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Bug#615035: FIEMAP wrongly reports holes for delayed-allocation extents



Package: linux-2.6
Version: 2.6.32-30
Severity: grave

The FIEMAP ioctl allows userland to query how file extents are mapped
to disk blocks.  Some filesystems that implement delayed allocation
(at least btrfs and ext4) will wrongly report that the file extents
for which blocks have not been allocated are holes in the file
(i.e. that no data has been written to them and they are treated as
all-zeroes).  Any program that relies on this information to optimise
file copying may fail to copy data that was recently appended to a
file on these types of filesystem.

See <http://lwn.net/Articles/429345/>.

Ben.

-- System Information:
Debian Release: wheezy/sid
  APT prefers oldstable-proposed-updates
  APT policy: (500, 'oldstable-proposed-updates'), (500, 'unstable'), (1, 'experimental')
Architecture: i386 (x86_64)

Kernel: Linux 2.6.37-1-amd64 (SMP w/2 CPU cores)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash


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