bug#6268: Suggestion: truncate should allow -r and -s options together

[Richard W.M. Jones]

The manpage for truncate says:

  Note that the -r and -s options are mutually exclusive.

and indeed you cannot have both:

  $ truncate -r /tmp/ref -s +10M /tmp/new
  truncate: you must specify one of `--size' or `--reference'

We suggest using the 'truncate' command in the 'virt-resize'
documentation[1].  We want users to create a file which is the size of
an existing file + some extra amount.  Naturally this would be:

  truncate -r old-disk.img -s +1G new-disk.img

but this does not work and we have to suggest that users use two
separate 'truncate' commands[2].

Related to this feature request, it would be nice if you could suffix
a size with a % sign to indicate that you want to increase a file by a
certain percentage of the old or reference size, eg:

  truncate -r old-disk.img -s +10% new-disk.img

  truncate -r old-disk.img -s 110% new-disk.img

Neither of these forms work at the moment.

Rich.

[1] http://libguestfs.org/virt-resize.1.html#expanding_a_virtual_machine_disk
[2] 
http://git.annexia.org/?p=libguestfs.git;a=commitdiff;h=0e28e4104d96bf0bf5b88fb07bb7e5f9f6e6f41f#patch1

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Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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