[Qemu-devel] [PATCH v9 0/9] qcow2: cluster space preallocation

[Qemu-devel] [PATCH v9 0/9] qcow2: cluster space preallocation

[Anton Nefedov]

hej,
yet another respin of this series :) now as 2.12 is released

v9: - fixed commentary wording in patches 4, 8
    - rebased (no conflicts)

v8: http://lists.nongnu.org/archive/html/qemu-devel/2018-03/msg03291.html

Anton Nefedov (9):
  mirror: inherit supported write/zero flags
  blkverify: set supported write/zero flags
  quorum: set supported write/zero flags
  block: introduce BDRV_REQ_ALLOCATE flag
  block: treat BDRV_REQ_ALLOCATE as serialising
  file-posix: support BDRV_REQ_ALLOCATE
  block: support BDRV_REQ_ALLOCATE in passthrough drivers
  qcow2: skip writing zero buffers to empty COW areas
  iotest 134: test cluster-misaligned encrypted write

 qapi/block-core.json       |  4 ++-
 block/qcow2.h              |  6 ++++
 include/block/block.h      |  8 ++++-
 include/block/block_int.h  |  2 +-
 block/blkdebug.c           |  3 +-
 block/blkverify.c          |  9 ++++++
 block/file-posix.c         | 10 +++++-
 block/io.c                 | 50 +++++++++++++++++++++++------
 block/mirror.c             | 11 +++++++
 block/qcow2-cluster.c      |  2 +-
 block/qcow2.c              | 80 ++++++++++++++++++++++++++++++++++++++++++++--
 block/quorum.c             | 21 ++++++++++++
 block/raw-format.c         |  3 +-
 block/trace-events         |  1 +
 tests/qemu-iotests/060     | 26 +++++++++------
 tests/qemu-iotests/060.out |  5 ++-
 tests/qemu-iotests/134     |  9 ++++++
 tests/qemu-iotests/134.out | 10 ++++++
 18 files changed, 231 insertions(+), 29 deletions(-)

-- 
2.7.4

[Qemu-devel] [PATCH v9 1/9] mirror: inherit supported write/zero flags

[Anton Nefedov]

Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
---
 block/mirror.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/block/mirror.c b/block/mirror.c
index 820f512..a22ddef 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1098,6 +1098,15 @@ static BlockDriver bdrv_mirror_top = {
     .bdrv_child_perm            = bdrv_mirror_top_child_perm,
 };
 
+static void mirror_top_set_supported_flags(BlockDriverState *bs)
+{
+    bs->supported_write_flags = BDRV_REQ_FUA &
+        bs->backing->bs->supported_write_flags;
+    bs->supported_zero_flags =
+        (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
+        bs->backing->bs->supported_zero_flags;
+}
+
 static void mirror_start_job(const char *job_id, BlockDriverState *bs,
                              int creation_flags, BlockDriverState *target,
                              const char *replaces, int64_t speed,
@@ -1163,6 +1172,8 @@ static void mirror_start_job(const char *job_id, BlockDriverState *bs,
         return;
     }
 
+    mirror_top_set_supported_flags(mirror_top_bs);
+
     /* Make sure that the source is not resized while the job is running */
     s = block_job_create(job_id, driver, NULL, mirror_top_bs,
                          BLK_PERM_CONSISTENT_READ,
-- 
2.7.4

[Qemu-devel] [PATCH v9 2/9] blkverify: set supported write/zero flags

[Anton Nefedov]

Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
---
 block/blkverify.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/block/blkverify.c b/block/blkverify.c
index 754cc9e..496ae09 100644
--- a/block/blkverify.c
+++ b/block/blkverify.c
@@ -141,6 +141,15 @@ static int blkverify_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
+    bs->supported_write_flags = BDRV_REQ_FUA &
+        bs->file->bs->supported_write_flags &
+        s->test_file->bs->supported_write_flags;
+
+    bs->supported_zero_flags =
+        (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
+        bs->file->bs->supported_zero_flags &
+        s->test_file->bs->supported_zero_flags;
+
     ret = 0;
 fail:
     qemu_opts_del(opts);
-- 
2.7.4

[Qemu-devel] [PATCH v9 3/9] quorum: set supported write/zero flags

[Anton Nefedov]

Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
---
 block/quorum.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/block/quorum.c b/block/quorum.c
index a5051da..26e7d78 100644
--- a/block/quorum.c
+++ b/block/quorum.c
@@ -867,6 +867,20 @@ static QemuOptsList quorum_runtime_opts = {
     },
 };
 
+static void quorum_set_supported_flags(BlockDriverState *bs)
+{
+    BDRVQuorumState *s = bs->opaque;
+    int i;
+
+    bs->supported_write_flags = BDRV_REQ_FUA;
+    bs->supported_zero_flags  = BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP;
+
+    for (i = 0; i < s->num_children; i++) {
+        bs->supported_write_flags &= s->children[i]->bs->supported_write_flags;
+        bs->supported_zero_flags  &= s->children[i]->bs->supported_zero_flags;
+    }
+}
+
 static int quorum_open(BlockDriverState *bs, QDict *options, int flags,
                        Error **errp)
 {
@@ -961,6 +975,8 @@ static int quorum_open(BlockDriverState *bs, QDict *options, int flags,
     }
     s->next_child_index = s->num_children;
 
+    quorum_set_supported_flags(bs);
+
     g_free(opened);
     goto exit;
 
@@ -1029,6 +1045,8 @@ static void quorum_add_child(BlockDriverState *bs, BlockDriverState *child_bs,
     s->children = g_renew(BdrvChild *, s->children, s->num_children + 1);
     s->children[s->num_children++] = child;
 
+    quorum_set_supported_flags(bs);
+
 out:
     bdrv_drained_end(bs);
 }
@@ -1064,6 +1082,8 @@ static void quorum_del_child(BlockDriverState *bs, BdrvChild *child,
     bdrv_unref_child(bs, child);
 
     bdrv_drained_end(bs);
+
+    quorum_set_supported_flags(bs);
 }
 
 static void quorum_refresh_filename(BlockDriverState *bs, QDict *options)
-- 
2.7.4

[Qemu-devel] [PATCH v9 4/9] block: introduce BDRV_REQ_ALLOCATE flag

[Anton Nefedov]

The flag is supposed to indicate that the region of the disk image has
to be sufficiently allocated so it reads as zeroes.

The call with the flag set must return -ENOTSUP if allocation cannot
be done efficiently.
This has to be made sure of by both
  - the drivers that support the flag
  - and the common block layer (so it will not fall back to any slowpath
    (like writing zero buffers) in case the driver does not support
    the flag).

Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
---
 include/block/block.h     |  8 +++++++-
 include/block/block_int.h |  2 +-
 block/io.c                | 18 ++++++++++++++++--
 3 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/include/block/block.h b/include/block/block.h
index cdec363..097feca 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -53,9 +53,15 @@ typedef enum {
     BDRV_REQ_NO_SERIALISING     = 0x8,
     BDRV_REQ_FUA                = 0x10,
     BDRV_REQ_WRITE_COMPRESSED   = 0x20,
+    /* The BDRV_REQ_ALLOCATE flag is used to indicate that the driver has to
+     * efficiently allocate the space so it reads as zeroes, or return an error.
+     * If this flag is set then BDRV_REQ_ZERO_WRITE must also be set.
+     * This flag cannot be set together with BDRV_REQ_MAY_UNMAP.
+     */
+    BDRV_REQ_ALLOCATE           = 0x40,
 
     /* Mask of valid flags */
-    BDRV_REQ_MASK               = 0x3f,
+    BDRV_REQ_MASK               = 0x7f,
 } BdrvRequestFlags;
 
 typedef struct BlockSizes {
diff --git a/include/block/block_int.h b/include/block/block_int.h
index c4dd1d4..7145823 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -661,7 +661,7 @@ struct BlockDriverState {
     /* Flags honored during pwrite (so far: BDRV_REQ_FUA) */
     unsigned int supported_write_flags;
     /* Flags honored during pwrite_zeroes (so far: BDRV_REQ_FUA,
-     * BDRV_REQ_MAY_UNMAP) */
+     * BDRV_REQ_MAY_UNMAP, BDRV_REQ_ALLOCATE) */
     unsigned int supported_zero_flags;
 
     /* the following member gives a name to every node on the bs graph. */
diff --git a/block/io.c b/block/io.c
index bd9a19a..660702a 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1417,7 +1417,7 @@ static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs,
             assert(!bs->supported_zero_flags);
         }
 
-        if (ret == -ENOTSUP) {
+        if (ret == -ENOTSUP && !(flags & BDRV_REQ_ALLOCATE)) {
             /* Fall back to bounce buffer if write zeroes is unsupported */
             BdrvRequestFlags write_flags = flags & ~BDRV_REQ_ZERO_WRITE;
 
@@ -1510,7 +1510,9 @@ static int coroutine_fn bdrv_aligned_pwritev(BdrvChild *child,
         !(flags & BDRV_REQ_ZERO_WRITE) && drv->bdrv_co_pwrite_zeroes &&
         qemu_iovec_is_zero(qiov)) {
         flags |= BDRV_REQ_ZERO_WRITE;
-        if (bs->detect_zeroes == BLOCKDEV_DETECT_ZEROES_OPTIONS_UNMAP) {
+        if (bs->detect_zeroes == BLOCKDEV_DETECT_ZEROES_OPTIONS_UNMAP &&
+            !(flags & BDRV_REQ_ALLOCATE))
+        {
             flags |= BDRV_REQ_MAY_UNMAP;
         }
     }
@@ -1586,6 +1588,9 @@ static int coroutine_fn bdrv_co_do_zero_pwritev(BdrvChild *child,
 
     assert(flags & BDRV_REQ_ZERO_WRITE);
     if (head_padding_bytes || tail_padding_bytes) {
+        if (flags & BDRV_REQ_ALLOCATE) {
+            return -ENOTSUP;
+        }
         buf = qemu_blockalign(bs, align);
         iov = (struct iovec) {
             .iov_base   = buf,
@@ -1671,6 +1676,9 @@ int coroutine_fn bdrv_co_pwritev(BdrvChild *child,
     bool use_local_qiov = false;
     int ret;
 
