On Mon, Nov 08, 2010 at 10:30:38PM -0500, Ted Ts'o wrote: > On Tue, Nov 09, 2010 at 12:12:22PM +1100, Dave Chinner wrote: > > Hole punching was not included originally in fallocate() for a > > variety of reasons. IIRC, they were along the lines of: > > > > 1 de-allocating of blocks in an allocation syscall is wrong. > > People wanted a new syscall for this functionality. .... > > I guess that leaves #1 to be debated; > > I don't think there is any problem with doing what you propose. > > I don't have a problem either. > > As a completely separate proposal, what do people think about an > FALLOCATE_FL_ZEROIZE after which time the blocks are allocated, but > reading from them returns zero. That's exactly the new XFS_IOC_ZERO_RANGE ioctl in 2.6.36 does (commit 447223520520b17d3b6d0631aa4838fbaf8eddb4 "xfs: Introduce XFS_IOC_ZERO_RANGE") The git commit I pointed to in the last email is the rudimentary fallocate() interface support I have for that code which goes along with an xfs_io patch I have. Given that there seems to be interest for this operation, I'll flesh it out into a proper patch.... > This could be done either by (a) > sending a discard in the case of devices where discard_zeros_data is > true and discard_granularty is less than the fs block size, or (b) by > setting the uninitialized flag in the extent tree. Implementation is up to the filesystem. However, XFS does (b) because: 1) it was extremely simple to implement (one of the advantages of having an exceedingly complex allocation interface to begin with :P) 2) conversion is atomic, fast and reliable 3) it is independent of the underlying storage; and 4) reads of unwritten extents operate at memory speed, not disk speed. 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
