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From 4290173219e15065e9a7c2e95774ac979b5fd869 Mon Sep 17 00:00:00 2001
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Mon, 8 Jun 2020 15:01:40 +0100
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Subject: [PATCH 12/17] qcow2: Forward ZERO_WRITE flag for full preallocation
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RH-Author: Kevin Wolf <kwolf@redhat.com>
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Message-id: <20200608150140.38218-12-kwolf@redhat.com>
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Patchwork-id: 97456
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O-Subject: [RHEL-AV-8.2.1 qemu-kvm PATCH 11/11] qcow2: Forward ZERO_WRITE flag for full preallocation
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Bugzilla: 1780574
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RH-Acked-by: Sergio Lopez Pascual <slp@redhat.com>
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RH-Acked-by: Eric Blake <eblake@redhat.com>
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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The BDRV_REQ_ZERO_WRITE is currently implemented in a way that first the
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image is possibly preallocated and then the zero flag is added to all
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clusters. This means that a copy-on-write operation may be needed when
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writing to these clusters, despite having used preallocation, negating
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one of the major benefits of preallocation.
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Instead, try to forward the BDRV_REQ_ZERO_WRITE to the protocol driver,
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and if the protocol driver can ensure that the new area reads as zeros,
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we can skip setting the zero flag in the qcow2 layer.
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Unfortunately, the same approach doesn't work for metadata
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preallocation, so we'll still set the zero flag there.
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Reviewed-by: Max Reitz <mreitz@redhat.com>
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Message-Id: <20200424142701.67053-1-kwolf@redhat.com>
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Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit eb8a0cf3ba26611f3981f8f45ac6a868975a68cc)
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
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---
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block/qcow2.c | 22 +++++++++++++++++++---
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tests/qemu-iotests/274.out | 4 ++--
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2 files changed, 21 insertions(+), 5 deletions(-)
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diff --git a/block/qcow2.c b/block/qcow2.c
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index f3d6cb0..b783662 100644
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--- a/block/qcow2.c
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+++ b/block/qcow2.c
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@@ -4153,9 +4153,25 @@ static int coroutine_fn qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
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/* Allocate the data area */
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new_file_size = allocation_start +
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nb_new_data_clusters * s->cluster_size;
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- /* Image file grows, so @exact does not matter */
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- ret = bdrv_co_truncate(bs->file, new_file_size, false, prealloc, 0,
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- errp);
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+ /*
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+ * Image file grows, so @exact does not matter.
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+ *
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+ * If we need to zero out the new area, try first whether the protocol
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+ * driver can already take care of this.
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+ */
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+ if (flags & BDRV_REQ_ZERO_WRITE) {
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+ ret = bdrv_co_truncate(bs->file, new_file_size, false, prealloc,
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+ BDRV_REQ_ZERO_WRITE, NULL);
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+ if (ret >= 0) {
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+ flags &= ~BDRV_REQ_ZERO_WRITE;
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+ }
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+ } else {
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+ ret = -1;
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+ }
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+ if (ret < 0) {
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+ ret = bdrv_co_truncate(bs->file, new_file_size, false, prealloc, 0,
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+ errp);
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+ }
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if (ret < 0) {
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error_prepend(errp, "Failed to resize underlying file: ");
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qcow2_free_clusters(bs, allocation_start,
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diff --git a/tests/qemu-iotests/274.out b/tests/qemu-iotests/274.out
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index 1a796fd..9d6fdeb 100644
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--- a/tests/qemu-iotests/274.out
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+++ b/tests/qemu-iotests/274.out
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@@ -187,7 +187,7 @@ read 65536/65536 bytes at offset 9437184
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10 MiB (0xa00000) bytes allocated at offset 5 MiB (0x500000)
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[{ "start": 0, "length": 5242880, "depth": 1, "zero": true, "data": false},
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-{ "start": 5242880, "length": 10485760, "depth": 0, "zero": true, "data": false, "offset": 327680}]
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+{ "start": 5242880, "length": 10485760, "depth": 0, "zero": false, "data": true, "offset": 327680}]
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=== preallocation=full ===
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Formatting 'TEST_DIR/PID-base', fmt=qcow2 size=16777216 cluster_size=65536 lazy_refcounts=off refcount_bits=16
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@@ -206,7 +206,7 @@ read 65536/65536 bytes at offset 11534336
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4 MiB (0x400000) bytes allocated at offset 8 MiB (0x800000)
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[{ "start": 0, "length": 8388608, "depth": 1, "zero": true, "data": false},
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-{ "start": 8388608, "length": 4194304, "depth": 0, "zero": true, "data": false, "offset": 327680}]
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+{ "start": 8388608, "length": 4194304, "depth": 0, "zero": false, "data": true, "offset": 327680}]
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=== preallocation=off ===
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Formatting 'TEST_DIR/PID-base', fmt=qcow2 size=393216 cluster_size=65536 lazy_refcounts=off refcount_bits=16
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--
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1.8.3.1
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