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    SubjectRe: devfs: "cd" device not showing up initially. [Fwd: Scan past lun 7 in

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    Ishikawa <> wrote:
    > I have begun using devfs for about a couple of weeks now and
    > thank you for the great addition to linux.
    > Now I am happy to see the device names on the
    > scsi chain which won't be changed just because
    > I add/delete a device.
    > However, I noticed that there seems to be a subtle interaction of
    > devfs (+devfsd) and
    > the device names that appear under luns for
    > a scsi chain.
    > Namely the name "generic" or "disc" seem to
    > exist from the start (after bootup), but
    > the entry "cd" doesn't exist until I do something
    > about accessing the CD somehow.
    > (It seems that I fail the initial
    > attempt to mount due to the missing name.)
    > [snip, ls on /dev/scsi/* looks correct]
    > Is it possible that the accessing the CD using the
    > compatibility device name /dev/sr* forced
    > the creation of the "cd" device name?

    Yes, the LOOKUP rule caused 'modprobe sr_mod' to be
    executed, then your cd devices will be visible in
    devfs and accessible. Under the old /dev system
    they were always "visible" but not accessible until
    you loaded sr_mod .

    > I consider the possibility of module loading. Both SCSI CD and
    > SCSI generic (sg) are modules now.
    > I checked /etc/devfs/devfs.conf (experimental Debian package
    > puts the config file here! ) has the following line:
    > So the module autoloading ought to work. ("generic" exists
    > somehow from the start.)

    The upper level scsi drivers (sd, sr, st, osst and sg) register
    and unregister device names with devfs. After the mid level
    recognizes a new scsi device it calls the detect() function
    in the builtin upper level drivers and those that are currently
    loaded as modules. That is your "problem", sr_mod.o is not
    loaded until you do something like "ls -l /dev/sr0" (due to
    that LOOKUP rule in /etc/devfsd.conf). The lsmod command will
    show which modules are loaded (in your case look for sr_mod).

    There is no "push" mechanism in the scsi mid level to load
    the sr_mod.o module when it sees a device with SCSI type
    CDROM. Devfs (specifically devfsd) supplies various "pull"
    mechanisms (e.g. LOOKUP) to load that module.

    Doug Gilbert

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