ext4: allocate entire range in zero range

Currently there is a bug in zero range code which causes zero range
calls to only allocate block aligned portion of the range, while
ignoring the rest in some cases.

In some cases, namely if the end of the range is past i_size, we do
attempt to preallocate the last nonaligned block. However this might
cause kernel to BUG() in some carefully designed zero range requests
on setups where page size > block size.

Fix this problem by first preallocating the entire range, including
the nonaligned edges and converting the written extents to unwritten
in the next step. This approach will also give us the advantage of
having the range to be as linearly contiguous as possible.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode,
			struct ext4_map_blocks *map,
			struct ext4_ext_path **ppath, int flags,
			unsigned int allocated, ext4_fsblk_t newblock)
{
	struct ext4_ext_path *path = *ppath;
	int ret = 0;
	int err = 0;
	ext4_io_end_t *io = ext4_inode_aio(inode);

	ext_debug("ext4_ext_handle_unwritten_extents: inode %lu, logical "
		  "block %llu, max_blocks %u, flags %x, allocated %u\n",
		  inode->i_ino, (unsigned long long)map->m_lblk, map->m_len,
		  flags, allocated);
	ext4_ext_show_leaf(inode, path);

	/*
	 * When writing into unwritten space, we should not fail to
	 * allocate metadata blocks for the new extent block if needed.
	 */
	flags |= EXT4_GET_BLOCKS_METADATA_NOFAIL;

	trace_ext4_ext_handle_unwritten_extents(inode, map, flags,
						    allocated, newblock);

	/* get_block() before submit the IO, split the extent */
	if (flags & EXT4_GET_BLOCKS_PRE_IO) {
		ret = ext4_split_convert_extents(handle, inode, map, ppath,
					 flags | EXT4_GET_BLOCKS_CONVERT);
		if (ret <= 0)
			goto out;
		/*
		 * Flag the inode(non aio case) or end_io struct (aio case)
		 * that this IO needs to conversion to written when IO is
		 * completed
		 */
		if (io)
			ext4_set_io_unwritten_flag(inode, io);
		else
			ext4_set_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
		map->m_flags |= EXT4_MAP_UNWRITTEN;
		goto out;
	}
	/* IO end_io complete, convert the filled extent to written */
	if (flags & EXT4_GET_BLOCKS_CONVERT) {
		ret = ext4_convert_unwritten_extents_endio(handle, inode, map,
							   ppath);
		if (ret >= 0) {
			ext4_update_inode_fsync_trans(handle, inode, 1);
			err = check_eofblocks_fl(handle, inode, map->m_lblk,
						 path, map->m_len);
		} else
			err = ret;
		map->m_flags |= EXT4_MAP_MAPPED;
		map->m_pblk = newblock;
		if (allocated > map->m_len)
			allocated = map->m_len;
		map->m_len = allocated;
		goto out2;
	}
	/* buffered IO case */
	/*
	 * repeat fallocate creation request
	 * we already have an unwritten extent
	 */
	if (flags & EXT4_GET_BLOCKS_UNWRIT_EXT) {
		map->m_flags |= EXT4_MAP_UNWRITTEN;
		goto map_out;
	}

	/* buffered READ or buffered write_begin() lookup */
	if ((flags & EXT4_GET_BLOCKS_CREATE) == 0) {
		/*
		 * We have blocks reserved already.  We
		 * return allocated blocks so that delalloc
		 * won't do block reservation for us.  But
		 * the buffer head will be unmapped so that
		 * a read from the block returns 0s.
		 */
		map->m_flags |= EXT4_MAP_UNWRITTEN;
		goto out1;
	}

	/* buffered write, writepage time, convert*/
	ret = ext4_ext_convert_to_initialized(handle, inode, map, ppath, flags);
	if (ret >= 0)
		ext4_update_inode_fsync_trans(handle, inode, 1);
out:
	if (ret <= 0) {
		err = ret;
		goto out2;
	} else
		allocated = ret;
	map->m_flags |= EXT4_MAP_NEW;
	/*
	 * if we allocated more blocks than requested
	 * we need to make sure we unmap the extra block
	 * allocated. The actual needed block will get
	 * unmapped later when we find the buffer_head marked
	 * new.
	 */
	if (allocated > map->m_len) {
		unmap_underlying_metadata_blocks(inode->i_sb->s_bdev,
					newblock + map->m_len,
					allocated - map->m_len);
		allocated = map->m_len;
	}
	map->m_len = allocated;

	/*
	 * If we have done fallocate with the offset that is already
	 * delayed allocated, we would have block reservation
	 * and quota reservation done in the delayed write path.
	 * But fallocate would have already updated quota and block
	 * count for this offset. So cancel these reservation
	 */
	if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE) {
		unsigned int reserved_clusters;
		reserved_clusters = get_reserved_cluster_alloc(inode,
				map->m_lblk, map->m_len);
		if (reserved_clusters)
			ext4_da_update_reserve_space(inode,
						     reserved_clusters,
						     0);
	}

map_out:
	map->m_flags |= EXT4_MAP_MAPPED;
	if ((flags & EXT4_GET_BLOCKS_KEEP_SIZE) == 0) {
		err = check_eofblocks_fl(handle, inode, map->m_lblk, path,
					 map->m_len);
		if (err < 0)
			goto out2;
	}
out1:
	if (allocated > map->m_len)
		allocated = map->m_len;
	ext4_ext_show_leaf(inode, path);
	map->m_pblk = newblock;
	map->m_len = allocated;
out2:
	return err ? err : allocated;
}

