Add 'zfs mount' support

By design the zfs utility is supposed to handle mounting and unmounting
a zfs filesystem.  We could allow zfs to do this directly.  There are
system calls available to mount/umount a filesystem.  And there are
library calls available to manipulate /etc/mtab.  But there are a
couple very good reasons not to take this appraoch... for now.

Instead of directly calling the system and library calls to (u)mount
the filesystem we fork and exec a (u)mount process.  The principle
reason for this is to delegate the responsibility for locking and
updating /etc/mtab to (u)mount(8).  This ensures maximum portability
and ensures the right locking scheme for your version of (u)mount
will be used.  If we didn't do this we would have to resort to an
autoconf test to determine what locking mechanism is used.

The downside to using mount(8) instead of mount(2) is that we lose
the exact errno which was returned by the kernel.  The return code
from mount(8) provides some insight in to what went wrong but it
not quite as good.  For the moment this is translated as a best
guess in to a errno for the higher layers of zfs.

In the long term a shared library called libmount is under development
which provides a common API to address the locking and errno issues.
Once the standard mount utility has been updated to use this library
we can then leverage it.  Until then this is the only safe solution.

  http://www.kernel.org/pub/linux/utils/util-linux/libmount-docs/index.html

4 files changed, 168 insertions, 128 deletions

diff --git a/lib/libspl/include/sys/mntent.h b/lib/libspl/include/sys/mntent.h
index c0594ca7b..d552c9c17 100644
--- a/lib/libspl/include/sys/mntent.h
+++ b/lib/libspl/include/sys/mntent.h
@@ -29,114 +29,74 @@
 #ifndef _SYS_MNTENT_H
 #define	_SYS_MNTENT_H
 
+#define	MNTTYPE_ZFS	"zfs"		/* ZFS file system */
 
-
-#ifdef	__cplusplus
-extern "C" {
-#endif
-
-#define	MNTTAB		"/proc/mounts"
-#define	VFSTAB		"/etc/vfstab"
+#define	FSTAB		"/etc/fstab"
 #define	MNTMAXSTR	128
 
-#define	MNTTYPE_ZFS	"zfs"		/* ZFS file system */
-#define	MNTTYPE_UFS	"ufs"		/* Unix file system */
-#define	MNTTYPE_SMBFS	"smbfs"		/* SMBFS file system */
-#define	MNTTYPE_NFS	"nfs"		/* NFS file system */
-#define	MNTTYPE_NFS3	"nfs3"		/* NFS Version 3 file system */
-#define	MNTTYPE_NFS4	"nfs4"		/* NFS Version 4 file system */
-#define	MNTTYPE_CACHEFS	"cachefs"	/* Cache File System */
-#define	MNTTYPE_PCFS	"pcfs"		/* PC (MSDOS) file system */
-#define	MNTTYPE_PC	MNTTYPE_PCFS	/* Deprecated name; use MNTTYPE_PCFS */
-#define	MNTTYPE_LOFS	"lofs"		/* Loop back file system */
-#define	MNTTYPE_LO	MNTTYPE_LOFS	/* Deprecated name; use MNTTYPE_LOFS */
-#define	MNTTYPE_HSFS	"hsfs"		/* High Sierra (9660) file system */
-#define	MNTTYPE_SWAP	"swap"		/* Swap file system */
-#define	MNTTYPE_TMPFS	"tmpfs"		/* Tmp volatile file system */
-#define	MNTTYPE_AUTOFS	"autofs"	/* Automounter ``file'' system */
-#define	MNTTYPE_MNTFS	"mntfs"		/* In-kernel mnttab */
-#define	MNTTYPE_DEV	"dev"		/* /dev file system */
-#define	MNTTYPE_CTFS	"ctfs"		/* Contract file system */
-#define	MNTTYPE_OBJFS	"objfs"		/* Kernel object file system */
-#define	MNTTYPE_SHAREFS	"sharefs"	/* Kernel sharetab file system */
-
+#define	MOUNT_SUCCESS	0x00		/* Success */
+#define	MOUNT_USAGE	0x01		/* Invalid invocation or permissions */
+#define	MOUNT_SYSERR	0x02		/* System error (ENOMEM, etc) */
+#define	MOUNT_SOFTWARE	0x04		/* Internal mount bug */
+#define	MOUNT_USER	0x08		/* Interrupted by user (EINTR) */
+#define	MOUNT_FILEIO	0x10		/* Error updating/locking /etc/mtab */
+#define	MOUNT_FAIL	0x20		/* Mount failed */
+#define	MOUNT_SOMEOK	0x40		/* At least on mount succeeded */
 
