btrfs: allow btrfs_submit_bio to split bios
Currently the I/O submitters have to split bios according to the chunk stripe boundaries. This leads to extra lookups in the extent trees and a lot of boilerplate code. To drop this requirement, split the bio when __btrfs_map_block returns a mapping that is smaller than the requested size and keep a count of pending bios in the original btrfs_bio so that the upper level completion is only invoked when all clones have completed. Based on a patch from Qu Wenruo. Reviewed-by:Josef Bacik <josef@toxicpanda.com> Reviewed-by:
Johannes Thumshirn <johannes.thumshirn@wdc.com> Reviewed-by:
Qu Wenruo <wqu@suse.com> Signed-off-by:
Christoph Hellwig <hch@lst.de> Signed-off-by:
David Sterba <dsterba@suse.com>
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542e300e
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