Document ->page_mkwrite() locking
There seems to be very little documentation about this callback in general.
The locking in particular is a bit tricky, so it's worth having this in
writing.
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index 970c8ec..91ec4b4 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -512,13 +512,22 @@
void (*close)(struct vm_area_struct*);
struct page *(*fault)(struct vm_area_struct*, struct fault_data *);
struct page *(*nopage)(struct vm_area_struct*, unsigned long, int *);
+ int (*page_mkwrite)(struct vm_area_struct *, struct page *);
locking rules:
- BKL mmap_sem
+ BKL mmap_sem PageLocked(page)
open: no yes
close: no yes
fault: no yes
nopage: no yes
+page_mkwrite: no yes no
+
+ ->page_mkwrite() is called when a previously read-only page is
+about to become writeable. The file system is responsible for
+protecting against truncate races. Once appropriate action has been
+taking to lock out truncate, the page range should be verified to be
+within i_size. The page mapping should also be checked that it is not
+NULL.
================================================================================
Dubious stuff