[PATCHSET RFC v2 00/10] add support for name_to, open_by_handle_at() to io_uring

[PATCHSET RFC v2 00/10] add support for name_to, open_by_handle_at() to io_uring

[Thomas Bertschinger]

This series adds support for name_to_handle_at() and open_by_handle_at()
to io_uring. The idea is for these opcodes to be useful for userspace
NFS servers that want to use io_uring.

The biggest change since [v1] is that this adds support for attempting
non-blocking open_by_handle_at(). When io_uring calls handle_to_path(),
it will set a flag to request that the call return -EAGAIN if it cannot
complete using cached data.

The same holds for the call to do_filp_path_open().

Supporting this for handle_to_path() requires a way to communicate to
the filesystem that it should not block in its fh_to_dentry()
implementation. This is done with a new flag FILEID_CACHED which is set
in the file handle by the VFS. If a filesystem supports this new flag,
it will indicate that with a new flag EXPORT_OP_NONBLOCK so that the VFS
knows not to call into a filesystem with the FILEID_CACHED flag, when
the FS does not know about that flag.

Support for the new FILEID_CACHED flag is added for xfs.

Thanks to Amir Goldstein for the review comments and suggesting this
approach on v1.

Testing
=======

As in v1, a liburing branch with a test is available at
https://github.com/bertschingert/liburing/tree/open_by_handle_at

and is run with

$ ./test/open_by_handle_at.t

v1 -> v2:
- rename some new helper functions:
	- do_name_to_handle_at() -> do_sys_name_to_handle_at()
	- __do_handle_open() -> do_filp_path_open()
- create a union member name_to_handle_flags in struct io_uring_sqe
- add new FILEID_CACHED and EXPORT_OP_NONBLOCK flags
- attempt non-blocking open_by_handle_at() in io_uring first, rather
  than always giving up and running in async context
- add support for FILEID_CACHED in xfs

[v1] https://lore.kernel.org/linux-fsdevel/20250814235431.995876-1-tahbertschinger@gmail.com/

Thomas Bertschinger (10):
  fhandle: create helper for name_to_handle_at(2)
  io_uring: add support for IORING_OP_NAME_TO_HANDLE_AT
  fhandle: helper for allocating, reading struct file_handle
  fhandle: create do_filp_path_open() helper
  fhandle: make do_filp_path_open() take struct open_flags
  exportfs: allow VFS flags in struct file_handle
  exportfs: new FILEID_CACHED flag for non-blocking fh lookup
  io_uring: add __io_open_prep() helper
  io_uring: add support for IORING_OP_OPEN_BY_HANDLE_AT
  xfs: add support for non-blocking fh_to_dentry()

 fs/exportfs/expfs.c           |  15 ++-
 fs/fhandle.c                  | 156 ++++++++++++++++-----------
 fs/internal.h                 |  13 +++
 fs/xfs/xfs_export.c           |  32 ++++--
 fs/xfs/xfs_export.h           |   3 +-
 fs/xfs/xfs_handle.c           |   2 +-
 include/linux/exportfs.h      |  34 +++++-
 include/uapi/linux/io_uring.h |   3 +
 io_uring/opdef.c              |  26 +++++
 io_uring/openclose.c          | 191 ++++++++++++++++++++++++++++++++--
 io_uring/openclose.h          |  13 +++
 11 files changed, 405 insertions(+), 83 deletions(-)


base-commit: 76eeb9b8de9880ca38696b2fb56ac45ac0a25c6c
-- 
2.51.0

[PATCH 10/10] xfs: add support for non-blocking fh_to_dentry()

[Thomas Bertschinger]

This is to support using open_by_handle_at(2) via io_uring. It is useful
for io_uring to request that opening a file via handle be completed
using only cached data, or fail with -EAGAIN if that is not possible.

The signature of xfs_nfs_get_inode() is extended with a new flags
argument that allows callers to specify XFS_IGET_INCORE.

That flag is set when the VFS passes the FILEID_CACHED flag via the
fileid_type argument.

