[Libguestfs] do_umount adjustment

[Jim Meyering]

Richard W.M. Jones wrote:
> On Wed, Aug 12, 2009 at 10:14:51AM +0200, Jim Meyering wrote:
>> Here's one final (I hope) question without a complete patch.
>> Given that I already ensure that stubs.c invokes
>> REQUIRE_ROOT_OR_RESOLVE_DEVICE just before calling do_umount,
>> does this new version of do_umount look ok?
>>
>> /* Again, use the external /bin/umount program, so that /etc/mtab
>>  * is kept updated.
>>  */
>> int
>> do_umount (const char *pathordevice)
>> {
>>   int r;
>>   char *err;
>>
>>   char *buf = sysroot_path (pathordevice);
>>   if (buf == NULL) {
>>     reply_with_perror ("malloc");
>>     return -1;
>>   }
>
> I think the problem here is you'll end up with a buf like
> '/sysroot/dev/vda'.
>
> In the original code:
>
>   if (strncmp (pathordevice, "/dev/", 5) == 0) {
>     buf = pathordevice;
>     IS_DEVICE (buf, -1);
>   } else {
>     buf = sysroot_path (pathordevice);
>     if (buf == NULL) {
>       reply_with_perror ("malloc");
>       return -1;
>     }
>     freeit = 1;
>   }
>
> it avoids prefixing /dev paths.
>
> If Pathname args turn into two parameters (the original path, and the
> sysroot-prefixed path), then maybe Pathname_or_device args should turn
> into several parameters too, like:
>
>   int is_device, const char *original_pathordevice, const char *sysroot_pathordevice
>
> (That's just an idea ...  maybe not a good one)

If do_umount is the only case like that (and it seems to be),
a more local change is possible: if pathordevice starts with
/sysroot/dev, remove the "/sysroot" part.

Not terribly pretty to add the prefix, and then to remove it
right afterwards, but...