ext4: add some kunit stub for mballoc kunit test

Multiblocks allocation will read and write block bitmap and group
descriptor which reside on disk. Add kunit stub to function
ext4_get_group_desc, ext4_read_block_bitmap_nowait, ext4_wait_block_bitmap
and ext4_mb_mark_context to avoid real IO to disk.

Signed-off-by: Kemeng Shi <[e-mail]>
Reviewed-by: "Ritesh Harjani (IBM)" <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Theodore Ts'o <[e-mail]>

fs/ext4/balloc.c

···
 #include "mballoc.h"
 
 #include <trace/events/ext4.h>
+#include <kunit/static_stub.h>
 
 static unsigned ext4_num_base_meta_clusters(struct super_block *sb,
 					    ext4_group_t block_group);
···
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	struct buffer_head *bh_p;
 
+	KUNIT_STATIC_STUB_REDIRECT(ext4_get_group_desc,
+				   sb, block_group, bh);
+
 	if (block_group >= ngroups) {
 		ext4_error(sb, "block_group >= groups_count - block_group = %u,"
 			   " groups_count = %u", block_group, ngroups);
···
 	ext4_fsblk_t bitmap_blk;
 	int err;
 
+	KUNIT_STATIC_STUB_REDIRECT(ext4_read_block_bitmap_nowait,
+				   sb, block_group, ignore_locked);
+
 	desc = ext4_get_group_desc(sb, block_group, NULL);
 	if (!desc)
 		return ERR_PTR(-EFSCORRUPTED);
···
 			   struct buffer_head *bh)
 {
 	struct ext4_group_desc *desc;
+
+	KUNIT_STATIC_STUB_REDIRECT(ext4_wait_block_bitmap,
+				   sb, block_group, bh);
 
 	if (!buffer_new(bh))
 		return 0;

fs/ext4/mballoc.c

···
 #include <linux/backing-dev.h>
 #include <linux/freezer.h>
 #include <trace/events/ext4.h>
+#include <kunit/static_stub.h>
 
 /*
  * MUSTDO:
···
 	struct buffer_head *gdp_bh;
 	int err;
 	unsigned int i, already, changed = len;
+
+	KUNIT_STATIC_STUB_REDIRECT(ext4_mb_mark_context,
+				   handle, sb, state, group, blkoff, len,
+				   flags, ret_changed);
 
 	if (ret_changed)
 		*ret_changed = 0;