On 7/9/06, Albert Cahalan <[email protected]> wrote:
Jon Smirl writes:
> On 7/8/06, Mike Galbraith <[email protected]> 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
[email protected]
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