btrfs: introduce btrfs_alloc_folio_array()

The new helper will do the same thing as btrfs_alloc_page_array(), but
with folios.

One extra difference is, there is no extra helper for bulk allocation,
thus it may not be as efficient as the page version.
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

@@ -666,6 +666,37 @@ static void end_bbio_data_read(struct btrfs_bio *bbio)
 	bio_put(bio);
 }
 
+/*
+ * Populate every free slot in a provided array with folios.
+ *
+ * @nr_folios:   number of folios to allocate
+ * @folio_array: the array to fill with folios; any existing non-NULL entries in
+ *		 the array will be skipped
+ * @extra_gfp:	 the extra GFP flags for the allocation
+ *
+ * Return: 0        if all folios were able to be allocated;
+ *         -ENOMEM  otherwise, the partially allocated folios would be freed and
+ *                  the array slots zeroed
+ */
+int btrfs_alloc_folio_array(unsigned int nr_folios, struct folio **folio_array,
+			    gfp_t extra_gfp)
+{
+	for (int i = 0; i < nr_folios; i++) {
+		if (folio_array[i])
+			continue;
+		folio_array[i] = folio_alloc(GFP_NOFS | extra_gfp, 0);
+		if (!folio_array[i])
+			goto error;
+	}
+	return 0;
+error:
+	for (int i = 0; i < nr_folios; i++) {
+		if (folio_array[i])
+			folio_put(folio_array[i]);
+	}
+	return -ENOMEM;
+}
+
 /*
  * Populate every free slot in a provided array with pages.
  *

fs/btrfs/extent_io.h

@@ -360,6 +360,8 @@ void btrfs_clear_buffer_dirty(struct btrfs_trans_handle *trans,
 
 int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array,
 			   gfp_t extra_gfp);
+int btrfs_alloc_folio_array(unsigned int nr_folios, struct folio **folio_array,
+			    gfp_t extra_gfp);
 
 #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
 bool find_lock_delalloc_range(struct inode *inode,