Pádraig Brady wrote: > On 02/04/11 12:16, Jim Meyering wrote: >> Hi Pádraig, >> As of this change, >> >> copy: with fiemap copy, only sync when needed >> http://git.savannah.gnu.org/cgit/coreutils.git/commit/?id=f69876e55 >> >> fiemap copy with extents beyond EOF can fail on ext4 even with >> Fedora 15 (2.6.38) and rawhide's 2.6.39 kernel. >> >> Here we construct an odd file. First, preallocate 10MB of space, >> and then write 5KiB of random data into the beginning of that: >> >> $ fallocate -l 10000000 -n k >> $ dd count=10 if=/dev/urandom conv=notrunc iflag=fullblock of=k >> >> However, when we try to copy "k", we get a file, "k2" of the >> expected size, but with only NUL bytes for contents: > > So the extent info is not updated until sync(), > which means cp will consider the "unwritten" extent > as NUL data and not bother to read it :( > > I guess this is a corner case that was missed > in the fixups for ext4 (and btrfs?) in 2.6.38 for this? > I've copied ext4 devs for clarification. > I.E. if you do this: > > fallocate -l 10000000 -n k > dd count=10 if=/dev/urandom conv=notrunc iflag=fullblock of=k > filefrag -v k > > Do you get all extents still unwritten. > I do on my 2.6.35.11-83.fc14.i686 kernel, but I expected that. Right. The new extent remains unwritten until after a sync with ext4 on both Fedora 15 and rawhide kernels. Here's F15: $ fallocate -l 10000000 -n k $ dd count=10 if=/dev/urandom conv=notrunc iflag=fullblock of=k ... $ filefrag -v k Filesystem type is: ef53 File size of k is 5120 (2 blocks, blocksize 4096) ext logical physical expected length flags 0 0 6498304 2442 unwritten,eof k: 1 extent found $ sync $ filefrag -v k Filesystem type is: ef53 File size of k is 5120 (2 blocks, blocksize 4096) ext logical physical expected length flags 0 0 6498304 2 eof 1 2 6498306 2440 unwritten,eof k: 1 extent found Same problem with rawhide, but slightly different layout: $ fallocate -l 10000000 -n k $ dd count=10 if=/dev/urandom conv=notrunc iflag=fullblock of=k ... $ filefrag -v k Filesystem type is: ef53 File size of k is 5120 (2 blocks, blocksize 4096) ext logical physical expected length flags 0 0 2054144 2048 unwritten,eof 1 2048 2060288 2056191 394 unwritten,eof k: 2 extents found $ filefrag -v k [Exit 1] $ sync $ filefrag -v k Filesystem type is: ef53 File size of k is 5120 (2 blocks, blocksize 4096) ext logical physical expected length flags 0 0 2054144 2 eof 1 2 2054146 2046 unwritten,eof 2 2048 2060288 2056191 394 unwritten,eof k: 2 extents found -- 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
