Non-active block commits do not discard blocks only containing zeros,
causing images to lose sparseness after the commit. This commit fixes
that by writing zero blocks using blk_co_pwrite_zeroes rather than
writing them out as any oother arbitrary data.
Signed-off-by: Vincent Vanlaer <libvirt-e6954efa@volkihar.be>
---
block/commit.c | 71 +++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 58 insertions(+), 13 deletions(-)
diff --git a/block/commit.c b/block/commit.c
index 7c3fdcb0ca..5bd97b5a74 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -12,9 +12,13 @@
*
*/
+#include "bits/time.h"
#include "qemu/osdep.h"
#include "qemu/cutils.h"
+#include "time.h"
#include "trace.h"
+#include "block/block-common.h"
+#include "block/coroutines.h"
#include "block/block_int.h"
#include "block/blockjob_int.h"
#include "qapi/error.h"
@@ -126,6 +130,12 @@ static void commit_clean(Job *job)
blk_unref(s->top);
}
+typedef enum CommitMethod {
+ COMMIT_METHOD_COPY,
+ COMMIT_METHOD_ZERO,
+ COMMIT_METHOD_IGNORE,
+} CommitMethod;
+
static int coroutine_fn commit_run(Job *job, Error **errp)
{
CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
@@ -156,8 +166,9 @@ static int coroutine_fn commit_run(Job *job, Error **errp)
buf = blk_blockalign(s->top, COMMIT_BUFFER_SIZE);
for (offset = 0; offset < len; offset += n) {
- bool copy;
bool error_in_source = true;
+ CommitMethod commit_method = COMMIT_METHOD_COPY;
+
/* Note that even when no rate limit is applied we need to yield
* with no pending I/O here so that bdrv_drain_all() returns.
@@ -167,21 +178,54 @@ static int coroutine_fn commit_run(Job *job, Error **errp)
break;
}
/* Copy if allocated above the base */
- ret = blk_co_is_allocated_above(s->top, s->base_overlay, true,
- offset, COMMIT_BUFFER_SIZE, &n);
- copy = (ret > 0);
+ WITH_GRAPH_RDLOCK_GUARD() {
+ ret = bdrv_co_common_block_status_above(blk_bs(s->top),
+ s->base_overlay, true, true, offset, COMMIT_BUFFER_SIZE,
+ &n, NULL, NULL, NULL);
+ }
+
trace_commit_one_iteration(s, offset, n, ret);
- if (copy) {
- assert(n < SIZE_MAX);
-
- ret = blk_co_pread(s->top, offset, n, buf, 0);
- if (ret >= 0) {
- ret = blk_co_pwrite(s->base, offset, n, buf, 0);
- if (ret < 0) {
- error_in_source = false;
+
+ if (ret >= 0 && !(ret & BDRV_BLOCK_ALLOCATED)) {
+ commit_method = COMMIT_METHOD_IGNORE;
+ } else if (ret >= 0 && ret & BDRV_BLOCK_ZERO) {
+ int64_t target_offset;
+ int64_t target_bytes;
+ WITH_GRAPH_RDLOCK_GUARD() {
+ bdrv_round_to_subclusters(s->base_bs, offset, n,
+ &target_offset, &target_bytes);
+ }
+
+ if (target_offset == offset &&
+ target_bytes == n) {
+ commit_method = COMMIT_METHOD_ZERO;
+ }
+ }
+
+ if (ret >= 0) {
+ switch (commit_method) {
+ case COMMIT_METHOD_COPY:
+ assert(n < SIZE_MAX);
+ ret = blk_co_pread(s->top, offset, n, buf, 0);
+ if (ret >= 0) {
+ ret = blk_co_pwrite(s->base, offset, n, buf, 0);
+ if (ret < 0) {
+ error_in_source = false;
+ }
}
+ break;
+ case COMMIT_METHOD_ZERO:
+ ret = blk_co_pwrite_zeroes(s->base, offset, n,
+ BDRV_REQ_MAY_UNMAP);
+ error_in_source = false;
+ break;
+ case COMMIT_METHOD_IGNORE:
+ break;
+ default:
+ abort();
}
}
+
if (ret < 0) {
BlockErrorAction action =
block_job_error_action(&s->common, s->on_error,
@@ -193,10 +237,11 @@ static int coroutine_fn commit_run(Job *job, Error **errp)
continue;
}
}
+
/* Publish progress */
job_progress_update(&s->common.job, n);
- if (copy) {
+ if (commit_method == COMMIT_METHOD_COPY) {
block_job_ratelimit_processed_bytes(&s->common, n);
}
}
--
2.42.0On 26.05.24 22:29, Vincent Vanlaer wrote:
> Non-active block commits do not discard blocks only containing zeros,
> causing images to lose sparseness after the commit. This commit fixes
> that by writing zero blocks using blk_co_pwrite_zeroes rather than
> writing them out as any oother arbitrary data.
Hi Vincent! Sorry for long delay.
Could you please split the commit into simpler parts?
