39 lines
1.4 KiB
Diff
39 lines
1.4 KiB
Diff
From f29fbf7c6b1c9a84f6931c1c222716fbe073e6e4 Mon Sep 17 00:00:00 2001
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Mon, 15 Apr 2019 16:25:01 +0200
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Subject: [PATCH] qcow2: Avoid COW during metadata preallocation
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Limiting the allocation to INT_MAX bytes isn't particularly clever
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because it means that the final cluster will be a partial cluster which
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will be completed through a COW operation. This results in unnecessary
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data read and write requests which lead to an unwanted non-sparse
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filesystem block for metadata preallocation.
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Align the maximum allocation size down to the cluster size to avoid this
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situation.
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Cc: qemu-stable@nongnu.org
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Reviewed-by: Eric Blake <eblake@redhat.com>
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(cherry-picked from commit f29fbf7c6b1c9a84f6931c1c222716fbe073e6e4)
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---
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block/qcow2.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/block/qcow2.c b/block/qcow2.c
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index 3ace3b2209..dfac74c264 100644
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--- a/block/qcow2.c
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+++ b/block/qcow2.c
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@@ -2734,7 +2734,7 @@ static int coroutine_fn preallocate_co(BlockDriverState *bs, uint64_t offset,
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bytes = new_length - offset;
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while (bytes) {
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- cur_bytes = MIN(bytes, INT_MAX);
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+ cur_bytes = MIN(bytes, QEMU_ALIGN_DOWN(INT_MAX, s->cluster_size));
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ret = qcow2_alloc_cluster_offset(bs, offset, &cur_bytes,
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&host_offset, &meta);
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if (ret < 0) {
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--
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2.19.1
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