Signed-off-by: Thomas Bertschinger <tahbertschinger@gmail.com>
---
 fs/xfs/xfs_export.c | 32 ++++++++++++++++++++++++++------
 fs/xfs/xfs_export.h |  3 ++-
 fs/xfs/xfs_handle.c |  2 +-
 3 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/fs/xfs/xfs_export.c b/fs/xfs/xfs_export.c
index 201489d3de08..ca2a9ed0eb16 100644
--- a/fs/xfs/xfs_export.c
+++ b/fs/xfs/xfs_export.c
@@ -106,7 +106,8 @@ struct inode *
 xfs_nfs_get_inode(
 	struct super_block	*sb,
 	u64			ino,
-	u32			generation)
+	u32			generation,
+	uint			flags)
 {
  	xfs_mount_t		*mp = XFS_M(sb);
 	xfs_inode_t		*ip;
@@ -123,7 +124,9 @@ xfs_nfs_get_inode(
 	 * fine and not an indication of a corrupted filesystem as clients can
 	 * send invalid file handles and we have to handle it gracefully..
 	 */
-	error = xfs_iget(mp, NULL, ino, XFS_IGET_UNTRUSTED, 0, &ip);
+	flags |= XFS_IGET_UNTRUSTED;
+
+	error = xfs_iget(mp, NULL, ino, flags, 0, &ip);
 	if (error) {
 
 		/*
@@ -140,6 +143,10 @@ xfs_nfs_get_inode(
 		case -EFSCORRUPTED:
 			error = -ESTALE;
 			break;
+		case -ENODATA:
+			if (flags & XFS_IGET_INCORE)
+				error = -EAGAIN;
+			break;
 		default:
 			break;
 		}
@@ -174,6 +181,12 @@ xfs_fs_fh_to_dentry(struct super_block *sb, struct fid *fid,
 {
 	struct xfs_fid64	*fid64 = (struct xfs_fid64 *)fid;
 	struct inode		*inode = NULL;
+	uint			flags = 0;
+
+	if (fileid_type & FILEID_CACHED)
+		flags = XFS_IGET_INCORE;
+
+	fileid_type = FILEID_TYPE(fileid_type);
 
 	if (fh_len < xfs_fileid_length(fileid_type))
 		return NULL;
@@ -181,11 +194,11 @@ xfs_fs_fh_to_dentry(struct super_block *sb, struct fid *fid,
 	switch (fileid_type) {
 	case FILEID_INO32_GEN_PARENT:
 	case FILEID_INO32_GEN:
-		inode = xfs_nfs_get_inode(sb, fid->i32.ino, fid->i32.gen);
+		inode = xfs_nfs_get_inode(sb, fid->i32.ino, fid->i32.gen, flags);
 		break;
 	case FILEID_INO32_GEN_PARENT | XFS_FILEID_TYPE_64FLAG:
 	case FILEID_INO32_GEN | XFS_FILEID_TYPE_64FLAG:
-		inode = xfs_nfs_get_inode(sb, fid64->ino, fid64->gen);
+		inode = xfs_nfs_get_inode(sb, fid64->ino, fid64->gen, flags);
 		break;
 	}
 
@@ -198,6 +211,12 @@ xfs_fs_fh_to_parent(struct super_block *sb, struct fid *fid,
 {
 	struct xfs_fid64	*fid64 = (struct xfs_fid64 *)fid;
 	struct inode		*inode = NULL;
+	uint			flags = 0;
+
+	if (fileid_type & FILEID_CACHED)
+		flags = XFS_IGET_INCORE;
+
+	fileid_type = FILEID_TYPE(fileid_type);
 
 	if (fh_len < xfs_fileid_length(fileid_type))
 		return NULL;
@@ -205,11 +224,11 @@ xfs_fs_fh_to_parent(struct super_block *sb, struct fid *fid,
 	switch (fileid_type) {
 	case FILEID_INO32_GEN_PARENT:
 		inode = xfs_nfs_get_inode(sb, fid->i32.parent_ino,
-					      fid->i32.parent_gen);
+					      fid->i32.parent_gen, flags);
 		break;
 	case FILEID_INO32_GEN_PARENT | XFS_FILEID_TYPE_64FLAG:
 		inode = xfs_nfs_get_inode(sb, fid64->parent_ino,
-					      fid64->parent_gen);
+					      fid64->parent_gen, flags);
 		break;
 	}
 
@@ -248,4 +267,5 @@ const struct export_operations xfs_export_operations = {
 	.map_blocks		= xfs_fs_map_blocks,
 	.commit_blocks		= xfs_fs_commit_blocks,
 #endif
+	.flags			= EXPORT_OP_NONBLOCK,
 };
diff --git a/fs/xfs/xfs_export.h b/fs/xfs/xfs_export.h
index 3cd85e8901a5..9addfcd5b1e1 100644
--- a/fs/xfs/xfs_export.h
+++ b/fs/xfs/xfs_export.h
@@ -57,6 +57,7 @@ struct xfs_fid64 {
 /* This flag goes on the wire.  Don't play with it. */
 #define XFS_FILEID_TYPE_64FLAG	0x80	/* NFS fileid has 64bit inodes */
 
