Re: SCSI DVD-RAM partitions

From: Christoph Hellwig (hch_at_infradead.org)
Date: 07/31/05

  • Next message: Michael Krufky: "Re: [HOWTO] set extra_cflags to indicate compilation against -mm kernels"
    Date:	Sun, 31 Jul 2005 15:01:57 +0100
    To: Thomas Heinz <thomasheinz@gmx.net>
    
    

    On Tue, Jul 12, 2005 at 10:23:17AM +0200, Thomas Heinz wrote:
    > Hi Christoph
    >
    > You wrote:
    > >While adding support for partitions on sr is trivial it has a huge
    > >drawback: it's chaning the dev_t space by using up device numbers
    > >for partitions, so /dev/sr0 ff will have different device numbers
    > >with that change applied. I have an old patch that's supposed to
    > >enable support for partitioned scsi removable devices at
    > >http://rechner.lst.de/~hch/hacks/sr-parts.diff, I'm not sure it
    > >actually ever worked (but you should get the basic idea from it)
    >
    > Ok, thanks for your valuable input. In fact, I thought about making
    > the device available both as /dev/srX and /dev/sdX at the same time
    > in order to support partitions. In my case it would even suffice to
    > make it available as /dev/sdX instead of /dev/srX.

    That doesn't make sense because sd is a very different driver from sd.
    Besides that aliasing different dev_ts to the same underlying blockdevice
    can't work, it's cause all sorts of aliasing problems.

    > Since I have no expert knowledge about this topic, I would be
    > interested in the general attitude towards "partitions on SCSI
    > DVD-RAM media / SCSI removable devices":
    > - Are partitions intentionally not supported? If so, why?

    Historical coincidence.

    > - Does it usually work but not with my specific DVD-RAM model?
    > If so, why?
    > - Do you think that this should be fixed?

    There's no nice way to fix it unfortunately.

    > Please note that personally, I can live with the "losetup hack"
    > since it is easy enough to write a program which encapsulates
    > partition mounting. However, there might be people which would
    > prefer plugging in a (possibly pre-)partitioned medium and
    > having the partitions work out of the box in the expected way.

    It would probably be better to use device-mapper than the loop device.
    I think there's already userland partition parsing code for dm, and
    having a simple command line tool to do that, and maybe even automatically
    run through udev and creating /dev/sr<num>p<partition> devices would
    be very nice to have as an almost invisible workaround.

    -
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