[Devel] [PATCH VZ9] dm-qcow2: allow specifying depth to merge intermediate images
Vasileios Almpanis
vasileios.almpanis at virtuozzo.com
Fri Sep 12 16:48:13 MSK 2025
Looks good to me.
Reviewed-by: Vasileios Almpanis <vasileios.almpanis at virtuozzo.com><mailto:andrey.zhadchenko at virtuozzo.com>
________________________________
From: devel-bounces at openvz.org <devel-bounces at openvz.org> on behalf of Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
Sent: Monday, September 8, 2025 7:27 PM
To: Konstantin Khorenko <khorenko at virtuozzo.com>; Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
Cc: devel at openvz.org <devel at openvz.org>
Subject: [Devel] [PATCH VZ9] dm-qcow2: allow specifying depth to merge intermediate images
dm-qcow2 is almost ready to merge intermediate images, thanks
to separated metadata tables and qio being per-qcow2.
So this patch mostly propagates which qcow2 we want to use
instead of tgt->top.
qcow2_merge_backward_complete is a bit harder due to in-middle
replacement and needing to recalculate img_id for a part of
image chain.
https://virtuozzo.atlassian.net/browse/VSTOR-101375
Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
---
drivers/md/dm-qcow2-cmd.c | 82 ++++++++++++++++++++++++++++-----------
drivers/md/dm-qcow2.h | 1 +
2 files changed, 61 insertions(+), 22 deletions(-)
diff --git a/drivers/md/dm-qcow2-cmd.c b/drivers/md/dm-qcow2-cmd.c
index e77052ad61e6b..d59fa82dbffbc 100644
--- a/drivers/md/dm-qcow2-cmd.c
+++ b/drivers/md/dm-qcow2-cmd.c
@@ -116,9 +116,9 @@ static int qcow2_service_iter(struct qcow2_target *tgt, struct qcow2 *qcow2,
}
ALLOW_ERROR_INJECTION(qcow2_service_iter, ERRNO);
-static int qcow2_merge_common(struct qcow2_target *tgt)
+static int qcow2_merge_common(struct qcow2_target *tgt, struct qcow2 *qcow2)
{
- struct qcow2 *qcow2 = tgt->top, *lower = qcow2->lower;
+ struct qcow2 *lower = qcow2->lower;
u32 clu_size = qcow2->clu_size;
loff_t end = lower->hdr.size;
@@ -139,9 +139,8 @@ static int qcow2_merge_forward(struct qcow2_target *tgt)
}
ALLOW_ERROR_INJECTION(qcow2_merge_forward, ERRNO);
-static int qcow2_break_l1cow(struct qcow2_target *tgt)
+static int qcow2_break_l1cow(struct qcow2_target *tgt, struct qcow2 *qcow2)
{
- struct qcow2 *qcow2 = tgt->top;
loff_t end = qcow2->hdr.size;
loff_t step = (u64)qcow2->l2_entries * qcow2->clu_size;
@@ -152,25 +151,35 @@ static int qcow2_break_l1cow(struct qcow2_target *tgt)
static void set_backward_merge_in_process(struct qcow2_target *tgt,
struct qcow2 *qcow2, bool set)
{
+ struct qcow2 *top = tgt->top;
LIST_HEAD(list);
+ /*
+ * There are no writes if it is not the top qcow2 image.
+ * so we do not need to stop and flush requests when setting
+ */
+ if (qcow2 != top && set) {
+ qcow2->backward_merge_in_process = set;
+ return;
+ }
+
/*
* To avoid race between allocations and COWS
* we completely stop queueing qios and wait
* for pending qios. Lock is for visability.
*/
- spin_lock_irq(&qcow2->deferred_lock);
- qcow2->pause_submitting_qios = true;
- spin_unlock_irq(&qcow2->deferred_lock);
+ spin_lock_irq(&top->deferred_lock);
+ top->pause_submitting_qios = true;
+ spin_unlock_irq(&top->deferred_lock);
qcow2_inflight_ref_switch(tgt);
/* queue is stopped */
- spin_lock_irq(&qcow2->deferred_lock);
+ spin_lock_irq(&top->deferred_lock);
WARN_ON_ONCE(qcow2->backward_merge_in_process == set);
qcow2->backward_merge_in_process = set;
- qcow2->pause_submitting_qios = false;
- list_splice_init(&qcow2->paused_qios, &list);
- spin_unlock_irq(&qcow2->deferred_lock);
+ top->pause_submitting_qios = false;
+ list_splice_init(&top->paused_qios, &list);
+ spin_unlock_irq(&top->deferred_lock);
qcow2_submit_embedded_qios(tgt, &list);
}
@@ -240,11 +249,15 @@ static int qcow2_merge_backward_progress(struct qcow2_target *tgt,
static int qcow2_merge_backward_set_eventfd(struct qcow2_target *tgt, int efd);
-static int qcow2_merge_backward_start(struct qcow2_target *tgt, int efd)
+static int qcow2_merge_backward_start(struct qcow2_target *tgt, int efd, int depth)
{
- struct qcow2 *qcow2 = tgt->top, *lower = qcow2->lower;
+ struct qcow2 *qcow2 = tgt->top, *lower;
int ret;
+ while (depth-- > 0 && qcow2->lower)
+ qcow2 = qcow2->lower;
+ lower = qcow2->lower;
+
lockdep_assert_held(&tgt->ctl_mutex);
if (!lower)
@@ -263,6 +276,7 @@ static int qcow2_merge_backward_start(struct qcow2_target *tgt, int efd)
if (ret)
return ret;
+ tgt->backward_merge.qcow2 = qcow2;
tgt->backward_merge.state = BACKWARD_MERGE_START;
__backward_merge_update_stage(tgt, BACKWARD_MERGE_STAGE_START);
tgt->backward_merge.error = 0;
@@ -291,7 +305,7 @@ void qcow2_merge_backward_work(struct work_struct *work)
__backward_merge_update_stage(tgt, BACKWARD_MERGE_STAGE_BREAK_L1COW);
mutex_unlock(&tgt->ctl_mutex);
- qcow2 = tgt->top;
+ qcow2 = tgt->backward_merge.qcow2;
lower = qcow2->lower;
/*
@@ -300,7 +314,7 @@ void qcow2_merge_backward_work(struct work_struct *work)
* we'd have to freeze IO going to all data clusters
* under every L1 entry related to several snapshots.
