On Tue, Jun 26, 2007 at 11:34:13AM -0400, Andreas Dilger wrote: > On Jun 26, 2007 16:02 +0530, Amit K. Arora wrote: > > On Mon, Jun 25, 2007 at 03:46:26PM -0600, Andreas Dilger wrote: > > > Can you clarify - what is the current behaviour when ENOSPC (or some other > > > error) is hit? Does it keep the current fallocate() or does it free it? > > > > Currently it is left on the file system implementation. In ext4, we do > > not undo preallocation if some error (say, ENOSPC) is hit. Hence it may > > end up with partial (pre)allocation. This is inline with dd and > > posix_fallocate, which also do not free the partially allocated space. > > Since I believe the XFS allocation ioctls do it the opposite way (free > preallocated space on error) this should be encoded into the flags. > Having it "filesystem dependent" just means that nobody will be happy. Ok, got your point. Maybe we can have a flag for this, as you suggested. But, default behavior IMHO should be _not_ to undo partial allocation (thus the file system will have the option of supporting this flag or not and it will be inline with posix_fallocate; XFS will obviously like to support this flag, inline with its existing behavior). > > > For FA_ZERO_SPACE - I'd think this would (IMHO) be the default - we > > > don't want to expose uninitialized disk blocks to userspace. I'm not > > > sure if this makes sense at all. > > > > I don't think we need to make it default - atleast for filesystems which > > have a mechanism to distinguish preallocated blocks from "regular" ones. > > What I mean is that any data read from the file should have the "appearance" > of being zeroed (whether zeroes are actually written to disk or not). What > I _think_ David is proposing is to allow fallocate() to return without > marking the blocks even "uninitialized" and subsequent reads would return > the old data from the disk. I can't think of a good reason for this (i.e. returning stale data from preallocated blocks). It is infact a security issue to me. Anyhow, this may though be beneficial for file systems which have noticable overhead in marking the blocks "uninitialized/preallocated". Can you or David please throw some light on how this option might really be helpful ? Thanks! -- Regards, Amit Arora - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
