vgone() calling VOP_CLOSE() -> blocked threads?

[Ed Schouten]

Hello Bruce,

* Bruce Evans <brde at optusnet.com.au> wrote:
> On Sat, 15 Mar 2008, Kostik Belousov wrote:
>
>> On Sun, Mar 16, 2008 at 03:55:18AM +1100, Bruce Evans wrote:
>>> Other problems near here:
>>> - neither vfs nor drivers currently know how many threads are in a
>>>   driver.  vfs uses vp->v_rdev->si_usecount, but this doesn't quite work
>> This is provided by si_threadcount.
>> See the dev(vn)_refthread and it usage in the devfs vnops and fops.
>
> So why doesn't reovoke() use it? :-).  All uses of si_usecount, which
> normally happen via vcount() and count_dev(), are suspect, especially
> the latter.
>
> vcount() is only used in revoke(), in svr4_fcntl.c to handle another
> revoke(), and for FreeBSD < 6 in reiserfs for an old multiple-mount
> check.
>
> count_dev() is only used in ata-tape.c (to decide in the same broken
> way as vfs if a close is the last one -- this driver uses D_TRACKCLOSE
> to get d_close() called on all closes.  This gives it the burden of
> deciding whether the close is the last one, and it can't do this any
> better than vfs.  D_TRACKCLOSE is used in a few other drivers which
> don't call count_dev()), in devfs_close() (to decide whether to release
> the controlling terminal and to decide when to call d_close()).
>
> Hmm, it seems to be not vfs but only devfs which handles last-close
> specially.  devfs is closer to devices, so it should know how to use
> si_threadcount here.  Hopefully si_threadcount counts threads sleeping
> in open or close, although si_usecount doesn't.  d_close (or something)
> should be called to wake up these threads even if si_usecount is 0.
> Drivers which support sleeping in open or close must support d_close
> (or something) being called to forcibly end such sleeps.  revoke()
> should forcibly end such sleeps, so it needs to check si_threadcount
> too.  si_usecount in its current form might end up being unused, so
> si_threadcount could be renamed back to it.

I just changed my TTY code to perform some garbage collecting on TTY's.
It now only performs a device cleanup when si_threadcount == 1 and
TF_OPENED is unset. Unfortunately, I'm checking for these conditions in
all the cdev ops, which is quite expensive.

It does the trick, but if someone has a better idea, I'm willing to
implement it.

Thanks!

-- 
 Ed Schouten <ed at 80386.nl>
 WWW: http://g-rave.nl/
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 195 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/freebsd-arch/attachments/20080319/0bd0eee7/attachment.pgp