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pve-qemu-qoup/debian/patches/pve/0049-qapi-blockdev-backup-add-discard-source-parameter.patch
Thomas Lamprecht 20209d8d73 implement support for backup fleecing 
Excerpt from Fiona's v3 cover-letter [0]:

When a backup for a VM is started, QEMU will install a
"copy-before-write" filter in its block layer. This filter ensures
that upon new guest writes, old data still needed for the backup is
sent to the backup target first. The guest write blocks until this
operation is finished so guest IO to not-yet-backed-up sectors will be
limited by the speed of the backup target.

With backup fleecing, such old data is cached in a fleecing image
rather than sent directly to the backup target. This can help guest IO
performance and even prevent hangs in certain scenarios, at the cost
of requiring more storage space.

With this series it will be possible to enable backup-fleecing via
e.g. `vzdump 123 --fleecing enabled=1,storage=local-lvm` with fleecing
images created on the storage `local-lvm`. The fleecing storage should
be a fast local storage which supports thin-provisioning and discard.
If the storage supports qcow2, that is used as the fleecing image
format. If the underlying file system does not support discard, with
qcow2 and preallocation=off, at least already allocated parts of the
image can be re-used later.

Fleecing images are created by qemu-server via pve-storage and
attached to QEMU before the backup starts, and cleaned up after the
backup finished or failed. The naming schema for fleecing images is
'vm-ID-fleece-N(.FORMAT)'. The allocated images are recorded in the
guest configuration, so that even after a hard failure, clean-up can
be re-attempted. While not too bad, it's a non-trivial amount of code
and I'm not 100% sure about the cost-benefit, so sending those as RFC.

The fleecing image needs to be the exact same size as the source, but
luckily, an explicit size can be specified when attaching a raw image
to QEMU so there are no size issues when using storages that have
coarser allocation/round up. For qcow2, it seems that virtual size can
be nearly arbitrary (i.e. modulo 512 byte granularity) during
allocation.

[0]: https://lists.proxmox.com/pipermail/pve-devel/2024-April/062815.html

Originally-by: Fiona Ebner <f.ebner@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
2024-04-11 20:05:02 +02:00

