From 1c3dc1731ed2b3757b25533c5245926ffc94f7dc Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Mon, 5 Jul 2021 10:00:58 +0800 Subject: btrfs: rework btrfs_decompress_buf2page() There are several bugs inside the function btrfs_decompress_buf2page() - @start_byte doesn't take bvec.bv_offset into consideration Thus it can't handle case where the target range is not page aligned. - Too many helper variables There are tons of helper variables, @buf_offset, @current_buf_start, @start_byte, @prev_start_byte, @working_bytes, @bytes. This hurts anyone who wants to read the function. - No obvious main cursor for the iteartion A new problem caused by previous problem. - Comments for parameter list makes no sense Like @buf_start is the offset to @buf, or offset inside the full decompressed extent? (Spoiler alert, the later case) And @total_out acts more like @buf_start + @size_of_buf. The worst is @disk_start. The real meaning of it is the file offset of the full decompressed extent. This patch will rework the whole function by: - Add a proper comment with ASCII art to explain the parameter list - Rework parameter list The old @buf_start is renamed to @decompressed, to show how many bytes are already decompressed inside the full decompressed extent. The old @total_out is replaced by @buf_len, which is the decompressed data size. For old @disk_start and @bio, just pass @compressed_bio in. - Use single main cursor The main cursor will be @cur_file_offset, to show what's the current file offset. Other helper variables will be declared inside the main loop, and only minimal amount of helper variables: * offset_inside_decompressed_buf: The only real helper * copy_start_file_offset: File offset we start memcpy * bvec_file_offset: File offset of current bvec Even with all these extensive comments, the final function is still smaller than the original function, which is definitely a win. Signed-off-by: Qu Wenruo Signed-off-by: David Sterba --- fs/btrfs/lzo.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) (limited to 'fs/btrfs/lzo.c') diff --git a/fs/btrfs/lzo.c b/fs/btrfs/lzo.c index 576a0e6142ad..6cab15e52cec 100644 --- a/fs/btrfs/lzo.c +++ b/fs/btrfs/lzo.c @@ -293,8 +293,6 @@ int lzo_decompress_bio(struct list_head *ws, struct compressed_bio *cb) unsigned long tot_len; char *buf; struct page **pages_in = cb->compressed_pages; - u64 disk_start = cb->start; - struct bio *orig_bio = cb->orig_bio; data_in = page_address(pages_in[0]); tot_len = read_compress_length(data_in); @@ -391,14 +389,14 @@ cont: buf_start = tot_out; tot_out += out_len; - ret2 = btrfs_decompress_buf2page(workspace->buf, buf_start, - tot_out, disk_start, orig_bio); + ret2 = btrfs_decompress_buf2page(workspace->buf, out_len, + cb, buf_start); if (ret2 == 0) break; } done: if (!ret) - zero_fill_bio(orig_bio); + zero_fill_bio(cb->orig_bio); return ret; } -- cgit v1.2.3