autofs4: add miscellaneous device for ioctls

Add a miscellaneous device to the autofs4 module for routing ioctls.  This
provides the ability to obtain an ioctl file handle for an autofs mount
point that is possibly covered by another mount.

The actual problem with autofs is that it can't reconnect to existing
mounts.  Immediately one things of just adding the ability to remount
autofs file systems would solve it, but alas, that can't work.  This is
because autofs direct mounts and the implementation of "on demand mount
and expire" of nested mount trees have the file system mounted on top of
the mount trigger dentry.

To resolve this a miscellaneous device node for routing ioctl commands to
these mount points has been implemented in the autofs4 kernel module and a
library added to autofs.  This provides the ability to open a file
descriptor for these over mounted autofs mount points.

Please refer to Documentation/filesystems/autofs4-mount-control.txt for a
discussion of the problem, implementation alternatives considered and a
description of the interface.

[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: build fix]
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/autofs4/Makefile

@@ -4,4 +4,4 @@
 
 obj-$(CONFIG_AUTOFS4_FS) += autofs4.o
 
-autofs4-objs := init.o inode.o root.o symlink.o waitq.o expire.o
+autofs4-objs := init.o inode.o root.o symlink.o waitq.o expire.o dev-ioctl.o

fs/autofs4/autofs_i.h

@@ -14,6 +14,7 @@
 /* Internal header file for autofs */
 
 #include <linux/auto_fs4.h>
+#include <linux/auto_dev-ioctl.h>
 #include <linux/mutex.h>
 #include <linux/list.h>
 
@@ -21,6 +22,9 @@
 #define AUTOFS_IOC_FIRST     AUTOFS_IOC_READY
 #define AUTOFS_IOC_COUNT     32
 
+#define AUTOFS_DEV_IOCTL_IOC_FIRST	(AUTOFS_DEV_IOCTL_VERSION)
+#define AUTOFS_DEV_IOCTL_IOC_COUNT	(AUTOFS_IOC_COUNT - 11)
+
 #define AUTOFS_TYPE_TRIGGER	(AUTOFS_TYPE_DIRECT|AUTOFS_TYPE_OFFSET)
 
 #include <linux/kernel.h>
@@ -37,11 +41,27 @@
 /* #define DEBUG */
 
 #ifdef DEBUG
-#define DPRINTK(fmt,args...) do { printk(KERN_DEBUG "pid %d: %s: " fmt "\n" , current->pid , __func__ , ##args); } while(0)
+#define DPRINTK(fmt, args...)				\
+do {							\
+	printk(KERN_DEBUG "pid %d: %s: " fmt "\n",	\
+		current->pid, __func__, ##args);	\
+} while (0)
 #else
-#define DPRINTK(fmt,args...) do {} while(0)
+#define DPRINTK(fmt, args...) do {} while (0)
 #endif
 
+#define AUTOFS_WARN(fmt, args...)			\
+do {							\
+	printk(KERN_WARNING "pid %d: %s: " fmt "\n",	\
+		current->pid, __func__, ##args);	\
+} while (0)
+
+#define AUTOFS_ERROR(fmt, args...)			\
+do {							\
+	printk(KERN_ERR "pid %d: %s: " fmt "\n",	\
+		current->pid, __func__, ##args);	\
+} while (0)
+
 /* Unified info structure.  This is pointed to by both the dentry and
    inode structures.  Each file in the filesystem has an instance of this
    structure.  It holds a reference to the dentry, so dentries are never
@@ -170,6 +190,17 @@ int autofs4_expire_run(struct super_block *, struct vfsmount *,
 			struct autofs_packet_expire __user *);
 int autofs4_expire_multi(struct super_block *, struct vfsmount *,
 			struct autofs_sb_info *, int __user *);
+struct dentry *autofs4_expire_direct(struct super_block *sb,
+				     struct vfsmount *mnt,
+				     struct autofs_sb_info *sbi, int how);
+struct dentry *autofs4_expire_indirect(struct super_block *sb,
+				       struct vfsmount *mnt,
+				       struct autofs_sb_info *sbi, int how);
+
+/* Device node initialization */
+
+int autofs_dev_ioctl_init(void);
+void autofs_dev_ioctl_exit(void);
 
 /* Operations structures */
 

fs/autofs4/expire.c

@@ -244,7 +244,7 @@ static struct dentry *autofs4_check_leaves(struct vfsmount *mnt,
 }
 
