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block/copy-before-write: implement cbw-timeout option

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In some scenarios, when copy-before-write operations lasts too long
time, it's better to cancel it.

Most useful would be to use the new option together with
on-cbw-error=break-snapshot: this way if cbw operation takes too long
time we'll just cancel backup process but do not disturb the guest too
much.

Note the tricky point of realization: we keep additional point in
bs->in_flight during block_copy operation even if it's timed-out.
Background "cancelled" block_copy operations will finish at some point
and will want to access state. We should care to not free the state in
.bdrv_close() earlier.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@openvz.org>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
  [vsementsov: use bdrv_inc_in_flight()/bdrv_dec_in_flight() instead of
   direct manipulation on bs->in_flight]
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2022-04-07 16:27:25 +03:00 committed by Vladimir Sementsov-Ogievskiy
parent 15df6e6987
commit 6db7fd1ca9
2 changed files with 28 additions and 2 deletions
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22
block/copy-before-write.c
View File

@ -42,6 +42,7 @@ typedef struct BDRVCopyBeforeWriteState {
BlockCopyState *bcs;
BdrvChild *target;
OnCbwError on_cbw_error;
uint32_t cbw_timeout_ns;
/*
* @lock: protects access to @access_bitmap, @done_bitmap and
@ -83,6 +84,13 @@ static coroutine_fn int cbw_co_preadv(
return bdrv_co_preadv(bs->file, offset, bytes, qiov, flags);
}
static void block_copy_cb(void *opaque)
{
BlockDriverState *bs = opaque;
bdrv_dec_in_flight(bs);
}
/*
* Do copy-before-write operation.
*
@ -111,7 +119,16 @@ static coroutine_fn int cbw_do_copy_before_write(BlockDriverState *bs,
off = QEMU_ALIGN_DOWN(offset, cluster_size);
end = QEMU_ALIGN_UP(offset + bytes, cluster_size);
ret = block_copy(s->bcs, off, end - off, true, 0, NULL, NULL);
/*
* Increase in_flight, so that in case of timed-out block-copy, the
* remaining background block_copy() request (which can't be immediately
* cancelled by timeout) is presented in bs->in_flight. This way we are
* sure that on bs close() we'll previously wait for all timed-out but yet
* running block_copy calls.
*/
bdrv_inc_in_flight(bs);
ret = block_copy(s->bcs, off, end - off, true, s->cbw_timeout_ns,
block_copy_cb, bs);
if (ret < 0 && s->on_cbw_error == ON_CBW_ERROR_BREAK_GUEST_WRITE) {
return ret;
}
@ -377,6 +394,7 @@ static BlockdevOptions *cbw_parse_options(QDict *options, Error **errp)
*/
qdict_extract_subqdict(options, NULL, "bitmap");
qdict_del(options, "on-cbw-error");
qdict_del(options, "cbw-timeout");
out:
visit_free(v);
@ -423,6 +441,8 @@ static int cbw_open(BlockDriverState *bs, QDict *options, int flags,
}
s->on_cbw_error = opts->has_on_cbw_error ? opts->on_cbw_error :
ON_CBW_ERROR_BREAK_GUEST_WRITE;
s->cbw_timeout_ns = opts->has_cbw_timeout ?
opts->cbw_timeout * NANOSECONDS_PER_SECOND : 0;
bs->total_sectors = bs->file->bs->total_sectors;
bs->supported_write_flags = BDRV_REQ_WRITE_UNCHANGED |

8
qapi/block-core.json
View File

@ -4227,12 +4227,18 @@
# @on-cbw-error: Behavior on failure of copy-before-write operation.
# Default is @break-guest-write. (Since 7.1)
#
# @cbw-timeout: Zero means no limit. Non-zero sets the timeout in seconds
# for copy-before-write operation. When a timeout occurs,
# the respective copy-before-write operation will fail, and
# the @on-cbw-error parameter will decide how this failure
# is handled. Default 0. (Since 7.1)
#
# Since: 6.2
##
{ 'struct': 'BlockdevOptionsCbw',
'base': 'BlockdevOptionsGenericFormat',
'data': { 'target': 'BlockdevRef', '*bitmap': 'BlockDirtyBitmap',
'*on-cbw-error': 'OnCbwError' } }
'*on-cbw-error': 'OnCbwError', '*cbw-timeout': 'uint32' } }
##
# @BlockdevOptions: