btrfs: refactor page status update into process_one_page()

In __process_pages_contig() we update page status according to page_ops.

That update process is a bunch of 'if' branches, which lie inside
two loops, this makes it pretty hard to expand for later subpage
operations.

So this patch will extract these operations into its own function,
process_one_pages().

Also since we're refactoring __process_pages_contig(), also move the new
helper and __process_pages_contig() before the first caller of them, to
remove the forward declaration.

Tested-by: Ritesh Harjani <riteshh@linux.ibm.com> # [ppc64]
Tested-by: Anand Jain <anand.jain@oracle.com> # [aarch64]
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -1808,10 +1808,118 @@ bool btrfs_find_delalloc_range(struct extent_io_tree *tree, u64 *start,
 	return found;
 }
 
+/*
+ * Process one page for __process_pages_contig().
+ *
+ * Return >0 if we hit @page == @locked_page.
+ * Return 0 if we updated the page status.
+ * Return -EGAIN if the we need to try again.
+ * (For PAGE_LOCK case but got dirty page or page not belong to mapping)
+ */
+static int process_one_page(struct address_space *mapping,
+			    struct page *page, struct page *locked_page,
+			    unsigned long page_ops)
+{
+	if (page_ops & PAGE_SET_ORDERED)
+		SetPageOrdered(page);
+
+	if (page == locked_page)
+		return 1;
+
+	if (page_ops & PAGE_SET_ERROR)
+		SetPageError(page);
+	if (page_ops & PAGE_START_WRITEBACK) {
+		clear_page_dirty_for_io(page);
+		set_page_writeback(page);
+	}
+	if (page_ops & PAGE_END_WRITEBACK)
+		end_page_writeback(page);
+	if (page_ops & PAGE_LOCK) {
+		lock_page(page);
+		if (!PageDirty(page) || page->mapping != mapping) {
+			unlock_page(page);
+			return -EAGAIN;
+		}
+	}
+	if (page_ops & PAGE_UNLOCK)
+		unlock_page(page);
+	return 0;
+}
+
 static int __process_pages_contig(struct address_space *mapping,
 				  struct page *locked_page,
 				  u64 start, u64 end, unsigned long page_ops,
-				  u64 *processed_end);
+				  u64 *processed_end)
+{
+	pgoff_t start_index = start >> PAGE_SHIFT;
+	pgoff_t end_index = end >> PAGE_SHIFT;
+	pgoff_t index = start_index;
+	unsigned long nr_pages = end_index - start_index + 1;
+	unsigned long pages_processed = 0;
+	struct page *pages[16];
+	int err = 0;
+	int i;
+
+	if (page_ops & PAGE_LOCK) {
+		ASSERT(page_ops == PAGE_LOCK);
+		ASSERT(processed_end && *processed_end == start);
+	}
+
+	if ((page_ops & PAGE_SET_ERROR) && nr_pages > 0)
+		mapping_set_error(mapping, -EIO);
+
+	while (nr_pages > 0) {
+		int found_pages;
+
+		found_pages = find_get_pages_contig(mapping, index,
+				     min_t(unsigned long,
+				     nr_pages, ARRAY_SIZE(pages)), pages);
+		if (found_pages == 0) {
+			/*
+			 * Only if we're going to lock these pages, we can find
+			 * nothing at @index.
+			 */
+			ASSERT(page_ops & PAGE_LOCK);
+			err = -EAGAIN;
+			goto out;
+		}
+
+		for (i = 0; i < found_pages; i++) {
+			int process_ret;
+
+			process_ret = process_one_page(mapping, pages[i],
+					locked_page, page_ops);
+			if (process_ret < 0) {
+				for (; i < found_pages; i++)
+					put_page(pages[i]);
+				err = -EAGAIN;
+				goto out;
+			}
+			put_page(pages[i]);
+			pages_processed++;
+		}
+		nr_pages -= found_pages;
+		index += found_pages;
+		cond_resched();
+	}
+out:
+	if (err && processed_end) {
+		/*
+		 * Update @processed_end. I know this is awful since it has
+		 * two different return value patterns (inclusive vs exclusive).
+		 *
+		 * But the exclusive pattern is necessary if @start is 0, or we
+		 * underflow and check against processed_end won't work as
+		 * expected.
+		 */
+		if (pages_processed)
+			*processed_end = min(end,
+			((u64)(start_index + pages_processed) << PAGE_SHIFT) - 1);
+		else
+			*processed_end = start;
+	}
+	return err;
+}
 
 static noinline void __unlock_for_delalloc(struct inode *inode,
 					   struct page *locked_page,
@@ -1939,102 +2047,6 @@ noinline_for_stack bool find_lock_delalloc_range(struct inode *inode,
 	return found;
 }
 
-static int __process_pages_contig(struct address_space *mapping,
-				  struct page *locked_page,
-				  u64 start, u64 end, unsigned long page_ops,
-				  u64 *processed_end)
-{
-	pgoff_t start_index = start >> PAGE_SHIFT;
-	pgoff_t end_index = end >> PAGE_SHIFT;
-	pgoff_t index = start_index;
-	unsigned long nr_pages = end_index - start_index + 1;
-	unsigned long pages_processed = 0;
-	struct page *pages[16];
-	unsigned ret;
-	int err = 0;
-	int i;
-
-	if (page_ops & PAGE_LOCK) {
-		ASSERT(page_ops == PAGE_LOCK);
-		ASSERT(processed_end && *processed_end == start);
-	}
-
-	if ((page_ops & PAGE_SET_ERROR) && nr_pages > 0)
-		mapping_set_error(mapping, -EIO);
-
-	while (nr_pages > 0) {
-		int found_pages;
-
-		found_pages = find_get_pages_contig(mapping, index,
-				     min_t(unsigned long,
-				     nr_pages, ARRAY_SIZE(pages)), pages);
-		if (found_pages == 0) {
-			/*
-			 * Only if we're going to lock these pages,
-			 * can we find nothing at @index.
-			 */
-			ASSERT(page_ops & PAGE_LOCK);
-			err = -EAGAIN;
-			goto out;
-		}
-
-		for (i = 0; i < ret; i++) {
-			if (page_ops & PAGE_SET_ORDERED)
-				SetPageOrdered(pages[i]);
-
-			if (locked_page && pages[i] == locked_page) {
-				put_page(pages[i]);
-				pages_processed++;
-				continue;
-			}
-			if (page_ops & PAGE_START_WRITEBACK) {
-				clear_page_dirty_for_io(pages[i]);
-				set_page_writeback(pages[i]);
-			}
-			if (page_ops & PAGE_SET_ERROR)
-				SetPageError(pages[i]);
-			if (page_ops & PAGE_END_WRITEBACK)
-				end_page_writeback(pages[i]);
-			if (page_ops & PAGE_UNLOCK)
-				unlock_page(pages[i]);
-			if (page_ops & PAGE_LOCK) {
-				lock_page(pages[i]);
-				if (!PageDirty(pages[i]) ||
-				    pages[i]->mapping != mapping) {
-					unlock_page(pages[i]);
-					for (; i < ret; i++)
-						put_page(pages[i]);
-					err = -EAGAIN;
-					goto out;
-				}
-			}
-			put_page(pages[i]);
-			pages_processed++;
-		}
-		nr_pages -= found_pages;
-		index += found_pages;
-		cond_resched();
-	}
-out:
-	if (err && processed_end) {
-		/*
-		 * Update @processed_end. I know this is awful since it has
-		 * two different return value patterns (inclusive vs exclusive).
-		 *
-		 * But the exclusive pattern is necessary if @start is 0, or we
-		 * underflow and check against processed_end won't work as
-		 * expected.
-		 */
-		if (pages_processed)
-			*processed_end = min(end,
-			((u64)(start_index + pages_processed) << PAGE_SHIFT) - 1);
-		else
-			*processed_end = start;
-
-	}
-	return err;
-}
-
 void extent_clear_unlock_delalloc(struct btrfs_inode *inode, u64 start, u64 end,
 				  struct page *locked_page,
 				  u32 clear_bits, unsigned long page_ops)