[PATCH] fuse: honor desc offset in readahead reads

[PATCH] fuse: honor desc offset in readahead reads

[Haofeng Li]

fuse_handle_readahead records non-zero descs[].offset when
iomap skips leading uptodate blocks in a folio, but
fuse_send_readpages built FUSE_READ from folio_pos() alone.
The reply was still copied at descs[0].offset, so wrong
file data was placed into the page cache.

Add descs[0].offset to the request position. Apply the
same correction in fuse_short_read for EOF size updates.

Fixes: 4ea907108a5c ("fuse: use iomap for readahead")
Signed-off-by: Haofeng Li <lihaofeng@kylinos.cn>
---
 fs/fuse/file.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index ceada75310b8..11272983c991 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -836,7 +836,8 @@ static void fuse_short_read(struct inode *inode, u64 attr_ver, size_t num_read,
 	 * reached the client fs yet.  So the hole is not present there.
 	 */
 	if (!fc->writeback_cache) {
-		loff_t pos = folio_pos(ap->folios[0]) + num_read;
+		loff_t pos = folio_pos(ap->folios[0]) +
+			     ap->descs[0].offset + num_read;
 		fuse_read_update_size(inode, pos, attr_ver);
 	}
 }
@@ -1057,7 +1058,8 @@ static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file,
 	struct fuse_file *ff = file->private_data;
 	struct fuse_mount *fm = ff->fm;
 	struct fuse_args_pages *ap = &ia->ap;
-	loff_t pos = folio_pos(ap->folios[0]);
+	loff_t pos = folio_pos(ap->folios[0]) +
+		     ap->descs[0].offset;
 	ssize_t res;
 	int err;
 
-- 
2.25.1

Re: [PATCH] fuse: honor desc offset in readahead reads

[Joanne Koong]

On Thu, Jul 16, 2026 at 2:41 AM Haofeng Li <lihaofeng@kylinos.cn> wrote:
>
> fuse_handle_readahead records non-zero descs[].offset when
> iomap skips leading uptodate blocks in a folio, but
> fuse_send_readpages built FUSE_READ from folio_pos() alone.
> The reply was still copied at descs[0].offset, so wrong
> file data was placed into the page cache.
>
> Add descs[0].offset to the request position. Apply the
> same correction in fuse_short_read for EOF size updates.
>
> Fixes: 4ea907108a5c ("fuse: use iomap for readahead")
> Signed-off-by: Haofeng Li <lihaofeng@kylinos.cn>
> ---
>  fs/fuse/file.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index ceada75310b8..11272983c991 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -836,7 +836,8 @@ static void fuse_short_read(struct inode *inode, u64 attr_ver, size_t num_read,
>          * reached the client fs yet.  So the hole is not present there.
>          */
>         if (!fc->writeback_cache) {
> -               loff_t pos = folio_pos(ap->folios[0]) + num_read;
> +               loff_t pos = folio_pos(ap->folios[0]) +
> +                            ap->descs[0].offset + num_read;
>                 fuse_read_update_size(inode, pos, attr_ver);
>         }
>  }
> @@ -1057,7 +1058,8 @@ static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file,
>         struct fuse_file *ff = file->private_data;
>         struct fuse_mount *fm = ff->fm;
>         struct fuse_args_pages *ap = &ia->ap;
> -       loff_t pos = folio_pos(ap->folios[0]);
> +       loff_t pos = folio_pos(ap->folios[0]) +
> +                    ap->descs[0].offset;

nit: is this newline needed?

>         ssize_t res;
>         int err>

LGTM. Thanks for catching this.

Reviewed-by: Joanne Koong <joannelkoong@gmail.com>

Re: [PATCH] fuse: honor desc offset in readahead reads

[Haofeng Li]

On Thu, 16 Jul 2026 11:11:10 -0700, Joanne Koong wrote:
> nit: is this newline needed?
>
> LGTM. Thanks for catching this.
>
> Reviewed-by: Joanne Koong <joannelkoong@gmail.com>

Thanks for the review. I'll remove the newline in v2 and keep your Reviewed-by tag, as the logic stays the same.

[PATCH v2] fuse: honor desc offset in readahead reads

[Haofeng Li]

fuse_handle_readahead records non-zero descs[].offset when
iomap skips leading uptodate blocks in a folio, but
fuse_send_readpages built FUSE_READ from folio_pos() alone.
The reply was still copied at descs[0].offset, so wrong
file data was placed into the page cache.

