Re: [PATCH U-BOOT 2/3] btrfs: btrfs_file_read: allow opportunistic read until the end

On 2023/4/18 09:17, Dominique Martinet wrote:

From: Dominique Martinet dominique.martinet@atmark-techno.com

btrfs_file_read main 'aligned read' loop would limit the last read to the aligned end even if the data is present in the extent: there is no reason not to read the data that we know will be presented correctly.

If that somehow fails cur only advances up to the aligned_end anyway and the file tail is read through the old code unchanged; this could be required if e.g. the end data is inlined.

Signed-off-by: Dominique Martinet dominique.martinet@atmark-techno.com

fs/btrfs/inode.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 3d6e39e6544d..efffec0f2e68 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -663,7 +663,8 @@ int btrfs_file_read(struct btrfs_root *root, u64 ino, u64 file_offset, u64 len, struct btrfs_path path; struct btrfs_key key; u64 aligned_start = round_down(file_offset, fs_info->sectorsize);

• u64 aligned_end = round_down(file_offset + len, fs_info->sectorsize);

• u64 end = file_offset + len;
• u64 aligned_end = round_down(end, fs_info->sectorsize); u64 next_offset; u64 cur = aligned_start; int ret = 0;

@@ -743,26 +744,26 @@ int btrfs_file_read(struct btrfs_root *root, u64 ino, u64 file_offset, u64 len, extent_num_bytes = btrfs_file_extent_num_bytes(path.nodes[0], fi); ret = btrfs_read_extent_reg(&path, fi, cur,

• 		min(extent_num_bytes, aligned_end - cur),
  

• 		min(extent_num_bytes, end - cur),
  	dest + cur - file_offset);
  

  if (ret < 0) goto out;

• cur += min(extent_num_bytes, aligned_end - cur);
  

• cur += min(extent_num_bytes, end - cur);
  

  }

  /* Read the tailing unaligned part*/

Can we remove this part completely?

IIRC if we read until the target end, the unaligned end part can be completely removed then.

Thanks, Qu

• if (file_offset + len != aligned_end) {

• if (file_offset + len != cur) { btrfs_release_path(&path);

• ret = lookup_data_extent(root, &path, ino, aligned_end,
  

• ret = lookup_data_extent(root, &path, ino, cur,
  		 &next_offset);
  

  /* <0 is error, >0 means no extent */ if (ret) goto out; fi = btrfs_item_ptr(path.nodes[0], path.slots[0], struct btrfs_file_extent_item);

• ret = read_and_truncate_page(&path, fi, aligned_end,
  

• 		file_offset + len - aligned_end,
  

• 		dest + aligned_end - file_offset);
  

• ret = read_and_truncate_page(&path, fi, cur,
  

• 		file_offset + len - cur,
  

• 		dest + cur - file_offset);
  

  } out: btrfs_release_path(&path);