Gui Hecheng
2014-Sep-18 03:34 UTC
[PATCH] btrfs-progs: fix page align issue for lzo compress in restore
When runing restore under lzo compression, "bad compress length"
problems are encountered.
It is because there is a page align problem with the @decompress_lzo,
as follows:
|------| |----|-| |------|...|------|
page ^ page page
|
3 bytes left
When lzo compress pages im RAM, lzo will ensure that
the 4 bytes len will be in one page as a whole.
There is a situation that 3 (or less) bytes are left
at the end of a page, and then the 4 bytes len is
stored at the start of the next page.
But the @decompress_lzo doesn't goto the start of
the next page and continue to read the next 4 bytes
which is across two pages, so a random value is fetched
as a "bad compress length".
So we just switch to the page-aligned start position to read
the len of next piece of data when "bad compress length" is
encounterd.
If we still get bad compress length in this case, then there is a
real "bad compress length", and we shall report error.
Signed-off-by: Gui Hecheng <guihc.fnst@cn.fujitsu.com>
---
cmds-restore.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/cmds-restore.c b/cmds-restore.c
index 38a131e..8b230ab 100644
--- a/cmds-restore.c
+++ b/cmds-restore.c
@@ -57,6 +57,9 @@ static int dry_run = 0;
#define LZO_LEN 4
#define PAGE_CACHE_SIZE 4096
+#define PAGE_CACHE_MASK (~(PAGE_CACHE_SIZE - 1))
+#define PAGE_CACHE_ALIGN(addr) (((addr) + PAGE_CACHE_SIZE - 1) \
+ & PAGE_CACHE_MASK)
#define lzo1x_worst_compress(x) ((x) + ((x) / 16) + 64 + 3)
static int decompress_zlib(char *inbuf, char *outbuf, u64 compress_len,
@@ -101,6 +104,8 @@ static int decompress_lzo(unsigned char *inbuf, char
*outbuf, u64 compress_len,
size_t out_len = 0;
size_t tot_len;
size_t tot_in;
+ size_t tot_in_aligned;
+ int aligned = 0;
int ret;
ret = lzo_init();
@@ -117,6 +122,20 @@ static int decompress_lzo(unsigned char *inbuf, char
*outbuf, u64 compress_len,
in_len = read_compress_length(inbuf);
if ((tot_in + LZO_LEN + in_len) > tot_len) {
+ /*
+ * The LZO_LEN bytes is guaranteed to be
+ * in one page as a whole, so if a page
+ * has fewer than LZO_LEN bytes left,
+ * the LZO_LEN bytes should be fetched
+ * at the start of the next page
+ */
+ if (!aligned) {
+ tot_in_aligned = PAGE_CACHE_ALIGN(tot_in);
+ inbuf += (tot_in_aligned - tot_in);
+ tot_in = tot_in_aligned;
+ aligned = 1;
+ continue;
+ }
fprintf(stderr, "bad compress length %lu\n",
(unsigned long)in_len);
return -1;
@@ -137,6 +156,7 @@ static int decompress_lzo(unsigned char *inbuf, char
*outbuf, u64 compress_len,
outbuf += new_len;
inbuf += in_len;
tot_in += in_len;
+ aligned = 0;
}
*decompress_len = out_len;
--
1.8.1.4
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