+    assert(!((flags & BDRV_REQ_ALLOCATE) && (flags & BDRV_REQ_MAY_UNMAP)));
+    assert(!((flags & BDRV_REQ_ALLOCATE) && !(flags & BDRV_REQ_ZERO_WRITE)));
+
     trace_bdrv_co_pwritev(child->bs, offset, bytes, flags);
 
     if (!bs->drv) {
@@ -1815,6 +1823,12 @@ int coroutine_fn bdrv_co_pwrite_zeroes(BdrvChild *child, int64_t offset,
 {
     trace_bdrv_co_pwrite_zeroes(child->bs, offset, bytes, flags);
 
+    if ((flags & BDRV_REQ_ALLOCATE) &&
+        !(child->bs->supported_zero_flags & BDRV_REQ_ALLOCATE))
+    {
+        return -ENOTSUP;
+    }
+
     if (!(child->bs->open_flags & BDRV_O_UNMAP)) {
         flags &= ~BDRV_REQ_MAY_UNMAP;
     }
-- 
2.7.4

[Qemu-devel] [PATCH v9 5/9] block: treat BDRV_REQ_ALLOCATE as serialising

[Anton Nefedov]

The idea is that ALLOCATE requests may overlap with other requests.
Reuse the existing block layer infrastructure for serialising requests.
Use the following approach:
  - mark ALLOCATE serialising, so subsequent requests to the area wait
  - ALLOCATE request itself must never wait if another request is in flight
    already. Return EAGAIN, let the caller reconsider.

Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
---
 block/io.c | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/block/io.c b/block/io.c
index 660702a..a2fb69a 100644
--- a/block/io.c
+++ b/block/io.c
@@ -598,12 +598,13 @@ void bdrv_dec_in_flight(BlockDriverState *bs)
     bdrv_wakeup(bs);
 }
 
-static bool coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self)
+static bool coroutine_fn find_or_wait_serialising_requests(
+    BdrvTrackedRequest *self, bool wait)
 {
     BlockDriverState *bs = self->bs;
     BdrvTrackedRequest *req;
     bool retry;
-    bool waited = false;
+    bool found = false;
 
     if (!atomic_read(&bs->serialising_in_flight)) {
         return false;
@@ -629,11 +630,14 @@ static bool coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self)
                  * will wait for us as soon as it wakes up, then just go on
                  * (instead of producing a deadlock in the former case). */
                 if (!req->waiting_for) {
+                    found = true;
+                    if (!wait) {
+                        break;
+                    }
                     self->waiting_for = req;
                     qemu_co_queue_wait(&req->wait_queue, &bs->reqs_lock);
                     self->waiting_for = NULL;
                     retry = true;
-                    waited = true;
                     break;
                 }
             }
@@ -641,7 +645,12 @@ static bool coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self)
         qemu_co_mutex_unlock(&bs->reqs_lock);
     } while (retry);
 
-    return waited;
+    return found;
+}
+
+static bool coroutine_fn wait_serialising_requests(BdrvTrackedRequest *self)
+{
+    return find_or_wait_serialising_requests(self, true);
 }
 
 static int bdrv_check_byte_request(BlockDriverState *bs, int64_t offset,
@@ -1473,7 +1482,7 @@ static int coroutine_fn bdrv_aligned_pwritev(BdrvChild *child,
 {
     BlockDriverState *bs = child->bs;
     BlockDriver *drv = bs->drv;
-    bool waited;
+    bool found;
     int ret;
 
     int64_t end_sector = DIV_ROUND_UP(offset + bytes, BDRV_SECTOR_SIZE);
@@ -1497,8 +1506,13 @@ static int coroutine_fn bdrv_aligned_pwritev(BdrvChild *child,
     max_transfer = QEMU_ALIGN_DOWN(MIN_NON_ZERO(bs->bl.max_transfer, INT_MAX),
                                    align);
 
-    waited = wait_serialising_requests(req);
-    assert(!waited || !req->serialising);
+    found = find_or_wait_serialising_requests(req,
+                                              !(flags & BDRV_REQ_ALLOCATE));
+    if (found && (flags & BDRV_REQ_ALLOCATE)) {
+        return -EAGAIN;
+    }
+
+    assert(!found || !req->serialising);
     assert(req->overlap_offset <= offset);
     assert(offset + bytes <= req->overlap_offset + req->overlap_bytes);
     assert(child->perm & BLK_PERM_WRITE);
@@ -1623,6 +1637,10 @@ static int coroutine_fn bdrv_co_do_zero_pwritev(BdrvChild *child,
         bytes -= zero_bytes;
     }
 
+    if (flags & BDRV_REQ_ALLOCATE) {
+        mark_request_serialising(req, align);
+    }
+
     assert(!bytes || (offset & (align - 1)) == 0);
     if (bytes >= align) {
         /* Write the aligned part in the middle. */
-- 
2.7.4

[Qemu-devel] [PATCH v9 6/9] file-posix: support BDRV_REQ_ALLOCATE

[Anton Nefedov]

