Re: [PATCH] udev callout for reading filesystem labels

[Arnd Bergmann <arnd@arndb.de>]

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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.

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.

	Arnd <><

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