[Libvir] RFC 'xen like scripts'

[Daniel P. Berrange]

On Tue, May 06, 2008 at 03:37:04PM +0200, Stefan de Konink wrote:
> On Tue, 6 May 2008, Daniel P. Berrange wrote:
> > >     /* Now figure out the stable path
> > >      *
> > >      * XXX this method is O(N) because it scans the pool target
> > >      * dir every time its run. Should figure out a more efficient
> > >      * way of doing this...
> > >      */
> > >     if ((vol->target.path = virStorageBackendStablePath(conn,
> > >                                                         pool,
> > >                                                         devpath)) == NULL)
> > >         goto cleanup;
> > >
> > >     if (devpath != vol->target.path)
> > >         free(devpath);
> > >     devpath = NULL;
> > >
> > > What are you trying to 'check' here?
> >
> > It is checking whether the input path (eg '/dev/sdf') is the same as the
> > returned path. If not, then it free's the original inpujt path since it
> > is now unused.
> 
> But is this input path the target path that is in the examples online (as
> last xmlnode)?

The 'devpath' parameter to virStorageBackendStablePath() is the path of the
LUN in question, typically eg, /dev/sdg.  The 'pool' object has an internal
attribute which is the 'target' element from the pool XML, eg '/dev/disk/by-path'.

The virStorageBackendStablePath(), then iterates over all the entries in
'/dev/disk/by-path' to find the one matching (symlinking to) '/dev/sdg'
and returns it, eg /dev/disk/by-path/ip-172.16.103.200:3260-iscsi-iqn.1992-08.com.netapp:sn.118046347:vf.88fa4694-0ba6-11dd-b8a9-00a09807592f-lun-1034
but if it doesn't find a matching symlink then it just returns the original
string '/dev/sdg'.

The latter scenario is depressingly common because soo many distros (including
RHEL-5) have broken udev rules for iSCSI. Its only since Fedora 8 that they
work properly for me

Dan
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