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![Kevin Wolf](/assets/img/avatar_default.png)
Most implementations of .bdrv_open first open their file child (which is an operation that internally takes the write lock and therefore we shouldn't hold the graph lock while calling it), and afterwards many operations that require holding the graph lock, e.g. for accessing bs->file. This changes block drivers that follow this pattern to take the graph lock after opening the child node. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Message-ID: <20231027155333.420094-24-kwolf@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
297 lines
8.5 KiB
C
297 lines
8.5 KiB
C
/*
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* Copy-on-read filter block driver
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*
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* Copyright (c) 2018 Red Hat, Inc.
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*
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* Author:
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* Max Reitz <mreitz@redhat.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 or
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* (at your option) version 3 of the License.
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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 "block/block-io.h"
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#include "block/block_int.h"
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#include "qemu/module.h"
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#include "qapi/error.h"
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#include "qapi/qmp/qdict.h"
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#include "block/copy-on-read.h"
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typedef struct BDRVStateCOR {
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BlockDriverState *bottom_bs;
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bool chain_frozen;
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} BDRVStateCOR;
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static int GRAPH_UNLOCKED
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cor_open(BlockDriverState *bs, QDict *options, int flags, Error **errp)
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{
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BlockDriverState *bottom_bs = NULL;
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BDRVStateCOR *state = bs->opaque;
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/* Find a bottom node name, if any */
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const char *bottom_node = qdict_get_try_str(options, "bottom");
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int ret;
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GLOBAL_STATE_CODE();
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ret = bdrv_open_file_child(NULL, options, "file", bs, errp);
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if (ret < 0) {
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return ret;
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}
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GRAPH_RDLOCK_GUARD_MAINLOOP();
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bs->supported_read_flags = BDRV_REQ_PREFETCH;
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bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
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(BDRV_REQ_FUA & bs->file->bs->supported_write_flags);
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bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
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((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
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bs->file->bs->supported_zero_flags);
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if (bottom_node) {
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bottom_bs = bdrv_find_node(bottom_node);
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if (!bottom_bs) {
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error_setg(errp, "Bottom node '%s' not found", bottom_node);
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qdict_del(options, "bottom");
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return -EINVAL;
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}
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qdict_del(options, "bottom");
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if (!bottom_bs->drv) {
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error_setg(errp, "Bottom node '%s' not opened", bottom_node);
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return -EINVAL;
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}
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if (bottom_bs->drv->is_filter) {
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error_setg(errp, "Bottom node '%s' is a filter", bottom_node);
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return -EINVAL;
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}
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if (bdrv_freeze_backing_chain(bs, bottom_bs, errp) < 0) {
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return -EINVAL;
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}
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state->chain_frozen = true;
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/*
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* We do freeze the chain, so it shouldn't be removed. Still, storing a
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* pointer worth bdrv_ref().
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*/
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bdrv_ref(bottom_bs);
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}
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state->bottom_bs = bottom_bs;
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/*
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* We don't need to call bdrv_child_refresh_perms() now as the permissions
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* will be updated later when the filter node gets its parent.
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*/
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return 0;
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}
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#define PERM_PASSTHROUGH (BLK_PERM_CONSISTENT_READ \
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| BLK_PERM_WRITE \
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| BLK_PERM_RESIZE)
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#define PERM_UNCHANGED (BLK_PERM_ALL & ~PERM_PASSTHROUGH)
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static void cor_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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*nperm = perm & PERM_PASSTHROUGH;
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*nshared = (shared & PERM_PASSTHROUGH) | PERM_UNCHANGED;
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/* We must not request write permissions for an inactive node, the child
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* cannot provide it. */
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if (!(bs->open_flags & BDRV_O_INACTIVE)) {
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*nperm |= BLK_PERM_WRITE_UNCHANGED;
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}
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}
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static int64_t coroutine_fn GRAPH_RDLOCK cor_co_getlength(BlockDriverState *bs)
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{
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return bdrv_co_getlength(bs->file->bs);
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}
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static int coroutine_fn GRAPH_RDLOCK
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cor_co_preadv_part(BlockDriverState *bs, 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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int64_t n;
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int local_flags;
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int ret;
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BDRVStateCOR *state = bs->opaque;
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if (!state->bottom_bs) {
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return bdrv_co_preadv_part(bs->file, offset, bytes, qiov, qiov_offset,
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flags | BDRV_REQ_COPY_ON_READ);
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}
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while (bytes) {