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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Date: Thu, 11 Apr 2024 11:29:25 +0200
Subject: [PATCH] qapi: blockdev-backup: add discard-source parameter
Add a parameter that enables discard-after-copy. That is mostly useful
in "push backup with fleecing" scheme, when source is snapshot-access
format driver node, based on copy-before-write filter snapshot-access
API:
[guest] [snapshot-access] ~~ blockdev-backup ~~> [backup target]
| |
| root | file
v v
[copy-before-write]
| |
| file | target
v v
[active disk] [temp.img]
In this case discard-after-copy does two things:
- discard data in temp.img to save disk space
- avoid further copy-before-write operation in discarded area
Note that we have to declare WRITE permission on source in
copy-before-write filter, for discard to work. Still we can't take it
unconditionally, as it will break normal backup from RO source. So, we
have to add a parameter and pass it thorough bdrv_open flags.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
---
block/backup.c | 5 +++--
block/block-copy.c | 9 +++++++++
block/copy-before-write.c | 15 +++++++++++++--
block/copy-before-write.h | 1 +
block/replication.c | 4 ++--
blockdev.c | 2 +-
include/block/block-common.h | 2 ++
include/block/block-copy.h | 1 +
include/block/block_int-global-state.h | 2 +-
qapi/block-core.json | 4 ++++
10 files changed, 37 insertions(+), 8 deletions(-)
diff --git a/block/backup.c b/block/backup.c
index af87fa6aa9..3dc955f625 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -332,7 +332,7 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
BlockDriverState *target, int64_t speed,
MirrorSyncMode sync_mode, BdrvDirtyBitmap *sync_bitmap,
BitmapSyncMode bitmap_mode,
- bool compress,
+ bool compress, bool discard_source,
const char *filter_node_name,
BackupPerf *perf,
BlockdevOnError on_source_error,
@@ -429,7 +429,8 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
goto error;
}
- cbw = bdrv_cbw_append(bs, target, filter_node_name, &bcs, errp);
+ cbw = bdrv_cbw_append(bs, target, filter_node_name, discard_source,
+ &bcs, errp);
if (!cbw) {
goto error;
}
diff --git a/block/block-copy.c b/block/block-copy.c
index b61685f1a2..3c61e52bae 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -137,6 +137,7 @@ typedef struct BlockCopyState {
CoMutex lock;
int64_t in_flight_bytes;
BlockCopyMethod method;
+ bool discard_source;
BlockReqList reqs;
QLIST_HEAD(, BlockCopyCallState) calls;
/*
@@ -348,6 +349,7 @@ static int64_t block_copy_calculate_cluster_size(BlockDriverState *target,
BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
BlockDriverState *copy_bitmap_bs,
const BdrvDirtyBitmap *bitmap,
+ bool discard_source,
Error **errp)
{
ERRP_GUARD();
@@ -409,6 +411,7 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
cluster_size),
};
+ s->discard_source = discard_source;
block_copy_set_copy_opts(s, false, false);
ratelimit_init(&s->rate_limit);
@@ -580,6 +583,12 @@ static coroutine_fn int block_copy_task_entry(AioTask *task)
co_put_to_shres(s->mem, t->req.bytes);
block_copy_task_end(t, ret);
+ if (s->discard_source && ret == 0) {
+ int64_t nbytes =
+ MIN(t->req.offset + t->req.bytes, s->len) - t->req.offset;
+ bdrv_co_pdiscard(s->source, t->req.offset, nbytes);
+ }
+
return ret;
}
diff --git a/block/copy-before-write.c b/block/copy-before-write.c
index d3b95bd600..3503702d71 100644
--- a/block/copy-before-write.c
+++ b/block/copy-before-write.c
@@ -44,6 +44,7 @@ typedef struct BDRVCopyBeforeWriteState {
BdrvChild *target;
OnCbwError on_cbw_error;
uint32_t cbw_timeout_ns;
+ bool discard_source;
/*
* @lock: protects access to @access_bitmap, @done_bitmap and
@@ -357,6 +358,8 @@ static void cbw_child_perm(BlockDriverState *bs, BdrvChild *c,
uint64_t perm, uint64_t shared,
uint64_t *nperm, uint64_t *nshared)
{
+ BDRVCopyBeforeWriteState *s = bs->opaque;
+
if (!(role & BDRV_CHILD_FILTERED)) {
/*
* Target child
@@ -381,6 +384,10 @@ static void cbw_child_perm(BlockDriverState *bs, BdrvChild *c,
* start
*/
*nperm = *nperm | BLK_PERM_CONSISTENT_READ;
+ if (s->discard_source) {
+ *nperm = *nperm | BLK_PERM_WRITE;
+ }
+
*nshared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE);
}
}
@@ -470,7 +477,9 @@ static int cbw_open(BlockDriverState *bs, QDict *options, int flags,
((BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK) &
bs->file->bs->supported_zero_flags);
- s->bcs = block_copy_state_new(bs->file, s->target, bs, bitmap, errp);
