linux-kernel - [PATCH] xenbus: Use proc_create_mount

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Date:   Mon, 29 Aug 2016 10:03:48 -0500
From:   Seth Forshee <seth.forshee@...onical.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        David Vrabel <david.vrabel@...rix.com>,
        Juergen Gross <jgross@...e.com>
Cc:     Seth Forshee <seth.forshee@...onical.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: [PATCH] xenbus: Use proc_create_mount_point() to create /proc/xen

Mounting proc in user namespace containers fails if the xenbus
filesystem is mounted on /proc/xen because this directory fails
the "permanently empty" test. proc_create_mount_point() exists
specifically to create such mountpoints in proc but is currently
proc-internal. Export this interface to modules, then use it in
xenbus when creating /proc/xen.

Signed-off-by: Seth Forshee <seth.forshee@...onical.com>
---
 drivers/xen/xenbus/xenbus_probe.c | 2 +-
 fs/proc/generic.c                 | 1 +
 fs/proc/internal.h                | 1 -
 include/linux/proc_fs.h           | 2 ++
 4 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index 33a31cfef55d..b5c1dec4a7c2 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -826,7 +826,7 @@ static int __init xenbus_init(void)
 	 * Create xenfs mountpoint in /proc for compatibility with
 	 * utilities that expect to find "xenbus" under "/proc/xen".
 	 */
-	proc_mkdir("xen", NULL);
+	proc_create_mount_point("xen");
 #endif
 
 out_error:
diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index c633476616e0..be014c544d50 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -477,6 +477,7 @@ struct proc_dir_entry *proc_create_mount_point(const char *name)
 	}
 	return ent;
 }
+EXPORT_SYMBOL(proc_create_mount_point);
 
 struct proc_dir_entry *proc_create_data(const char *name, umode_t mode,
 					struct proc_dir_entry *parent,
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index 7931c558c192..ff7259559d70 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -195,7 +195,6 @@ static inline bool is_empty_pde(const struct proc_dir_entry *pde)
 {
 	return S_ISDIR(pde->mode) && !pde->proc_iops;
 }
-struct proc_dir_entry *proc_create_mount_point(const char *name);
 
 /*
  * inode.c
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index b97bf2ef996e..8bd2f726436a 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -21,6 +21,7 @@ extern struct proc_dir_entry *proc_mkdir_data(const char *, umode_t,
 					      struct proc_dir_entry *, void *);
 extern struct proc_dir_entry *proc_mkdir_mode(const char *, umode_t,
 					      struct proc_dir_entry *);
+struct proc_dir_entry *proc_create_mount_point(const char *name);
  
 extern struct proc_dir_entry *proc_create_data(const char *, umode_t,
 					       struct proc_dir_entry *,
@@ -56,6 +57,7 @@ static inline struct proc_dir_entry *proc_symlink(const char *name,
 		struct proc_dir_entry *parent,const char *dest) { return NULL;}
 static inline struct proc_dir_entry *proc_mkdir(const char *name,
 	struct proc_dir_entry *parent) {return NULL;}
+static inline struct proc_dir_entry *proc_create_mount_point(const char *name) { return NULL; }
 static inline struct proc_dir_entry *proc_mkdir_data(const char *name,
 	umode_t mode, struct proc_dir_entry *parent, void *data) { return NULL; }
 static inline struct proc_dir_entry *proc_mkdir_mode(const char *name,
-- 
2.7.4