btrfs: raid56: make steal_rbio() subpage compatible

Function steal_rbio() will take all the uptodate pages from the source
rbio to destination rbio.

With the new stripe_sectors[] array, we also need to do the extra check:

- Check sector::flags to make sure the full page is uptodate
  Now we don't use PageUptodate flag for subpage cases to indicate
  if the page is uptodate.

  Instead we need to check all the sectors belong to the page to be sure
  about whether it's full page uptodate.

  So here we introduce a new helper, full_page_sectors_uptodate() to do
  the check.

- Update rbio::stripe_sectors[] to use the new page pointer
  We only need to change the page pointer, no need to change anything
  else.

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/raid56.c

@@ -309,6 +309,24 @@ static int rbio_bucket(struct btrfs_raid_bio *rbio)
 	return hash_64(num >> 16, BTRFS_STRIPE_HASH_TABLE_BITS);
 }
 
+static bool full_page_sectors_uptodate(struct btrfs_raid_bio *rbio,
+				       unsigned int page_nr)
+{
+	const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
+	const u32 sectors_per_page = PAGE_SIZE / sectorsize;
+	int i;
+
+	ASSERT(page_nr < rbio->nr_pages);
+
+	for (i = sectors_per_page * page_nr;
+	     i < sectors_per_page * page_nr + sectors_per_page;
+	     i++) {
+		if (!rbio->stripe_sectors[i].uptodate)
+			return false;
+	}
+	return true;
+}
+
 /*
  * Update the stripe_sectors[] array to use correct page and pgoff
  *
@@ -330,8 +348,11 @@ static void index_stripe_sectors(struct btrfs_raid_bio *rbio)
 }
 
 /*
- * stealing an rbio means taking all the uptodate pages from the stripe
- * array in the source rbio and putting them into the destination rbio
+ * Stealing an rbio means taking all the uptodate pages from the stripe array
+ * in the source rbio and putting them into the destination rbio.
+ *
+ * This will also update the involved stripe_sectors[] which are referring to
+ * the old pages.
  */
 static void steal_rbio(struct btrfs_raid_bio *src, struct btrfs_raid_bio *dest)
 {
@@ -344,9 +365,8 @@ static void steal_rbio(struct btrfs_raid_bio *src, struct btrfs_raid_bio *dest)
 
 	for (i = 0; i < dest->nr_pages; i++) {
 		s = src->stripe_pages[i];
-		if (!s || !PageUptodate(s)) {
+		if (!s || !full_page_sectors_uptodate(src, i))
 			continue;
-		}
 
 		d = dest->stripe_pages[i];
 		if (d)