-struct inode *xfs_nfs_get_inode(struct super_block *sb, u64 ino, u32 gen);
+struct inode *xfs_nfs_get_inode(struct super_block *sb, u64 ino, u32 gen,
+				uint flags);
 
 #endif	/* __XFS_EXPORT_H__ */
diff --git a/fs/xfs/xfs_handle.c b/fs/xfs/xfs_handle.c
index f19fce557354..7d877ff504d6 100644
--- a/fs/xfs/xfs_handle.c
+++ b/fs/xfs/xfs_handle.c
@@ -193,7 +193,7 @@ xfs_khandle_to_inode(
 		return ERR_PTR(-EINVAL);
 
 	inode = xfs_nfs_get_inode(mp->m_super, handle->ha_fid.fid_ino,
-			handle->ha_fid.fid_gen);
+			handle->ha_fid.fid_gen, 0);
 	if (IS_ERR(inode))
 		return ERR_CAST(inode);
 
-- 
2.51.0

Re: [PATCH 10/10] xfs: add support for non-blocking fh_to_dentry()

[Christoph Hellwig]

On Wed, Sep 10, 2025 at 03:49:27PM -0600, Thomas Bertschinger wrote:
> This is to support using open_by_handle_at(2) via io_uring. It is useful
> for io_uring to request that opening a file via handle be completed
> using only cached data, or fail with -EAGAIN if that is not possible.
> 
> The signature of xfs_nfs_get_inode() is extended with a new flags
> argument that allows callers to specify XFS_IGET_INCORE.
> 
> That flag is set when the VFS passes the FILEID_CACHED flag via the
> fileid_type argument.

Please post the entire series to all list.  No one has any idea what your
magic new flag does without seeing all the patches.

Re: [PATCH 10/10] xfs: add support for non-blocking fh_to_dentry()

[Amir Goldstein]

On Thu, Sep 11, 2025 at 2:29 PM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Wed, Sep 10, 2025 at 03:49:27PM -0600, Thomas Bertschinger wrote:
> > This is to support using open_by_handle_at(2) via io_uring. It is useful
> > for io_uring to request that opening a file via handle be completed
> > using only cached data, or fail with -EAGAIN if that is not possible.
> >
> > The signature of xfs_nfs_get_inode() is extended with a new flags
> > argument that allows callers to specify XFS_IGET_INCORE.
> >
> > That flag is set when the VFS passes the FILEID_CACHED flag via the
> > fileid_type argument.
>
> Please post the entire series to all list.  No one has any idea what your
> magic new flag does without seeing all the patches.
>

Might as well re-post your entire v2 patches with v2 subjects and
cc xfs list.

Thanks,
Amir.

Re: [PATCH 10/10] xfs: add support for non-blocking fh_to_dentry()

[Thomas Bertschinger]

On Thu Sep 11, 2025 at 6:39 AM MDT, Amir Goldstein wrote:
> On Thu, Sep 11, 2025 at 2:29 PM Christoph Hellwig <hch@infradead.org> wrote:
>>
>> On Wed, Sep 10, 2025 at 03:49:27PM -0600, Thomas Bertschinger wrote:
>> > This is to support using open_by_handle_at(2) via io_uring. It is useful
>> > for io_uring to request that opening a file via handle be completed
>> > using only cached data, or fail with -EAGAIN if that is not possible.
>> >
>> > The signature of xfs_nfs_get_inode() is extended with a new flags
>> > argument that allows callers to specify XFS_IGET_INCORE.
>> >
>> > That flag is set when the VFS passes the FILEID_CACHED flag via the
>> > fileid_type argument.
>>
>> Please post the entire series to all list.  No one has any idea what your
>> magic new flag does without seeing all the patches.
>>
>
> Might as well re-post your entire v2 patches with v2 subjects and
> cc xfs list.
>
> Thanks,
> Amir.


Thanks for the advice, sorry for messing up the procedure...

Since there are a few quick fixups I can make, I may go straight to
sending v3 with the correct subject and cc. Any reason for me to not do
that -- is it preferable to resend v2 right away with no changes?

