Re: [PATCH] udev callout for reading filesystem labels

[Kay Sievers <kay.sievers@vrfy.org>]

On Thu, May 06, 2004 at 11:30:23AM +0200, Arnd Bergmann wrote:
> On Thursday 29 April 2004 23:04, Kay Sievers wrote:
> > Hi,
> > here is a small udev toy, which enables udev to name partitions by
> > its filesystem label or uuid's.
> > 
> > The following udev rule:
> > 
> >   KERNEL="sd*", PROGRAM="/sbin/udev_volume_id -M%M -m%m -u", SYMLINK="%c"
> > 
> > creates a symlink with the uuid read from the filesystem. If no label or
> > uuid is found the program exits with nonzero and the rule will fail.
> 
> Cool. I've tried to do something similar for dasd device labels before
> but not come up with a working solution yet.
> 
> Do you think that udev_volume_id can be extended so that it can also
> read disk labels and not just partition labels? The method for
> detecting and reading a dasd label is the same as for fs labels,
> and I have the necessary parsing code here.

Sure, we can do this. How much code do we need, for the parsing?

> The trouble is that the label is stored in the partition table, not
> in the partition itself, so I would need to pass the minor number
> from e.g. block/dasda/dev instead of block/dasda/dasda{1,2,3}/dev
> to udev_volume_id.
> 
> > +/* open volume by major/minor */
> > +struct volume_id *volume_id_open_dev_t(dev_t devt)
> > +{
> > +       struct volume_id *id;
> > +       char tmp_node[VOLUME_ID_PATH_MAX];
> > +
> > +       snprintf(tmp_node, VOLUME_ID_PATH_MAX,
> > +                "/tmp/volume-%u-%u", major(devt), minor(devt));
> > +       tmp_node[VOLUME_ID_PATH_MAX] = '\0';
> 
> This looks like a malicious user can easily prevent it from working
> by creating files in /tmp. You might need to use something similar
> to tmpfile(3) here.

Hmm, I really like to be able to compile with klibc and it doesn't
support tmpfile(). What about simply unlinking it, before creating the node?

thanks,
Kay



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