Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)

Markus Trippelsdorf
2011-04-15T15:41:28Z

On 2011.04.14 at 10:56 -0500, Eric Sandeen wrote:
> On 4/14/11 10:52 AM, Pádraig Brady wrote:
> > On 14/04/11 16:50, Eric Sandeen wrote:
> >> On 4/14/11 9:59 AM, Pádraig Brady wrote:
> >>> On 14/04/11 15:02, Markus Trippelsdorf wrote:
> >>>>>> Hi Pádraig,
> >>>>>>
> >>>>>> here you go:
> >>>>>> + filefrag -v unwritten.withdata
> >>>>>> Filesystem type is: ef53
> >>>>>> File size of unwritten.withdata is 5120 (2 blocks, blocksize 4096)
> >>>>>> ext logical physical expected length flags
> >>>>>> 0 0 274432 2560 unwritten,eof
> >>>>>> unwritten.withdata: 1 extent found
> >>>>>>
> >>>>>> Please notice that this also happens with ext4 on the same kernel.
> >>>>>> Btrfs is fine.
> >>>>>
> >>>> `filefrag -vs` fixes the issue on both xfs and ext4.
> >>>
> >>> So in summary, currently on (2.6.39-rc3), the following
> >>> will (usually?) report a single unwritten extent,
> >>> on both ext4 and xfs
> >>>
> >>> fallocate -l 10MiB -n k
> >>> dd count=10 if=/dev/urandom conv=notrunc iflag=fullblock of=k
> >>> filefrag -v k # grep for an extent without unwritten || fail
> >>
> >> right, that's what I see too in testing.
> >>
> >> But would the coreutils install have done a preallocation of the destination file?
> >>
> >> Otherwise this looks like a different bug...
> >>
> >>> This particular issue has been discussed so far at:
> >>> http://debbugs.gnu.org/cgi/bugreport.cgi?bug=8411
> >>> Note there it was stated there that ext4 had this
> >>> fixed as of 2.6.39-rc1, so maybe there is something lurking?
> >>
> >> ext4 got a fix, but not xfs, I guess. My poor brain can't remember, I think I started looking into it, but it's clearly still broken.
> >>
> >> Still, I don't know for sure what happened to Markus - did something preallocate, in his case?
> >
> > Well that preallocate test is failing for him
> > when the source file is either on ext4 or xfs.
> > He noticed the issue initially on XFS when copying
> > none preallocated files, so XFS probably just has
> > the general issue of needing a sync before fiemap,
> > where as EXT4 just has this preallocate one
> > (though I've not seen it myself).
> >
> > cheers,
> > Pádraig.
> >
>
> well, if I simply take the preallocation step out of the testcase, it works fine on xfs without a sync.
>
> So I still don't know what Markus hit...

Maybe it's delalloc:

x4 /tmp # dd count=10 if=/dev/urandom conv=notrunc iflag=fullblock of=k
10+0 records in
10+0 records out
5120 bytes (5.1 kB) copied, 0.0021822 s, 2.3 MB/s
x4 /tmp # filefrag -v k
Filesystem type is: 58465342
File size of k is 5120 (2 blocks, blocksize 4096)
ext logical physical expected length flags
0 0 0 16 unknown,delalloc,eof
k: 1 extent found
x4 /tmp # sync
x4 /tmp # filefrag -v k
Filesystem type is: 58465342
File size of k is 5120 (2 blocks, blocksize 4096)
ext logical physical expected length flags
0 0 26960045 16 eof
k: 1 extent found

--
Markus