Linux-kernel mailing list archive 1998-31,: Re: DEVFSv50 and /dev/fb? (or /dev/fb/? ???)

# Re: DEVFSv50 and /dev/fb? (or /dev/fb/? ???)

Richard Gooch (Richard.Gooch@atnf.CSIRO.AU)
Sat, 8 Aug 1998 10:00:07 +1000

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kragen@pobox.com writes:
> I must have missed the explanation of how autoloading of device-driver
> modules works with devfs. If a device is to be automatically loaded
> and configured when someone tries to access it, and devfs creates names
> in /dev as devices are loaded and configured, then how do you try to
> access the unloaded, unconfigured device?

When you attempt to access a device node which isn't there (say
"ide/cd/c0b0t0u0") then for each path component that doesn't exist,
devfs sends that to kmod. Thus, potentially, you have have the
following sequence of strings sent to kmod: "ide", "ide/cd",
"ide/cd/c0b0t0u0".
In practice, people will have IDE configured into their kernel, so the
"ide" component is already there. Then the "ide/cd" string will be
sent to kmod. Now, if you have

# /etc/modules.conf
alias ide/cd ide-cd

then the ide-cd module will be loaded as required. Then the module
will detect your CD-ROM and will also register the "c0b0t0u0"
entry. So in general only one request is made to kmod: "ide/cd".

Something to keep in mind here is that while device entries don't
appear/exist at first, an explicit lookup of the inode (any syscall
that provides a pathname) will trigger kmod. So it all just magically
works.

Regards,

Richard....

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