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. cheers, Pádraig.
