ext4: Refactor mpage_map_and_submit_buffers function

This patch refactors mpage_map_and_submit_buffers to take
out the page buffers processing, as a separate function.
This will be required to add support for blocksize < pagesize
for dioread_nolock feature.

No functionality change in this patch.

Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/20191016073711.4141-4-riteshh@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/inode.c

@@ -2340,6 +2340,75 @@ static int mpage_process_page_bufs(struct mpage_da_data *mpd,
 	return lblk < blocks;
 }
 
+/*
+ * mpage_process_page - update page buffers corresponding to changed extent and
+ *		       may submit fully mapped page for IO
+ *
+ * @mpd		- description of extent to map, on return next extent to map
+ * @m_lblk	- logical block mapping.
+ * @m_pblk	- corresponding physical mapping.
+ * @map_bh	- determines on return whether this page requires any further
+ *		  mapping or not.
+ * Scan given page buffers corresponding to changed extent and update buffer
+ * state according to new extent state.
+ * We map delalloc buffers to their physical location, clear unwritten bits.
+ * If the given page is not fully mapped, we update @map to the next extent in
+ * the given page that needs mapping & return @map_bh as true.
+ */
+static int mpage_process_page(struct mpage_da_data *mpd, struct page *page,
+			      ext4_lblk_t *m_lblk, ext4_fsblk_t *m_pblk,
+			      bool *map_bh)
+{
+	struct buffer_head *head, *bh;
+	ext4_io_end_t *io_end = mpd->io_submit.io_end;
+	ext4_lblk_t lblk = *m_lblk;
+	ext4_fsblk_t pblock = *m_pblk;
+	int err = 0;
+
+	bh = head = page_buffers(page);
+	do {
+		if (lblk < mpd->map.m_lblk)
+			continue;
+		if (lblk >= mpd->map.m_lblk + mpd->map.m_len) {
+			/*
+			 * Buffer after end of mapped extent.
+			 * Find next buffer in the page to map.
+			 */
+			mpd->map.m_len = 0;
+			mpd->map.m_flags = 0;
+
+			/*
+			 * FIXME: If dioread_nolock supports
+			 * blocksize < pagesize, we need to make
+			 * sure we add size mapped so far to
+			 * io_end->size as the following call
+			 * can submit the page for IO.
+			 */
+			err = mpage_process_page_bufs(mpd, head, bh, lblk);
+			if (err > 0)
+				err = 0;
+			*map_bh = true;
+			goto out;
+		}
+		if (buffer_delay(bh)) {
+			clear_buffer_delay(bh);
+			bh->b_blocknr = pblock++;
+		}
+		clear_buffer_unwritten(bh);
+	} while (lblk++, (bh = bh->b_this_page) != head);
+	/*
+	 * FIXME: This is going to break if dioread_nolock
+	 * supports blocksize < pagesize as we will try to
+	 * convert potentially unmapped parts of inode.
+	 */
+	io_end->size += PAGE_SIZE;
+	*map_bh = false;
+out:
+	*m_lblk = lblk;
+	*m_pblk = pblock;
+	return err;
+}
+
 /*
  * mpage_map_buffers - update buffers corresponding to changed extent and
  *		       submit fully mapped pages for IO
@@ -2359,12 +2428,12 @@ static int mpage_map_and_submit_buffers(struct mpage_da_data *mpd)
 	struct pagevec pvec;
 	int nr_pages, i;
 	struct inode *inode = mpd->inode;
-	struct buffer_head *head, *bh;
 	int bpp_bits = PAGE_SHIFT - inode->i_blkbits;
 	pgoff_t start, end;
 	ext4_lblk_t lblk;
-	sector_t pblock;
+	ext4_fsblk_t pblock;
 	int err;
+	bool map_bh = false;
 
 	start = mpd->map.m_lblk >> bpp_bits;
 	end = (mpd->map.m_lblk + mpd->map.m_len - 1) >> bpp_bits;
@@ -2380,57 +2449,29 @@ static int mpage_map_and_submit_buffers(struct mpage_da_data *mpd)
 		for (i = 0; i < nr_pages; i++) {
 			struct page *page = pvec.pages[i];
 
-			bh = head = page_buffers(page);
-			do {
-				if (lblk < mpd->map.m_lblk)
-					continue;
-				if (lblk >= mpd->map.m_lblk + mpd->map.m_len) {
-					/*
-					 * Buffer after end of mapped extent.
-					 * Find next buffer in the page to map.
-					 */
-					mpd->map.m_len = 0;
-					mpd->map.m_flags = 0;
-					/*
-					 * FIXME: If dioread_nolock supports
-					 * blocksize < pagesize, we need to make
-					 * sure we add size mapped so far to
-					 * io_end->size as the following call
-					 * can submit the page for IO.
-					 */
-					err = mpage_process_page_bufs(mpd, head,
-								      bh, lblk);
-					pagevec_release(&pvec);
-					if (err > 0)
-						err = 0;
-					return err;
-				}
-				if (buffer_delay(bh)) {
-					clear_buffer_delay(bh);
-					bh->b_blocknr = pblock++;
-				}
-				clear_buffer_unwritten(bh);
-			} while (lblk++, (bh = bh->b_this_page) != head);
-
+			err = mpage_process_page(mpd, page, &lblk, &pblock,
+						 &map_bh);
 			/*
-			 * FIXME: This is going to break if dioread_nolock
-			 * supports blocksize < pagesize as we will try to
-			 * convert potentially unmapped parts of inode.
+			 * If map_bh is true, means page may require further bh
+			 * mapping, or maybe the page was submitted for IO.
+			 * So we return to call further extent mapping.
 			 */
-			mpd->io_submit.io_end->size += PAGE_SIZE;
+			if (err < 0 || map_bh == true)
+				goto out;
 			/* Page fully mapped - let IO run! */
 			err = mpage_submit_page(mpd, page);
-			if (err < 0) {
-				pagevec_release(&pvec);
-				return err;
-			}
+			if (err < 0)
+				goto out;
 		}
 		pagevec_release(&pvec);
 	}
 	/* Extent fully mapped and matches with page boundary. We are done. */
 	mpd->map.m_len = 0;
 	mpd->map.m_flags = 0;
 	return 0;
+out:
+	pagevec_release(&pvec);
+	return err;
 }
 
 static int mpage_map_one_extent(handle_t *handle, struct mpage_da_data *mpd)