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https://github.com/Motorhead1991/qemu.git
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c33159dec7
This patch is purely mechanical, changing bool want_zero into an unsigned int for bitwise-or of flags. As of this patch, all implementations are unchanged (the old want_zero==true is now mode==BDRV_WANT_PRECISE which is a superset of BDRV_WANT_ZERO); but the callers in io.c that used to pass want_zero==false are now prepared for future driver changes that can now distinguish bewteen BDRV_WANT_ZERO vs. BDRV_WANT_ALLOCATED. The next patch will actually change the file-posix driver along those lines, now that we have more-specific hints. As for the background why this patch is useful: right now, the file-posix driver recognizes that if allocation is being queried, the entire image can be reported as allocated (there is no backing file to refer to) - but this throws away information on whether the entire image reads as zero (trivially true if lseek(SEEK_HOLE) at offset 0 returns -ENXIO, a bit more complicated to prove if the raw file was created with 'qemu-img create' since we intentionally allocate a small chunk of all-zero data to help with alignment probing). Later patches will add a generic algorithm for seeing if an entire file reads as zeroes. Signed-off-by: Eric Blake <eblake@redhat.com> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com> Message-ID: <20250509204341.3553601-16-eblake@redhat.com>
135 lines
4.2 KiB
C
135 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 "system/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 int coroutine_fn GRAPH_RDLOCK
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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 GRAPH_RDLOCK
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snapshot_access_co_block_status(BlockDriverState *bs,
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unsigned int mode, 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, mode, offset,
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bytes, pnum, map, file);
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}
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static int coroutine_fn GRAPH_RDLOCK
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snapshot_access_co_pdiscard(BlockDriverState *bs, 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 GRAPH_RDLOCK 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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GRAPH_RDLOCK_GUARD_MAINLOOP();
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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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static 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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