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Message-ID: <CAPjX3FfMaOWtCZ8mjVTbBQ9yt0O-mAistyDsVq7Q1aR-65R_hA@mail.gmail.com>
Date: Thu, 13 Nov 2025 20:07:50 +0100
From: Daniel Vacek <neelx@...e.com>
To: Qu Wenruo <wqu@...e.com>
Cc: Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>,
linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 3/8] btrfs: add a bio argument to btrfs_csum_one_bio
On Wed, 12 Nov 2025 at 22:02, Qu Wenruo <wqu@...e.com> wrote:
> 在 2025/11/13 06:06, Daniel Vacek 写道:
> > From: Josef Bacik <josef@...icpanda.com>
> >
> > We only ever needed the bbio in btrfs_csum_one_bio, since that has the
> > bio embedded in it. However with encryption we'll have a different bio
> > with the encrypted data in it, and the original bbio. Update
> > btrfs_csum_one_bio to take the bio we're going to csum as an argument,
> > which will allow us to csum the encrypted bio and stuff the csums into
> > the corresponding bbio to be used later when the IO completes.
>
> I'm wondering why we can not do it in a layered bio way.
>
> E.g. on device-mapper based solutions, the upper layer send out the bio
> containing the plaintext data.
> Then the dm-crypto send out a new bio, containing the encrypted data.
This is similar but fscrypt works on FS level. It gets the original
plaintext bio (the btrfs_bio::bio one) and gives us a callback with
the encrypted bio to calculate the checksum of the encrypted data. No
plaintext bio goes to the storage layer.
--nX
> The storage layer doesn't need to bother the plaintext bio at all, they
> just write the encrypted one to disk.
>
> And it's the dm-crypto tracking the plaintext bio <-> encrypted bio mapping.
>
>
> So why we can not just create a new bio for the final csum caculation,
> just like compression?
>
> Thanks,
> Qu
>
> >
> > Signed-off-by: Josef Bacik <josef@...icpanda.com>
> > Signed-off-by: Daniel Vacek <neelx@...e.com>
> > ---
> > Compared to v5 this needed to adapt to recent async csum changes.
> > ---
> > fs/btrfs/bio.c | 4 ++--
> > fs/btrfs/bio.h | 1 +
> > fs/btrfs/file-item.c | 17 ++++++++---------
> > fs/btrfs/file-item.h | 2 +-
> > 4 files changed, 12 insertions(+), 12 deletions(-)
> >
> > diff --git a/fs/btrfs/bio.c b/fs/btrfs/bio.c
> > index a73652b8724a..a69174b2b6b6 100644
> > --- a/fs/btrfs/bio.c
> > +++ b/fs/btrfs/bio.c
> > @@ -542,9 +542,9 @@ static int btrfs_bio_csum(struct btrfs_bio *bbio)
> > if (bbio->bio.bi_opf & REQ_META)
> > return btree_csum_one_bio(bbio);
> > #ifdef CONFIG_BTRFS_EXPERIMENTAL
> > - return btrfs_csum_one_bio(bbio, true);
> > + return btrfs_csum_one_bio(bbio, &bbio->bio, true);
> > #else
> > - return btrfs_csum_one_bio(bbio, false);
> > + return btrfs_csum_one_bio(bbio, &bbio->bio, false);
> > #endif
> > }
> >
> > diff --git a/fs/btrfs/bio.h b/fs/btrfs/bio.h
> > index deaeea3becf4..c5a6c66d51a0 100644
> > --- a/fs/btrfs/bio.h
> > +++ b/fs/btrfs/bio.h
> > @@ -58,6 +58,7 @@ struct btrfs_bio {
> > struct btrfs_ordered_sum *sums;
> > struct work_struct csum_work;
> > struct completion csum_done;
> > + struct bio *csum_bio;
> > struct bvec_iter csum_saved_iter;
> > u64 orig_physical;
> > };
> > diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
> > index 72be3ede0edf..474949074da8 100644