Current write_zeroes implementation is good enough to satisfy this flag too

Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
---
 block/file-posix.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index 3794c00..3795e1c 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -560,7 +560,10 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
     }
     if (S_ISREG(st.st_mode)) {
         s->discard_zeroes = true;
+#ifdef CONFIG_FALLOCATE
         s->has_fallocate = true;
+        bs->supported_zero_flags |= BDRV_REQ_ALLOCATE;
+#endif
     }
     if (S_ISBLK(st.st_mode)) {
 #ifdef BLKDISCARDZEROES
@@ -595,10 +598,11 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
 #ifdef CONFIG_XFS
     if (platform_test_xfs_fd(s->fd)) {
         s->is_xfs = true;
+        bs->supported_zero_flags |= BDRV_REQ_ALLOCATE;
     }
 #endif
 
-    bs->supported_zero_flags = s->discard_zeroes ? BDRV_REQ_MAY_UNMAP : 0;
+    bs->supported_zero_flags |= s->discard_zeroes ? BDRV_REQ_MAY_UNMAP : 0;
     ret = 0;
 fail:
     if (filename && (bdrv_flags & BDRV_O_TEMPORARY)) {
@@ -1416,6 +1420,10 @@ static ssize_t handle_aiocb_write_zeroes(RawPosixAIOData *aiocb)
         }
         s->has_fallocate = false;
     }
+
+    if (!s->has_fallocate) {
+        aiocb->bs->supported_zero_flags &= ~BDRV_REQ_ALLOCATE;
+    }
 #endif
 
     return -ENOTSUP;
-- 
2.7.4

[Qemu-devel] [PATCH v9 7/9] block: support BDRV_REQ_ALLOCATE in passthrough drivers

[Anton Nefedov]

Support the flag if the underlying BDS supports it

Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
---
 block/blkdebug.c   | 3 ++-
 block/blkverify.c  | 2 +-
 block/mirror.c     | 2 +-
 block/quorum.c     | 3 ++-
 block/raw-format.c | 3 ++-
 5 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/block/blkdebug.c b/block/blkdebug.c
index 053372c..f5f1232 100644
--- a/block/blkdebug.c
+++ b/block/blkdebug.c
@@ -400,7 +400,8 @@ static int blkdebug_open(BlockDriverState *bs, QDict *options, int flags,
 
     bs->supported_write_flags = BDRV_REQ_FUA &
         bs->file->bs->supported_write_flags;
-    bs->supported_zero_flags = (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
+    bs->supported_zero_flags =
+        (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_ALLOCATE) &
         bs->file->bs->supported_zero_flags;
     ret = -EINVAL;
 
diff --git a/block/blkverify.c b/block/blkverify.c
index 496ae09..fa95f22 100644
--- a/block/blkverify.c
+++ b/block/blkverify.c
@@ -146,7 +146,7 @@ static int blkverify_open(BlockDriverState *bs, QDict *options, int flags,
         s->test_file->bs->supported_write_flags;
 
     bs->supported_zero_flags =
-        (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
+        (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_ALLOCATE) &
         bs->file->bs->supported_zero_flags &
         s->test_file->bs->supported_zero_flags;
 
diff --git a/block/mirror.c b/block/mirror.c
index a22ddef..6fb3aa6 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -1103,7 +1103,7 @@ static void mirror_top_set_supported_flags(BlockDriverState *bs)
     bs->supported_write_flags = BDRV_REQ_FUA &
         bs->backing->bs->supported_write_flags;
     bs->supported_zero_flags =
-        (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
+        (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_ALLOCATE) &
         bs->backing->bs->supported_zero_flags;
 }
 
diff --git a/block/quorum.c b/block/quorum.c
index 26e7d78..349bdc3 100644
--- a/block/quorum.c
+++ b/block/quorum.c
@@ -873,7 +873,8 @@ static void quorum_set_supported_flags(BlockDriverState *bs)
     int i;
 
     bs->supported_write_flags = BDRV_REQ_FUA;
-    bs->supported_zero_flags  = BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP;
+    bs->supported_zero_flags  =
+        BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_ALLOCATE;
 
     for (i = 0; i < s->num_children; i++) {
         bs->supported_write_flags &= s->children[i]->bs->supported_write_flags;
diff --git a/block/raw-format.c b/block/raw-format.c
index a378547..ca65f86 100644
--- a/block/raw-format.c
+++ b/block/raw-format.c
@@ -417,7 +417,8 @@ static int raw_open(BlockDriverState *bs, QDict *options, int flags,
     bs->sg = bs->file->bs->sg;
     bs->supported_write_flags = BDRV_REQ_FUA &
         bs->file->bs->supported_write_flags;
-    bs->supported_zero_flags = (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
+    bs->supported_zero_flags =
+        (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP | BDRV_REQ_ALLOCATE) &
         bs->file->bs->supported_zero_flags;
 
     if (bs->probed && !bdrv_is_read_only(bs)) {
-- 
2.7.4

[Qemu-devel] [PATCH v9 8/9] qcow2: skip writing zero buffers to empty COW areas

[Anton Nefedov]

If COW areas of the newly allocated clusters are zeroes on the backing image,
efficient bdrv_write_zeroes(flags=BDRV_REQ_ALLOCATE) can be used on the whole
cluster instead of writing explicit zero buffers later in perform_cow().

iotest 060:
write to the discarded cluster does not trigger COW anymore.
Use a backing image instead.

Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
---
 qapi/block-core.json       |  4 ++-
 block/qcow2.h              |  6 ++++
 block/qcow2-cluster.c      |  2 +-
 block/qcow2.c              | 80 ++++++++++++++++++++++++++++++++++++++++++++--
 block/trace-events         |  1 +
 tests/qemu-iotests/060     | 26 +++++++++------
 tests/qemu-iotests/060.out |  5 ++-
 7 files changed, 109 insertions(+), 15 deletions(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index c50517b..816c44b 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -2900,6 +2900,8 @@
 #
 # @cor_write: a write due to copy-on-read (since 2.11)
 #
+# @cluster_alloc_space: an allocation of file space for a cluster (since 2.13)
+#
 # Since: 2.9
 ##
 { 'enum': 'BlkdebugEvent', 'prefix': 'BLKDBG',
@@ -2918,7 +2920,7 @@
             'pwritev_rmw_tail', 'pwritev_rmw_after_tail', 'pwritev',
             'pwritev_zero', 'pwritev_done', 'empty_image_prepare',
             'l1_shrink_write_table', 'l1_shrink_free_l2_clusters',
-            'cor_write'] }
+            'cor_write', 'cluster_alloc_space'] }
 
 ##
 # @BlkdebugInjectErrorOptions:
diff --git a/block/qcow2.h b/block/qcow2.h
index adf5c39..2633853 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -380,6 +380,12 @@ typedef struct QCowL2Meta
     Qcow2COWRegion cow_end;
 
     /**
+     * Indicates that COW regions are already handled and do not require
+     * any more processing.
+     */
+    bool skip_cow;
+
+    /**
      * The I/O vector with the data from the actual guest write request.
      * If non-NULL, this is meant to be merged together with the data
      * from @cow_start and @cow_end into one single write operation.
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 1aee726..d364d29 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -806,7 +806,7 @@ static int perform_cow(BlockDriverState *bs, QCowL2Meta *m)
     assert(start->offset + start->nb_bytes <= end->offset);
     assert(!m->data_qiov || m->data_qiov->size == data_bytes);
 
-    if (start->nb_bytes == 0 && end->nb_bytes == 0) {
+    if ((start->nb_bytes == 0 && end->nb_bytes == 0) || m->skip_cow) {
         return 0;
     }
 
diff --git a/block/qcow2.c b/block/qcow2.c
index 2f36e63..019b54b 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1916,6 +1916,11 @@ static bool merge_cow(uint64_t offset, unsigned bytes,
             continue;
         }
 
+        /* If COW regions are handled already, skip this too */
+        if (m->skip_cow) {
+            continue;
+        }
+
         /* The data (middle) region must be immediately after the
          * start region */
         if (l2meta_cow_start(m) + m->cow_start.nb_bytes != offset) {
@@ -1941,6 +1946,68 @@ static bool merge_cow(uint64_t offset, unsigned bytes,
     return false;
 }
 
+static bool is_unallocated(BlockDriverState *bs, int64_t offset, int64_t bytes)
+{
+    int64_t nr;
+    return !bytes ||
+        (!bdrv_is_allocated_above(bs, NULL, offset, bytes, &nr) && nr == bytes);
+}
+
+static bool is_zero_cow(BlockDriverState *bs, QCowL2Meta *m)
+{
+    /* This check is designed for optimization shortcut so it must be
+     * efficient.
+     * Instead of is_zero(), use is_unallocated() as it is faster (but not
+     * as accurate and can result in false negatives). */
+    return is_unallocated(bs, m->offset + m->cow_start.offset,
+                          m->cow_start.nb_bytes) &&
+           is_unallocated(bs, m->offset + m->cow_end.offset,
+                          m->cow_end.nb_bytes);
+}
+
+static int handle_alloc_space(BlockDriverState *bs, QCowL2Meta *l2meta)
+{
+    BDRVQcow2State *s = bs->opaque;
+    QCowL2Meta *m;
+
+    if (!(bs->file->bs->supported_zero_flags & BDRV_REQ_ALLOCATE)) {
+        return 0;
+    }
+
+    if (bs->encrypted) {
+        return 0;
+    }
+
+    for (m = l2meta; m != NULL; m = m->next) {
+        int ret;
+
+        if (!m->cow_start.nb_bytes && !m->cow_end.nb_bytes) {
+            continue;
+        }
+
+        if (!is_zero_cow(bs, m)) {
+            continue;
+        }
+
+        BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC_SPACE);
+        /* instead of writing zero COW buffers,
+           efficiently zero out the whole clusters */
+        ret = bdrv_co_pwrite_zeroes(bs->file, m->alloc_offset,
+                                    m->nb_clusters * s->cluster_size,
+                                    BDRV_REQ_ALLOCATE);
+        if (ret < 0) {
+            if (ret != -ENOTSUP && ret != -EAGAIN) {
+                return ret;
+            }
+            continue;
+        }
+
+        trace_qcow2_skip_cow(qemu_coroutine_self(), m->offset, m->nb_clusters);
+        m->skip_cow = true;
+    }
+    return 0;
+}
+
 static coroutine_fn int qcow2_co_pwritev(BlockDriverState *bs, uint64_t offset,
                                          uint64_t bytes, QEMUIOVector *qiov,
                                          int flags)
@@ -2023,24 +2090,33 @@ static coroutine_fn int qcow2_co_pwritev(BlockDriverState *bs, uint64_t offset,
             goto fail;
         }
 
