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. > 2 no glibc interface needs it > 3 at the time, only XFS supported punching holes, so there > is not need to support it in a generic interface > 4 the use cases presented were not considered compelling > enough to justify the additional complexity (!) > > In the end, I gave up arguing for it to be included because just > getting the FALLOC_FL_KEEP_SIZE functionality was a hard enough > battle. > > Anyway, #3 isn't the case any more, #4 was just an excuse not to > support anything ext4 couldn't do and lots of apps are calling > fallocate directly (because glibc can't use FALLOC_FL_KEEP_SIZE) so > #2 isn't an issue, either. I don't recall anyone arguing #4 because of ext4, but I get very tired of the linux-fsdevel bike-shed painting parties, so I often will concede whatever is necessary just to get the !@#! interface in, assuming we could add more flags later.... glibc does support fallocate(), BTW; it's just posix_fallocate() that doesn't use FALLOC_FL_KEEP_SIZE. > 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. 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. - Ted -- 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
