Re: Does sysfs really provides persistent hardware path to devices?

[Greg KH <greg@kroah.com>]

On Sat, Jan 17, 2004 at 11:34:13PM +0300, Andrey Borzenkov wrote:
> On Thursday 25 September 2003 01:18, Greg KH wrote:

Heh, nothing like a long time between responses :)

> > On Sun, Aug 31, 2003 at 02:54:06PM +0400, Andrey Borzenkov wrote:
> > > On Tuesday 19 August 2003 00:42, Greg KH wrote:
> > > > On Mon, Aug 18, 2003 at 10:21:22AM +0400, "Andrey Borzenkov"  wrote:
> > > > > just to show what I expected from sysfs - here is entry from Solaris
> > > > > /devices:
> > > > >
> > > > > brw-r-----   1 root     sys       32,240 Jan 24  2002
> > > > > /devices/pci@16,4000/scsi@5,1/sd@0,0:a
> > > > >
> > > > > this entry identifies disk partition 0 on drive with SCSI ID 0, LUN 0
> > > > > connected to bus 1 of controller in slot 5 of PCI bus identified
> > > > > by 16. Now you can use whatever policy you like to give human
> > > > > meaningful name to this entry. And if you have USB it will continue
> > > > > further giving you exact topology starting from the root of your
> > > > > device tree.
> > > > >
> > > > > and this path does not contain single logical id so it is not subject
> > > > > to change if I add the same controller somewhere else.
> > > > >
> > > > > hopefully it clarifies what I mean ...
> > > >
> > > > Hm, a bit.  First, have you looked at what sysfs provides?  Here's one
> > > > of my machines and tell me if it has all the info you are looking for:
> > > >
> > > > $ tree /sys/bus/scsi/
> > > > /sys/bus/scsi/
> > > >
> > > > |-- devices
> > > > |   `-- 0:0:0:0 ->
> > > > | ../../../devices/pci0000:00/0000:00:1e.0/0000:02:05.0/host0/0:0:0:0
> > >
> > >                                                               ^ ^unstable
> >
> > Heh, so are the pci ids in that link too :)
> >
> 
> I am not sure if you are just making fun here. No, in _this_ link pci ids are 
> not unstable because I do not have hotpug PCI.

Your PCI ids could change over reboots for a number of different
reasons (bios changes, adding or removing cards, phase of the moon,
etc.)  My point is, PCI ids can not be guananteed to be stable for
everyone.

> But SCSI hosts are unstable:

Exactly.

> given current sysfs implementation - using wildcards remains the only 
> solution. I for now am using this trivial script:

You know that udev now supports wildcards in its pattern matching,
right?

> pts/0}% cat /etc/udev/scripts/removables
> #!/usr/bin/perl
> 
> my $devpath, $base;
> 
> $base = $1 if ($ARGV[0] =~ /(.*\D)\d*$/);
> $devpath = readlink "/sys/block/$base/device";
> 
> if ($devpath =~ 
> m|/devices/pci0000:00/0000:00:1f.4/usb2/2-2/2-2.4/2-2.4:1.0/host\d+/\d+:0:0:0|) 
> {
>         print "flash0";

ick, isn't there a unique sysfs id in this location for this device that
you can query off of?  model?  vendor?  scsi uuid?

> } elsif ($devpath =~ 
> m|/devices/pci0000:00/0000:00:1f.4/usb2/2-2/2-2.1/2-2.1:1.0/host\d+/\d+:0:0:0|) 
> {
>         print "flash1";
> } elsif ($devpath =~ m|/devices/legacy/host\d+/\d+:0:4:0|) {
>         print "jaz";
> } else {
>         exit(1);
> }
> 
> 1;
> 
> with config
> 
> KERNEL="sd*" PROGRAM="/etc/udev/scripts/removables %k" SYMLINK="%c/%D"

I just removed %D from udev too :)

> > And patches for udev are always welcome :)
> >
> 
> as example shows it probably can be done without serious patches. The only 
> problem is to make devpath available; at this point udev already computed it. 
> If you think it makes sense, patch will follow.

I could see making devpath available as a % modifier.

thanks,

greg k-h