linux-kernel - Re: [PATCH 2/3] namei: Allow follow

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Date:   Wed, 14 Dec 2022 15:15:21 +0000
From:   Chuck Lever III <chuck.lever@...cle.com>
To:     Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
CC:     Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Jeff Layton <jlayton@...nel.org>,
        Anna Schumaker <anna@...nel.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Ian Kent <raven@...maw.net>,
        "chris.chilvers@...sbroker.com" <chris.chilvers@...sbroker.com>,
        "david.young@...sbroker.com" <david.young@...sbroker.com>,
        "luis.turcitu@...sbroker.com" <luis.turcitu@...sbroker.com>,
        "david@...ma-star.at" <david@...ma-star.at>,
        "benmaynard@...gle.com" <benmaynard@...gle.com>,
        Richard Weinberger <richard@....at>
Subject: Re: [PATCH 2/3] namei: Allow follow_down() to uncover auto mounts



> On Dec 7, 2022, at 3:43 AM, Richard Weinberger <richard@....at> wrote:
> 
> This function is only used by NFSD to cross mount points.
> If a mount point is of type auto mount, follow_down() will
> not uncover it. Add LOOKUP_AUTOMOUNT to the lookup flags
> to have ->d_automount() called when NFSD walks down the
> mount tree.
> 
> Signed-off-by: Richard Weinberger <richard@....at>
> ---
> fs/namei.c            | 6 +++---
> fs/nfsd/vfs.c         | 6 +++++-
> include/linux/namei.h | 2 +-
> 3 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index 578c2110df02..a6bb6863bf0c 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -1458,11 +1458,11 @@ EXPORT_SYMBOL(follow_down_one);
>  * point, the filesystem owning that dentry may be queried as to whether the
>  * caller is permitted to proceed or not.
>  */
> -int follow_down(struct path *path)
> +int follow_down(struct path *path, unsigned int flags)
> {
> 	struct vfsmount *mnt = path->mnt;
> 	bool jumped;
> -	int ret = traverse_mounts(path, &jumped, NULL, 0);
> +	int ret = traverse_mounts(path, &jumped, NULL, flags);
> 
> 	if (path->mnt != mnt)
> 		mntput(mnt);
> @@ -2864,7 +2864,7 @@ int path_pts(struct path *path)
> 
> 	path->dentry = child;
> 	dput(parent);
> -	follow_down(path);
> +	follow_down(path, 0);
> 	return 0;
> }
> #endif
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index 157f0df0e93a..ced04fc2b947 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -63,9 +63,13 @@ nfsd_cross_mnt(struct svc_rqst *rqstp, struct dentry **dpp,
> 	struct dentry *dentry = *dpp;
> 	struct path path = {.mnt = mntget(exp->ex_path.mnt),
> 			    .dentry = dget(dentry)};
> +	unsigned int follow_flags = 0;
> 	int err = 0;
> 
> -	err = follow_down(&path);
> +	if (exp->ex_flags & NFSEXP_CROSSMOUNT)
> +		follow_flags = LOOKUP_AUTOMOUNT;
> +
> +	err = follow_down(&path, follow_flags);
> 	if (err < 0)
> 		goto out;
> 	if (path.mnt == exp->ex_path.mnt && path.dentry == dentry &&
> diff --git a/include/linux/namei.h b/include/linux/namei.h
> index 00fee52df842..6f96db73a70a 100644
> --- a/include/linux/namei.h
> +++ b/include/linux/namei.h
> @@ -77,7 +77,7 @@ struct dentry *lookup_one_positive_unlocked(struct user_namespace *mnt_userns,
> 					    struct dentry *base, int len);
> 
> extern int follow_down_one(struct path *);
> -extern int follow_down(struct path *);
> +extern int follow_down(struct path *, unsigned int flags);
> extern int follow_up(struct path *);
> 
> extern struct dentry *lock_rename(struct dentry *, struct dentry *);
> -- 
> 2.26.2
> 

I plan to take this through the nfsd tree, thus this one needs
an Ack from the VFS maintainer(s).


--
Chuck Lever