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| author | Artem Bityutskiy <Artem.Bityutskiy@nokia.com> | 2011-02-06 17:41:06 +0300 |
|---|---|---|
| committer | Artem Bityutskiy <Artem.Bityutskiy@nokia.com> | 2011-02-06 19:59:30 +0300 |
| commit | be7b42a5cb4c5050bcab4f57022007155c119d45 (patch) | |
| tree | eb5a75d2e816747e1e953ba515097d4f865ebdf4 /fs/ubifs/recovery.c | |
| parent | 822ed64c5b5d15474c6abb1834726643e2cff558 (diff) | |
| download | linux-be7b42a5cb4c5050bcab4f57022007155c119d45.tar.xz | |
UBIFS: describe UBIFS recovery logic some more
This patch adds more commentaries about UBIFS recovery logic which should
explain the famous UBIFS "corrupt empty space" errors.
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Diffstat (limited to 'fs/ubifs/recovery.c')
| -rw-r--r-- | fs/ubifs/recovery.c | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/fs/ubifs/recovery.c b/fs/ubifs/recovery.c index 77e9b874b6c2..6ecbc91ef9ac 100644 --- a/fs/ubifs/recovery.c +++ b/fs/ubifs/recovery.c @@ -28,6 +28,23 @@ * UBIFS always cleans away all remnants of an unclean un-mount, so that * errors do not accumulate. However UBIFS defers recovery if it is mounted * read-only, and the flash is not modified in that case. + * + * The general UBIFS approach to the recovery is that it recovers from + * corruptions which could be caused by power cuts, but it refuses to recover + * from corruption caused by other reasons. And UBIFS tries to distinguish + * between these 2 reasons of corruptions and silently recover in the former + * case and loudly complain in the latter case. + * + * UBIFS writes only to erased LEBs, so it writes only to the flash space + * containing only 0xFFs. UBIFS also always writes strictly from the beginning + * of the LEB to the end. And UBIFS assumes that the underlying flash media + * writes in @c->min_io_unit bytes at a time. + * + * Hence, if UBIFS finds a corrupted node at offset X, it expects only the min. + * I/O unit corresponding to offset X to contain corrupted data, all the + * following min. I/O units have to contain empty space (all 0xFFs). If this is + * not true, the corruption cannot be the result of a power cut, and UBIFS + * refuses to mount. */ #include <linux/crc32.h> @@ -671,6 +688,10 @@ struct ubifs_scan_leb *ubifs_recover_leb(struct ubifs_info *c, int lnum, } else { int corruption = first_non_ff(buf, len); + /* + * See header comment for this file for more + * explanations about the reasons we have this check. + */ ubifs_err("corrupt empty space LEB %d:%d, corruption " "starts at %d", lnum, offs, corruption); /* Make sure we dump interesting non-0xFF data */ |