ext4: use ext4_get_block_write in buffer write

Allocate uninitialized extent before ext4 buffer write and
convert the extent to initialized after io completes.
The purpose is to make sure an extent can only be marked
initialized after it has been written with new data so
we can safely drop the i_mutex lock in ext4 DIO read without
exposing stale data. This helps to improve multi-thread DIO
read performance on high-speed disks.

Skip the nobh and data=journal mount cases to make things simple for now.

Signed-off-by: Jiaying Zhang <jiayingz@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
		struct ext4_ext_path *path, ext4_lblk_t start)
{
	int err = 0, correct_index = 0;
	int depth = ext_depth(inode), credits;
	struct ext4_extent_header *eh;
	ext4_lblk_t a, b, block;
	unsigned num;
	ext4_lblk_t ex_ee_block;
	unsigned short ex_ee_len;
	unsigned uninitialized = 0;
	struct ext4_extent *ex;

	/* the header must be checked already in ext4_ext_remove_space() */
	ext_debug("truncate since %u in leaf\n", start);
	if (!path[depth].p_hdr)
		path[depth].p_hdr = ext_block_hdr(path[depth].p_bh);
	eh = path[depth].p_hdr;
	BUG_ON(eh == NULL);

	/* find where to start removing */
	ex = EXT_LAST_EXTENT(eh);

	ex_ee_block = le32_to_cpu(ex->ee_block);
	ex_ee_len = ext4_ext_get_actual_len(ex);

	while (ex >= EXT_FIRST_EXTENT(eh) &&
			ex_ee_block + ex_ee_len > start) {

		if (ext4_ext_is_uninitialized(ex))
			uninitialized = 1;
		else
			uninitialized = 0;

		ext_debug("remove ext %u:[%d]%d\n", ex_ee_block,
			 uninitialized, ex_ee_len);
		path[depth].p_ext = ex;

		a = ex_ee_block > start ? ex_ee_block : start;
		b = ex_ee_block + ex_ee_len - 1 < EXT_MAX_BLOCK ?
			ex_ee_block + ex_ee_len - 1 : EXT_MAX_BLOCK;

		ext_debug("  border %u:%u\n", a, b);

		if (a != ex_ee_block && b != ex_ee_block + ex_ee_len - 1) {
			block = 0;
			num = 0;
			BUG();
		} else if (a != ex_ee_block) {
			/* remove tail of the extent */
			block = ex_ee_block;
			num = a - block;
		} else if (b != ex_ee_block + ex_ee_len - 1) {
			/* remove head of the extent */
			block = a;
			num = b - a;
			/* there is no "make a hole" API yet */
			BUG();
		} else {
			/* remove whole extent: excellent! */
			block = ex_ee_block;
			num = 0;
			BUG_ON(a != ex_ee_block);
			BUG_ON(b != ex_ee_block + ex_ee_len - 1);
		}

		/*
		 * 3 for leaf, sb, and inode plus 2 (bmap and group
		 * descriptor) for each block group; assume two block
		 * groups plus ex_ee_len/blocks_per_block_group for
		 * the worst case
		 */
		credits = 7 + 2*(ex_ee_len/EXT4_BLOCKS_PER_GROUP(inode->i_sb));
		if (ex == EXT_FIRST_EXTENT(eh)) {
			correct_index = 1;
			credits += (ext_depth(inode)) + 1;
		}
		credits += EXT4_MAXQUOTAS_TRANS_BLOCKS(inode->i_sb);

		err = ext4_ext_truncate_extend_restart(handle, inode, credits);
		if (err)
			goto out;

		err = ext4_ext_get_access(handle, inode, path + depth);
		if (err)
			goto out;

		err = ext4_remove_blocks(handle, inode, ex, a, b);
		if (err)
			goto out;

		if (num == 0) {
			/* this extent is removed; mark slot entirely unused */
			ext4_ext_store_pblock(ex, 0);
			le16_add_cpu(&eh->eh_entries, -1);
		}

		ex->ee_block = cpu_to_le32(block);
		ex->ee_len = cpu_to_le16(num);
		/*
		 * Do not mark uninitialized if all the blocks in the
		 * extent have been removed.
		 */
		if (uninitialized && num)
			ext4_ext_mark_uninitialized(ex);

		err = ext4_ext_dirty(handle, inode, path + depth);
		if (err)
			goto out;

		ext_debug("new extent: %u:%u:%llu\n", block, num,
				ext_pblock(ex));
		ex--;
		ex_ee_block = le32_to_cpu(ex->ee_block);
		ex_ee_len = ext4_ext_get_actual_len(ex);
	}

	if (correct_index && eh->eh_entries)
		err = ext4_ext_correct_indexes(handle, inode, path);

