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authorPeter Wu <peter@lekensteyn.nl>2014-12-26 00:26:38 +0100
committerPeter Wu <peter@lekensteyn.nl>2014-12-27 15:47:24 +0100
commitc090e0700e4403d084423f56990b85749c62a829 (patch)
tree1c42ba4f25b0b4c7872a94c5f00055547d1c1a7e
parentbae85ae6bf66bd2c40cdf27ea61fc507d624bf61 (diff)
downloadqemu-c090e0700e4403d084423f56990b85749c62a829.tar.gz
block/dmg: improve zeroes handling
Disk images may contain large all-zeroes gaps (1.66k sectors or 812 MiB is seen in the real world). These blocks (type 2) do not need to be extracted into a temporary buffer, there is no need to allocate memory for these blocks nor to check its length. (For the test image, the maximum uncompressed size is 1054371 bytes, probably for a bzip2-compressed block.) Signed-off-by: Peter Wu <peter@lekensteyn.nl>
-rw-r--r--block/dmg.c18
1 files changed, 13 insertions, 5 deletions
diff --git a/block/dmg.c b/block/dmg.c
index 67d4e2bb42..b84ba7e690 100644
--- a/block/dmg.c
+++ b/block/dmg.c
@@ -137,7 +137,9 @@ static void update_max_chunk_size(BDRVDMGState *s, uint32_t chunk,
uncompressed_sectors = (s->lengths[chunk] + 511) / 512;
break;
case 2: /* zero */
- uncompressed_sectors = s->sectorcounts[chunk];
+ /* as the all-zeroes block may be large, it is treated specially: the
+ * sector is not copied from a large buffer, a simple memset is used
+ * instead. Therefore uncompressed_sectors does not need to be set. */
break;
}
@@ -260,7 +262,9 @@ static int dmg_read_mish_block(BDRVDMGState *s, DmgHeaderState *ds,
s->sectorcounts[i] = buff_read_uint64(buffer, offset);
offset += 8;
- if (s->sectorcounts[i] > DMG_SECTORCOUNTS_MAX) {
+ /* all-zeroes sector (type 2) does not need to be "uncompressed" and can
+ * therefore be unbounded. */
+ if (s->types[i] != 2 && s->sectorcounts[i] > DMG_SECTORCOUNTS_MAX) {
error_report("sector count %" PRIu64 " for chunk %" PRIu32
" is larger than max (%u)",
s->sectorcounts[i], i, DMG_SECTORCOUNTS_MAX);
@@ -621,9 +625,6 @@ static inline int dmg_read_chunk(BlockDriverState *bs, uint64_t sector_num)
return -1;
}
break;
- case 2: /* zero */
- memset(s->uncompressed_chunk, 0, 512 * s->sectorcounts[chunk]);
- break;
}
s->current_chunk = chunk;
}
@@ -641,6 +642,13 @@ static int dmg_read(BlockDriverState *bs, int64_t sector_num,
if (dmg_read_chunk(bs, sector_num + i) != 0) {
return -1;
}
+ /* Special case: current chunk is all zeroes. Do not perform a memcpy as
+ * s->uncompressed_chunk may be too small to cover the large all-zeroes
+ * section. */
+ if (s->types[s->current_chunk] == 2) { /* all zeroes block entry */
+ memset(buf + i * 512, 0, 512);
+ continue;
+ }
sector_offset_in_chunk = sector_num + i - s->sectors[s->current_chunk];
memcpy(buf + i * 512,
s->uncompressed_chunk + sector_offset_in_chunk * 512, 512);