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Wong" , Joanne Koong , linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-block@vger.kernel.org, gfs2@lists.linux.dev Subject: Re: [PATCH 11/12] iomap: add read_folio_range() handler for buffered writes Message-ID: References: <20250627070328.975394-1-hch@lst.de> <20250627070328.975394-12-hch@lst.de> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250627070328.975394-12-hch@lst.de> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 On Fri, Jun 27, 2025 at 09:02:44AM +0200, Christoph Hellwig wrote: > From: Joanne Koong > > Add a read_folio_range() handler for buffered writes that filesystems > may pass in if they wish to provide a custom handler for synchronously > reading in the contents of a folio. > > Signed-off-by: Joanne Koong > [hch: renamed to read_folio_range, pass less arguments] > Signed-off-by: Christoph Hellwig > --- > .../filesystems/iomap/operations.rst | 6 +++++ > fs/iomap/buffered-io.c | 25 +++++++++++-------- > include/linux/iomap.h | 10 ++++++++ > 3 files changed, 31 insertions(+), 10 deletions(-) > > diff --git a/Documentation/filesystems/iomap/operations.rst b/Documentation/filesystems/iomap/operations.rst > index 167d3ca7819c..04432f40e7a2 100644 > --- a/Documentation/filesystems/iomap/operations.rst > +++ b/Documentation/filesystems/iomap/operations.rst > @@ -68,6 +68,8 @@ The following address space operations can be wrapped easily: > void (*put_folio)(struct inode *inode, loff_t pos, unsigned copied, > struct folio *folio); > bool (*iomap_valid)(struct inode *inode, const struct iomap *iomap); > + int (*read_folio_range)(const struct iomap_iter *iter, > + struct folio *folio, loff_t pos, size_t len); Whitespace ^ > }; > > iomap calls these functions: ... > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > index a77686977a2e..1a9ade77aeeb 100644 > --- a/fs/iomap/buffered-io.c > +++ b/fs/iomap/buffered-io.c > @@ -667,22 +667,23 @@ iomap_write_failed(struct inode *inode, loff_t pos, unsigned len) > pos + len - 1); > } > > -static int iomap_read_folio_sync(loff_t block_start, struct folio *folio, > - size_t poff, size_t plen, const struct iomap *iomap) > +static int iomap_read_folio_range(const struct iomap_iter *iter, > + struct folio *folio, loff_t pos, size_t len) > { > + const struct iomap *srcmap = iomap_iter_srcmap(iter); > struct bio_vec bvec; > struct bio bio; > > - bio_init(&bio, iomap->bdev, &bvec, 1, REQ_OP_READ); > - bio.bi_iter.bi_sector = iomap_sector(iomap, block_start); > - bio_add_folio_nofail(&bio, folio, plen, poff); > + bio_init(&bio, srcmap->bdev, &bvec, 1, REQ_OP_READ); > + bio.bi_iter.bi_sector = iomap_sector(srcmap, pos); > + bio_add_folio_nofail(&bio, folio, len, offset_in_folio(folio, pos)); > return submit_bio_wait(&bio); > } Hmm, so this kind of makes my brain hurt... pos here is now the old block_start and len is the old plen. We used to pass poff to the add_folio_nofail() call, and now that is dropped and instead we use offset_in_folio(..., pos). The old poff is an output of the previous iomap_adjust_read_range() call, which is initially set to offset_in_folio(folio, *pos), of which *pos is block_start and is bumped in that function in the same places that poff is. Therefore old poff and new offset_in_folio(folio, pos) are logically equivalent. Am I following that correctly? Brian > > -static int __iomap_write_begin(const struct iomap_iter *iter, size_t len, > +static int __iomap_write_begin(const struct iomap_iter *iter, > + const struct iomap_write_ops *write_ops, size_t len, > struct folio *folio) > { > - const struct iomap *srcmap = iomap_iter_srcmap(iter); > struct iomap_folio_state *ifs; > loff_t pos = iter->pos; > loff_t block_size = i_blocksize(iter->inode); > @@ -731,8 +732,12 @@ static int __iomap_write_begin(const struct iomap_iter *iter, size_t len, > if (iter->flags & IOMAP_NOWAIT) > return -EAGAIN; > > - status = iomap_read_folio_sync(block_start, folio, > - poff, plen, srcmap); > + if (write_ops && write_ops->read_folio_range) > + status = write_ops->read_folio_range(iter, > + folio, block_start, plen); > + else > + status = iomap_read_folio_range(iter, > + folio, block_start, plen); > if (status) > return status; > } > @@ -848,7 +853,7 @@ static int iomap_write_begin(struct iomap_iter *iter, > else if (srcmap->flags & IOMAP_F_BUFFER_HEAD) > status = __block_write_begin_int(folio, pos, len, NULL, srcmap); > else > - status = __iomap_write_begin(iter, len, folio); > + status = __iomap_write_begin(iter, write_ops, len, folio); > > if (unlikely(status)) > goto out_unlock; > diff --git a/include/linux/iomap.h b/include/linux/iomap.h > index 482787013ff7..b3588dd43105 100644 > --- a/include/linux/iomap.h > +++ b/include/linux/iomap.h > @@ -166,6 +166,16 @@ struct iomap_write_ops { > * locked by the iomap code. > */ > bool (*iomap_valid)(struct inode *inode, const struct iomap *iomap); > + > + /* > + * Optional if the filesystem wishes to provide a custom handler for > + * reading in the contents of a folio, otherwise iomap will default to > + * submitting a bio read request. > + * > + * The read must be done synchronously. > + */ > + int (*read_folio_range)(const struct iomap_iter *iter, > + struct folio *folio, loff_t pos, size_t len); > }; > > /* > -- > 2.47.2 > >