ext4: introduce lseek SEEK_DATA/SEEK_HOLE support
This patch makes ext4 really support SEEK_DATA/SEEK_HOLE flags. Block-mapped and extent-mapped files are fully implemented together because ext4_map_blocks hides this differences. After applying this patch, it will cause a failure in xfstest #285 when the file is block-mapped due to block-mapped file isn't support fallocate(2). I had tried to use ext4_ext_walk_space() to retrieve the offset for a extent-mapped file. But finally I decide to keep using ext4_map_blocks() to support SEEK_DATA/SEEK_HOLE because ext4_map_blocks() can hide the difference between block-mapped file and extent-mapped file. Moreover, in next step, extent status tree will track all extent status, and we can get all mappings from this tree. So I think that using ext4_map_blocks() is a better choice. CC: Hugh Dickins <hughd@google.com> Signed-off-by: NJie Liu <jeff.liu@oracle.com> Signed-off-by: NZheng Liu <wenqing.lz@taobao.com> Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
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