On 05/18/2012 09:32 PM, Alex Lyakas wrote:

Thank you, Hugo, for the detailed explanation. I am now able to find
the CHUNK_ITEMs and to successfully locate the file data on disk.
Can you maybe address several follow-up questions I have?

# When looking for CHUNK_ITEMs, should I check that their
btrfs_chunk::type==BTRFS_BLOCK_GROUP_DATA (and not SYSTEM/METADATA
etc)? Or file extent should always be mapped to BTRFS_BLOCK_GROUP_DATA
chunk?

# It looks like I don't even need to bother with the extent tree at
this point, because from EXTENT_DATA in fs tree I can navigate
directly to CHUNK_ITEM in chunk tree, correct?

# For replicating RAID levels, you said there will be multiple
CHUNK_ITEMs. How do I find them then? Should I know in advance how
much there should be, and look for them, considering only
btrfs_chunk::type==BTRFS_BLOCK_GROUP_DATA? (I don't bother for
replication at this point, though).

# If I find in the fs tree an EXTENT_DATA of type
BTRFS_FILE_EXTENT_PREALLOC, how should I treat it? What does it mean?
(BTRFS_FILE_EXTENT_INLINE are easy to treat).

# One of my files has two EXTENT_DATAs, like this:
	item 14 key (270 EXTENT_DATA 0) itemoff 1812 itemsize 53
		extent data disk byte 432508928 nr 1474560
		extent data offset 0 nr 1470464 ram 1474560
		extent compression 0
	item 15 key (270 EXTENT_DATA 1470464) itemoff 1759 itemsize 53
		extent data disk byte 432082944 nr 126976
		extent data offset 0 nr 126976 ram 126976
		extent compression 0
Summing btrfs_file_extent_item::num_bytes gives
1470464+126976=1597440. (I know that I should not be summing
btrfs_file_extent_item::disk_num_bytes, but num_bytes).
However, it's INODE_ITEM gives size of 1593360, which is less:
	item 11 key (270 INODE_ITEM 0) itemoff 1970 itemsize 160
		inode generation 26 size 1593360 block group 0 mode 100700 links 1

Is this a valid situation, or I should always consider size in
INODE_ITEM as the correct one?

Hi Alex,

Have you tried btrfsck on this 'inode size mismatch' box?

And I'm interest in if it can be reproduced and how?


thanks,
liubo

Thanks again,
Alex.
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