NFS: Add comment banners to some NFS functions

Add comment banners to some NFS functions so that they can be modified by the
NFS fscache patches for further information.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Steve Dickson <steved@redhat.com>
Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Daire Byrne <Daire.Byrne@framestore.com>

fs/nfs/file.c

@@ -409,6 +409,13 @@ static int nfs_write_end(struct file *file, struct address_space *mapping,
 	return copied;
 }
 
+/*
+ * Partially or wholly invalidate a page
+ * - Release the private state associated with a page if undergoing complete
+ *   page invalidation
+ * - Called if either PG_private or PG_private_2 is set on the page
+ * - Caller holds page lock
+ */
 static void nfs_invalidate_page(struct page *page, unsigned long offset)
 {
 	dfprintk(PAGECACHE, "NFS: invalidate_page(%p, %lu)\n", page, offset);
@@ -419,6 +426,12 @@ static void nfs_invalidate_page(struct page *page, unsigned long offset)
 	nfs_wb_page_cancel(page->mapping->host, page);
 }
 
+/*
+ * Attempt to release the private state associated with a page
+ * - Called if either PG_private or PG_private_2 is set on the page
+ * - Caller holds page lock
+ * - Return true (may release page) or false (may not)
+ */
 static int nfs_release_page(struct page *page, gfp_t gfp)
 {
 	dfprintk(PAGECACHE, "NFS: release_page(%p)\n", page);
@@ -427,6 +440,14 @@ static int nfs_release_page(struct page *page, gfp_t gfp)
 	return 0;
 }
 
+/*
+ * Attempt to clear the private state associated with a page when an error
+ * occurs that requires the cached contents of an inode to be written back or
+ * destroyed
+ * - Called if either PG_private or PG_private_2 is set on the page
+ * - Caller holds page lock
+ * - Return 0 if successful, -error otherwise
+ */
 static int nfs_launder_page(struct page *page)
 {
 	struct inode *inode = page->mapping->host;
@@ -451,6 +472,11 @@ const struct address_space_operations nfs_file_aops = {
 	.launder_page = nfs_launder_page,
 };
 
+/*
+ * Notification that a PTE pointing to an NFS page is about to be made
+ * writable, implying that someone is about to modify the page through a
+ * shared-writable mapping
+ */
 static int nfs_vm_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
 	struct page *page = vmf->page;