exportfs: add flag to allow marking export operations as only supporting file handles

[PATCH 1/4] exportfs: add flag to indicate local file handles

Posted by Christian Brauner 1 year, 2 months ago

Some filesystems like kernfs and pidfs support file handles as a
convenience to use name_to_handle_at(2) and open_by_handle_at(2) but
don't want to and cannot be reliably exported. Add a flag that allows
them to mark their export operations accordingly.

Fixes: aa8188253474 ("kernfs: add exportfs operations")
Cc: stable <stable@kernel.org> # >= 4.14
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 fs/nfsd/export.c         | 8 +++++++-
 include/linux/exportfs.h | 1 +
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
index eacafe46e3b673cb306bd3c7caabd3283a1e54b1..786551595cc1c2043e8c195c00ca72ef93c769d6 100644
--- a/fs/nfsd/export.c
+++ b/fs/nfsd/export.c
@@ -417,6 +417,7 @@ static struct svc_export *svc_export_lookup(struct svc_export *);
 static int check_export(struct path *path, int *flags, unsigned char *uuid)
 {
 	struct inode *inode = d_inode(path->dentry);
+	const struct export_operations *nop;
 
 	/*
 	 * We currently export only dirs, regular files, and (for v4
@@ -449,11 +450,16 @@ static int check_export(struct path *path, int *flags, unsigned char *uuid)
 		return -EINVAL;
 	}
 
-	if (!exportfs_can_decode_fh(inode->i_sb->s_export_op)) {
+	if (!exportfs_can_decode_fh(nop)) {
 		dprintk("exp_export: export of invalid fs type.\n");
 		return -EINVAL;
 	}
 
+	if (nop && nop->flags & EXPORT_OP_LOCAL_FILE_HANDLE) {
+		dprintk("exp_export: filesystem only supports non-exportable file handles.\n");
+		return -EINVAL;
+	}
+
 	if (is_idmapped_mnt(path->mnt)) {
 		dprintk("exp_export: export of idmapped mounts not yet supported.\n");
 		return -EINVAL;
diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
index a087606ace194ccc9d1250f990ce55627aaf8dc5..40f78c8e4f31b97b2101b66634e8d1807c1bcc14 100644
--- a/include/linux/exportfs.h
+++ b/include/linux/exportfs.h
@@ -280,6 +280,7 @@ struct export_operations {
 						*/
 #define EXPORT_OP_FLUSH_ON_CLOSE	(0x20) /* fs flushes file data on close */
 #define EXPORT_OP_ASYNC_LOCK		(0x40) /* fs can do async lock request */
+#define EXPORT_OP_LOCAL_FILE_HANDLE		(0x80) /* fs only supports file handles, no proper export */
 	unsigned long	flags;
 };
 

-- 
2.45.2

Re: [PATCH 1/4] exportfs: add flag to indicate local file handles

Posted by Dave Chinner 1 year, 2 months ago

On Sun, Dec 01, 2024 at 02:12:25PM +0100, Christian Brauner wrote:
> Some filesystems like kernfs and pidfs support file handles as a
> convenience to use name_to_handle_at(2) and open_by_handle_at(2) but
> don't want to and cannot be reliably exported. Add a flag that allows
> them to mark their export operations accordingly.
> 
> Fixes: aa8188253474 ("kernfs: add exportfs operations")
> Cc: stable <stable@kernel.org> # >= 4.14
> Signed-off-by: Christian Brauner <brauner@kernel.org>
> ---
>  fs/nfsd/export.c         | 8 +++++++-
>  include/linux/exportfs.h | 1 +
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
> index eacafe46e3b673cb306bd3c7caabd3283a1e54b1..786551595cc1c2043e8c195c00ca72ef93c769d6 100644
> --- a/fs/nfsd/export.c
> +++ b/fs/nfsd/export.c
> @@ -417,6 +417,7 @@ static struct svc_export *svc_export_lookup(struct svc_export *);
>  static int check_export(struct path *path, int *flags, unsigned char *uuid)
>  {
>  	struct inode *inode = d_inode(path->dentry);
> +	const struct export_operations *nop;
>  
>  	/*
>  	 * We currently export only dirs, regular files, and (for v4
> @@ -449,11 +450,16 @@ static int check_export(struct path *path, int *flags, unsigned char *uuid)
>  		return -EINVAL;
>  	}
>  
> -	if (!exportfs_can_decode_fh(inode->i_sb->s_export_op)) {
> +	if (!exportfs_can_decode_fh(nop)) {

Where is nop initialised?

>  		dprintk("exp_export: export of invalid fs type.\n");
>  		return -EINVAL;
>  	}
>  
> +	if (nop && nop->flags & EXPORT_OP_LOCAL_FILE_HANDLE) {

Also, please use () around & operations so we can understand that
this is not an accidental typo. i.e:

	if (nop && (nop->flags & EXPORT_OP_LOCAL_FILE_HANDLE)) {

clearly expresses the intent of the code, and now it is obviously
correct at a glance.

-Dave.

