Messages in this thread |  | | Date | Wed, 16 May 2001 12:08:44 +0100 | From | Alex Bligh - linux-kernel <> | Subject | RE: LANANA: To Pending Device Number Registrants |
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> I believe thats why there are persistant superblocks on the RAID > partitions. You can switch them around, and it still knows which drive > holds which RAID partition... That's the only way booting off RAID > works, and the only reason for the "RAID Autodetect" partition type... > you can find those shuffled partitions correctly. The only time it > really looks at the file, is if you try to rebuild the partition I > believe... and some other circumstance that dosn't come to mind.
OK. I obviously asked slightly the wrong question as I was talking about a theoretical case and chose badly.
What I meant was 'Wouldn't it be better to use some form of static identifier / volume serial / MAC address / whatever, which /dev/[device-type]/[ID] exactly identifies, and continues to identify, even across config changes, than (a) go look for these ID's, then (b) sequence them in number disk0..N so that if one is removed, all the rest of them shuffle down'. IE isn't the point being argued here: 'don't identify devices by major/minor device number pairs chosen on a rather arbitrary and wasteful basis which describes how the given device is physically connected' and not 'the devices shall be dynamically ordered 0..N and rely on the order of detection, and the number of other devices, to determine their numbering'.
As has been pointed out elsewhere, if you expose /dev/disk/0/serial-number and/or /dev/disk/0/interface/scsi/ whatever, in a format trivially readable by a script, the problem largely goes away (+/- a linear search). However, if you don't at least try to keep (say) disk names static across reboot with trivial reconfig change (like inserting a PCMCIA flash card), I can see people are going to need to rewrite stuff like mount to look at (say) an fstab where the first field is not /dev/hda0, it is something which identifies a disk beyond /dev/disk/0 and actually goes looks at the tree under that for some form of serial number (or whatever), or mount -a will produce surprising results (for instance there's no reason a PCMCIA flash card might not be detected before a PCMCIA HD). I understood 2.4 was meant to be pretty static in terms of external interface.
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