*/
- ret = qcow2_break_l1cow(tgt);
+ ret = qcow2_break_l1cow(tgt, qcow2);
if (ret) {
QC_ERR(tgt->ti, "Can't break L1 COW");
goto out_err;
@@ -316,7 +330,7 @@ void qcow2_merge_backward_work(struct work_struct *work)
/* Start merge */
backward_merge_update_stage(tgt, BACKWARD_MERGE_STAGE_RUNNING);
- ret = qcow2_merge_common(tgt);
+ ret = qcow2_merge_common(tgt, qcow2);
if (ret) {
set_backward_merge_in_process(tgt, qcow2, false);
ret2 = qcow2_set_image_file_features(lower, false);
@@ -357,9 +371,29 @@ static int qcow2_merge_backward_complete(struct qcow2_target *tgt)
if (tgt->backward_merge.state != BACKWARD_MERGE_WAIT_COMPLETION)
return -EBUSY;
+
+ if (tgt->top == tgt->backward_merge.qcow2) {
+ tgt->top = lower;
+ } else {
+ struct qcow2 *top = tgt->top;
+
+ while (top && top->lower != tgt->backward_merge.qcow2)
+ top = top->lower;
+ if (!top)
+ return -EFAULT;
+
+ qcow2 = tgt->backward_merge.qcow2;
+ lower = qcow2->lower;
+ top->lower = lower;
+
+ top = tgt->top;
+ while (top != lower) {
+ top->img_id--;
+ top = top->lower;
+ }
+ }
+
__backward_merge_update_stage(tgt, BACKWARD_MERGE_STAGE_COMPLETING);
-
- tgt->top = lower;
smp_wmb(); /* Pairs with qcow2_ref_inc() */
qcow2_inflight_ref_switch(tgt); /* Pending qios */
qcow2_flush_deferred_activity(tgt, qcow2); /* Delayed md pages */
@@ -396,7 +430,7 @@ void qcow2_merge_backward_cancel(struct qcow2_target *tgt)
} else if (tgt->backward_merge.state == BACKWARD_MERGE_STOP) {
flush = true;
} else if (tgt->backward_merge.state == BACKWARD_MERGE_WAIT_COMPLETION) {
- set_backward_merge_in_process(tgt, tgt->top, false);
+ set_backward_merge_in_process(tgt, tgt->backward_merge.qcow2, false);
tgt->backward_merge.state = BACKWARD_MERGE_STOPPED;
__backward_merge_update_stage(tgt, BACKWARD_MERGE_STAGE_NONE);
}
@@ -572,7 +606,7 @@ int qcow2_message(struct dm_target *ti, unsigned int argc, char **argv,
struct qcow2_target *tgt = to_qcow2_target(ti);
int ret = -EPERM;
u32 val, val2;
- int efd;
+ int efd, depth = 0;
if (!capable(CAP_SYS_ADMIN))
goto out;
@@ -652,11 +686,15 @@ int qcow2_message(struct dm_target *ti, unsigned int argc, char **argv,
} else if (!strcmp(argv[0], "merge_backward")) {
/* argc >= 2 */
if (!strcmp(argv[1], "start")) {
- if (argc != 3 || kstrtoint(argv[2], 10, &efd) || efd < 0) {
+ if (argc < 3 || argc > 4 || kstrtoint(argv[2], 10, &efd) || efd < 0) {
ret = -EINVAL;
goto out_unlock;
}
- ret = qcow2_merge_backward_start(tgt, efd);
+ if (argc == 4 && kstrtou32(argv[3], 10, &depth)) {
+ ret = -EINVAL;
+ goto out_unlock;
+ }
+ ret = qcow2_merge_backward_start(tgt, efd, depth);
} else if (!strcmp(argv[1], "complete")) {
if (argc != 2) {
ret = -EINVAL;
diff --git a/drivers/md/dm-qcow2.h b/drivers/md/dm-qcow2.h
index 5aa00c6a5ebd5..c2b2193561461 100644
--- a/drivers/md/dm-qcow2.h
+++ b/drivers/md/dm-qcow2.h
@@ -172,6 +172,7 @@ enum qcow2_backward_merge_stage {
struct qcow2_backward_merge {
struct work_struct work;
+ struct qcow2 *qcow2;
enum qcow2_backward_merge_state state;
int error;
struct eventfd_ctx *eventfd_ctx;
--
2.43.5
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