Re: Opinions on removing /proc/tty?

["Jon Smirl" <jonsmirl@gmail.com>]

On 7/9/06, Albert Cahalan <acahalan@gmail.com> wrote:
> Jon Smirl writes:
> > On 7/8/06, Mike Galbraith <efault@gmx.de> wrote:
> >> On Fri, 2006-07-07 at 22:56 -0400, Jon Smirl wrote:
>
> >>> Does anyone use the info in /proc/tty? The hard coded device
> >>> names aren't compatible with udev's ability to rename things.
> >>>
> >>> There also doesn't appear to be any useful info in the drivers
> >>> portion that isn't already available in sysfs. I can add some code
> >>> to make a list of registered line disciplines appear in sysfs.
> >>>
> >>> Does anyone have a problem with deleting /proc/tty if
> >>> ldisc enum support is added to sysfs?
> >>
> >> ps uses /proc/tty/drivers, so some coordination would be needed.
> >
> > Greg, I just looked at the source for ps and it has a bunch
> > of fixed code for turning major/minor into /dev/name.  Isn't
> > that something udevinfo should be doing? But looking at the
> > help for udevinfo I don't see any way to turn a major/minor
> > into /dev/name. The altermative seems to be search /dev
> > looking for the right device node.
>
> By far, the best thing for procps (ps, top, etc.) would
> be /proc/*/tty links. Code that, give everybody a year
> to upgrade, and then... maybe.
>
> There is no way I'm going to have the procps run a "udevinfo"
> program, and I very much dislike relying on oddball libraries.
> Reliability and performance matter; this isn't some GNOME/KDE
> thing that can break just because 1 of 200 libraries changed.
>
> In order, the procps code tries:
>
> 1. /proc/*/tty symlink (effectively commented out)
Doesn't existing the the current kernel.

> 2. /proc/tty/drivers
This info can be wrong due to udev renames.  For example tty1 vs tty/1
The info in /proc/tty/drivers describes hardware not processes, it
belongs in sysfs, not /proc.

> 3. /proc/*/fd/2 symlink
Working in the current kernel

> 4. hard-coded guess
This will be wrong because of udev renames. For example tty1 vs tty/1

> 5. /proc/*/fd/255 symlink
Working in the current kernel

> 6. "?"
Always good

> Long ago, procps would search /dev for the mapping. This was
> too slow to be done directly when ps ran, so a binary file in
> /etc was used to cache the data. Keeping that file updated
> was a major problem.

This is what udev does, it maintains the mapping between devices and
names. Udevinfo is how you query the database. /etc/udev is where you
control how the device numbers are mapped into names.

Now we have a good example of the impact of pushing something (udev)
into user space and not shipping the binary as part of the kernel
tree. What is the API for converting a device node number to a name?


> BTW, cruft gets ripped out some time after Debian-obsolete no
> longer supports the old kernels.


--
Jon Smirl
jonsmirl@gmail.com
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