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Commit a42afc5f authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

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: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 5a87b7a5

fs/ext4/inode.c

+25 −48
Original line number Diff line number Diff line
@@ -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 {

		/*

		 * 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.

		 */

		ret = block_prepare_write(page, 0, len,

					  noalloc_get_block_write);

		if (!ret) {

		commit_write = 1;

	}

	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

		 * 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

		 */

			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);