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From: Kevin Wolf <kwolf@redhat.com>
To: qemu-block@nongnu.org
Subject: [PULL 06/15] qcow2: Support BDRV_REQ_ZERO_WRITE for truncate
Date: Thu, 30 Apr 2020 17:52:22 +0200
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If BDRV_REQ_ZERO_WRITE is set and we're extending the image, calling
qcow2_cluster_zeroize() with flags=3D0 does the right thing: It doesn't
undo any previous preallocation, but just adds the zero flag to all
relevant L2 entries. If an external data file is in use, a write_zeroes
request to the data file is made instead.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20200424125448.63318-5-kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
block/qcow2-cluster.c | 2 +-
block/qcow2.c | 34 ++++++++++++++++++++++++++++++++++
2 files changed, 35 insertions(+), 1 deletion(-)
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 17f1363279..4b5fc8c4a7 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1795,7 +1795,7 @@ int qcow2_cluster_zeroize(BlockDriverState *bs, uint6=
4_t offset,
/* Caller must pass aligned values, except at image end */
assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
assert(QEMU_IS_ALIGNED(end_offset, s->cluster_size) ||
- end_offset =3D=3D bs->total_sectors << BDRV_SECTOR_BITS);
+ end_offset >=3D bs->total_sectors << BDRV_SECTOR_BITS);
=20
/* The zero flag is only supported by version 3 and newer */
if (s->qcow_version < 3) {
diff --git a/block/qcow2.c b/block/qcow2.c
index 9cfbdfc939..98065d7808 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1726,6 +1726,7 @@ static int coroutine_fn qcow2_do_open(BlockDriverStat=
e *bs, QDict *options,
=20
bs->supported_zero_flags =3D header.version >=3D 3 ?
BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK :=
0;
+ bs->supported_truncate_flags =3D BDRV_REQ_ZERO_WRITE;
=20
/* Repair image if dirty */
if (!(flags & (BDRV_O_CHECK | BDRV_O_INACTIVE)) && !bs->read_only &&
@@ -4214,6 +4215,39 @@ static int coroutine_fn qcow2_co_truncate(BlockDrive=
rState *bs, int64_t offset,
g_assert_not_reached();
}
=20
+ if ((flags & BDRV_REQ_ZERO_WRITE) && offset > old_length) {
+ uint64_t zero_start =3D QEMU_ALIGN_UP(old_length, s->cluster_size);
+
+ /*
+ * Use zero clusters as much as we can. qcow2_cluster_zeroize()
+ * requires a cluster-aligned start. The end may be unaligned if i=
t is
+ * at the end of the image (which it is here).
+ */
+ ret =3D qcow2_cluster_zeroize(bs, zero_start, offset - zero_start,=
0);
+ if (ret < 0) {
+ error_setg_errno(errp, -ret, "Failed to zero out new clusters"=
);
+ goto fail;
+ }
+
+ /* Write explicit zeros for the unaligned head */
+ if (zero_start > old_length) {
+ uint64_t len =3D zero_start - old_length;
+ uint8_t *buf =3D qemu_blockalign0(bs, len);
+ QEMUIOVector qiov;
+ qemu_iovec_init_buf(&qiov, buf, len);
+
+ qemu_co_mutex_unlock(&s->lock);
+ ret =3D qcow2_co_pwritev_part(bs, old_length, len, &qiov, 0, 0=
);
+ qemu_co_mutex_lock(&s->lock);
+
+ qemu_vfree(buf);
+ if (ret < 0) {
+ error_setg_errno(errp, -ret, "Failed to zero out the new a=
rea");
+ goto fail;
+ }
+ }
+ }
+
if (prealloc !=3D PREALLOC_MODE_OFF) {
/* Flush metadata before actually changing the image size */
ret =3D qcow2_write_caches(bs);
--=20
2.25.3