btrfs: tests: add table of most common errors

Allocation of main objects like fs_info or extent buffers is in each
test so let's simplify and unify the error messages to a table and add a
convenience helper.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/tests/btrfs-tests.c

@@ -17,6 +17,16 @@
 
 static struct vfsmount *test_mnt = NULL;
 
+const char *test_error[] = {
+	[TEST_ALLOC_FS_INFO]	     = "cannot allocate fs_info",
+	[TEST_ALLOC_ROOT]	     = "cannot allocate root",
+	[TEST_ALLOC_EXTENT_BUFFER]   = "cannot extent buffer",
+	[TEST_ALLOC_PATH]	     = "cannot allocate path",
+	[TEST_ALLOC_INODE]	     = "cannot allocate inode",
+	[TEST_ALLOC_BLOCK_GROUP]     = "cannot allocate block group",
+	[TEST_ALLOC_EXTENT_MAP]      = "cannot allocate extent map",
+};
+
 static const struct super_operations btrfs_test_super_ops = {
 	.alloc_inode	= btrfs_alloc_inode,
 	.destroy_inode	= btrfs_test_destroy_inode,

fs/btrfs/tests/btrfs-tests.h

@@ -13,6 +13,20 @@ int btrfs_run_sanity_tests(void);
 #define test_err(fmt, ...) pr_err("BTRFS: selftest: %s:%d " fmt "\n",	\
 		__FILE__, __LINE__, ##__VA_ARGS__)
 
+#define test_std_err(index)	test_err("%s", test_error[index])
+
+enum {
+	TEST_ALLOC_FS_INFO,
+	TEST_ALLOC_ROOT,
+	TEST_ALLOC_EXTENT_BUFFER,
+	TEST_ALLOC_PATH,
+	TEST_ALLOC_INODE,
+	TEST_ALLOC_BLOCK_GROUP,
+	TEST_ALLOC_EXTENT_MAP,
+};
+
+extern const char *test_error[];
+
 struct btrfs_root;
 struct btrfs_trans_handle;