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 check page alignment every time before we are going to
fetch the next @len and after the former piece of data is decompressed.
If the current page that we reach has less than 4 bytes left,
then we should fetch the next @len at the start of next page.
Signed-off-by: Gui Hecheng <guihc.f...@cn.fujitsu.com>
Reviewed-by: Marc Dietrich <marvi...@gmx.de>
---
changelog
v1->v2: adopt alignment check method suggested by Marc
v2->v3: make code more readable
v3->v4: keep type safety & reformat comments
---
cmds-restore.c | 27 +++++++++++++++++++++++++--
1 file changed, 25 insertions(+), 2 deletions(-)
diff --git a/cmds-restore.c b/cmds-restore.c
index e09acc4..1fe2df0 100644
--- a/cmds-restore.c
+++ b/cmds-restore.c
@@ -56,7 +56,10 @@ static int get_xattrs = 0;
static int dry_run = 0;
#define LZO_LEN 4
-#define PAGE_CACHE_SIZE 4096
+#define PAGE_CACHE_SIZE 4096UL
+#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,
@@ -93,6 +96,26 @@ static inline size_t read_compress_length(unsigned char *buf)
return le32_to_cpu(dlen);
}
+static void align_if_need(size_t *tot_in, size_t *in_len)
+{
+ size_t tot_in_aligned;
+ size_t bytes_left;
+
+ tot_in_aligned = PAGE_CACHE_ALIGN(*tot_in);
+ bytes_left = tot_in_aligned - *tot_in;
+
+ if (bytes_left >= LZO_LEN)
+ return;
+
+ /*
+ * 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
+ */
+ *in_len += bytes_left;
+ *tot_in = tot_in_aligned;
+}
+
static int decompress_lzo(unsigned char *inbuf, char *outbuf, u64 compress_len,
u64 *decompress_len)
{
@@ -135,8 +158,8 @@ static int decompress_lzo(unsigned char *inbuf, char
*outbuf, u64 compress_len,
}
out_len += new_len;
outbuf += new_len;
+ align_if_need(&tot_in, &in_len);
inbuf += in_len;
- tot_in += in_len;
}
*decompress_len = out_len;
--
1.8.1.4
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