libfs: Open code simple_commit_write into only user

* simple_commit_write was only called by simple_write_end.
  Open coding it makes it tiny bit less heavy on the arithmetic and
  much more readable.

* While at it use zero_user() for clearing a partial page.
* While at it add a docbook comment for simple_write_end.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 35 insertions, 24 deletions

diff --git a/fs/libfs.c b/fs/libfs.c
index 6e8d17e1dc4c..cd88abdcb436 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -370,40 +370,51 @@ int simple_write_begin(struct file *file, struct address_space *mapping,
         return simple_prepare_write(file, page, from, from+len);
 }
 
-static int simple_commit_write(struct file *file, struct page *page,
-                               unsigned from, unsigned to)
-{
-        struct inode *inode = page->mapping->host;
-        loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
-
-        if (!PageUptodate(page))
-                SetPageUptodate(page);
-        /*
-         * No need to use i_size_read() here, the i_size
-         * cannot change under us because we hold the i_mutex.
-         */
-        if (pos > inode->i_size)
-                i_size_write(inode, pos);
-        set_page_dirty(page);
-        return 0;
-}
-
+/**
+ * simple_write_end - .write_end helper for non-block-device FSes
+ * @available: See .write_end of address_space_operations
+ * @file:               "
+ * @mapping:            "
+ * @pos:                "
+ * @len:                "
+ * @copied:             "
+ * @page:               "
+ * @fsdata:             "
+ *
+ * simple_write_end does the minimum needed for updating a page after writing is
+ * done. It has the same API signature as the .write_end of
+ * address_space_operations vector. So it can just be set onto .write_end for
+ * FSes that don't need any other processing. i_mutex is assumed to be held.
+ * Block based filesystems should use generic_write_end().
+ * NOTE: Even though i_size might get updated by this function, mark_inode_dirty
+ * is not called, so a filesystem that actually does store data in .write_inode
+ * should extend on what's done here with a call to mark_inode_dirty() in the
+ * case that i_size has changed.
+ */
 int simple_write_end(struct file *file, struct address_space *mapping,
                         loff_t pos, unsigned len, unsigned copied,
                         struct page *page, void *fsdata)
 {
-        unsigned from = pos & (PAGE_CACHE_SIZE - 1);
+        struct inode *inode = page->mapping->host;
+        loff_t last_pos = pos + copied;
 
         /* zero the stale part of the page if we did a short copy */
         if (copied < len) {
-                void *kaddr = kmap_atomic(page, KM_USER0);
-                memset(kaddr + from + copied, 0, len - copied);
-                flush_dcache_page(page);
-                kunmap_atomic(kaddr, KM_USER0);
+                unsigned from = pos & (PAGE_CACHE_SIZE - 1);
+
+                zero_user(page, from + copied, len - copied);
         }
 
-        simple_commit_write(file, page, from, from+copied);
+        if (!PageUptodate(page))
+                SetPageUptodate(page);
+        /*
+         * No need to use i_size_read() here, the i_size
+         * cannot change under us because we hold the i_mutex.
+         */
+        if (last_pos > inode->i_size)
+                i_size_write(inode, last_pos);
 
+        set_page_dirty(page);
         unlock_page(page);
         page_cache_release(page);