Re: [PATCH 10/10] xfs: add support for non-blocking fh_to_dentry()

[Amir Goldstein]

On Thu, Sep 11, 2025 at 5:10 PM Thomas Bertschinger
<tahbertschinger@gmail.com> wrote:
>
> On Thu Sep 11, 2025 at 6:39 AM MDT, Amir Goldstein wrote:
> > On Thu, Sep 11, 2025 at 2:29 PM Christoph Hellwig <hch@infradead.org> wrote:
> >>
> >> On Wed, Sep 10, 2025 at 03:49:27PM -0600, Thomas Bertschinger wrote:
> >> > This is to support using open_by_handle_at(2) via io_uring. It is useful
> >> > for io_uring to request that opening a file via handle be completed
> >> > using only cached data, or fail with -EAGAIN if that is not possible.
> >> >
> >> > The signature of xfs_nfs_get_inode() is extended with a new flags
> >> > argument that allows callers to specify XFS_IGET_INCORE.
> >> >
> >> > That flag is set when the VFS passes the FILEID_CACHED flag via the
> >> > fileid_type argument.
> >>
> >> Please post the entire series to all list.  No one has any idea what your
> >> magic new flag does without seeing all the patches.
> >>
> >
> > Might as well re-post your entire v2 patches with v2 subjects and
> > cc xfs list.
> >
> > Thanks,
> > Amir.
>
>
> Thanks for the advice, sorry for messing up the procedure...
>
> Since there are a few quick fixups I can make, I may go straight to
> sending v3 with the correct subject and cc. Any reason for me to not do
> that -- is it preferable to resend v2 right away with no changes?

No worries. v3 is fine.
But maybe give it a day or two for other people to comment on v2
before posting v3. Some people may even be mid review of v2
and that can be a bit annoying to get v3 while in the middle of review of v2.

Thanks,
Amir.

Re: [PATCH 10/10] xfs: add support for non-blocking fh_to_dentry()

[Amir Goldstein]

On Wed, Sep 10, 2025 at 11:48 PM Thomas Bertschinger
<tahbertschinger@gmail.com> wrote:
>
> This is to support using open_by_handle_at(2) via io_uring. It is useful
> for io_uring to request that opening a file via handle be completed
> using only cached data, or fail with -EAGAIN if that is not possible.
>
> The signature of xfs_nfs_get_inode() is extended with a new flags
> argument that allows callers to specify XFS_IGET_INCORE.
>
> That flag is set when the VFS passes the FILEID_CACHED flag via the
> fileid_type argument.
>
> Signed-off-by: Thomas Bertschinger <tahbertschinger@gmail.com>

I'll let xfs developers review this, but its looks pretty straightforward,
so on my part you may add:

Acked-by: Amir Goldstein <amir73il@gmail.com>

One small nit below

> ---
>  fs/xfs/xfs_export.c | 32 ++++++++++++++++++++++++++------
>  fs/xfs/xfs_export.h |  3 ++-
>  fs/xfs/xfs_handle.c |  2 +-
>  3 files changed, 29 insertions(+), 8 deletions(-)
>
> diff --git a/fs/xfs/xfs_export.c b/fs/xfs/xfs_export.c
> index 201489d3de08..ca2a9ed0eb16 100644
> --- a/fs/xfs/xfs_export.c
> +++ b/fs/xfs/xfs_export.c
> @@ -106,7 +106,8 @@ struct inode *
>  xfs_nfs_get_inode(
>         struct super_block      *sb,
>         u64                     ino,
> -       u32                     generation)
> +       u32                     generation,
> +       uint                    flags)
>  {
>         xfs_mount_t             *mp = XFS_M(sb);
>         xfs_inode_t             *ip;
> @@ -123,7 +124,9 @@ xfs_nfs_get_inode(
>          * fine and not an indication of a corrupted filesystem as clients can
>          * send invalid file handles and we have to handle it gracefully..
>          */
> -       error = xfs_iget(mp, NULL, ino, XFS_IGET_UNTRUSTED, 0, &ip);
> +       flags |= XFS_IGET_UNTRUSTED;
> +
> +       error = xfs_iget(mp, NULL, ino, flags, 0, &ip);
>         if (error) {
>
>                 /*
> @@ -140,6 +143,10 @@ xfs_nfs_get_inode(
>                 case -EFSCORRUPTED:
>                         error = -ESTALE;
>                         break;
> +               case -ENODATA:
> +                       if (flags & XFS_IGET_INCORE)
> +                               error = -EAGAIN;
> +                       break;
>                 default:
>                         break;
>                 }
> @@ -174,6 +181,12 @@ xfs_fs_fh_to_dentry(struct super_block *sb, struct fid *fid,
>  {
>         struct xfs_fid64        *fid64 = (struct xfs_fid64 *)fid;
>         struct inode            *inode = NULL;
> +       uint                    flags = 0;
> +
> +       if (fileid_type & FILEID_CACHED)
> +               flags = XFS_IGET_INCORE;
> +
> +       fileid_type = FILEID_TYPE(fileid_type);

That is a smelly practice.
It's better to rename the function argument to fileid_flags or fileid_type_flags
and use a local fileid_type var for fileid_type = FILEID_TYPE(fileid_flags)

Thanks,
Amir.

