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? Thanks again, Alex. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
