file locking.

[Jeff Roberson]

On Thu, 16 Aug 2007, John Baldwin wrote:

> On Thursday 16 August 2007 03:01:18 am Jeff Roberson wrote:
>> I have been looking at file locking for 8.0 and have come up with a way to
>> completely eliminate the file lock, reduce the size of struct file by
>> ~4 pointers (22%), remove the global list of files and associated lock,
>> and restrict the scope of unp_gc while removing several race conditions.
>

Thanks for the review.

> I like finit().  I would maybe change socketpair() to pass so1 and so2 to
> finit() rather than setting f_data twice.

I'm not sure what you mean?

>
> Did you consider using refcount_* for f_count rather than using the atomic
> operations directly?

Yes, I may change it.  I was investigating some schemes where it may not 
have been sufficient but I think it will work fine for what I've settled 
on.

I also think I'll wrap some atomics for manipulating f_type in macros.

>
> It appears you never call unp_discard() and thus 'closef()' on the sockets in
> unp_gc() now.  Perhaps the fdrop()'s in the end of the loop should be
> unp_discard()'s instead?

unp_discard() happens as a side-effect of sorflush().

>
> Also, it's a bit of a shame to lose 'show files' from ddb.

Yes, I can re-implement that using the same technique as sysctl kern.file. 
What's more troubling is the continued erosion of support for libkvm as it 
uses filelist.  I don't think libkvm is a strong enough case to keep 
filelist around.  I guess I will have to hack it to work similarly to 
sysctl as well.

Do we have an official stance on libkvm?  Now that we have sysctl for 
run-time it's only useful for crashdump debugging.  Really in most cases 
it could be replaced with a reasonable set of gcc scripts.

Jeff

>
> -- 
> John Baldwin
>