Re: LANANA: To Pending Device Number Registrants

Richard Gooch
2001-05-15T19:32:05Z

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.

Regards,

Richard....
Permanent: rgooch@atnf.csiro.au
Current: rgooch@ras.ucalgary.ca