locking questions (regarding file systems)

Shane Adams adamsch1 at yahoo.com
Wed Aug 2 19:54:49 UTC 2006

I just look around in the sources for other filesystems for similar patterns and try to infer whats going on.  Thats how (in my case) I figured out how to create a file on the filesystem from within the kernel.


----- Original Message ----
From: Eric Anderson <anderson at centtech.com>
To: R. B. Riddick <arne_woerner at yahoo.com>
Cc: freebsd-fs at freebsd.org
Sent: Wednesday, August 2, 2006 12:40:08 PM
Subject: Re: locking questions (regarding file systems)

On 08/02/06 14:34, R. B. Riddick wrote:
> --- Eric Anderson <anderson at centtech.com> wrote:
>> Here's basically what I do:
>> in the mount function for the FS, I do something like this:
>> g_topology_lock();
>> error = g_vfs_open(devvp, &cp, "fsname", 0);
>> g_topology_unlock();
>> What is needed in my unmount function to release those locks?  I've
>> tried some combinations of things, like:
>> g_topology_lock();
>> # wedges here
>> g_vfs_close(cp, td);
>> g_topology_unlock();
>> vrele(devvp);
> So the first un-mount works fine?
> And the second un-mount wedges _before_ g_vfs_close?

I never get to a second unmount, because I can't mount or mdconfig -d 
the device after the first mount.

> I cannot find anything really suspicious in ur code...
> Just 2 thoughts:
> 1. Do we really hold GIANT, when we mount and un-mount something?

I don't know - how can I check?

> 2. R u sure, that we need vrele()? I mean: Why doesn't g_vfs_close() call
> vrele(), if g_vfs_open() increases that use-count variable? Can u print the
> use-count variable in the beginning and the end of the mount/un-mount
> functions?

Good idea - I'll look into that..



Eric Anderson        Sr. Systems Administrator        Centaur Technology
Anything that works is better than anything that doesn't.
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