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[Qemu-devel] [PATCH v6 15/24] qemu-img: Add find_nonzero()
From: |
Eric Blake |
Subject: |
[Qemu-devel] [PATCH v6 15/24] qemu-img: Add find_nonzero() |
Date: |
Wed, 11 Oct 2017 22:47:11 -0500 |
During 'qemu-img compare', when we are checking that an allocated
portion of one file is all zeros, we don't need to waste time
computing how many additional sectors after the first non-zero
byte are also non-zero. Create a new helper find_nonzero() to do
the check for a first non-zero sector, and rebase
check_empty_sectors() to use it.
The new interface intentionally uses bytes in its interface, even
though it still crawls the buffer a sector at a time; it is robust
to a partial sector at the end of the buffer.
Signed-off-by: Eric Blake <address@hidden>
Reviewed-by: John Snow <address@hidden>
---
v4-v5: no change
v3: new patch
---
qemu-img.c | 32 ++++++++++++++++++++++++++++----
1 file changed, 28 insertions(+), 4 deletions(-)
diff --git a/qemu-img.c b/qemu-img.c
index e4b84c4f56..89f1093d81 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1065,6 +1065,28 @@ done:
}
/*
+ * Returns -1 if 'buf' contains only zeroes, otherwise the byte index
+ * of the first sector boundary within buf where the sector contains a
+ * non-zero byte. This function is robust to a buffer that is not
+ * sector-aligned.
+ */
+static int64_t find_nonzero(const uint8_t *buf, int64_t n)
+{
+ int64_t i;
+ int64_t end = QEMU_ALIGN_DOWN(n, BDRV_SECTOR_SIZE);
+
+ for (i = 0; i < end; i += BDRV_SECTOR_SIZE) {
+ if (!buffer_is_zero(buf + i, BDRV_SECTOR_SIZE)) {
+ return i;
+ }
+ }
+ if (i < n && !buffer_is_zero(buf + i, n - end)) {
+ return i;
+ }
+ return -1;
+}
+
+/*
* Returns true iff the first sector pointed to by 'buf' contains at least
* a non-NUL byte.
*
@@ -1189,7 +1211,9 @@ static int check_empty_sectors(BlockBackend *blk, int64_t
sect_num,
int sect_count, const char *filename,
uint8_t *buffer, bool quiet)
{
- int pnum, ret = 0;
+ int ret = 0;
+ int64_t idx;
+
ret = blk_pread(blk, sect_num << BDRV_SECTOR_BITS, buffer,
sect_count << BDRV_SECTOR_BITS);
if (ret < 0) {
@@ -1197,10 +1221,10 @@ static int check_empty_sectors(BlockBackend *blk,
int64_t sect_num,
sectors_to_bytes(sect_num), filename, strerror(-ret));
return ret;
}
- ret = is_allocated_sectors(buffer, sect_count, &pnum);
- if (ret || pnum != sect_count) {
+ idx = find_nonzero(buffer, sect_count * BDRV_SECTOR_SIZE);
+ if (idx >= 0) {
qprintf(quiet, "Content mismatch at offset %" PRId64 "!\n",
- sectors_to_bytes(ret ? sect_num : sect_num + pnum));
+ sectors_to_bytes(sect_num) + idx);
return 1;
}
--
2.13.6
- [Qemu-devel] [PATCH v6 05/24] block: Switch bdrv_make_zero() to byte-based, (continued)
- [Qemu-devel] [PATCH v6 05/24] block: Switch bdrv_make_zero() to byte-based, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 04/24] qcow2: Switch is_zero_sectors() to byte-based, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 06/24] qemu-img: Switch get_block_status() to byte-based, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 09/24] block: Switch BdrvCoGetBlockStatusData to byte-based, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 07/24] block: Convert bdrv_get_block_status() to bytes, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 11/24] block: Switch bdrv_co_get_block_status_above() to byte-based, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 10/24] block: Switch bdrv_common_block_status_above() to byte-based, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 08/24] block: Switch bdrv_co_get_block_status() to byte-based, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 12/24] block: Convert bdrv_get_block_status_above() to bytes, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 13/24] qemu-img: Simplify logic in img_compare(), Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 15/24] qemu-img: Add find_nonzero(),
Eric Blake <=
- [Qemu-devel] [PATCH v6 14/24] qemu-img: Speed up compare on pre-allocated larger file, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 17/24] qemu-img: Change check_empty_sectors() to byte-based, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 16/24] qemu-img: Drop redundant error message in compare, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 18/24] qemu-img: Change compare_sectors() to be byte-based, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 19/24] qemu-img: Change img_rebase() to be byte-based, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 20/24] qemu-img: Change img_compare() to be byte-based, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 22/24] block: Relax bdrv_aligned_preadv() assertion, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 21/24] block: Align block status requests, Eric Blake, 2017/10/11
- [Qemu-devel] [PATCH v6 23/24] qcow2: Relax is_zero() assertion, Eric Blake, 2017/10/11