+ s->discard_source = flags & BDRV_O_CBW_DISCARD_SOURCE;
+ s->bcs = block_copy_state_new(bs->file, s->target, bs, bitmap,
+ flags & BDRV_O_CBW_DISCARD_SOURCE, errp);
if (!s->bcs) {
error_prepend(errp, "Cannot create block-copy-state: ");
ret = -EINVAL;
@@ -544,12 +553,14 @@ BlockDriver bdrv_cbw_filter = {
BlockDriverState *bdrv_cbw_append(BlockDriverState *source,
BlockDriverState *target,
const char *filter_node_name,
+ bool discard_source,
BlockCopyState **bcs,
Error **errp)
{
BDRVCopyBeforeWriteState *state;
BlockDriverState *top;
QDict *opts;
+ int flags = BDRV_O_RDWR | (discard_source ? BDRV_O_CBW_DISCARD_SOURCE : 0);
assert(source->total_sectors == target->total_sectors);
GLOBAL_STATE_CODE();
@@ -562,7 +573,7 @@ BlockDriverState *bdrv_cbw_append(BlockDriverState *source,
qdict_put_str(opts, "file", bdrv_get_node_name(source));
qdict_put_str(opts, "target", bdrv_get_node_name(target));
- top = bdrv_insert_node(source, opts, BDRV_O_RDWR, errp);
+ top = bdrv_insert_node(source, opts, flags, errp);
if (!top) {
return NULL;
}
diff --git a/block/copy-before-write.h b/block/copy-before-write.h
index 6e72bb25e9..01af0cd3c4 100644
--- a/block/copy-before-write.h
+++ b/block/copy-before-write.h
@@ -39,6 +39,7 @@
BlockDriverState *bdrv_cbw_append(BlockDriverState *source,
BlockDriverState *target,
const char *filter_node_name,
+ bool discard_source,
BlockCopyState **bcs,
Error **errp);
void bdrv_cbw_drop(BlockDriverState *bs);
diff --git a/block/replication.c b/block/replication.c
index ea4bf1aa80..39ad78cf98 100644
--- a/block/replication.c
+++ b/block/replication.c
@@ -579,8 +579,8 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
s->backup_job = backup_job_create(
NULL, s->secondary_disk->bs, s->hidden_disk->bs,
- 0, MIRROR_SYNC_MODE_NONE, NULL, 0, false, NULL,
- &perf,
+ 0, MIRROR_SYNC_MODE_NONE, NULL, 0, false, false,
+ NULL, &perf,
BLOCKDEV_ON_ERROR_REPORT,
BLOCKDEV_ON_ERROR_REPORT, JOB_INTERNAL,
backup_job_completed, bs, NULL, &local_err);
diff --git a/blockdev.c b/blockdev.c
index 7793143d76..ce3fef924c 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2802,7 +2802,7 @@ static BlockJob *do_backup_common(BackupCommon *backup,
job = backup_job_create(backup->job_id, bs, target_bs, backup->speed,
backup->sync, bmap, backup->bitmap_mode,
- backup->compress,
+ backup->compress, backup->discard_source,
backup->filter_node_name,
&perf,
backup->on_source_error,
diff --git a/include/block/block-common.h b/include/block/block-common.h
index e15395f2cb..913a8b259c 100644
--- a/include/block/block-common.h
+++ b/include/block/block-common.h
@@ -234,6 +234,8 @@ typedef enum {
read-write fails */
#define BDRV_O_IO_URING 0x40000 /* use io_uring instead of the thread pool */
+#define BDRV_O_CBW_DISCARD_SOURCE 0x80000 /* for copy-before-write filter */
+
#define BDRV_O_CACHE_MASK (BDRV_O_NOCACHE | BDRV_O_NO_FLUSH)
diff --git a/include/block/block-copy.h b/include/block/block-copy.h
index 8b41643bfa..bdc703bacd 100644
--- a/include/block/block-copy.h
+++ b/include/block/block-copy.h
@@ -27,6 +27,7 @@ typedef struct BlockCopyCallState BlockCopyCallState;
BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
BlockDriverState *copy_bitmap_bs,
const BdrvDirtyBitmap *bitmap,
+ bool discard_source,
Error **errp);
/* Function should be called prior any actual copy request */
diff --git a/include/block/block_int-global-state.h b/include/block/block_int-global-state.h
index 32f0f9858a..546f2b5532 100644
--- a/include/block/block_int-global-state.h
+++ b/include/block/block_int-global-state.h
@@ -189,7 +189,7 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
MirrorSyncMode sync_mode,
BdrvDirtyBitmap *sync_bitmap,
BitmapSyncMode bitmap_mode,
- bool compress,
+ bool compress, bool discard_source,
const char *filter_node_name,
BackupPerf *perf,
BlockdevOnError on_source_error,
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 09de550c95..4297e5beda 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1816,6 +1816,9 @@
# node specified by @drive. If this option is not given, a node
# name is autogenerated. (Since: 4.2)
#
+# @discard-source: Discard blocks on source which are already copied
+# to the target. (Since 9.0)
+#
# @x-perf: Performance options. (Since 6.0)
#
# Features:
@@ -1837,6 +1840,7 @@
'*on-target-error': 'BlockdevOnError',
'*auto-finalize': 'bool', '*auto-dismiss': 'bool',
'*filter-node-name': 'str',
+ '*discard-source': 'bool',
'*x-perf': { 'type': 'BackupPerf',
'features': [ 'unstable' ] } } }
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