Kemeng Shi [off-list ref] writes:

I suppose desc and gd_bh are just the place holders so that
ext4_mb_new_blocks_simple() doesn't fail right? Is there any other use
of this? Because I don't see we initializing these.

+
+struct mb_ctx {
+	struct mb_grp_ctx *grp_ctx;
+};
+
+struct fake_super_block {
+	struct super_block sb;
+	struct mb_ctx mb_ctx;
+};
+
+#define MB_CTX(_sb) (&(container_of((_sb), struct fake_super_block, sb)->mb_ctx))
+#define MB_GRP_CTX(_sb, _group) (&MB_CTX(_sb)->grp_ctx[_group])
+
+static struct super_block *alloc_fake_super_block(void)
+{
+	struct ext4_super_block *es = kzalloc(sizeof(*es), GFP_KERNEL);
+	struct ext4_sb_info *sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
+	struct fake_super_block *fsb = kzalloc(sizeof(*fsb), GFP_KERNEL);
+
+	if (fsb == NULL || sbi == NULL || es == NULL)
+		goto out;
+
+	sbi->s_es = es;
+	fsb->sb.s_fs_info = sbi;
+	return &fsb->sb;
+
+out:
+	kfree(fsb);
+	kfree(sbi);
+	kfree(es);
+	return NULL;
+}
+
+static void free_fake_super_block(struct super_block *sb)
+{
+	struct fake_super_block *fsb = container_of(sb, struct fake_super_block, sb);
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+
+	kfree(sbi->s_es);
+	kfree(sbi);
+	kfree(fsb);
+}
+
+struct ext4_block_layout {
+	unsigned char blocksize_bits;
+	unsigned int cluster_bits;
+	unsigned long blocks_per_group;
+	ext4_group_t group_count;
+	unsigned long desc_size;
+};
+
+static void init_sb_layout(struct super_block *sb,
+			  struct ext4_block_layout *layout)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct ext4_super_block *es = sbi->s_es;
+
+	sb->s_blocksize = 1UL << layout->blocksize_bits;
+	sb->s_blocksize_bits = layout->blocksize_bits;
+
+	sbi->s_groups_count = layout->group_count;
+	sbi->s_blocks_per_group = layout->blocks_per_group;
+	sbi->s_cluster_bits = layout->cluster_bits;
+	sbi->s_cluster_ratio = 1U << layout->cluster_bits;
+	sbi->s_clusters_per_group = layout->blocks_per_group >>
+				    layout->cluster_bits;
+	sbi->s_desc_size = layout->desc_size;
+
+	es->s_first_data_block = cpu_to_le32(0);
+	es->s_blocks_count_lo = cpu_to_le32(layout->blocks_per_group *
+					    layout->group_count);
+}
+
+static int mb_grp_ctx_init(struct super_block *sb,
+			   struct mb_grp_ctx *grp_ctx)
+{
+	grp_ctx->bitmap_bh.b_data = kzalloc(EXT4_BLOCK_SIZE(sb), GFP_KERNEL);
+	if (grp_ctx->bitmap_bh.b_data == NULL)
+		return -ENOMEM;
+
+	get_bh(&grp_ctx->bitmap_bh);
+	get_bh(&grp_ctx->gd_bh);
+	return 0;
+}
+
+static void mb_grp_ctx_release(struct mb_grp_ctx *grp_ctx)
+{
+	kfree(grp_ctx->bitmap_bh.b_data);
+	grp_ctx->bitmap_bh.b_data = NULL;

No brelse() here?

