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

Amir Goldstein
2024-12-01T13:44:21Z

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.