Re: Opinions on removing /proc/tty?

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On 7/9/06, Ray Lee <[email protected]> wrote:
On 7/9/06, Albert Cahalan <[email protected]> wrote:
> In any case, I'm NOT running a udevinfo program or linking
> to a screwball library. Random failures are not OK.

Complete agreement, but it seems like there's a third option here.
We're talking about nothing more complicated than a table lookup here.
Having a `udevinfo` invocation would indeed be overkill (and slower
than just stating the entire /dev hierarchy, I'm sure), but
Greg's/Jon's point that udev is the original authoritative source of
the data remains.

A simple solution would be for udev to just maintain a list in a flat
file (e.g., /dev/.mappings) that could be read (very quickly) by ps
upon startup. This could be yet another strategy somewhere in your
list of heroic efforts to derive a /dev/ node :-).

Having anyone other than udev try to maintain that mappings cache file
is doomed to failure, as you already noted.

BSD just uses devname(3) in libc, which asks the kernel via
the kern.devname sysctl. So, /proc/sys/kern/devname for us.
This is essentially what /proc/tty/drivers is today, except
that FreeBSD standardized on a fully functional devfs.

Solaris uses _ttyname_dev(dev_t,buf,bufsize), also in libc.
This is horribly slow, involving a recursive search of
directories listed in the /etc/ttysrch file. The interface
is nice though. You get: ttyname, ttyname_r, _ttyname_dev.

Note that our glibc is often defective, not always upgraded,
and not even the only C library. I won't be relying on it
even if _ttyname_dev() or devname() gets implemented.

If you insist on bringing back the dead though...

I already have code, probably written in 1996 by Charles Blake.
Use /etc/psdevtab for the filename.

File format:

There are 16 tty major numbers (as of the Linux 1.1 kernel,
or thereabouts) with 256 minors each, and the names are 8
characters long. That makes for a 32 KiB file; procps will
verify the length. Major numbers are to be stored in the
following order:

2,3,4,5,19,20,22,23,24,25,32,33,46,47,48,49

The structure is thus like this:

char psdevtab[16][256][8]

Names should be zero-padded, not zero-terminated.

(seriously, a binary file with a tree structure is best)
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