+}
+
+static void mb_ctx_mark_used(struct super_block *sb, ext4_group_t group,
+			     unsigned int start, unsigned int len)
+{
+	struct mb_grp_ctx *grp_ctx = MB_GRP_CTX(sb, group);
+
+	mb_set_bits(grp_ctx->bitmap_bh.b_data, start, len);
+}
+
+/* called after init_sb_layout */
+static int mb_ctx_init(struct super_block *sb)
+{
+	struct mb_ctx *ctx = MB_CTX(sb);
+	ext4_group_t i, ngroups = ext4_get_groups_count(sb);
+
+	ctx->grp_ctx = kcalloc(ngroups, sizeof(struct mb_grp_ctx),
+			       GFP_KERNEL);
+	if (ctx->grp_ctx == NULL)
+		return -ENOMEM;
+
+	for (i = 0; i < ngroups; i++)
+		if (mb_grp_ctx_init(sb, &ctx->grp_ctx[i]))
+			goto out;
+
+	/*
+	 * first data block(first cluster in first group) is used by
+	 * metadata, mark it used to avoid to alloc data block at first
+	 * block which will fail ext4_sb_block_valid check.
+	 */
+	mb_set_bits(ctx->grp_ctx[0].bitmap_bh.b_data, 0, 1);
+
+	return 0;
+out:
+	while (i-- > 0)
+		mb_grp_ctx_release(&ctx->grp_ctx[i]);
+	kfree(ctx->grp_ctx);
+	return -ENOMEM;
+}
+
+static void mb_ctx_release(struct super_block *sb)
+{
+	struct mb_ctx *ctx = MB_CTX(sb);
+	ext4_group_t i, ngroups = ext4_get_groups_count(sb);
+
+	for (i = 0; i < ngroups; i++)
+		mb_grp_ctx_release(&ctx->grp_ctx[i]);
+	kfree(ctx->grp_ctx);
+}
+
+static struct buffer_head *
+ext4_read_block_bitmap_nowait_stub(struct super_block *sb, ext4_group_t block_group,
+				   bool ignore_locked)
+{
+	struct mb_grp_ctx *grp_ctx = MB_GRP_CTX(sb, block_group);
+
+	get_bh(&grp_ctx->bitmap_bh);

I don't know how will you call brelse() for this?
It should be ok anyways since it's not a real buffer_head. But may be it
will be good to add a comment about it.

+	return &grp_ctx->bitmap_bh;
+}
+
+static int ext4_wait_block_bitmap_stub(struct super_block *sb,
+				ext4_group_t block_group,
+				struct buffer_head *bh)
+{
+	return 0;
+}
+
+static struct ext4_group_desc *
+ext4_get_group_desc_stub(struct super_block *sb, ext4_group_t block_group,
+			 struct buffer_head **bh)
+{
+	struct mb_grp_ctx *grp_ctx = MB_GRP_CTX(sb, block_group);
+
+	if (bh != NULL)
+		*bh = &grp_ctx->gd_bh;
+
+	return &grp_ctx->desc;
+}
+
+static int ext4_mb_mark_group_bb_stub(struct ext4_mark_context *mc,
+			       ext4_group_t group, ext4_grpblk_t blkoff,
+			       ext4_grpblk_t len, int flags)
+{
+	struct mb_grp_ctx *grp_ctx = MB_GRP_CTX(mc->sb, group);
+	struct buffer_head *bitmap_bh = &grp_ctx->bitmap_bh;
+
+	if (mc->state)
+		mb_set_bits(bitmap_bh->b_data, blkoff, len);
+	else
+		mb_clear_bits(bitmap_bh->b_data, blkoff, len);
+
+	return 0;
+}
+
+#define TEST_BLOCKSIZE_BITS 10
+#define TEST_CLUSTER_BITS 3
+#define TEST_BLOCKS_PER_GROUP 8192
+#define TEST_GROUP_COUNT 4
+#define TEST_DESC_SIZE 64
+#define TEST_GOAL_GROUP 1

Rather then defining this statically, can we add a test for testing
different options. like for e.g. bs=1k, 4k, and 64k to be tested in a
loop or something with maybe diffrent group_count values to start with? 

At a high level, I went over the code and this looks like a good
first start to me. One suggestion is to prefix the mballoc kunit tests
with some string to differentiate what is kunit related and what is
actual ext4/mballoc calls. Once this kunit test grows, I am sure it will
be difficult to make out the differece between test related APIs and
actual kernel APIs.

maybe something like mbt_

so mb_grp_ctx -> mbt_grp_ctx
mb_ctx -> mbt_ctx
fake_super_block -> mbt_ext4_super_block
alloc/free_fake_super_block -> mbt_ext4_alloc/free_super_block

ext4_block_layout -> mbt_ext4_block_layout

init_sb_layout -> mbt_init_sb_layout

mb_grp_ctx_init/release -> mbt_grp_ctx_init/release
mb_ctx_mark_used -> mbt_ctx_mark_used

mballoc_test_init -> mbt_kunit_init
ext4_mballoc_test_cases -> mbt_test_cases 

funtions with _stub looks ok to me, as we can clearly differentiate them
from actual functions. 


-ritesh