+        qemu_co_mutex_unlock(&s->lock);
+
+        ret = handle_alloc_space(bs, l2meta);
+        if (ret < 0) {
+            qemu_co_mutex_lock(&s->lock);
+            goto fail;
+        }
+
         /* If we need to do COW, check if it's possible to merge the
          * writing of the guest data together with that of the COW regions.
          * If it's not possible (or not necessary) then write the
          * guest data now. */
         if (!merge_cow(offset, cur_bytes, &hd_qiov, l2meta)) {
-            qemu_co_mutex_unlock(&s->lock);
             BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO);
             trace_qcow2_writev_data(qemu_coroutine_self(),
                                     cluster_offset + offset_in_cluster);
             ret = bdrv_co_pwritev(bs->file,
                                   cluster_offset + offset_in_cluster,
                                   cur_bytes, &hd_qiov, 0);
-            qemu_co_mutex_lock(&s->lock);
             if (ret < 0) {
+                qemu_co_mutex_lock(&s->lock);
                 goto fail;
             }
         }
 
+        qemu_co_mutex_lock(&s->lock);
+
         while (l2meta != NULL) {
             QCowL2Meta *next;
 
diff --git a/block/trace-events b/block/trace-events
index f8c50b4..f85a980 100644
--- a/block/trace-events
+++ b/block/trace-events
@@ -70,6 +70,7 @@ qcow2_writev_done_part(void *co, int cur_bytes) "co %p cur_bytes %d"
 qcow2_writev_data(void *co, uint64_t offset) "co %p offset 0x%" PRIx64
 qcow2_pwrite_zeroes_start_req(void *co, int64_t offset, int count) "co %p offset 0x%" PRIx64 " count %d"
 qcow2_pwrite_zeroes(void *co, int64_t offset, int count) "co %p offset 0x%" PRIx64 " count %d"
+qcow2_skip_cow(void *co, uint64_t offset, int nb_clusters) "co %p offset 0x%" PRIx64 " nb_clusters %d"
 
 # block/qcow2-cluster.c
 qcow2_alloc_clusters_offset(void *co, uint64_t offset, int bytes) "co %p offset 0x%" PRIx64 " bytes %d"
diff --git a/tests/qemu-iotests/060 b/tests/qemu-iotests/060
index 6c7407f..e6ed8b2 100755
--- a/tests/qemu-iotests/060
+++ b/tests/qemu-iotests/060
@@ -143,27 +143,33 @@ $QEMU_IO -c "$OPEN_RO" -c "read -P 1 0 512" | _filter_qemu_io
 echo
 echo "=== Testing overlap while COW is in flight ==="
 echo
+BACKING_IMG=$TEST_IMG.base
+TEST_IMG=$BACKING_IMG _make_test_img 1G
+
+$QEMU_IO -c 'write 64k 64k' "$BACKING_IMG" | _filter_qemu_io
+
 # compat=0.10 is required in order to make the following discard actually
-# unallocate the sector rather than make it a zero sector - we want COW, after
-# all.
-IMGOPTS='compat=0.10' _make_test_img 1G
+# unallocate the sector rather than make it a zero sector as we would like
+# to reuse it for another guest offset
+IMGOPTS='compat=0.10' _make_test_img -b "$BACKING_IMG" 1G
 # Write two clusters, the second one enforces creation of an L2 table after
 # the first data cluster.
 $QEMU_IO -c 'write 0k 64k' -c 'write 512M 64k' "$TEST_IMG" | _filter_qemu_io
-# Discard the first cluster. This cluster will soon enough be reallocated and
-# used for COW.
+# Discard the first cluster. This cluster will soon enough be reallocated
 $QEMU_IO -c 'discard 0k 64k' "$TEST_IMG" | _filter_qemu_io
 # Now, corrupt the image by marking the second L2 table cluster as free.
 poke_file "$TEST_IMG" '131084' "\x00\x00" # 0x2000c
-# Start a write operation requiring COW on the image stopping it right before
-# doing the read; then, trigger the corruption prevention by writing anything to
-# any unallocated cluster, leading to an attempt to overwrite the second L2
+# Start a write operation requiring COW on the image;
+# this write will reuse the host offset released by a previous discard.
+# Stop it right before doing the read.
+# Then, trigger the corruption prevention by writing anything to
+# another unallocated cluster, leading to an attempt to overwrite the second L2
 # table. Finally, resume the COW write and see it fail (but not crash).
 echo "open -o file.driver=blkdebug $TEST_IMG
 break cow_read 0
-aio_write 0k 1k
+aio_write 64k 1k
 wait_break 0
-write 64k 64k
+write 128k 64k
 resume 0" | $QEMU_IO | _filter_qemu_io
 
 echo
diff --git a/tests/qemu-iotests/060.out b/tests/qemu-iotests/060.out
index 25d5c39..00a6702 100644
--- a/tests/qemu-iotests/060.out
+++ b/tests/qemu-iotests/060.out
@@ -97,7 +97,10 @@ read 512/512 bytes at offset 0
 
