• Robbie Ko's avatar
    Btrfs: send, improve clone range · 040ee612
    Robbie Ko authored
    Improve clone_range in two scenarios.
    
    1. Remove the limit of inode size when find clone inodes We can do
       partial clone, so there is no need to limit the size of the candidate
       inode.  When clone a range, we clone the legal range only by bytenr,
       offset, len, inode size.
    
    2. In the scenarios of rewrite or clone_range, data_offset rarely
       matches exactly, so the chance of a clone is missed.
    
    e.g.
        1. Write a 1M file
            dd if=/dev/zero of=1M bs=1M count=1
    
        2. Clone 1M file
           cp --reflink 1M clone
    
        3. Rewrite 4k on the clone file
           dd if=/dev/zero of=clone bs=4k count=1 conv=notrunc
    
        The disk layout is as follows:
        item 16 key (257 EXTENT_DATA 0) itemoff 15353 itemsize 53
    	extent data disk byte 1103101952 nr 1048576
    	extent data offset 0 nr 1048576 ram 1048576
    	extent compression(none)
        ...
        item 22 key (258 EXTENT_DATA 0) itemoff 14959 itemsize 53
    	extent data disk byte 1104150528 nr 4096
    	extent data offset 0 nr 4096 ram 4096
    	extent compression(none)
        item 23 key (258 EXTENT_DATA 4096) itemoff 14906 itemsize 53
    	extent data disk byte 1103101952 nr 1048576
    	extent data offset 4096 nr 1044480 ram 1048576
    	extent compression(none)
    
    When send, inode 258 file offset 4096~1048576 (item 23) has a chance to
    clone_range, but because data_offset does not match inode 257 (item 16),
    it causes missed clone and can only transfer actual data.
    
    Improve the problem by judging whether the current data_offset has
    overlap with the file extent item, and if so, adjusting offset and
    extent_len so that we can clone correctly.
    Reviewed-by: default avatarFilipe Manana <fdmanana@suse.com>
    Signed-off-by: default avatarRobbie Ko <robbieko@synology.com>
    Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
    040ee612
send.c 164 KB