockDriverState *bs,
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bool want_zero, int64_t offset,
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int64_t bytes, int64_t *pnum,
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int64_t *map, BlockDriverState **file)
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{
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return bdrv_co_snapshot_block_status(bs->file->bs, want_zero, offset,
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bytes, pnum, map, file);
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}
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static int coroutine_fn snapshot_access_co_pdiscard(BlockDriverState *bs,
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int64_t offset, int64_t bytes)
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{
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return bdrv_co_pdiscard_snapshot(bs->file->bs, offset, bytes);
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}
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static int coroutine_fn
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snapshot_access_co_pwrite_zeroes(BlockDriverState *bs,
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int64_t offset, int64_t bytes,
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BdrvRequestFlags flags)
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{
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return -ENOTSUP;
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}
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static coroutine_fn int
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snapshot_access_co_pwritev_part(BlockDriverState *bs,
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int64_t offset, int64_t bytes,
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QEMUIOVector *qiov, size_t qiov_offset,
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BdrvRequestFlags flags)
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{
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return -ENOTSUP;
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}
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static void snapshot_access_refresh_filename(BlockDriverState *bs)
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{
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pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
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bs->file->bs->filename);
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}
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static int snapshot_access_open(BlockDriverState *bs, QDict *options, int flags,
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Error **errp)
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{
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bdrv_open_child(NULL, options, "file", bs, &child_of_bds,
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BDRV_CHILD_DATA | BDRV_CHILD_PRIMARY,
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false, errp);
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if (!bs->file) {
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return -EINVAL;
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}
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bs->total_sectors = bs->file->bs->total_sectors;
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return 0;
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}
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static void snapshot_access_child_perm(BlockDriverState *bs, BdrvChild *c,
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BdrvChildRole role,
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BlockReopenQueue *reopen_queue,
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uint64_t perm, uint64_t shared,
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uint64_t *nperm, uint64_t *nshared)
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{
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/*
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* Currently, we don't need any permissions. If bs->file provides
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* snapshot-access API, we can use it.
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*/
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*nperm = 0;
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*nshared = BLK_PERM_ALL;
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}
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BlockDriver bdrv_snapshot_access_drv = {
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.format_name = "snapshot-access",
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.bdrv_open = snapshot_access_open,
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.bdrv_co_preadv_part = snapshot_access_co_preadv_part,
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.bdrv_co_pwritev_part = snapshot_access_co_pwritev_part,
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.bdrv_co_pwrite_zeroes = snapshot_access_co_pwrite_zeroes,
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.bdrv_co_pdiscard = snapshot_access_co_pdiscard,
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.bdrv_co_block_status = snapshot_access_co_block_status,
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.bdrv_refresh_filename = snapshot_access_refresh_filename,
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.bdrv_child_perm = snapshot_access_child_perm,
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};
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static void snapshot_access_init(void)
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{
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bdrv_register(&bdrv_snapshot_access_drv);
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}
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block_init(snapshot_access_init);
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