Messages in this thread | | | From | (Eric W. Biederman) | Subject | Re: [PATCHSET 3/4] sysfs: divorce sysfs from kobject and driver model | Date | Fri, 05 Oct 2007 06:12:41 -0600 |
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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.
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