-- 
Dave Chinner
david@fromorbit.com

Re: [PATCH 1/4] exportfs: add flag to indicate local file handles

Posted by Christian Brauner 1 year, 2 months ago

On Mon, Dec 02, 2024 at 10:12:49AM +1100, Dave Chinner wrote:
> On Sun, Dec 01, 2024 at 02:12:25PM +0100, Christian Brauner wrote:
> > Some filesystems like kernfs and pidfs support file handles as a
> > convenience to use name_to_handle_at(2) and open_by_handle_at(2) but
> > don't want to and cannot be reliably exported. Add a flag that allows
> > them to mark their export operations accordingly.
> > 
> > Fixes: aa8188253474 ("kernfs: add exportfs operations")
> > Cc: stable <stable@kernel.org> # >= 4.14
> > Signed-off-by: Christian Brauner <brauner@kernel.org>
> > ---
> >  fs/nfsd/export.c         | 8 +++++++-
> >  include/linux/exportfs.h | 1 +
> >  2 files changed, 8 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
> > index eacafe46e3b673cb306bd3c7caabd3283a1e54b1..786551595cc1c2043e8c195c00ca72ef93c769d6 100644
> > --- a/fs/nfsd/export.c
> > +++ b/fs/nfsd/export.c
> > @@ -417,6 +417,7 @@ static struct svc_export *svc_export_lookup(struct svc_export *);
> >  static int check_export(struct path *path, int *flags, unsigned char *uuid)
> >  {
> >  	struct inode *inode = d_inode(path->dentry);
> > +	const struct export_operations *nop;
> >  
> >  	/*
> >  	 * We currently export only dirs, regular files, and (for v4
> > @@ -449,11 +450,16 @@ static int check_export(struct path *path, int *flags, unsigned char *uuid)
> >  		return -EINVAL;
> >  	}
> >  
> > -	if (!exportfs_can_decode_fh(inode->i_sb->s_export_op)) {
> > +	if (!exportfs_can_decode_fh(nop)) {
> 
> Where is nop initialised?

Yep, already fixed in tree yesterday. Thanks for catching this though!

> 
> >  		dprintk("exp_export: export of invalid fs type.\n");
> >  		return -EINVAL;
> >  	}
> >  
> > +	if (nop && nop->flags & EXPORT_OP_LOCAL_FILE_HANDLE) {
> 
> Also, please use () around & operations so we can understand that
> this is not an accidental typo. i.e:
> 
> 	if (nop && (nop->flags & EXPORT_OP_LOCAL_FILE_HANDLE)) {
> 
> clearly expresses the intent of the code, and now it is obviously
> correct at a glance.

Done.

Re: [PATCH 1/4] exportfs: add flag to indicate local file handles

Posted by Amir Goldstein 1 year, 2 months ago

On Sun, Dec 1, 2024 at 2:13 PM Christian Brauner <brauner@kernel.org> wrote:
>
> Some filesystems like kernfs and pidfs support file handles as a
> convenience to use name_to_handle_at(2) and open_by_handle_at(2) but
> don't want to and cannot be reliably exported. Add a flag that allows
> them to mark their export operations accordingly.
>
> Fixes: aa8188253474 ("kernfs: add exportfs operations")
> Cc: stable <stable@kernel.org> # >= 4.14
> Signed-off-by: Christian Brauner <brauner@kernel.org>
> ---
>  fs/nfsd/export.c         | 8 +++++++-
>  include/linux/exportfs.h | 1 +
>  2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
> index eacafe46e3b673cb306bd3c7caabd3283a1e54b1..786551595cc1c2043e8c195c00ca72ef93c769d6 100644
> --- a/fs/nfsd/export.c
> +++ b/fs/nfsd/export.c
> @@ -417,6 +417,7 @@ static struct svc_export *svc_export_lookup(struct svc_export *);
>  static int check_export(struct path *path, int *flags, unsigned char *uuid)
>  {
>         struct inode *inode = d_inode(path->dentry);
> +       const struct export_operations *nop;
>
>         /*
>          * We currently export only dirs, regular files, and (for v4
> @@ -449,11 +450,16 @@ static int check_export(struct path *path, int *flags, unsigned char *uuid)
>                 return -EINVAL;
>         }
>
> -       if (!exportfs_can_decode_fh(inode->i_sb->s_export_op)) {
> +       if (!exportfs_can_decode_fh(nop)) {
>                 dprintk("exp_export: export of invalid fs type.\n");
>                 return -EINVAL;
>         }
>
> +       if (nop && nop->flags & EXPORT_OP_LOCAL_FILE_HANDLE) {
> +               dprintk("exp_export: filesystem only supports non-exportable file handles.\n");
> +               return -EINVAL;
> +       }
> +
>         if (is_idmapped_mnt(path->mnt)) {
>                 dprintk("exp_export: export of idmapped mounts not yet supported.\n");
>                 return -EINVAL;
> diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
> index a087606ace194ccc9d1250f990ce55627aaf8dc5..40f78c8e4f31b97b2101b66634e8d1807c1bcc14 100644
> --- a/include/linux/exportfs.h
> +++ b/include/linux/exportfs.h
> @@ -280,6 +280,7 @@ struct export_operations {
>                                                 */
>  #define EXPORT_OP_FLUSH_ON_CLOSE       (0x20) /* fs flushes file data on close */
>  #define EXPORT_OP_ASYNC_LOCK           (0x40) /* fs can do async lock request */
> +#define EXPORT_OP_LOCAL_FILE_HANDLE            (0x80) /* fs only supports file handles, no proper export */
>         unsigned long   flags;
>  };

Please update Documentation/filesystems/nfs/exporting.rst.

Thanks,
Amir.