From: Mark Fasheh 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 Cc: Nick Piggin Cc: David Howells Signed-off-by: Andrew Morton --- Documentation/filesystems/Locking | 11 ++++++++++- 1 files changed, 10 insertions(+), 1 deletion(-) diff -puN Documentation/filesystems/Locking~document-page_mkwrite-locking Documentation/filesystems/Locking --- a/Documentation/filesystems/Locking~document-page_mkwrite-locking +++ a/Documentation/filesystems/Locking @@ -512,13 +512,22 @@ prototypes: 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 _