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

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Message-ID: <Z0ztcToKjCY05xq9@dread.disaster.area>
Date: Mon, 2 Dec 2024 10:12:49 +1100
From: Dave Chinner <david@...morbit.com>
To: Christian Brauner <brauner@...nel.org>
Cc: Amir Goldstein <amir73il@...il.com>, Jeff Layton <jlayton@...nel.org>,
	Erin Shepherd <erin.shepherd@....eu>,
	Chuck Lever <chuck.lever@...cle.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
	stable <stable@...nel.org>
Subject: Re: [PATCH 1/4] exportfs: add flag to indicate local file handles

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@...nel.org> # >= 4.14
> Signed-off-by: Christian Brauner <brauner@...nel.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@...morbit.com