[2/8] Sane locks (UNPOSIX locks)

[Boaz Harrosh <bharrosh@panasas.com>]

In this topic we do not actually know what it will look like
but we know what we do not like.

The most troublesome is the POSIX crap. POSIX says that if
any fd of a process on an inode is closed, all locks are lost,
even if we used another fd with other modes to acquire those
locks. (They had good stuff to smoke at when that stuff was
defined)

This is real crap, because it completely kills our ability
to acquire some other resources on the file, and/or keep
correct access modes. Because as soon as we need a lock
we need to open the fd in read/write mode, because if in future
a clients need a write access, we cannot do a re-open of the
file, we will loose the locks. Now if we open in RW, then we will
immediately loose our delegations and also in PNFS a write-open
means a different thing then read-open.

So what we urgently need is new locks API that is strictly
per fd. When we open an fd for read and then acquire a read
lock, we can continue to serve delegations. Only the close
of that specific fd will loose the locks. Any other parallel
activity in the background will not affect anything.

We can craft an API that is very similar to today's API only
with the semantic changes. But we should also consider a
completely new API that can cover all the kind of locks, including
a notification API. Perhaps also unite that API with the delegations
API we want in the next topic.

Thanks
Boaz