On Mon, 2018-02-05 at 11:45 +0100, Julian Andres Klode wrote:
> On Mon, Feb 05, 2018 at 11:32:13AM +0100, Martin Wilck wrote:
> > On Mon, 2018-02-05 at 09:58 +0100, Julian Andres Klode wrote:
> > > C
> > > close (fd);
> > >
> > > - if (0 == strcmp(filename, loopinfo.lo_name)) {
> > > + if (0 == strcmp(filename, loopinfo.lo_name) ||
> > > + 0 == strcmp(rfilename, loopinfo.lo_name) ||
> > > + (realpath(loopinfo.lo_name, rloopfilename)
> > > &&
> > > + 0 == strcmp(rfilename, rloopfilename))) {
> > > found = realpath(path, NULL);
> > > break;
> > > }
> >
> > That "if x matches y or x matches y' or x' matches y" feels like
> > guesswork. Can't we simply call realpath() on both loopinfo.lo_name
> > and
> > filename, and compare the two?
>
> Probably yes. That said there might be some corner cases:
>
> (1) What happens if the backing file of a loopback is deleted -
> realpath
> can fail with ENOENT.
> (2) A path could be longer than PATH_MAX and it would fail with
> ENAMETOOLONG
> - this is a "problem" with the initial realpath as well, but less
> so, because
> the user can control that.
Both are scenarios in which kpartx would have good reason to fail (with
a meaningful error message). That's better than guessing, IMO.
kpartx' functionality to work with loop file names (as opposed to just
block devices) is a convenience feature anyway. I'd rather be certain
to avoid deleting stuff we aren't supposed to.
Regards
Martin
>
> I guess the 0 == strcmp(rfilename, loopinfo.lo_name) is not likely to
> happen, but
> in the end, I did not want to think that much about it and go with
> something that
> definitely works as best as possible.
>
--
Dr. Martin Wilck <mwilck@xxxxxxxx>, Tel. +49 (0)911 74053 2107
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)
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