On Tue, Sep 29, 2015 at 05:34:24PM +0800, Qu Wenruo wrote: > Normally, a bull fallocate call on a fully written and synced file > should not add an extent.
Why not? Filesystems can do whatever they want with extents during a fallocate call. e.g. if the blocks are shared, then fallocate might break the block sharing so future overwrites don't get ENOSPC. This is a requirement set down by posix_fallocate(3) "After a successful call to posix_fallocate(), subsequent writes to bytes in the specified range are guaranteed not to fail because of lack of disk space." Hence if you've got a file with shared blocks, a "full fallocate" must change the extent layout to break the sharing. As such, the premise of this test is wrong. That's not to say that btrfs has a bug: > Btrfs has a bug to always truncate the last page if the fallocate start > offset is smaller than inode size. But it' not clear that this behaviour is actually a bug if it's not changing the file data. Cheers, Dave. -- Dave Chinner [email protected] -- To unsubscribe from this list: send the line "unsubscribe fstests" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
