f2fs: don't rely on F2FS_MAP_* in f2fs_iomap_begin

When testing with a mixed zoned / convention device combination, there
are regular but not 100% reproducible failures in xfstests generic/113
where the __is_valid_data_blkaddr assert hits due to finding a hole.

This seems to be because f2fs_map_blocks can set this flag on a hole
when it was found in the extent cache.

Rework f2fs_iomap_begin to just check the special block numbers directly.
This has the added benefits of the WARN_ON showing which invalid block
address we found, and being properly error out on delalloc blocks that
are confusingly called unwritten but not actually suitable for direct
I/O.

Fixes: 1517c1a7 ("f2fs: implement iomap operations")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -4153,20 +4153,24 @@ static int f2fs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 	 */
 	map.m_len = fscrypt_limit_io_blocks(inode, map.m_lblk, map.m_len);
 
-	if (map.m_flags & (F2FS_MAP_MAPPED | F2FS_MAP_UNWRITTEN)) {
-		iomap->length = blks_to_bytes(inode, map.m_len);
-		if (map.m_flags & F2FS_MAP_MAPPED) {
-			iomap->type = IOMAP_MAPPED;
-			iomap->flags |= IOMAP_F_MERGED;
-		} else {
-			iomap->type = IOMAP_UNWRITTEN;
-		}
-		if (WARN_ON_ONCE(!__is_valid_data_blkaddr(map.m_pblk)))
-			return -EINVAL;
+	/*
+	 * We should never see delalloc or compressed extents here based on
+	 * prior flushing and checks.
+	 */
+	if (WARN_ON_ONCE(map.m_pblk == NEW_ADDR))
+		return -EINVAL;
+	if (WARN_ON_ONCE(map.m_pblk == COMPRESS_ADDR))
+		return -EINVAL;
 
+	if (map.m_pblk != NULL_ADDR) {
+		iomap->length = blks_to_bytes(inode, map.m_len);
+		iomap->type = IOMAP_MAPPED;
+		iomap->flags |= IOMAP_F_MERGED;
 		iomap->bdev = map.m_bdev;
 		iomap->addr = blks_to_bytes(inode, map.m_pblk);
 	} else {
+		if (flags & IOMAP_WRITE)
+			return -ENOTBLK;
 		iomap->length = blks_to_bytes(inode, next_pgofs) -
 				iomap->offset;
 		iomap->type = IOMAP_HOLE;