Re: making a file sparse - in-place?

[Rodrigo Campos]

On Fri, Jan 24, 2014 at 03:30:20AM +0000, Pádraig Brady wrote:
> On 01/24/2014 03:12 AM, Rodrigo Campos wrote:
> > On Fri, Jan 24, 2014 at 02:59:41AM +0000, Pádraig Brady wrote:
> >> On 01/24/2014 02:41 AM, Rodrigo Campos wrote:
> >>> On Fri, Jan 24, 2014 at 01:07:21AM +0000, Pádraig Brady wrote:
> >>>> On 01/24/2014 12:47 AM, Bernhard Voelker wrote:
> >>>>> Inspired by a recent post on util-linux ML [1], talking about turning
> >>>>> a file into a sparse file in-place, i.e. not using a 2-step approach
> >>>>> like `cp --sparse file file2 && mv file2 file`), I thought, hey, don't
> >>>>> we have this in coreutils already?
> >>>>
> > 
> > But, a question about policy: is it okay to implement linux-only extensions 
> > here ?
> 
> If the current system doesn't support in place sparsify,
> then be could document that limitation along the
> same lines as the conv=notrunc case above.

Sorry, not sure I follow you here. If we have the same documentation, the
conv=notrunc case never says anything platform nor filesystem specific. And that
is a big difference, IMHO. And, also, truncate() is a quite common function.

I mean, is there any linux specific extension to a tool in coreutils ?
(optimization underneath, using linux-only features is totally different IMHO).

But it's just a matter of policy. Do you know what the policy is ?

> If one wanted more portable guarantees about sparsifying a file,
> then it would be best to use a temporary file anyway.

¿? What do you mean by this ?

> If there are other methods to punch a hole in a file
> on other systems, they can be added as an option to coreutils
> without changing the interface.

AFAIK, there aren't. And, as I said, is not linux specific only, it also is fs
specific.

If I have to guess, this flag is like other useful flags linux adds and most
other platforms don't. So you are exposing a feature here, that will only will
work on linux with certain filesystems. Probably there is a policy already
esablished for this ? (I mean, if it's ok or not)




Thanks,
Rodrigo