 /* Check if we can expire a direct mount (possibly a tree) */
-static struct dentry *autofs4_expire_direct(struct super_block *sb,
+struct dentry *autofs4_expire_direct(struct super_block *sb,
 				     struct vfsmount *mnt,
 				     struct autofs_sb_info *sbi,
 				     int how)
@@ -283,7 +283,7 @@ static struct dentry *autofs4_expire_direct(struct super_block *sb,
  *  - it is unused by any user process
  *  - it has been unused for exp_timeout time
  */
-static struct dentry *autofs4_expire_indirect(struct super_block *sb,
+struct dentry *autofs4_expire_indirect(struct super_block *sb,
 				       struct vfsmount *mnt,
 				       struct autofs_sb_info *sbi,
 				       int how)

fs/autofs4/init.c

@@ -29,11 +29,20 @@ static struct file_system_type autofs_fs_type = {
 
 static int __init init_autofs4_fs(void)
 {
-	return register_filesystem(&autofs_fs_type);
+	int err;
+
+	err = register_filesystem(&autofs_fs_type);
+	if (err)
+		return err;
+
+	autofs_dev_ioctl_init();
+
+	return err;
 }
 
 static void __exit exit_autofs4_fs(void)
 {
+	autofs_dev_ioctl_exit();
 	unregister_filesystem(&autofs_fs_type);
 }
 

