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

[Pádraig Brady]

On 31/05/10 07:31, Voelker, Bernhard wrote:
> Pádraig Brady wrote:
>> Jim Meyering wrote:
>>> what about --ref=non-regular-file ?
> 
>> Yes that's safer. st_size is only defined for regular files
>> (or shared mem), so I'll only allow regular files.
>> I'll push a separate patch soon.
> 
> what about --ref=- ?
> 
> one wants to have a file with the size
> of a partition plus 5G, e.g.
>       truncate --ref=/dev/sda5 -s +5G myfile
> This will fail and will be rejected with such a patch.
> So the user could use:
>       truncate --ref=- -s +5G myfile < /dev/sda5
> 
> Just a thought ...

Well we never supported referencing stdin as
we stat() the name. Also one needs to use a separate
operation to get the size of a block device,
so before the patch we just returned 0 which was invalid.

I wrote a comment in the code to say referencing
the size of a block device is probably useful,
but we'll need to worry about portability of that.

cheers,
Pádraig.