Backport of the following upstream commits

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commit 5d9ac7fd32f600f9451ea58abdb07f7ed42e921d
Author: Jeff Layton <jlayton>
Date:   Thu Aug 5 13:58:22 2010 -0400

cifs: clean up error handling in cifs_mknod

Get rid of some nesting and add a label we can goto on error.

Signed-off-by: Jeff Layton <jlayton>
Signed-off-by: Steve French <sfrench.com>
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commit fa2989f4473413a86890066aa3a5676a53b541e4
Author: Pavel Shilovsky <piastry>
Date:   Thu May 26 10:01:59 2011 +0400

CIFS: Use pid saved from cifsFileInfo in writepages and set_file_size

We need it to make them work with mandatory locking style because
we can fail in a situation like when kernel need to flush dirty pages
and there is a lock held by a process who opened file.

Signed-off-by: Pavel Shilovsky <piastry>
Signed-off-by: Steve French <sfrench.com>
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commit d4ffff1fa9695c5b5c0bf337e208d8833b88ff2d
Author: Pavel Shilovsky <piastry>
Date:   Thu May 26 06:02:00 2011 +0000

CIFS: Add rwpidforward mount option

Add rwpidforward mount option that switches on a mode when we forward
pid of a process who opened a file to any read and write operation.

This can prevent applications like WINE from failing on read or write
operation on a previously locked file region from the same netfd from
another process if we use mandatory brlock style.

It is actual for WINE because during a run of WINE program two processes
work on the same netfd - share the same file struct between several VFS
fds:
1) WINE-server does open and lock;
2) WINE-application does read and write.

Signed-off-by: Pavel Shilovsky <piastry>
Signed-off-by: Steve French <sfrench.com>
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