fs: small rcu-walk documentation fixes

[recommended]

	vfs now tries to do path walking in "rcu-walk mode", which avoids

atomic operations and scalability hazards on dentries and inodes (see

Documentation/filesystems/path-walk.txt). d_hash and d_compare changes (above)

are examples of the changes required to support this. For more complex

Documentation/filesystems/path-lookup.txt). d_hash and d_compare changes

(above) are examples of the changes required to support this. For more complex

filesystem callbacks, the vfs drops out of rcu-walk mode before the fs call, so

no changes are required to the filesystem. However, this is costly and loses

the benefits of rcu-walk mode. We will begin to add filesystem callbacks that

	permission and check_acl are inode permission checks that are called

on many or all directory inodes on the way down a path walk (to check for

exec permission). These must now be rcu-walk aware (flags & IPERM_RCU). See

Documentation/filesystems/vfs.txt for more details.

exec permission). These must now be rcu-walk aware (flags & IPERM_FLAG_RCU).

See Documentation/filesystems/vfs.txt for more details.

  permission: called by the VFS to check for access rights on a POSIX-like

  	filesystem.

	May be called in rcu-walk mode (flags & IPERM_RCU). If in rcu-walk

	May be called in rcu-walk mode (flags & IPERM_FLAG_RCU). If in rcu-walk

        mode, the filesystem must check the permission without blocking or

	storing to the inode.