Messages in this thread | | | From | (Eric W. Biederman) | Date | Sun, 06 Jul 2008 02:25:30 -0700 | Subject | Re: [PATCH] parport/ppdev: fix registration of sysctl entries |
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Al Viro <viro@ZenIV.linux.org.uk> writes:
> On Sat, Jul 05, 2008 at 11:49:26PM -0700, Eric W. Biederman wrote: >> So our choices appear to be. >> - Change the name in sysctl so each parport device always has a unique name. >> - Only allow one opener of ppdev for a given port. > > Can't do - it's a legitimate use of ppdev (several userland programs > multiplexing the sucker).
Yep. And if didn't happen we wouldn't have the bug report. > >> - Take the approach of the initial patch and export to sysctl when we claim >> the port and unexport when we release the port. > > You do realize that we need exclusion around that lazy registration in > any case? sysctl is not the only problem there...
Totally. I was giving credit to the general idea rather then refering to specific implementation details.
>> - Give up and simply don't register with sysctl for ppdev. >> >> I did a quick google search and I could not find any hits (except for >> this bug report on devices/ppdev) so I am inclined just to special >> case ppdev and not even bother registering with sysctl. I did not >> see any other fields that would have problems with a duplicate name. >> >> The only other backwards compatible and viable approach appears >> to be registering ppdev parport devices when they are claimed. >> >> The only reason we would be able to change the name without breakage >> is if no one uses the /proc interface in which case I don't see a >> point in continuing to provide it for ppdev. > > Not quite. /proc/sys/.../timeslice is a generically documented way to > tune the damn thing when we have several things on the same port. Note > that while one of those might be in userland, the rest might be in kernel > and very different. In this case the parameter is both relevant *and* > currently usable.
Yes. I was only thinking about killing it off for ppdev. You do have a point something that is tuning this based on all openers could be looking at it generically.
> Frankly, I'd go for IDR and rename in cases when we have additional openers. It looks like we can walk port->physport->devices to see if we are the first ppdev to register. So that should not be too hard.
That will provide maximum compatibility. Right now the first ppdev on a minor shows up in sysctl and the rest error out sysctl wise. Having the others show up at a different name is exactly equivalent except that they show up.
The unfortunate thing is that we won't have a good way to tie those additional sysctl entries back to whoever opened them. Oh well.
> _And_ add a mutex around delayed allocation - that's a separate problem.
Yes. We need locking so that only one process can set or clear PP_CLAIMED.
Eric
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