qemu/block/copy-on-read.c
Max Reitz 228345bf5d block: Support BDRV_REQ_WRITE_UNCHANGED in filters
Update the rest of the filter drivers to support
BDRV_REQ_WRITE_UNCHANGED.  They already forward write request flags to
their children, so we just have to announce support for it.

This patch does not cover the replication driver because that currently
does not support flags at all, and because it just grabs the WRITE
permission for its children when it can, so we should be fine just
submitting the incoming WRITE_UNCHANGED requests as normal writes.

It also does not cover format drivers for similar reasons.  They all use
bdrv_format_default_perms() as their .bdrv_child_perm() implementation
so they just always grab the WRITE permission for their file children
whenever possible.  In addition, it often would be difficult to
ascertain whether incoming unchanging writes end up as unchanging writes
in their files.  So we just leave them as normal potentially changing
writes.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 20180421132929.21610-7-mreitz@redhat.com
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
2018-05-15 16:15:21 +02:00

174 lines
5.2 KiB
C

/*
* Copy-on-read filter block driver
*
* Copyright (c) 2018 Red Hat, Inc.
*
* Author:
* Max Reitz <mreitz@redhat.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 or
* (at your option) version 3 of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#include "qemu/osdep.h"
#include "block/block_int.h"
static int cor_open(BlockDriverState *bs, QDict *options, int flags,
Error **errp)
{
bs->file = bdrv_open_child(NULL, options, "file", bs, &child_file, false,
errp);
if (!bs->file) {
return -EINVAL;
}
bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |
(BDRV_REQ_FUA &
bs->file->bs->supported_write_flags);
bs->supported_zero_flags = BDRV_REQ_WRITE_UNCHANGED |
((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
bs->file->bs->supported_zero_flags);
return 0;
}
static void cor_close(BlockDriverState *bs)
{
}
#define PERM_PASSTHROUGH (BLK_PERM_CONSISTENT_READ \
| BLK_PERM_WRITE \
| BLK_PERM_RESIZE)
#define PERM_UNCHANGED (BLK_PERM_ALL & ~PERM_PASSTHROUGH)
static void cor_child_perm(BlockDriverState *bs, BdrvChild *c,
const BdrvChildRole *role,
BlockReopenQueue *reopen_queue,
uint64_t perm, uint64_t shared,
uint64_t *nperm, uint64_t *nshared)
{
if (c == NULL) {
*nperm = (perm & PERM_PASSTHROUGH) | BLK_PERM_WRITE_UNCHANGED;
*nshared = (shared & PERM_PASSTHROUGH) | PERM_UNCHANGED;
return;
}
*nperm = (perm & PERM_PASSTHROUGH) |
(c->perm & PERM_UNCHANGED);
*nshared = (shared & PERM_PASSTHROUGH) |
(c->shared_perm & PERM_UNCHANGED);
}
static int64_t cor_getlength(BlockDriverState *bs)
{
return bdrv_getlength(bs->file->bs);
}
static int cor_truncate(BlockDriverState *bs, int64_t offset,
PreallocMode prealloc, Error **errp)
{
return bdrv_truncate(bs->file, offset, prealloc, errp);
}
static int coroutine_fn cor_co_preadv(BlockDriverState *bs,
uint64_t offset, uint64_t bytes,
QEMUIOVector *qiov, int flags)
{
return bdrv_co_preadv(bs->file, offset, bytes, qiov,
flags | BDRV_REQ_COPY_ON_READ);
}
static int coroutine_fn cor_co_pwritev(BlockDriverState *bs,
uint64_t offset, uint64_t bytes,
QEMUIOVector *qiov, int flags)
{
return bdrv_co_pwritev(bs->file, offset, bytes, qiov, flags);
}
static int coroutine_fn cor_co_pwrite_zeroes(BlockDriverState *bs,
int64_t offset, int bytes,
BdrvRequestFlags flags)
{
return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
}
static int coroutine_fn cor_co_pdiscard(BlockDriverState *bs,
int64_t offset, int bytes)
{
return bdrv_co_pdiscard(bs->file->bs, offset, bytes);
}
static void cor_eject(BlockDriverState *bs, bool eject_flag)
{
bdrv_eject(bs->file->bs, eject_flag);
}
static void cor_lock_medium(BlockDriverState *bs, bool locked)
{
bdrv_lock_medium(bs->file->bs, locked);
}
static bool cor_recurse_is_first_non_filter(BlockDriverState *bs,
BlockDriverState *candidate)
{
return bdrv_recurse_is_first_non_filter(bs->file->bs, candidate);
}
BlockDriver bdrv_copy_on_read = {
.format_name = "copy-on-read",
.bdrv_open = cor_open,
.bdrv_close = cor_close,
.bdrv_child_perm = cor_child_perm,
.bdrv_getlength = cor_getlength,
.bdrv_truncate = cor_truncate,
.bdrv_co_preadv = cor_co_preadv,
.bdrv_co_pwritev = cor_co_pwritev,
.bdrv_co_pwrite_zeroes = cor_co_pwrite_zeroes,
.bdrv_co_pdiscard = cor_co_pdiscard,
.bdrv_eject = cor_eject,
.bdrv_lock_medium = cor_lock_medium,
.bdrv_co_block_status = bdrv_co_block_status_from_file,
.bdrv_recurse_is_first_non_filter = cor_recurse_is_first_non_filter,
.has_variable_length = true,
.is_filter = true,
};
static void bdrv_copy_on_read_init(void)
{
bdrv_register(&bdrv_copy_on_read);
}
block_init(bdrv_copy_on_read_init);