include/linux/auto_dev-ioctl.h

+/*
+ * Copyright 2008 Red Hat, Inc. All rights reserved.
+ * Copyright 2008 Ian Kent <raven@themaw.net>
+ *
+ * This file is part of the Linux kernel and is made available under
+ * the terms of the GNU General Public License, version 2, or at your
+ * option, any later version, incorporated herein by reference.
+ */
+
+#ifndef _LINUX_AUTO_DEV_IOCTL_H
+#define _LINUX_AUTO_DEV_IOCTL_H
+
+#include <linux/types.h>
+
+#define AUTOFS_DEVICE_NAME		"autofs"
+
+#define AUTOFS_DEV_IOCTL_VERSION_MAJOR	1
+#define AUTOFS_DEV_IOCTL_VERSION_MINOR	0
+
+#define AUTOFS_DEVID_LEN		16
+
+#define AUTOFS_DEV_IOCTL_SIZE		sizeof(struct autofs_dev_ioctl)
+
+/*
+ * An ioctl interface for autofs mount point control.
+ */
+
+/*
+ * All the ioctls use this structure.
+ * When sending a path size must account for the total length
+ * of the chunk of memory otherwise is is the size of the
+ * structure.
+ */
+
+struct autofs_dev_ioctl {
+	__u32 ver_major;
+	__u32 ver_minor;
+	__u32 size;		/* total size of data passed in
+				 * including this struct */
+	__s32 ioctlfd;		/* automount command fd */
+
+	__u32 arg1;		/* Command parameters */
+	__u32 arg2;
+
+	char path[0];
+};
+
+static inline void init_autofs_dev_ioctl(struct autofs_dev_ioctl *in)
+{
+	in->ver_major = AUTOFS_DEV_IOCTL_VERSION_MAJOR;
+	in->ver_minor = AUTOFS_DEV_IOCTL_VERSION_MINOR;
+	in->size = sizeof(struct autofs_dev_ioctl);
+	in->ioctlfd = -1;
+	in->arg1 = 0;
+	in->arg2 = 0;
+	return;
+}
+
+/*
+ * If you change this make sure you make the corresponding change
+ * to autofs-dev-ioctl.c:lookup_ioctl()
+ */
+enum {
+	/* Get various version info */
+	AUTOFS_DEV_IOCTL_VERSION_CMD = 0x71,
+	AUTOFS_DEV_IOCTL_PROTOVER_CMD,
+	AUTOFS_DEV_IOCTL_PROTOSUBVER_CMD,
+
+	/* Open mount ioctl fd */
+	AUTOFS_DEV_IOCTL_OPENMOUNT_CMD,
+
+	/* Close mount ioctl fd */
+	AUTOFS_DEV_IOCTL_CLOSEMOUNT_CMD,
+
+	/* Mount/expire status returns */
+	AUTOFS_DEV_IOCTL_READY_CMD,
+	AUTOFS_DEV_IOCTL_FAIL_CMD,
+
+	/* Activate/deactivate autofs mount */
+	AUTOFS_DEV_IOCTL_SETPIPEFD_CMD,
+	AUTOFS_DEV_IOCTL_CATATONIC_CMD,
+
+	/* Expiry timeout */
+	AUTOFS_DEV_IOCTL_TIMEOUT_CMD,
+
+	/* Get mount last requesting uid and gid */
+	AUTOFS_DEV_IOCTL_REQUESTER_CMD,
+
+	/* Check for eligible expire candidates */
+	AUTOFS_DEV_IOCTL_EXPIRE_CMD,
+
+	/* Request busy status */
+	AUTOFS_DEV_IOCTL_ASKUMOUNT_CMD,
+
+	/* Check if path is a mountpoint */
+	AUTOFS_DEV_IOCTL_ISMOUNTPOINT_CMD,
+};
+
+#define AUTOFS_IOCTL 0x93
+
+#define AUTOFS_DEV_IOCTL_VERSION \
+	_IOWR(AUTOFS_IOCTL, \
+	      AUTOFS_DEV_IOCTL_VERSION_CMD, struct autofs_dev_ioctl)
+
+#define AUTOFS_DEV_IOCTL_PROTOVER \
+	_IOWR(AUTOFS_IOCTL, \
+	      AUTOFS_DEV_IOCTL_PROTOVER_CMD, struct autofs_dev_ioctl)
+
+#define AUTOFS_DEV_IOCTL_PROTOSUBVER \
+	_IOWR(AUTOFS_IOCTL, \
+	      AUTOFS_DEV_IOCTL_PROTOSUBVER_CMD, struct autofs_dev_ioctl)
+
+#define AUTOFS_DEV_IOCTL_OPENMOUNT \
+	_IOWR(AUTOFS_IOCTL, \
+	      AUTOFS_DEV_IOCTL_OPENMOUNT_CMD, struct autofs_dev_ioctl)
+
+#define AUTOFS_DEV_IOCTL_CLOSEMOUNT \
+	_IOWR(AUTOFS_IOCTL, \
+	      AUTOFS_DEV_IOCTL_CLOSEMOUNT_CMD, struct autofs_dev_ioctl)
+
+#define AUTOFS_DEV_IOCTL_READY \
+	_IOWR(AUTOFS_IOCTL, \
+	      AUTOFS_DEV_IOCTL_READY_CMD, struct autofs_dev_ioctl)
+
+#define AUTOFS_DEV_IOCTL_FAIL \
+	_IOWR(AUTOFS_IOCTL, \
+	      AUTOFS_DEV_IOCTL_FAIL_CMD, struct autofs_dev_ioctl)
+
+#define AUTOFS_DEV_IOCTL_SETPIPEFD \
+	_IOWR(AUTOFS_IOCTL, \
+	      AUTOFS_DEV_IOCTL_SETPIPEFD_CMD, struct autofs_dev_ioctl)
+
+#define AUTOFS_DEV_IOCTL_CATATONIC \
+	_IOWR(AUTOFS_IOCTL, \
+	      AUTOFS_DEV_IOCTL_CATATONIC_CMD, struct autofs_dev_ioctl)
+
+#define AUTOFS_DEV_IOCTL_TIMEOUT \
+	_IOWR(AUTOFS_IOCTL, \
+	      AUTOFS_DEV_IOCTL_TIMEOUT_CMD, struct autofs_dev_ioctl)
+
+#define AUTOFS_DEV_IOCTL_REQUESTER \
+	_IOWR(AUTOFS_IOCTL, \
+	      AUTOFS_DEV_IOCTL_REQUESTER_CMD, struct autofs_dev_ioctl)
+
+#define AUTOFS_DEV_IOCTL_EXPIRE \
+	_IOWR(AUTOFS_IOCTL, \
+	      AUTOFS_DEV_IOCTL_EXPIRE_CMD, struct autofs_dev_ioctl)
+
+#define AUTOFS_DEV_IOCTL_ASKUMOUNT \
+	_IOWR(AUTOFS_IOCTL, \
+	      AUTOFS_DEV_IOCTL_ASKUMOUNT_CMD, struct autofs_dev_ioctl)
+
+#define AUTOFS_DEV_IOCTL_ISMOUNTPOINT \
+	_IOWR(AUTOFS_IOCTL, \
+	      AUTOFS_DEV_IOCTL_ISMOUNTPOINT_CMD, struct autofs_dev_ioctl)
+
+#endif	/* _LINUX_AUTO_DEV_IOCTL_H */

include/linux/auto_fs4.h

@@ -23,7 +23,7 @@
 #define AUTOFS_MIN_PROTO_VERSION	3
 #define AUTOFS_MAX_PROTO_VERSION	5
 
-#define AUTOFS_PROTO_SUBVERSION		0
+#define AUTOFS_PROTO_SUBVERSION		1
 
 /* Mask for expire behaviour */
 #define AUTOFS_EXP_IMMEDIATE		1