Re: Best practice for new linux block driver device naming?

["Lennart Sorensen" <lsorense@csclub.uwaterloo.ca>]

On Fri, Mar 08, 2013 at 02:07:18PM -0600, scameron@beardog.cce.hp.com wrote:
> I'm just wondering if there are best pratices for new linux block
> drivers that are adding new devices nodes of which grub is currently
> not cognizant.
> 
> E.g. when we added the HP Smart Array cciss driver to the kernel
> many years ago, it had device nodes like /dev/cciss/c*d*, and there's
> code in grub to handle this in util/getroot.c, in
> convert_system_partition_to_system_disk():
> 
>       /* If this is a CCISS disk.  */
>       if (strncmp ("cciss/c", p, sizeof ("cciss/c") - 1) == 0)
>         {
>           /* /dev/cciss/c[0-9]+d[0-9]+(p[0-9]+)? */
>           p = strchr (p, 'p');
>           if (p)
>             {
>               *is_part = 1;
>               *p = '\0';
>             }
> 
>           return path;
>         }
> 
> And there is similar code for other weird device names is in there
> as well.
> 
> Ideally, I'm hoping there's a way to introduce new devices nodes
> with a new block driver which does not any require grub modifications.
> Looking over the code, it's not clear to me whether or not this is
> possible, and if it is, how to do it, what the constraints may be, etc.
> 
> Currently I have a new driver which adds devices like /dev/sop0  with
> partitions like /dev/sop0p1, /dev/sop0p2, etc.
> 
> If there is some better way to do this to enable grub to work with
> these devices, it is not yet too late for me to change it.
> 
> Or on the other hand, if it turns out that it is not possible to add
> new block devices to linux and have grub support for those devices without
> also modifying grub, then I wonder if it might be worth looking into to
> adding some kind of shared device namespace for block devices to linux, so
> new block drivers could use that and have a common naming system for block devices,
> and grub could be modified to support this new common naming system,
> much as scsi hba device drivers share the /dev/sd* namespace for their attached
> disks, so it is easy to add new scsi hba drivers to linux and automatically have
> grub support for them.  It would be nice if it were similarly easy to add new
> block device drivers to linux without also requiring modifications to grub.
> (It also occurs to me that this is such an obvious desire that if it is not 
> already supported, perhaps there's a good reason why not, but if that's the
> case, I'm don't know what the reason might be.)
> 
> Thoughts?

Well currently, SCSI, SATA, IDE, most well behaved raid controllers,
USB storage, and many others all show up simple as /dev/sd*.  You better
have a really good reason to not do so if you make a new controller.
Certainly the IBM serveraid cards I have worked with just present sd*
devices (as well as some sg* devices for the controller and hotswap
backplane and such).  I think the CCISS is a sample of a horrible design
as far as the device names in linux are concerned.

By creating a new type of block device you force everyone else to do work
to support it (or choose to ignore your device because no one cares).
By emulating a plain old scsi device interface, everything else just
works, and all the work is done by you in your device driver to pretend
to my just a scsi disk.  If you want your device taken seriously,
I don't think you have a choice.  Sysadmin's hate things that are
different for no good reason.

-- 
Len Sorensen