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authorKevin Wolf2020-07-07 16:46:29 +0200
committerKevin Wolf2020-07-14 15:18:59 +0200
commitd0ceea88dea053e0c1c038d42ca98782c2e3872d (patch)
tree64388483bf4ed6fb56a4eee157092efb2007e56c /qemu-img.c
parentiotests: Simplify _filter_img_create() a bit (diff)
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qemu-img map: Don't limit block status request size
Limiting each loop iteration of qemu-img map to 1 GB was arbitrary from the beginning, though it only cut the maximum in half then because the interface was a signed 32 bit byte count. These days, bdrv_block_status supports a 64 bit byte count, so the arbitrary limit is even worse. On file-posix, bdrv_block_status() eventually maps to SEEK_HOLE and SEEK_DATA, which don't support a limit, but always do all of the work necessary to find the start of the next hole/data. Much of this work may be repeated if we don't use this information fully, but query with an only slightly larger offset in the next loop iteration. Therefore, if bdrv_block_status() is called in a loop, it should always pass the full number of bytes that the whole loop is interested in. This removes the arbitrary limit and speeds up 'qemu-img map' significantly on heavily fragmented images. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Message-Id: <20200707144629.51235-1-kwolf@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'qemu-img.c')
-rw-r--r--qemu-img.c5
1 files changed, 1 insertions, 4 deletions
diff --git a/qemu-img.c b/qemu-img.c
index 498fbf42fe..4548dbff82 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -3210,12 +3210,9 @@ static int img_map(int argc, char **argv)
curr.start = start_offset;
while (curr.start + curr.length < length) {
int64_t offset = curr.start + curr.length;
- int64_t n;
+ int64_t n = length - offset;
- /* Probe up to 1 GiB at a time. */
- n = MIN(1 * GiB, length - offset);
ret = get_block_status(bs, offset, n, &next);
-
if (ret < 0) {
error_report("Could not read file metadata: %s", strerror(-ret));
goto out;