	/* if this leaf is free, then we should
	 * remove it from index block above */
	if (err == 0 && eh->eh_entries == 0 && path[depth].p_bh != NULL)
		err = ext4_ext_rm_idx(handle, inode, path + depth);

out:
	return err;
}

ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
		struct ext4_ext_path *path, ext4_lblk_t start)
{
	int err = 0, correct_index = 0;
	int depth = ext_depth(inode), credits;
	struct ext4_extent_header *eh;
	ext4_lblk_t a, b, block;
	unsigned num;
	ext4_lblk_t ex_ee_block;
	unsigned short ex_ee_len;
	unsigned uninitialized = 0;
	struct ext4_extent *ex;

	/* the header must be checked already in ext4_ext_remove_space() */
	ext_debug("truncate since %u in leaf\n", start);
	if (!path[depth].p_hdr)
		path[depth].p_hdr = ext_block_hdr(path[depth].p_bh);
	eh = path[depth].p_hdr;
	BUG_ON(eh == NULL);

	/* find where to start removing */
	ex = EXT_LAST_EXTENT(eh);

	ex_ee_block = le32_to_cpu(ex->ee_block);
	ex_ee_len = ext4_ext_get_actual_len(ex);

	while (ex >= EXT_FIRST_EXTENT(eh) &&
			ex_ee_block + ex_ee_len > start) {

		if (ext4_ext_is_uninitialized(ex))
			uninitialized = 1;
		else
			uninitialized = 0;

		ext_debug("remove ext %u:[%d]%d\n", ex_ee_block,
			 uninitialized, ex_ee_len);
		path[depth].p_ext = ex;

		a = ex_ee_block > start ? ex_ee_block : start;
		b = ex_ee_block + ex_ee_len - 1 < EXT_MAX_BLOCK ?
			ex_ee_block + ex_ee_len - 1 : EXT_MAX_BLOCK;

		ext_debug("  border %u:%u\n", a, b);

		if (a != ex_ee_block && b != ex_ee_block + ex_ee_len - 1) {
			block = 0;
			num = 0;
			BUG();
		} else if (a != ex_ee_block) {
			/* remove tail of the extent */
			block = ex_ee_block;
			num = a - block;
		} else if (b != ex_ee_block + ex_ee_len - 1) {
			/* remove head of the extent */
			block = a;
			num = b - a;
			/* there is no "make a hole" API yet */
			BUG();
		} else {
			/* remove whole extent: excellent! */
			block = ex_ee_block;
			num = 0;
			BUG_ON(a != ex_ee_block);
			BUG_ON(b != ex_ee_block + ex_ee_len - 1);
		}

		/*
		 * 3 for leaf, sb, and inode plus 2 (bmap and group
		 * descriptor) for each block group; assume two block
		 * groups plus ex_ee_len/blocks_per_block_group for
		 * the worst case
		 */
		credits = 7 + 2*(ex_ee_len/EXT4_BLOCKS_PER_GROUP(inode->i_sb));
		if (ex == EXT_FIRST_EXTENT(eh)) {
			correct_index = 1;
			credits += (ext_depth(inode)) + 1;
		}
		credits += EXT4_MAXQUOTAS_TRANS_BLOCKS(inode->i_sb);

		err = ext4_ext_truncate_extend_restart(handle, inode, credits);
		if (err)
			goto out;

		err = ext4_ext_get_access(handle, inode, path + depth);
		if (err)
			goto out;

		err = ext4_remove_blocks(handle, inode, ex, a, b);
		if (err)
			goto out;

		if (num == 0) {
			/* this extent is removed; mark slot entirely unused */
			ext4_ext_store_pblock(ex, 0);
			le16_add_cpu(&eh->eh_entries, -1);
		}

		ex->ee_block = cpu_to_le32(block);
		ex->ee_len = cpu_to_le16(num);
		/*
		 * Do not mark uninitialized if all the blocks in the
		 * extent have been removed.
		 */
		if (uninitialized && num)
			ext4_ext_mark_uninitialized(ex);

		err = ext4_ext_dirty(handle, inode, path + depth);
		if (err)
			goto out;

		ext_debug("new extent: %u:%u:%llu\n", block, num,
				ext_pblock(ex));
		ex--;
		ex_ee_block = le32_to_cpu(ex->ee_block);
		ex_ee_len = ext4_ext_get_actual_len(ex);
	}

	if (correct_index && eh->eh_entries)
		err = ext4_ext_correct_indexes(handle, inode, path);

	/* if this leaf is free, then we should
	 * remove it from index block above */
	if (err == 0 && eh->eh_entries == 0 && path[depth].p_bh != NULL)
		err = ext4_ext_rm_idx(handle, inode, path + depth);

out:
	return err;
}