> > --- a/fs/btrfs/file-item.c
> > +++ b/fs/btrfs/file-item.c
> > @@ -765,21 +765,19 @@ int btrfs_lookup_csums_bitmap(struct btrfs_root *root, struct btrfs_path *path,
> > return ret;
> > }
> >
> > -static void csum_one_bio(struct btrfs_bio *bbio, struct bvec_iter *src)
> > +static void csum_one_bio(struct btrfs_bio *bbio, struct bio *bio, struct bvec_iter *iter)
> > {
> > struct btrfs_inode *inode = bbio->inode;
> > struct btrfs_fs_info *fs_info = inode->root->fs_info;
> > SHASH_DESC_ON_STACK(shash, fs_info->csum_shash);
> > - struct bio *bio = &bbio->bio;
> > struct btrfs_ordered_sum *sums = bbio->sums;
> > - struct bvec_iter iter = *src;
> > phys_addr_t paddr;
> > const u32 blocksize = fs_info->sectorsize;
> > int index = 0;
> >
> > shash->tfm = fs_info->csum_shash;
> >
> > - btrfs_bio_for_each_block(paddr, bio, &iter, blocksize) {
> > + btrfs_bio_for_each_block(paddr, bio, iter, blocksize) {
> > btrfs_calculate_block_csum(fs_info, paddr, sums->sums + index);
> > index += fs_info->csum_size;
> > }
> > @@ -791,19 +789,18 @@ static void csum_one_bio_work(struct work_struct *work)
> >
> > ASSERT(btrfs_op(&bbio->bio) == BTRFS_MAP_WRITE);
> > ASSERT(bbio->async_csum == true);
> > - csum_one_bio(bbio, &bbio->csum_saved_iter);
> > + csum_one_bio(bbio, bbio->csum_bio, &bbio->csum_saved_iter);
> > complete(&bbio->csum_done);
> > }
> >
> > /*
> > * Calculate checksums of the data contained inside a bio.
> > */
> > -int btrfs_csum_one_bio(struct btrfs_bio *bbio, bool async)
> > +int btrfs_csum_one_bio(struct btrfs_bio *bbio, struct bio *bio, bool async)
> > {
> > struct btrfs_ordered_extent *ordered = bbio->ordered;
> > struct btrfs_inode *inode = bbio->inode;
> > struct btrfs_fs_info *fs_info = inode->root->fs_info;
> > - struct bio *bio = &bbio->bio;
> > struct btrfs_ordered_sum *sums;
> > unsigned nofs_flag;
> >
> > @@ -822,12 +819,14 @@ int btrfs_csum_one_bio(struct btrfs_bio *bbio, bool async)
> > btrfs_add_ordered_sum(ordered, sums);
> >
> > if (!async) {
> > - csum_one_bio(bbio, &bbio->bio.bi_iter);
> > + struct bvec_iter iter = bio->bi_iter;
> > + csum_one_bio(bbio, bio, &iter);
> > return 0;
> > }
> > init_completion(&bbio->csum_done);
> > bbio->async_csum = true;
> > - bbio->csum_saved_iter = bbio->bio.bi_iter;
> > + bbio->csum_bio = bio;
> > + bbio->csum_saved_iter = bio->bi_iter;
> > INIT_WORK(&bbio->csum_work, csum_one_bio_work);
> > schedule_work(&bbio->csum_work);
> > return 0;
> > diff --git a/fs/btrfs/file-item.h b/fs/btrfs/file-item.h
> > index 5645c5e3abdb..d16fd2144552 100644
> > --- a/fs/btrfs/file-item.h
> > +++ b/fs/btrfs/file-item.h
> > @@ -64,7 +64,7 @@ int btrfs_lookup_file_extent(struct btrfs_trans_handle *trans,
> > int btrfs_csum_file_blocks(struct btrfs_trans_handle *trans,
> > struct btrfs_root *root,
> > struct btrfs_ordered_sum *sums);
> > -int btrfs_csum_one_bio(struct btrfs_bio *bbio, bool async);
> > +int btrfs_csum_one_bio(struct btrfs_bio *bbio, struct bio *bio, bool async);
> > int btrfs_alloc_dummy_sum(struct btrfs_bio *bbio);
> > int btrfs_lookup_csums_range(struct btrfs_root *root, u64 start, u64 end,
> > struct list_head *list, int search_commit,
>
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