On Fri, May 28, 2010 at 09:59:39AM +0200, Jim Meyering wrote: > Pádraig Brady wrote: > > Subject: [PATCH] truncate: support sizes relative to an existing file > > > > * doc/coreutils.texi (truncate invocation): Mention that --reference > > bases the --size rather than just setting it. > > * src/truncate.c (usage): Likewise. Also remove the clause > > describing --size and --reference as being mutually exclusive. > > (do_truncate): Add an extra parameter to hold the size > > of a referenced file, and use it if positive. > > (main): Pass the size of a referenced file to do_truncate(). > > * tests/misc/truncate-parameters: Adjust for the new combinations. > > * NEWS: Mention the change > > Suggested by Richard W.M. Jones > > Nice. Thanks! > > Not new with this change, but what about --ref=non-regular-file ? > > Perhaps truncate should refuse to use st_size info from > a non-regular file. > > Here's a pathological example: > > $ echo abcdefgh > bar > $ strace -e ftruncate ./truncate --ref=/dev/tty bar > ftruncate(3, 0) = 0 > $ wc -c bar > 0 bar > > It's obvious that such an example is not likely in practice, but since > currently truncate's --ref uses stat, it would follow a symlink, too. > > For a directory you'd get unportable and probably surprising results. > Using such a reference size deserves at least a warning.
And of course the right behaviour for block devices might be to get their size (ie. blockdev --getsize64 or the equivalent set of ioctls). Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into Xen guests. http://et.redhat.com/~rjones/virt-p2v