 === Testing overlap while COW is in flight ===
 
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1073741824
+Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=1073741824
+wrote 65536/65536 bytes at offset 65536
+64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1073741824 backing_file=TEST_DIR/t.IMGFMT.base
 wrote 65536/65536 bytes at offset 0
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 65536/65536 bytes at offset 536870912
-- 
2.7.4

[Qemu-devel] [PATCH v9 9/9] iotest 134: test cluster-misaligned encrypted write

[Anton Nefedov]

COW (even empty/zero) areas require encryption too

Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
---
 tests/qemu-iotests/134     |  9 +++++++++
 tests/qemu-iotests/134.out | 10 ++++++++++
 2 files changed, 19 insertions(+)

diff --git a/tests/qemu-iotests/134 b/tests/qemu-iotests/134
index 9914415..6083ae4 100755
--- a/tests/qemu-iotests/134
+++ b/tests/qemu-iotests/134
@@ -59,6 +59,15 @@ echo "== reading whole image =="
 $QEMU_IO --object $SECRET -c "read 0 $size" --image-opts $IMGSPEC | _filter_qemu_io | _filter_testdir
 
 echo
+echo "== rewriting cluster part =="
+$QEMU_IO --object $SECRET -c "write -P 0xb 512 512" --image-opts $IMGSPEC | _filter_qemu_io | _filter_testdir
+
+echo
+echo "== verify pattern =="
+$QEMU_IO --object $SECRET -c "read -P 0 0 512"  --image-opts $IMGSPEC | _filter_qemu_io | _filter_testdir
+$QEMU_IO --object $SECRET -c "read -P 0xb 512 512"  --image-opts $IMGSPEC | _filter_qemu_io | _filter_testdir
+
+echo
 echo "== rewriting whole image =="
 $QEMU_IO --object $SECRET -c "write -P 0xa 0 $size" --image-opts $IMGSPEC | _filter_qemu_io | _filter_testdir
 
diff --git a/tests/qemu-iotests/134.out b/tests/qemu-iotests/134.out
index 972be49..09d46f6 100644
--- a/tests/qemu-iotests/134.out
+++ b/tests/qemu-iotests/134.out
@@ -5,6 +5,16 @@ Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728 encryption=on encrypt.
 read 134217728/134217728 bytes at offset 0
 128 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 
+== rewriting cluster part ==
+wrote 512/512 bytes at offset 512
+512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+== verify pattern ==
+read 512/512 bytes at offset 0
+512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+read 512/512 bytes at offset 512
+512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
 == rewriting whole image ==
 wrote 134217728/134217728 bytes at offset 0
 128 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-- 
2.7.4

Re: [Qemu-devel] [PATCH v9 4/9] block: introduce BDRV_REQ_ALLOCATE flag

[Alberto Garcia]

On Tue 08 May 2018 04:58:11 PM CEST, Anton Nefedov wrote:
> The flag is supposed to indicate that the region of the disk image has
> to be sufficiently allocated so it reads as zeroes.
>
> The call with the flag set must return -ENOTSUP if allocation cannot
> be done efficiently.
> This has to be made sure of by both
>   - the drivers that support the flag
>   - and the common block layer (so it will not fall back to any slowpath
>     (like writing zero buffers) in case the driver does not support
>     the flag).
>
> Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>

Reviewed-by: Alberto Garcia <berto@igalia.com>

Berto

Re: [Qemu-devel] [PATCH v9 6/9] file-posix: support BDRV_REQ_ALLOCATE

[Alberto Garcia]

On Tue 08 May 2018 04:58:13 PM CEST, Anton Nefedov wrote:
> Current write_zeroes implementation is good enough to satisfy this flag too
>
> Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>

Reviewed-by: Alberto Garcia <berto@igalia.com>

Berto

Re: [Qemu-devel] [PATCH v9 8/9] qcow2: skip writing zero buffers to empty COW areas

[Alberto Garcia]

On Tue 08 May 2018 04:58:15 PM CEST, Anton Nefedov wrote:
> If COW areas of the newly allocated clusters are zeroes on the backing image,
> efficient bdrv_write_zeroes(flags=BDRV_REQ_ALLOCATE) can be used on the whole
> cluster instead of writing explicit zero buffers later in perform_cow().
>
> iotest 060:
> write to the discarded cluster does not trigger COW anymore.
> Use a backing image instead.
>
> Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>

Reviewed-by: Alberto Garcia <berto@igalia.com>

Berto

Re: [Qemu-devel] [PATCH v9 1/9] mirror: inherit supported write/zero flags

[Eric Blake]

