For forcealign enabled, the allocation unit size is in ip->i_extsize, and
this must never be zero.

Add helper xfs_inode_alloc_fsbsize() to return alloc unit in FSBs, and use
it in xfs_inode_alloc_unitsize().

Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: John Garry <john.g.garry@oracle.com>
---
 fs/xfs/xfs_inode.c | 17 +++++++++++++----
 fs/xfs/xfs_inode.h |  1 +
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 7dc6f326936c..5af12f35062d 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -3107,17 +3107,26 @@ xfs_break_layouts(
 	return error;
 }
 
-/* Returns the size of fundamental allocation unit for a file, in bytes. */
 unsigned int
-xfs_inode_alloc_unitsize(
+xfs_inode_alloc_fsbsize(
 	struct xfs_inode	*ip)
 {
 	unsigned int		blocks = 1;
 
-	if (XFS_IS_REALTIME_INODE(ip))
+	if (xfs_inode_has_forcealign(ip))
+		blocks = ip->i_extsize;
+	else if (XFS_IS_REALTIME_INODE(ip))
 		blocks = ip->i_mount->m_sb.sb_rextsize;
 
-	return XFS_FSB_TO_B(ip->i_mount, blocks);
+	return blocks;
+}
+
+/* Returns the size of fundamental allocation unit for a file, in bytes. */
+unsigned int
+xfs_inode_alloc_unitsize(
+	struct xfs_inode	*ip)
+{
+	return XFS_FSB_TO_B(ip->i_mount, xfs_inode_alloc_fsbsize(ip));
 }
 
 /* Should we always be using copy on write for file writes? */
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index 3e7664ec4d6c..158afad8c7a4 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -641,6 +641,7 @@ int xfs_inode_reload_unlinked(struct xfs_inode *ip);
 bool xfs_ifork_zapped(const struct xfs_inode *ip, int whichfork);
 void xfs_inode_count_blocks(struct xfs_trans *tp, struct xfs_inode *ip,
 		xfs_filblks_t *dblocks, xfs_filblks_t *rblocks);
+unsigned int xfs_inode_alloc_fsbsize(struct xfs_inode *ip);
 unsigned int xfs_inode_alloc_unitsize(struct xfs_inode *ip);
 
 int xfs_icreate_dqalloc(const struct xfs_icreate_args *args,
-- 
2.31.1