On Sun, Jun 23, 2013 at 11:12:35PM -0400, Theodore Ts'o wrote: > On Mon, Jun 24, 2013 at 12:44:59PM +1000, Dave Chinner wrote: > > > > Hence, at minimum, this should be a fallocate() operation, not a ext4 > > specific ioctl as it is relatively trivial to implement on most > > extent based filesystems. > > The fallocate() uses a units of bytes for the offset and length; would > a FALLOC_FL_COLLAPSE_RANGE be guaranteed to work on any arbitrary > offset and length? Or would it only work if the offset and length are > multiples of the file system blocksize? There's nothing stopping us from restricting the offset/len to specific alignments if the operation cannot be done on arbitrary byte ranges. We do that for direct IO, and the sky hasn't fallen yet. > The the EXT4_IOC_TRUNCATE_BLOCK_RANGE interface solves this problem by > using units of file system blocks (i.e., __u32 start_block), but that > raises another issue, which is it forces the user space program to > somehow figure out the file system block size, which seems a bit nasty. Yeah, exactly. We can do that internally very easily, and EINVAL can be returned when the alignment is bad just like we do for direct IO... But, well, I pine for a generic XFS_IOC_DIOINFO interface so the filesystem can tell users about alignment restrictions.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