On 05/08/2018 09:58 AM, Anton Nefedov wrote:
> Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
> Reviewed-by: Alberto Garcia <berto@igalia.com>
> ---
>   block/mirror.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)

Reviewed-by: Eric Blake <eblake@redhat.com>

That said,

> 
> diff --git a/block/mirror.c b/block/mirror.c
> index 820f512..a22ddef 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -1098,6 +1098,15 @@ static BlockDriver bdrv_mirror_top = {
>       .bdrv_child_perm            = bdrv_mirror_top_child_perm,
>   };
>   
> +static void mirror_top_set_supported_flags(BlockDriverState *bs)
> +{
> +    bs->supported_write_flags = BDRV_REQ_FUA &
> +        bs->backing->bs->supported_write_flags;
> +    bs->supported_zero_flags =
> +        (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
> +        bs->backing->bs->supported_zero_flags;
> +}
> +

This is a pretty short static function...

>   static void mirror_start_job(const char *job_id, BlockDriverState *bs,
>                                int creation_flags, BlockDriverState *target,
>                                const char *replaces, int64_t speed,
> @@ -1163,6 +1172,8 @@ static void mirror_start_job(const char *job_id, BlockDriverState *bs,
>           return;
>       }
>   
> +    mirror_top_set_supported_flags(mirror_top_bs);

...with exactly one caller.  Wouldn't it be easier to just inline it?

> +
>       /* Make sure that the source is not resized while the job is running */
>       s = block_job_create(job_id, driver, NULL, mirror_top_bs,
>                            BLK_PERM_CONSISTENT_READ,
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [Qemu-devel] [PATCH v9 2/9] blkverify: set supported write/zero flags

[Eric Blake]

On 05/08/2018 09:58 AM, Anton Nefedov wrote:
> Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
> Reviewed-by: Alberto Garcia <berto@igalia.com>
> Reviewed-by: Max Reitz <mreitz@redhat.com>
> ---
>   block/blkverify.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/block/blkverify.c b/block/blkverify.c
> index 754cc9e..496ae09 100644
> --- a/block/blkverify.c
> +++ b/block/blkverify.c
> @@ -141,6 +141,15 @@ static int blkverify_open(BlockDriverState *bs, QDict *options, int flags,
>           goto fail;
>       }
>   
> +    bs->supported_write_flags = BDRV_REQ_FUA &
> +        bs->file->bs->supported_write_flags &
> +        s->test_file->bs->supported_write_flags;

I wonder if it's worth the effort to support the flags if the main file 
supports them natively but the test_file does not (and just emulate the 
flag on the test file, in that situation).  But for now, I'm fine with 
your choice that both files must support a flag before the blkverify 
layer claims the flag as well.

> +
> +    bs->supported_zero_flags =
> +        (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
> +        bs->file->bs->supported_zero_flags &
> +        s->test_file->bs->supported_zero_flags;
> +
>       ret = 0;
>   fail:
>       qemu_opts_del(opts);
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [Qemu-devel] [PATCH v9 3/9] quorum: set supported write/zero flags

[Eric Blake]

On 05/08/2018 09:58 AM, Anton Nefedov wrote:
> Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
> Reviewed-by: Alberto Garcia <berto@igalia.com>
> ---
>   block/quorum.c | 20 ++++++++++++++++++++
>   1 file changed, 20 insertions(+)
> 

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

Re: [Qemu-devel] [PATCH v9 1/9] mirror: inherit supported write/zero flags

[Anton Nefedov]

On 15/5/2018 5:35 PM, Eric Blake wrote:
> On 05/08/2018 09:58 AM, Anton Nefedov wrote:
>> diff --git a/block/mirror.c b/block/mirror.c
>> index 820f512..a22ddef 100644
>> --- a/block/mirror.c
>> +++ b/block/mirror.c
>> @@ -1098,6 +1098,15 @@ static BlockDriver bdrv_mirror_top = {
>>       .bdrv_child_perm            = bdrv_mirror_top_child_perm,
>>   };
>> +static void mirror_top_set_supported_flags(BlockDriverState *bs)
>> +{
>> +    bs->supported_write_flags = BDRV_REQ_FUA &
>> +        bs->backing->bs->supported_write_flags;
>> +    bs->supported_zero_flags =
>> +        (BDRV_REQ_FUA | BDRV_REQ_MAY_UNMAP) &
>> +        bs->backing->bs->supported_zero_flags;
>> +}
>> +
> 
> This is a pretty short static function...
> 
>>   static void mirror_start_job(const char *job_id, BlockDriverState *bs,
>>                                int creation_flags, BlockDriverState 
>> *target,
>>                                const char *replaces, int64_t speed,
>> @@ -1163,6 +1172,8 @@ static void mirror_start_job(const char *job_id, 
>> BlockDriverState *bs,
>>           return;
>>       }
>> +    mirror_top_set_supported_flags(mirror_top_bs);
> 
> ...with exactly one caller.  Wouldn't it be easier to just inline it?
> 

idk, I felt mirror_start_job() was quite massive already, even
considering there are just a few new lines.