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authorZbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>2015-12-11 09:10:33 -0500
committerZbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>2015-12-13 14:54:47 -0500
commit1f4b467daa2999ab0e4345c1f1069567852f567f (patch)
treef15a02037237dfd9313cbac7aaff3d71a259698e /src
parent2aaec9b4f61c1c1fa3374f40f0f1e828b6c53e1e (diff)
journal: in some cases we have to decompress the full lz4 field
lz4 has to decompress a whole "sequence" at a time. When the compressed data is composed of a repeating pattern, the whole set of repeats has do be docompressed, and the output buffer has to be big enough. This is unfortunate, because potentially the slowdown is very big. We are only interested in the field name, but we might have to decompress the whole thing. But the full cost will be borne out only when the full entry is a repeating pattern. In practice this shouldn't happen (apart from tests and the like). Hopefully lz4 will be fixed to avoid this problem, or it will grow a new function which we can use [1], so this fix should be remporary. [1] https://groups.google.com/d/msg/lz4c/_3kkz5N6n00/oTahzqErCgAJ
Diffstat (limited to 'src')
-rw-r--r--src/journal/compress.c15
1 files changed, 12 insertions, 3 deletions
diff --git a/src/journal/compress.c b/src/journal/compress.c
index 1a3d2cdd80..a3de0882a5 100644
--- a/src/journal/compress.c
+++ b/src/journal/compress.c
@@ -306,6 +306,7 @@ int decompress_startswith_lz4(const void *src, uint64_t src_size,
* prefix */
int r;
+ size_t size;
assert(src);
assert(src_size > 0);
@@ -322,10 +323,18 @@ int decompress_startswith_lz4(const void *src, uint64_t src_size,
r = LZ4_decompress_safe_partial(src + 8, *buffer, src_size - 8,
prefix_len + 1, *buffer_size);
+ if (r >= 0)
+ size = (unsigned) r;
+ else {
+ /* lz4 always tries to decode full "sequence", so in
+ * pathological cases might need to decompress the
+ * full field. */
+ r = decompress_blob_lz4(src, src_size, buffer, buffer_size, &size, 0);
+ if (r < 0)
+ return r;
+ }
- if (r < 0)
- return -EBADMSG;
- if ((unsigned) r >= prefix_len + 1)
+ if (size >= prefix_len + 1)
return memcmp(*buffer, prefix, prefix_len) == 0 &&
((const uint8_t*) *buffer)[prefix_len] == extra;
else