-#define	MNTOPT_RO	"ro"		/* Read only */
-#define	MNTOPT_RW	"rw"		/* Read/write */
-#define	MNTOPT_RQ	"rq"		/* Read/write with quotas */
-#define	MNTOPT_QUOTA	"quota"		/* Check quotas */
-#define	MNTOPT_NOQUOTA	"noquota"	/* Don't check quotas */
-#define	MNTOPT_ONERROR	"onerror"	/* action to taken on error */
-#define	MNTOPT_SOFT	"soft"		/* Soft mount */
-#define	MNTOPT_SEMISOFT	"semisoft"	/* partial soft, uncommited interface */
-#define	MNTOPT_HARD	"hard"		/* Hard mount */
-#define	MNTOPT_SUID	"suid"		/* Both setuid and devices allowed */
-#define	MNTOPT_NOSUID	"nosuid"	/* Neither setuid nor devices allowed */
-#define	MNTOPT_DEVICES	"devices"	/* Device-special allowed */
-#define	MNTOPT_NODEVICES	"nodevices"	/* Device-special disallowed */
-#define	MNTOPT_SETUID	"setuid"	/* Set uid allowed */
-#define	MNTOPT_NOSETUID	"nosetuid"	/* Set uid not allowed */
-#define	MNTOPT_GRPID	"grpid"		/* SysV-compatible gid on create */
-#define	MNTOPT_REMOUNT	"remount"	/* Change mount options */
-#define	MNTOPT_NOSUB	"nosub"		/* Disallow mounts on subdirs */
-#define	MNTOPT_MULTI	"multi"		/* Do multi-component lookup */
-#define	MNTOPT_INTR	"intr"		/* Allow NFS ops to be interrupted */
-#define	MNTOPT_NOINTR	"nointr"	/* Don't allow interrupted ops */
-#define	MNTOPT_PORT	"port"		/* NFS server IP port number */
-#define	MNTOPT_SECURE	"secure"	/* Secure (AUTH_DES) mounting */
-#define	MNTOPT_RSIZE	"rsize"		/* Max NFS read size (bytes) */
-#define	MNTOPT_WSIZE	"wsize"		/* Max NFS write size (bytes) */
-#define	MNTOPT_TIMEO	"timeo"		/* NFS timeout (1/10 sec) */
-#define	MNTOPT_RETRANS	"retrans"	/* Max retransmissions (soft mnts) */
-#define	MNTOPT_ACTIMEO	"actimeo"	/* Attr cache timeout (sec) */
-#define	MNTOPT_ACREGMIN	"acregmin"	/* Min attr cache timeout (files) */
-#define	MNTOPT_ACREGMAX	"acregmax"	/* Max attr cache timeout (files) */
-#define	MNTOPT_ACDIRMIN	"acdirmin"	/* Min attr cache timeout (dirs) */
-#define	MNTOPT_ACDIRMAX	"acdirmax"	/* Max attr cache timeout (dirs) */
-#define	MNTOPT_NOAC	"noac"		/* Don't cache attributes at all */
-#define	MNTOPT_NOCTO	"nocto"		/* No close-to-open consistency */
-#define	MNTOPT_BG	"bg"		/* Do mount retries in background */
-#define	MNTOPT_FG	"fg"		/* Do mount retries in foreground */
-#define	MNTOPT_RETRY	"retry"		/* Number of mount retries */
-#define	MNTOPT_DEV	"dev"		/* Device id of mounted fs */
-#define	MNTOPT_POSIX	"posix"		/* Get static pathconf for mount */
-#define	MNTOPT_MAP	"map"		/* Automount map */
-#define	MNTOPT_DIRECT	"direct"	/* Automount   direct map mount */
-#define	MNTOPT_INDIRECT	"indirect"	/* Automount indirect map mount */
-#define	MNTOPT_LLOCK	"llock"		/* Local locking (no lock manager) */
-#define	MNTOPT_IGNORE	"ignore"	/* Ignore this entry */
-#define	MNTOPT_VERS	"vers"		/* protocol version number indicator */
-#define	MNTOPT_PROTO	"proto"		/* protocol network_id indicator */
-#define	MNTOPT_SEC	"sec"		/* Security flavor indicator */
-#define	MNTOPT_SYNCDIR	"syncdir"	/* Synchronous local directory ops */
-#define	MNTOPT_NOSETSEC	"nosec"		/* Do no allow setting sec attrs */
-#define	MNTOPT_NOPRINT	"noprint"	/* Do not print messages */
-#define	MNTOPT_LARGEFILES "largefiles"	/* allow large files */
-#define	MNTOPT_NOLARGEFILES "nolargefiles" /* don't allow large files */
-#define	MNTOPT_FORCEDIRECTIO "forcedirectio" /* Force DirectIO on all files */
-#define	MNTOPT_NOFORCEDIRECTIO "noforcedirectio" /* No Force DirectIO */
-#define	MNTOPT_DISABLEDIRECTIO "disabledirectio" /* Disable DirectIO ioctls */
-#define	MNTOPT_PUBLIC	"public"	/* Use NFS public file handlee */
-#define	MNTOPT_LOGGING "logging" 	/* enable logging */