ext4_ext_handle_unwritten_extents(handle_t *handle, struct inode *inode,
			struct ext4_map_blocks *map,
			struct ext4_ext_path **ppath, int flags,
			unsigned int allocated, ext4_fsblk_t newblock)
{
	struct ext4_ext_path *path = *ppath;
	int ret = 0;
	int err = 0;
	ext4_io_end_t *io = ext4_inode_aio(inode);

	ext_debug("ext4_ext_handle_unwritten_extents: inode %lu, logical "
		  "block %llu, max_blocks %u, flags %x, allocated %u\n",
		  inode->i_ino, (unsigned long long)map->m_lblk, map->m_len,
		  flags, allocated);
	ext4_ext_show_leaf(inode, path);

	/*
	 * When writing into unwritten space, we should not fail to
	 * allocate metadata blocks for the new extent block if needed.
	 */
	flags |= EXT4_GET_BLOCKS_METADATA_NOFAIL;

	trace_ext4_ext_handle_unwritten_extents(inode, map, flags,
						    allocated, newblock);

	/* get_block() before submit the IO, split the extent */
	if (flags & EXT4_GET_BLOCKS_PRE_IO) {
		ret = ext4_split_convert_extents(handle, inode, map, ppath,
					 flags | EXT4_GET_BLOCKS_CONVERT);
		if (ret <= 0)
			goto out;
		/*
		 * Flag the inode(non aio case) or end_io struct (aio case)
		 * that this IO needs to conversion to written when IO is
		 * completed
		 */
		if (io)
			ext4_set_io_unwritten_flag(inode, io);
		else
			ext4_set_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
		map->m_flags |= EXT4_MAP_UNWRITTEN;
		goto out;
	}
	/* IO end_io complete, convert the filled extent to written */
	if (flags & EXT4_GET_BLOCKS_CONVERT) {
		ret = ext4_convert_unwritten_extents_endio(handle, inode, map,
							   ppath);
		if (ret >= 0) {
			ext4_update_inode_fsync_trans(handle, inode, 1);
			err = check_eofblocks_fl(handle, inode, map->m_lblk,
						 path, map->m_len);
		} else
			err = ret;
		map->m_flags |= EXT4_MAP_MAPPED;
		map->m_pblk = newblock;
		if (allocated > map->m_len)
			allocated = map->m_len;
		map->m_len = allocated;
		goto out2;
	}
	/* buffered IO case */
	/*
	 * repeat fallocate creation request
	 * we already have an unwritten extent
	 */
	if (flags & EXT4_GET_BLOCKS_UNWRIT_EXT) {
		map->m_flags |= EXT4_MAP_UNWRITTEN;
		goto map_out;
	}

	/* buffered READ or buffered write_begin() lookup */
	if ((flags & EXT4_GET_BLOCKS_CREATE) == 0) {
		/*
		 * We have blocks reserved already.  We
		 * return allocated blocks so that delalloc
		 * won't do block reservation for us.  But
		 * the buffer head will be unmapped so that
		 * a read from the block returns 0s.
		 */
		map->m_flags |= EXT4_MAP_UNWRITTEN;
		goto out1;
	}

	/* buffered write, writepage time, convert*/
	ret = ext4_ext_convert_to_initialized(handle, inode, map, ppath, flags);
	if (ret >= 0)
		ext4_update_inode_fsync_trans(handle, inode, 1);
out:
	if (ret <= 0) {
		err = ret;
		goto out2;
	} else
		allocated = ret;
	map->m_flags |= EXT4_MAP_NEW;
	/*
	 * if we allocated more blocks than requested
	 * we need to make sure we unmap the extra block
	 * allocated. The actual needed block will get
	 * unmapped later when we find the buffer_head marked
	 * new.
	 */
	if (allocated > map->m_len) {
		unmap_underlying_metadata_blocks(inode->i_sb->s_bdev,
					newblock + map->m_len,
					allocated - map->m_len);
		allocated = map->m_len;
	}
	map->m_len = allocated;

	/*
	 * If we have done fallocate with the offset that is already
	 * delayed allocated, we would have block reservation
	 * and quota reservation done in the delayed write path.
	 * But fallocate would have already updated quota and block
	 * count for this offset. So cancel these reservation
	 */
	if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE) {
		unsigned int reserved_clusters;
		reserved_clusters = get_reserved_cluster_alloc(inode,
				map->m_lblk, map->m_len);
		if (reserved_clusters)
			ext4_da_update_reserve_space(inode,
						     reserved_clusters,
						     0);
	}

map_out:
	map->m_flags |= EXT4_MAP_MAPPED;
	if ((flags & EXT4_GET_BLOCKS_KEEP_SIZE) == 0) {
		err = check_eofblocks_fl(handle, inode, map->m_lblk, path,
					 map->m_len);
		if (err < 0)
			goto out2;
	}
out1:
	if (allocated > map->m_len)
		allocated = map->m_len;
	ext4_ext_show_leaf(inode, path);
	map->m_pblk = newblock;
	map->m_len = allocated;
out2:
	return err ? err : allocated;
}
