Date: Tue, 27 May 2008 18:57:53 +0200 From: Ed Schouten <ed@80386.nl> To: Kostik Belousov <kostikbel@gmail.com> Cc: arch@freebsd.org Subject: Re: Simplifying devfs: minor == unit Message-ID: <20080527165753.GK64397@hoeg.nl> In-Reply-To: <20080527150244.GN21317@deviant.kiev.zoral.com.ua> References: <20080527130615.GJ64397@hoeg.nl> <20080527150244.GN21317@deviant.kiev.zoral.com.ua>
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* Kostik Belousov <kostikbel@gmail.com> wrote:
> > - I've seen most drivers only use the device cloner, because they need
> > descriptor local storage. It turns out more drivers need this than I
> > initially thought. kib@ has a patch for this, so I hope this gets
> > committed one of these {days,weeks,months}.
> The patch was committed ~ a week ago.
Great. Looks like I wasn't paying attention back then.
> > - After we've got file descriptor local storage, I think we can live
> > without the cloner. This means we could consider removing the minor
> > number argument from make_dev(), removing the unique unit number
> > restriction we currently have inside devfs, which causes many drivers
> > to use number pools for no obvious reason.
> I think we cannot live without clones regardless of devfs_cdevpriv.
> The model assumed for the pty, snp and probably several other devices
> actually requires new cdev instead of the priv data.
The pty driver does not use the clone_* interface. It only uses the
eventhandler, which should indeed be left intact. The snp driver does
use the clone_* interface, but not in a way that can't be done using the
eventhandler, validating the device name and calling make_dev()
directly.
Please take a look at src/usr.sbin/watch/watch.c:open_snp(). We might as
well turn snp(4) into a single /dev/snp, where the kernel space driver
uses per-descriptor data to distinguish the instances. This provides
some advantages:
- No more silly open()-loops.
- A system administrator can change the permissions on /dev/snp, which
automatically sets a system wide policy, instead on one of the device
nodes.
- We don't fill up the system with a lot of unused nodes.
for i in `seq 1000`
do
ls /dev/bpf$i > /dev/null
done
> > I was thinking about discussing this patch with my mentor + committing
> > it somewhere in the nearby future. Any comments?
>
> Making minor == unit number looks to be not a bad idea, please, look at
> the saga of the tty_pty.c revs. 1.153, 156, 1.157. Making the devices use
> si_drv0 directly probably is not so good since we remove the indirection
> layer that is already present and allows for some (minor) freedom in the
> devfs/kern_conf implementation.
But why isn't this done for si_drv1 and si_drv2 then? My idea is to turn
si_drv0 in an integer field that can be freely used. There is reason to
force a policy on this field.
--
Ed Schouten <ed@80386.nl>
WWW: http://80386.nl/
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