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Subject: [PATCH 04/11] VFS: export lookup_mnt()
From:   NeilBrown <neilb@suse.de>
To:     Christoph Hellwig <hch@infradead.org>,
        Josef Bacik <josef@toxicpanda.com>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Chuck Lever <chuck.lever@oracle.com>, Chris Mason <clm@fb.com>,
        David Sterba <dsterba@suse.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>
Cc:     linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org,
        linux-btrfs@vger.kernel.org
Date:   Wed, 28 Jul 2021 08:37:45 +1000
Message-ID: <162742546551.32498.5847026750506620683.stgit@noble.brown>
In-Reply-To: <162742539595.32498.13687924366155737575.stgit@noble.brown>
References: <162742539595.32498.13687924366155737575.stgit@noble.brown>
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In order to support filehandle lookup in filesystems with internal
mounts (multiple subvols in the one filesystem) reconnect_path() in
exportfs will need to find out if a given dentry is already mounted.
This can be done with the function lookup_mnt(), so export that to make
it available.

Signed-off-by: NeilBrown <neilb@suse.de>
---
 fs/internal.h         |    1 -
 fs/namespace.c        |    1 +
 include/linux/mount.h |    2 ++
 3 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/internal.h b/fs/internal.h
index 3ce8edbaa3ca..0feb2722d2e5 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -81,7 +81,6 @@ int do_renameat2(int olddfd, struct filename *oldname, int newdfd,
 /*
  * namespace.c
  */
-extern struct vfsmount *lookup_mnt(const struct path *);
 extern int finish_automount(struct vfsmount *, struct path *);
 
 extern int sb_prepare_remount_readonly(struct super_block *);
diff --git a/fs/namespace.c b/fs/namespace.c
index 81b0f2b2e701..73bbdb921e24 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -662,6 +662,7 @@ struct vfsmount *lookup_mnt(const struct path *path)
 	rcu_read_unlock();
 	return m;
 }
+EXPORT_SYMBOL(lookup_mnt);
 
 static inline void lock_ns_list(struct mnt_namespace *ns)
 {
diff --git a/include/linux/mount.h b/include/linux/mount.h
index 5d92a7e1a742..1d3daed88f83 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -118,6 +118,8 @@ extern unsigned int sysctl_mount_max;
 
 extern bool path_is_mountpoint(const struct path *path);
 
+extern struct vfsmount *lookup_mnt(const struct path *);
+
 extern void kern_unmount_array(struct vfsmount *mnt[], unsigned int num);
 
 #endif /* _LINUX_MOUNT_H */