gfs2: Add gfs2_max_stuffed_size

Add a small inline function for computing the maximum size of a stuffed
inode instead of open coding that in several places throughout the code.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
diff --git a/fs/gfs2/bmap.c b/fs/gfs2/bmap.c
index 2ec1198..8686379 100644
--- a/fs/gfs2/bmap.c
+++ b/fs/gfs2/bmap.c
@@ -69,8 +69,8 @@
 		void *kaddr = kmap(page);
 		u64 dsize = i_size_read(inode);
  
-		if (dsize > (dibh->b_size - sizeof(struct gfs2_dinode)))
-			dsize = dibh->b_size - sizeof(struct gfs2_dinode);
+		if (dsize > gfs2_max_stuffed_size(ip))
+			dsize = gfs2_max_stuffed_size(ip);
 
 		memcpy(kaddr, dibh->b_data + sizeof(struct gfs2_dinode), dsize);
 		memset(kaddr + dsize, 0, PAGE_SIZE - dsize);
@@ -1692,8 +1692,7 @@
 	int error;
 	int unstuff = 0;
 
-	if (gfs2_is_stuffed(ip) &&
-	    (size > (sdp->sd_sb.sb_bsize - sizeof(struct gfs2_dinode)))) {
+	if (gfs2_is_stuffed(ip) && size > gfs2_max_stuffed_size(ip)) {
 		error = gfs2_quota_lock_check(ip, &ap);
 		if (error)
 			return error;
@@ -1928,8 +1927,7 @@
 		return 0;
 
 	if (gfs2_is_stuffed(ip)) {
-		if (offset + len >
-		    sdp->sd_sb.sb_bsize - sizeof(struct gfs2_dinode))
+		if (offset + len > gfs2_max_stuffed_size(ip))
 			return 1;
 		return 0;
 	}