Re: LANANA: To Pending Device Number Registrants

[H. Peter Anvin]

Richard Gooch wrote:
> 
> Ingo Oeser writes:
> > On Tue, May 15, 2001 at 08:10:29AM -0700, Linus Torvalds wrote:
> > > and I don't see why we couldn't expose the "driver
> > > name" for any file descriptor.
> >
> > Because we dont like to replace:
> >
> >    if (st.device == MAJOR_1)
> >       bla
> >    else if ...
> >
> > with
> >
> >    if (!strcmp(st.device,"driver_1") )
> >       bla
> >    else if ...
> >
> > ?
> >
> > There is no win doing it this way, because every time we add a
> > new driver that fits or change the name of one, we need add
> > support for it.
> 
> Now look at how we can already do these things with devfs. Let's say
> I've opened /dev/cdroms/cdrom0 and it's sitting on fd=3.
> % ls -lF /proc/self/fd/3
> lrwx------   1 root     root           64 May 15 13:24 /proc/self/fd/3 -> /dev/ide/host0/bus0/target1/lun0/cd
> 
> So, in my application I do:
>         len = readlink ("/proc/self/3", buffer, buflen);
>         if (strcmp (buffer + len - 2, "cd") != 0) {
>                 fprintf (stderr, "Not a CD-ROM! Bugger off.\n");
>                 exit (1);
>         }
>         if (strncmp (buffer, "/dev/ide", 8) == 0) do_ide (fd);
>         else if (strncmp (buffer, "/dev/scsi", 9) == 0) do_scsi (fd);
>         else do_generic (fd);
> 
> That's a lot cleaner than relying on magic numbers, IMNSHO.
> 

You know, Richard, this was an example on what *NOT* to do!

	-hpa

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