Re: [RFC] Add support for semaphore-like structure with support for asynchronous I/O

[Christoph Hellwig <hch@infradead.org>]

On Tue, Apr 05, 2005 at 11:46:41AM -0400, Benjamin LaHaise wrote:
> On Mon, Apr 04, 2005 at 01:56:35PM -0400, Trond Myklebust wrote:
> > IOW: the current semaphore implementations really all need to die, and
> > be replaced by a single generic version to which it is actually
> > practical to add new functionality.
> 
> I can see that goal, but I don't think introducing iosems is the right 
> way to acheive it.  Instead (and I'll start tackling this), how about 
> factoring out the existing semaphore implementations to use a common 
> lib/semaphore.c, much like lib/rwsem.c?  The iosems can be used as a 
> basis for the implementation, but we can avoid having to do a giant 
> s/semaphore/iosem/g over the kernel tree.

Note that iosem is also a total misowner, it's not a counting semaphore
but a sleeping mutex with some special features.

Now if someone wants my two cent on how to resolve the two gazillion different
implementations mess:

 - switch all current semaphore users that don't need counting semaphores
   over to use a mutex_t type.  For now it can map to struct semaphore.
 - rip out all existing complicated struct semaphore implementations and
   replace it with a portable C implementation.  There's not a lot of users
   anyway.  Add a mutex_t implementation that allows sensible assembly hooks
   for architectures instead of reimplementing all of it
 - add more features to mutex_t where nessecary