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local_flags = flags;
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/* In case of failure, try to copy-on-read anyway */
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ret = bdrv_co_is_allocated(bs->file->bs, offset, bytes, &n);
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if (ret <= 0) {
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ret = bdrv_co_is_allocated_above(bdrv_backing_chain_next(bs->file->bs),
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state->bottom_bs, true, offset,
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n, &n);
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if (ret > 0 || ret < 0) {
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local_flags |= BDRV_REQ_COPY_ON_READ;
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}
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/* Finish earlier if the end of a backing file has been reached */
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if (n == 0) {
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break;
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}
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}
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/* Skip if neither read nor write are needed */
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if ((local_flags & (BDRV_REQ_PREFETCH | BDRV_REQ_COPY_ON_READ)) !=
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BDRV_REQ_PREFETCH) {
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ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, qiov_offset,
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local_flags);
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if (ret < 0) {
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return ret;
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}
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}
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offset += n;
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qiov_offset += n;
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bytes -= n;
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}
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return 0;
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}
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static int coroutine_fn GRAPH_RDLOCK
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cor_co_pwritev_part(BlockDriverState *bs, 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 bdrv_co_pwritev_part(bs->file, offset, bytes, qiov, qiov_offset,
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flags);
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}
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static int coroutine_fn GRAPH_RDLOCK
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cor_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset, int64_t bytes,
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BdrvRequestFlags flags)
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{
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return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
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}
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static int coroutine_fn GRAPH_RDLOCK
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cor_co_pdiscard(BlockDriverState *bs, int64_t offset, int64_t bytes)
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{
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return bdrv_co_pdiscard(bs->file, offset, bytes);
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}
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static int coroutine_fn GRAPH_RDLOCK
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cor_co_pwritev_compressed(BlockDriverState *bs, int64_t offset, int64_t bytes,
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QEMUIOVector *qiov)
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{
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return bdrv_co_pwritev(bs->file, offset, bytes, qiov,
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BDRV_REQ_WRITE_COMPRESSED);
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}
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static void coroutine_fn GRAPH_RDLOCK
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cor_co_eject(BlockDriverState *bs, bool eject_flag)
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{
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bdrv_co_eject(bs->file->bs, eject_flag);
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}
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static void coroutine_fn GRAPH_RDLOCK
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cor_co_lock_medium(BlockDriverState *bs, bool locked)
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{
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bdrv_co_lock_medium(bs->file->bs, locked);
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}
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static void GRAPH_UNLOCKED cor_close(BlockDriverState *bs)
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{
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BDRVStateCOR *s = bs->opaque;
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GLOBAL_STATE_CODE();
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if (s->chain_frozen) {
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bdrv_graph_rdlock_main_loop();
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s->chain_frozen = false;
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bdrv_unfreeze_backing_chain(bs, s->bottom_bs);
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bdrv_graph_rdunlock_main_loop();
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}
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bdrv_unref(s->bottom_bs);
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}
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static BlockDriver bdrv_copy_on_read = {
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.format_name = "copy-on-read",
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.instance_size = sizeof(BDRVStateCOR),
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.bdrv_open = cor_open,
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.bdrv_close = cor_close,
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.bdrv_child_perm = cor_child_perm,
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.bdrv_co_getlength = cor_co_getlength,
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.bdrv_co_preadv_part = cor_co_preadv_part,
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.bdrv_co_pwritev_part = cor_co_pwritev_part,
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.bdrv_co_pwrite_zeroes = cor_co_pwrite_zeroes,
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.bdrv_co_pdiscard = cor_co_pdiscard,
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.bdrv_co_pwritev_compressed = cor_co_pwritev_compressed,
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.bdrv_co_eject = cor_co_eject,
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.bdrv_co_lock_medium = cor_co_lock_medium,
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.is_filter = true,
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};
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void no_coroutine_fn bdrv_cor_filter_drop(BlockDriverState *cor_filter_bs)
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{
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BDRVStateCOR *s = cor_filter_bs->opaque;
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GLOBAL_STATE_CODE();
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/* unfreeze, as otherwise bdrv_replace_node() will fail */
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if (s->chain_frozen) {
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GRAPH_RDLOCK_GUARD_MAINLOOP();
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s->chain_frozen = false;
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bdrv_unfreeze_backing_chain(cor_filter_bs, s->bottom_bs);
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}
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bdrv_drop_filter(cor_filter_bs, &error_abort);
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bdrv_unref(cor_filter_bs);
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}
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static void bdrv_copy_on_read_init(void)
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{
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bdrv_register(&bdrv_copy_on_read);
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}
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block_init(bdrv_copy_on_read_init);
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