udf: Move handling of uniqueID into a helper function and protect it by a s_alloc_mutex

uniqueID handling has been duplicated in three places. Move it into a common
helper. Since we modify an LVID buffer with uniqueID update, we take
sbi->s_alloc_mutex to protect agaist other modifications of the structure.

Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/udf/ialloc.c b/fs/udf/ialloc.c
index 75d9304..6fb7e0a 100644
--- a/fs/udf/ialloc.c
+++ b/fs/udf/ialloc.c
@@ -92,28 +92,19 @@
 		return NULL;
 	}
 
-	mutex_lock(&sbi->s_alloc_mutex);
 	if (sbi->s_lvid_bh) {
-		struct logicalVolIntegrityDesc *lvid =
-			(struct logicalVolIntegrityDesc *)
-			sbi->s_lvid_bh->b_data;
-		struct logicalVolIntegrityDescImpUse *lvidiu =
-							udf_sb_lvidiu(sbi);
-		struct logicalVolHeaderDesc *lvhd;
-		uint64_t uniqueID;
-		lvhd = (struct logicalVolHeaderDesc *)
-				(lvid->logicalVolContentsUse);
+		struct logicalVolIntegrityDescImpUse *lvidiu;
+
+		iinfo->i_unique = lvid_get_unique_id(sb);
+		mutex_lock(&sbi->s_alloc_mutex);
+		lvidiu = udf_sb_lvidiu(sbi);
 		if (S_ISDIR(mode))
 			le32_add_cpu(&lvidiu->numDirs, 1);
 		else
 			le32_add_cpu(&lvidiu->numFiles, 1);
-		iinfo->i_unique = uniqueID = le64_to_cpu(lvhd->uniqueID);
-		if (!(++uniqueID & 0x00000000FFFFFFFFUL))
-			uniqueID += 16;
-		lvhd->uniqueID = cpu_to_le64(uniqueID);
 		udf_updated_lvid(sb);
+		mutex_unlock(&sbi->s_alloc_mutex);
 	}
-	mutex_unlock(&sbi->s_alloc_mutex);
 
 	inode_init_owner(inode, dir, mode);