On Apr 18, 2008 17:09 -0400, Josef Bacik wrote:
> Here is my patch for fiemap support on ext3. The main reason for doing this is
> because it will make it easier for application developers who are wanting to
> take advantage of fiemap on extent based fs's to be able to use the same
> interface for ext3 as well without having to fallback onto something like
> fibmap. Fibmap also means you are calling ext3_get_block for _every_ block in
> the file, which is ineffecient when ext3_get_blocks can map multiple contiguous
> blocks all at once, reducing the number of times you have to call
> ext3_get_blocks. Tested this with sandeens fiemap test program and verified it
> with filefrag. Thanks much,
>
> Signed-off-by: Josef Bacik <jbacik@xxxxxxxxxx>
Josef, thanks for doing this work. Having more than a single filesystem
implement FIEMAP (especially a block-mapped one) is very useful. Did you
look at all at making a "generic_fiemap()" function? It seems very little
of ext3_fiemap() is ext3 specific, only the call to ext3_force_commit()
(which could just be a sync on the inode), ext3_block_map() (generic for
all block-based filesystems), and truncate_mutex (would i_sem be enough?).
> +int ext3_fiemap(struct inode *inode, unsigned long arg)
> +{
> + /*
> + * if fm_start is in the middle of the current block, get the next
> + * block so we don't end up returning a start thats before the given
> + * fm_start
> + */
> + start_blk = (fiemap_s->fm_start + (1 << inode->i_blkbits) - 1) >>
> + inode->i_blkbits;
Hmm, I'd think that if someone is requesting the mapping for bytes [50-5000]
they wouldn't be very happy with the mapping returned being [4096-8191],
because it is missing part of the requested range. Instead, the fm_start
should be rounded down to the start of the first block and up to the end
of the last block to return [0-8191] (fm_start = 0, fm_length = 8192).
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
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