>
>         if (fh_len < xfs_fileid_length(fileid_type))
>                 return NULL;
> @@ -181,11 +194,11 @@ xfs_fs_fh_to_dentry(struct super_block *sb, struct fid *fid,
>         switch (fileid_type) {
>         case FILEID_INO32_GEN_PARENT:
>         case FILEID_INO32_GEN:
> -               inode = xfs_nfs_get_inode(sb, fid->i32.ino, fid->i32.gen);
> +               inode = xfs_nfs_get_inode(sb, fid->i32.ino, fid->i32.gen, flags);
>                 break;
>         case FILEID_INO32_GEN_PARENT | XFS_FILEID_TYPE_64FLAG:
>         case FILEID_INO32_GEN | XFS_FILEID_TYPE_64FLAG:
> -               inode = xfs_nfs_get_inode(sb, fid64->ino, fid64->gen);
> +               inode = xfs_nfs_get_inode(sb, fid64->ino, fid64->gen, flags);
>                 break;
>         }
>
> @@ -198,6 +211,12 @@ xfs_fs_fh_to_parent(struct super_block *sb, struct fid *fid,
>  {
>         struct xfs_fid64        *fid64 = (struct xfs_fid64 *)fid;
>         struct inode            *inode = NULL;
> +       uint                    flags = 0;
> +
> +       if (fileid_type & FILEID_CACHED)
> +               flags = XFS_IGET_INCORE;
> +
> +       fileid_type = FILEID_TYPE(fileid_type);
>
>         if (fh_len < xfs_fileid_length(fileid_type))
>                 return NULL;
> @@ -205,11 +224,11 @@ xfs_fs_fh_to_parent(struct super_block *sb, struct fid *fid,
>         switch (fileid_type) {
>         case FILEID_INO32_GEN_PARENT:
>                 inode = xfs_nfs_get_inode(sb, fid->i32.parent_ino,
> -                                             fid->i32.parent_gen);
> +                                             fid->i32.parent_gen, flags);
>                 break;
>         case FILEID_INO32_GEN_PARENT | XFS_FILEID_TYPE_64FLAG:
>                 inode = xfs_nfs_get_inode(sb, fid64->parent_ino,
> -                                             fid64->parent_gen);
> +                                             fid64->parent_gen, flags);
>                 break;
>         }
>
> @@ -248,4 +267,5 @@ const struct export_operations xfs_export_operations = {
>         .map_blocks             = xfs_fs_map_blocks,
>         .commit_blocks          = xfs_fs_commit_blocks,
>  #endif
> +       .flags                  = EXPORT_OP_NONBLOCK,
>  };
> diff --git a/fs/xfs/xfs_export.h b/fs/xfs/xfs_export.h
> index 3cd85e8901a5..9addfcd5b1e1 100644
> --- a/fs/xfs/xfs_export.h
> +++ b/fs/xfs/xfs_export.h
> @@ -57,6 +57,7 @@ struct xfs_fid64 {
>  /* This flag goes on the wire.  Don't play with it. */
>  #define XFS_FILEID_TYPE_64FLAG 0x80    /* NFS fileid has 64bit inodes */
>
> -struct inode *xfs_nfs_get_inode(struct super_block *sb, u64 ino, u32 gen);
> +struct inode *xfs_nfs_get_inode(struct super_block *sb, u64 ino, u32 gen,
> +                               uint flags);
>
>  #endif /* __XFS_EXPORT_H__ */
> diff --git a/fs/xfs/xfs_handle.c b/fs/xfs/xfs_handle.c
> index f19fce557354..7d877ff504d6 100644
> --- a/fs/xfs/xfs_handle.c
> +++ b/fs/xfs/xfs_handle.c
> @@ -193,7 +193,7 @@ xfs_khandle_to_inode(
>                 return ERR_PTR(-EINVAL);
>
>         inode = xfs_nfs_get_inode(mp->m_super, handle->ha_fid.fid_ino,
> -                       handle->ha_fid.fid_gen);
> +                       handle->ha_fid.fid_gen, 0);
>         if (IS_ERR(inode))
>                 return ERR_CAST(inode);
>
> --
> 2.51.0
>
>