Add descs[0].offset to the request position. Apply the
same correction in fuse_short_read for EOF size updates.

Fixes: 4ea907108a5c ("fuse: use iomap for readahead")
Signed-off-by: Haofeng Li <lihaofeng@kylinos.cn>
Reviewed-by: Joanne Koong <joannelkoong@gmail.com>

---
Changes in v2:
- Collapse the split line in fuse_send_readpages back into one line.
- Add Joanne's Reviewed-by tag.
---
 fs/fuse/file.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index ceada75310b8..9718a0353d26 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -836,7 +836,8 @@ static void fuse_short_read(struct inode *inode, u64 attr_ver, size_t num_read,
 	 * reached the client fs yet.  So the hole is not present there.
 	 */
 	if (!fc->writeback_cache) {
-		loff_t pos = folio_pos(ap->folios[0]) + num_read;
+		loff_t pos = folio_pos(ap->folios[0]) +
+			     ap->descs[0].offset + num_read;
 		fuse_read_update_size(inode, pos, attr_ver);
 	}
 }
@@ -1057,7 +1058,7 @@ static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file,
 	struct fuse_file *ff = file->private_data;
 	struct fuse_mount *fm = ff->fm;
 	struct fuse_args_pages *ap = &ia->ap;
-	loff_t pos = folio_pos(ap->folios[0]);
+	loff_t pos = folio_pos(ap->folios[0]) + ap->descs[0].offset;
 	ssize_t res;
 	int err;
 
-- 
2.25.1

Re: [PATCH v2] fuse: honor desc offset in readahead reads

[Miklos Szeredi]

On Fri, 17 Jul 2026 at 05:28, Haofeng Li <lihaofeng@kylinos.cn> wrote:
>
> fuse_handle_readahead records non-zero descs[].offset when
> iomap skips leading uptodate blocks in a folio, but
> fuse_send_readpages built FUSE_READ from folio_pos() alone.
> The reply was still copied at descs[0].offset, so wrong
> file data was placed into the page cache.
>
> Add descs[0].offset to the request position. Apply the
> same correction in fuse_short_read for EOF size updates.
>
> Fixes: 4ea907108a5c ("fuse: use iomap for readahead")
> Signed-off-by: Haofeng Li <lihaofeng@kylinos.cn>
> Reviewed-by: Joanne Koong <joannelkoong@gmail.com>

Sashiko founds some more cases:
https://sashiko.dev/#/patchset/20260717032835.922433-1-lihaofeng%40kylinos.cn

This is a large folio issue, right?  I do wonder why fsx-linux missed
these with the large folios enabled.

Thanks,
Miklos

Re: Re: [PATCH v2] fuse: honor desc offset in readahead reads

[Horst Birthelmer]

On Fri, Jul 17, 2026 at 10:56:20AM +0200, Miklos Szeredi wrote:
> On Fri, 17 Jul 2026 at 05:28, Haofeng Li <lihaofeng@kylinos.cn> wrote:
> >
> > fuse_handle_readahead records non-zero descs[].offset when
> > iomap skips leading uptodate blocks in a folio, but
> > fuse_send_readpages built FUSE_READ from folio_pos() alone.
> > The reply was still copied at descs[0].offset, so wrong
> > file data was placed into the page cache.
> >
> > Add descs[0].offset to the request position. Apply the
> > same correction in fuse_short_read for EOF size updates.
> >
> > Fixes: 4ea907108a5c ("fuse: use iomap for readahead")
> > Signed-off-by: Haofeng Li <lihaofeng@kylinos.cn>
> > Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
> 
> Sashiko founds some more cases:
> https://sashiko.dev/#/patchset/20260717032835.922433-1-lihaofeng%40kylinos.cn
> 
> This is a large folio issue, right?  I do wonder why fsx-linux missed
> these with the large folios enabled.

I think it probably never occured since fuse_readahead() only fills in folio boundaries?
This could be coincidence or readahead controls 'job'. I'm not that familiar with that code.

I just got suspicious on your question, since I have large folios enabled in testing, too, and
have not seen the case.

> 
> Thanks,
> Miklos
>