[PATCH] readahead commentary

Add a few comments surrounding the generic readahead API.

Also convert some ulongs into pgoff_t: the identifier for PAGE_CACHE_SIZE
offsets into pagecache.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5c1fb0a..7b115fe 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -932,13 +932,13 @@
 					 * turning readahead off */
 
 int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
-			unsigned long offset, unsigned long nr_to_read);
+			pgoff_t offset, unsigned long nr_to_read);
 int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
-			unsigned long offset, unsigned long nr_to_read);
-unsigned long  page_cache_readahead(struct address_space *mapping,
+			pgoff_t offset, unsigned long nr_to_read);
+unsigned long page_cache_readahead(struct address_space *mapping,
 			  struct file_ra_state *ra,
 			  struct file *filp,
-			  unsigned long offset,
+			  pgoff_t offset,
 			  unsigned long size);
 void handle_ra_miss(struct address_space *mapping, 
 		    struct file_ra_state *ra, pgoff_t offset);