Messages in this thread |  | | From | (H. Peter Anvin) | Subject | Re: SCSI device numbering (was: Re: Ideas for v2.1 | Date | 3 Jul 1996 01:03:22 GMT |
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Followup to: <9607011143.ZM3962@aib.com> By author: "Eric Youngdale" <eric@aib.com> In newsgroup: linux.dev.kernel > > If you suggesting that we use one common major number for every > device on a given bus, then we need to decide how we assign minor numbers in > light of the fact that we can have a mix of disk, tape, cdrom and generic > device nodes trying to use the same major number. My guess is that for > cdroms the 'partition' field would be 0. For tapes, the partition field > could be used for the rewinding/non-rewinding part. This strikes me > as a bit unclean, but I could be talked into it. I need to think about > this a bit to see whether there are any other potential problems. >
Actually, CD-ROMs have (one or more) sessions, which can be very effectively treated as partitions. I would love to have a multisession CD-ROM where I could mount any session I wanted. Let's face it -- CD-ROMs are just removable, read-only disks with a couple of quirks.
Tape drives and generic-SCSI are character devices, whereas disks and CD-ROM are block devices. The former we could easily distinguish by a bit in the minor.
> > My main objection to the dynamic major idea is that it still leaves > potential problems with devices being remapped to different major numbers > if you move controller cards around. Some utility like scsidev would still > be required to maintain the /dev entries that correspond to the dynamic > majors. If people don't mind this level of inconvenience, then I have > no problem with it, but I thought the point of this exercise was to try and > see whether we could completely get away from dynamic assignment of device > numbers. >
Let's face it... we'll never get people to actually use *device names* that incorporate bus information; they are simply too long. On Solaris, which has such names, *everyone* uses the dynamically-assigned "short" equivalent (the controller part is dynamic.)
> Also, there are some people who would like to have one common > major number for *all* cdrom drives on the system (ide, scsi, etc). > A top level driver would essentially dispatch through a table down to > whatever the appropriate driver is to do the job. Dynamic majors take > us further from this, although a sort of virtual device driver would > probably also do the job here.
The people that call for that are basically the ones that want all CD-ROMs on the same major (i.e. /dev/cdrom would be a bona fide device.) I personally think it is useless -- that can be done by a boot script if desired -- but there probably should be a uniform way to find which devices correspond to actual CD-ROM, tape etc. devices.
-hpa
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