Re: [PATCHSET 3/4] sysfs: divorce sysfs from kobject and driver model

Eric W. Biederman
2007-10-05T12:14:18Z

Greg KH <greg@kroah.com> writes:
>
>> Also fun is that the dev file implementation needs to be able to
>> report different major:minor numbers based on which mount of
>> sysfs we are dealing with.
>
> Um, no, that's not going to happen. /dev/sda will _always_ have the
> same major:minor number, as defined by the LSB spec. You can not break
> that at all. So while you might not want to show all mounts
> /sys/devices/block/sda/ the ones that you do, will all have the LSB
> defined major:minor number assigned to it.

Hmm. If that is in the LSB it must come from
Documentation/devices.txt I'm not after changing the user
visible major/minor assignments.

Let me see if a concrete example will help. Suppose I have
have a SAN with two disks: disk-1 and disk-2. I have
two machines A and B. On machine A I get the mapping:
sda -> disk-1, sdb ->disk-2. On machine B I wind up with
a different probe order so I get the mapping: sda -> disk-2
sdb ->disk-1.

To be very clear by sda I mean the block device with major 8 and
minor 0, and by sdb I mean the block device with major 8 and minor
16.

So I decide I want an environment on machine B that looks just
like the environment on machine A, so I can bring transfer over
a running program or whatever. So I run around looking at UUID
labels and what not and I discover that the machine B knows disk-1 as
sdb and that machine A knows disk-1 as sda. So I want to say:
/sys/devices/block/sdb show up in this other device namespace as
/sys/devices/block/sda.

In that instance a running program won't notice the difference.

Eric