Re: [PATCH 13/17] btrfs: extent_io: only require sector size alignment for page read

Nikolay Borisov
2020-09-11T15:46:34Z

On 8.09.20 г. 10:52 ч., Qu Wenruo wrote:
> If we're reading partial page, btrfs will warn about this as our
> read/write are always done in sector size, which equals page size.
>
> But for the incoming subpage RO support, our data read is only aligned
> to sectorsize, which can be smaller than page size.
>
> Thus here we change the warning condition to check it against
> sectorsize, thus the behavior is not changed for regular sectorsize ==
> PAGE_SIZE case, while won't report error for subpage read.
>
> Also, pass the proper start/end with bv_offset for check_data_csum() to
> handle.
>
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
> fs/btrfs/extent_io.c | 19 ++++++++++++-------
> 1 file changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index 81e43d99feda..a83b63ecc5f8 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -2819,6 +2819,7 @@ static void end_bio_extent_readpage(struct bio *bio)
> struct page *page = bvec->bv_page;
> struct inode *inode = page->mapping->host;
> struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> + u32 sectorsize = fs_info->sectorsize;
> bool data_inode = btrfs_ino(BTRFS_I(inode))
> != BTRFS_BTREE_INODE_OBJECTID;
>
> @@ -2829,13 +2830,17 @@ static void end_bio_extent_readpage(struct bio *bio)
> tree = &BTRFS_I(inode)->io_tree;
> failure_tree = &BTRFS_I(inode)->io_failure_tree;
>
> - /* We always issue full-page reads, but if some block
> + /*
> + * We always issue full-sector reads, but if some block
> * in a page fails to read, blk_update_request() will
> * advance bv_offset and adjust bv_len to compensate.
> - * Print a warning for nonzero offsets, and an error
> - * if they don't add up to a full page. */
> - if (bvec->bv_offset || bvec->bv_len != PAGE_SIZE) {
> - if (bvec->bv_offset + bvec->bv_len != PAGE_SIZE)
> + * Print a warning for unaligned offsets, and an error
> + * if they don't add up to a full sector.
> + */
> + if (!IS_ALIGNED(bvec->bv_offset, sectorsize) ||
> + !IS_ALIGNED(bvec->bv_offset + bvec->bv_len, sectorsize)) {
> + if (!IS_ALIGNED(bvec->bv_offset + bvec->bv_len,
> + sectorsize))

Duplicated check ...

> btrfs_err(fs_info,
> "partial page read in btrfs with offset %u and length %u",
> bvec->bv_offset, bvec->bv_len);
> @@ -2845,8 +2850,8 @@ static void end_bio_extent_readpage(struct bio *bio)
> bvec->bv_offset, bvec->bv_len);
> }
>
> - start = page_offset(page);
> - end = start + bvec->bv_offset + bvec->bv_len - 1;
> + start = page_offset(page) + bvec->bv_offset;
> + end = start + bvec->bv_len - 1;

nit: 'start' and 'end' must really be renamed - to file_offset and
file_end because they represent values in the logical namespace of the
file. And given the context they are used i.e endio handler where we
also deal with extent starts and physical offsets such a rename is long
over due. Perhaps you can create a separate patch when you are
resending the series alternatively I'll make a sweep across those
low-level functions to clean that up.

> len = bvec->bv_len;
>
> mirror = io_bio->mirror_num;
>