Something like this:
1. refactor to use direct bdrv_co_common_block_status_above()
2. refactor to use CommitMethod (with two possible modes)
3. add new mode
(The idea is to split parts of no-logic-change refactoring from real logic changes and keep the latter smaller and clearer)
>
> Signed-off-by: Vincent Vanlaer <libvirt-e6954efa@volkihar.be>
> ---
> block/commit.c | 71 +++++++++++++++++++++++++++++++++++++++++---------
> 1 file changed, 58 insertions(+), 13 deletions(-)
>
> diff --git a/block/commit.c b/block/commit.c
> index 7c3fdcb0ca..5bd97b5a74 100644
> --- a/block/commit.c
> +++ b/block/commit.c
> @@ -12,9 +12,13 @@
> *
> */
>
> +#include "bits/time.h"
> #include "qemu/osdep.h"
> #include "qemu/cutils.h"
> +#include "time.h"
> #include "trace.h"
> +#include "block/block-common.h"
> +#include "block/coroutines.h"
> #include "block/block_int.h"
> #include "block/blockjob_int.h"
> #include "qapi/error.h"
> @@ -126,6 +130,12 @@ static void commit_clean(Job *job)
> blk_unref(s->top);
> }
>
> +typedef enum CommitMethod {
> + COMMIT_METHOD_COPY,
> + COMMIT_METHOD_ZERO,
> + COMMIT_METHOD_IGNORE,
> +} CommitMethod;
> +
> static int coroutine_fn commit_run(Job *job, Error **errp)
> {
> CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
> @@ -156,8 +166,9 @@ static int coroutine_fn commit_run(Job *job, Error **errp)
> buf = blk_blockalign(s->top, COMMIT_BUFFER_SIZE);
>
> for (offset = 0; offset < len; offset += n) {
> - bool copy;
> bool error_in_source = true;
> + CommitMethod commit_method = COMMIT_METHOD_COPY;
> +
>
> /* Note that even when no rate limit is applied we need to yield
> * with no pending I/O here so that bdrv_drain_all() returns.
> @@ -167,21 +178,54 @@ static int coroutine_fn commit_run(Job *job, Error **errp)
> break;
> }
> /* Copy if allocated above the base */
> - ret = blk_co_is_allocated_above(s->top, s->base_overlay, true,
> - offset, COMMIT_BUFFER_SIZE, &n);
> - copy = (ret > 0);
> + WITH_GRAPH_RDLOCK_GUARD() {
> + ret = bdrv_co_common_block_status_above(blk_bs(s->top),
> + s->base_overlay, true, true, offset, COMMIT_BUFFER_SIZE,
> + &n, NULL, NULL, NULL);
> + }
> +
> trace_commit_one_iteration(s, offset, n, ret);
> - if (copy) {
> - assert(n < SIZE_MAX);
> -
> - ret = blk_co_pread(s->top, offset, n, buf, 0);
> - if (ret >= 0) {
> - ret = blk_co_pwrite(s->base, offset, n, buf, 0);
> - if (ret < 0) {
> - error_in_source = false;
> +
> + if (ret >= 0 && !(ret & BDRV_BLOCK_ALLOCATED)) {
> + commit_method = COMMIT_METHOD_IGNORE;
> + } else if (ret >= 0 && ret & BDRV_BLOCK_ZERO) {
> + int64_t target_offset;
> + int64_t target_bytes;
> + WITH_GRAPH_RDLOCK_GUARD() {
> + bdrv_round_to_subclusters(s->base_bs, offset, n,
> + &target_offset, &target_bytes);
> + }
> +
> + if (target_offset == offset &&
> + target_bytes == n) {
> + commit_method = COMMIT_METHOD_ZERO;
> + }
> + }
> +
> + if (ret >= 0) {
> + switch (commit_method) {
> + case COMMIT_METHOD_COPY:
> + assert(n < SIZE_MAX);
> + ret = blk_co_pread(s->top, offset, n, buf, 0);
> + if (ret >= 0) {
> + ret = blk_co_pwrite(s->base, offset, n, buf, 0);
> + if (ret < 0) {
> + error_in_source = false;
> + }
> }
> + break;
> + case COMMIT_METHOD_ZERO:
> + ret = blk_co_pwrite_zeroes(s->base, offset, n,
> + BDRV_REQ_MAY_UNMAP);
> + error_in_source = false;
> + break;
> + case COMMIT_METHOD_IGNORE:
> + break;
> + default:
> + abort();
> }
> }
> +
> if (ret < 0) {
> BlockErrorAction action =
> block_job_error_action(&s->common, s->on_error,
> @@ -193,10 +237,11 @@ static int coroutine_fn commit_run(Job *job, Error **errp)
> continue;
> }
> }
> +
> /* Publish progress */
> job_progress_update(&s->common.job, n);
>
> - if (copy) {
> + if (commit_method == COMMIT_METHOD_COPY) {
> block_job_ratelimit_processed_bytes(&s->common, n);
> }
> }
--
Best regards,
Vladimir
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