ext4: simplify ext4_writepage()

The actual code in ext4_writepage() is unnecessarily convoluted.
Simplify it so it is easier to understand, but otherwise logically
equivalent.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 55961ff4efc2383a86c8776f1a3e187e1d8af680..a08ec795995f3b50800e050c13dcc4f3a7d7bfaa 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2704,7 +2704,7 @@ static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate);
 static int ext4_writepage(struct page *page,
                          struct writeback_control *wbc)
 {
-       int ret = 0;
+       int ret = 0, commit_write = 0;
        loff_t size;
        unsigned int len;
        struct buffer_head *page_bufs = NULL;
@@ -2717,60 +2717,37 @@ static int ext4_writepage(struct page *page,
        else
                len = PAGE_CACHE_SIZE;
 
-       if (page_has_buffers(page)) {
-               page_bufs = page_buffers(page);
-               if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
-                                       ext4_bh_delay_or_unwritten)) {
-                       /*
-                        * We don't want to do  block allocation
-                        * So redirty the page and return
-                        * We may reach here when we do a journal commit
-                        * via journal_submit_inode_data_buffers.
-                        * If we don't have mapping block we just ignore
-                        * them. We can also reach here via shrink_page_list
-                        */
+       /*
+        * If the page does not have buffers (for whatever reason),
+        * try to create them using block_prepare_write.  If this
+        * fails, redirty the page and move on.
+        */
+       if (!page_buffers(page)) {
+               if (block_prepare_write(page, 0, len,
+                                       noalloc_get_block_write)) {
+               redirty_page:
                        redirty_page_for_writepage(wbc, page);
                        unlock_page(page);
                        return 0;
                }
-       } else {
+               commit_write = 1;
+       }
+       page_bufs = page_buffers(page);
+       if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
+                             ext4_bh_delay_or_unwritten)) {
                /*
-                * The test for page_has_buffers() is subtle:
-                * We know the page is dirty but it lost buffers. That means
-                * that at some moment in time after write_begin()/write_end()
-                * has been called all buffers have been clean and thus they
-                * must have been written at least once. So they are all
-                * mapped and we can happily proceed with mapping them
-                * and writing the page.
-                *
-                * Try to initialize the buffer_heads and check whether
-                * all are mapped and non delay. We don't want to
-                * do block allocation here.
+                * We don't want to do block allocation So redirty the
+                * page and return We may reach here when we do a
+                * journal commit via
+                * journal_submit_inode_data_buffers.  If we don't
+                * have mapping block we just ignore them. We can also
+                * reach here via shrink_page_list
                 */
-               ret = block_prepare_write(page, 0, len,
-                                         noalloc_get_block_write);
-               if (!ret) {
-                       page_bufs = page_buffers(page);
-                       /* check whether all are mapped and non delay */
-                       if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
-                                               ext4_bh_delay_or_unwritten)) {
-                               redirty_page_for_writepage(wbc, page);
-                               unlock_page(page);
-                               return 0;
-                       }
-               } else {
-                       /*
-                        * We can't do block allocation here
-                        * so just redity the page and unlock
-                        * and return
-                        */
-                       redirty_page_for_writepage(wbc, page);
-                       unlock_page(page);
-                       return 0;
-               }
+               goto redirty_page;
+       }
+       if (commit_write)
                /* now mark the buffer_heads as dirty and uptodate */
                block_commit_write(page, 0, len);
-       }
 
        if (PageChecked(page) && ext4_should_journal_data(inode)) {
                /*
@@ -2781,7 +2758,7 @@ static int ext4_writepage(struct page *page,
                return __ext4_journalled_writepage(page, len);
        }
 
-       if (page_bufs && buffer_uninit(page_bufs)) {
+       if (buffer_uninit(page_bufs)) {
                ext4_set_bh_endio(page_bufs, inode);
                ret = block_write_full_page_endio(page, noalloc_get_block_write,
                                            wbc, ext4_end_io_buffer_write);