On Tue, 15 May 2012, Allison Henderson wrote: > On 05/13/2012 02:13 PM, Hugh Dickins wrote: > > On Thu, 12 Jan 2012, Allison Henderson wrote: > >> On 01/11/2012 07:55 PM, Dave Chinner wrote: > >>> On Wed, Jan 11, 2012 at 05:02:12PM -0800, Hugh Dickins wrote: > >>>> Hi Allison, > >>>> > >>>> In thinking about fallocate() on tmpfs, I cross-check with ext4 > >>>> and find this bug in its implementation of FALLOC_FL_PUNCH_HOLE: > >>>> > >>>> rm -f temp > >>>> fallocate -l 4096 temp > >>>> du temp # shows 4, right > >>>> fallocate -p -l 4096 temp > >>>> du temp # shows 0, right > >>>> rm -f temp > >>>> fallocate -n -l 4096 temp > >>>> du temp # shows 4, right > >>>> fallocate -p -l 4096 temp > >>>> du temp # shows 4, wrong > >>>> rm temp > >>>> > >>>> ext4_ext_punch_hole() contains /* No need to punch hole beyond i_size */ > >>>> early return, and trimming to i_size below, but forgets that the other > >>>> variety of fallocate(), with FALLOC_FL_KEEP_SIZE set, may have allocated > >>>> blocks beyond i_size. They can be removed with ftruncate(), but it is > >>>> unexpected for fallocate() not to undo its own work, and xfs does so. > >>> > >>> I'm pretty sure that's a bug as XFS allows punching holes in extents > >>> beyond EOF. > >>> > >>> Cheers, > >>> > >>> Dave. > >> > >> Oh I see, I'll take a look at it, I think it will be ok to just take out the > >> early return. Thx! > > > > I see the -EOPNOTSUPPs have gone into 3.4's ext4_punch_hole() - thanks - > > but the i_size issue remains unfixed. I wouldn't be surprised if it were > > more complicated than you had hoped - I had no intention of trying a patch > > myself! It's not an actual problem for me, but I thought I'd just send a > > reminder, before I move out of the hole-punching business. > > Hi all, > > I had a fix for this a while ago and I believe Lukas had rebased it > when he was working on some punch hole optimizations, but Im not sure > what happened to it after that. I think Lukas might still be working > on that set? If not, I can take a peek at it again and see if I can > get it updated and resent. Thx! > > Allison Henderson Thanks, Allison. I just added Jan to the Cc list to make sure he sees, since we mentioned this in the inode_dio_wait thread (which I skilfully directed to an almost disjoint set of addressees - though I expect he already saw via linux-ext4). Hugh -- 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