-#define	MNTOPT_NOLOGGING "nologging" 	/* disable logging */
+#define	MNTOPT_ASYNC	"async"		/* all I/O is asynchronous */
 #define	MNTOPT_ATIME	"atime"		/* update atime for files */
-#define	MNTOPT_NOATIME  "noatime"	/* do not update atime for files */
-#define	MNTOPT_GLOBAL	"global"	/* Cluster-wide global mount */
-#define	MNTOPT_NOGLOBAL	"noglobal"	/* Mount local to single node */
-#define	MNTOPT_DFRATIME	"dfratime"	/* Deferred access time updates */
-#define	MNTOPT_NODFRATIME "nodfratime"	/* No Deferred access time updates */
-#define	MNTOPT_NBMAND	"nbmand"	/* allow non-blocking mandatory locks */
-#define	MNTOPT_NONBMAND	"nonbmand"	/* deny non-blocking mandatory locks */
-#define	MNTOPT_XATTR	"xattr"		/* enable extended attributes */
-#define	MNTOPT_NOXATTR	"noxattr"	/* disable extended attributes */
+#define	MNTOPT_NOATIME	"noatime"	/* do not update atime for files */
+#define	MNTOPT_AUTO	"auto"		/* automount */
+#define	MNTOPT_NOAUTO	"noauto"	/* do not automount */
+#define	MNTOPT_CONTEXT	"context"	/* selinux context */
+#define	MNTOPT_FSCONTEXT "fscontext"	/* selinux fscontext */
+#define	MNTOPT_DEFCONTEXT "defcontext"	/* selinux defcontext */
+#define	MNTOPT_ROOTCONTEXT "rootcontext" /* selinux rootcontext */
+#define	MNTOPT_DEFAULTS	"defaults"	/* defaults */
+#define	MNTOPT_DEVICES	"dev"		/* device-special allowed */
+#define	MNTOPT_NODEVICES "nodev"	/* device-special disallowed */
+#define	MNTOPT_DIRATIME	"diratime"	/* update atime for dirs */
+#define	MNTOPT_NODIRATIME "nodiratime"	/* do not update atime for dirs */
+#define	MNTOPT_DIRSYNC	"dirsync"	/* do dir updates synchronously */
 #define	MNTOPT_EXEC	"exec"		/* enable executables */
 #define	MNTOPT_NOEXEC	"noexec"	/* disable executables */
-#define	MNTOPT_RESTRICT	"restrict"	/* restricted autofs mount */
-#define	MNTOPT_BROWSE	"browse"	/* browsable autofs mount */
-#define	MNTOPT_NOBROWSE	"nobrowse"	/* non-browsable autofs mount */
-
-#ifdef	__cplusplus
-}
-#endif
+#define	MNTOPT_GROUP	"group"		/* allow group mount */
+#define	MNTOPT_NOGROUP	"nogroup"	/* do not allow group mount */
+#define	MNTOPT_IVERSION	"iversion"	/* update inode version */
+#define	MNTOPT_NOIVERSION "noiversion"	/* do not update inode version */
+#define	MNTOPT_NBMAND	"mand"		/* allow non-blocking mandatory locks */
+#define	MNTOPT_NONBMAND	"nomand"	/* deny non-blocking mandatory locks */
+#define	MNTOPT_NETDEV	"_netdev"	/* network device */
+#define	MNTOPT_NOFAIL	"nofail"	/* no failure */
+#define	MNTOPT_RELATIME	"relatime"	/* allow relative time updates */
+#define	MNTOPT_NORELATIME "norelatime"	/* do not allow relative time updates */
+#define	MNTOPT_DFRATIME	"strictatime"	/* Deferred access time updates */
+#define	MNTOPT_NODFRATIME "nostrictatime" /* No Deferred access time updates */
+#define	MNTOPT_SETUID	"suid"		/* Both setuid and devices allowed */
+#define	MNTOPT_NOSETUID	"nosuid"	/* Neither setuid nor devices allowed */
+#define	MNTOPT_OWNER	"owner"		/* allow owner mount */
+#define	MNTOPT_NOOWNER	"noowner"	/* do not allow owner mount */
+#define	MNTOPT_REMOUNT	"remount"	/* change mount options */
+#define	MNTOPT_RO	"ro"		/* read only */
+#define	MNTOPT_RW	"rw"		/* read/write */
+#define	MNTOPT_SYNC	"sync"		/* all I/O is synchronous */
+#define	MNTOPT_USER	"user"		/* allow user mount */
+#define	MNTOPT_NOUSER	"nouser"	/* do not allow user mount */
+#define	MNTOPT_USERS	"users"		/* allow user mount */
+#define	MNTOPT_NOUSERS	"nousers"	/* do not allow user mount */
+#define	MNTOPT_SUB	"sub"		/* allow mounts on subdirs */
+#define	MNTOPT_NOSUB	"nosub"		/* do not allow mounts on subdirs */
+#define	MNTOPT_QUIET	"quiet"		/* quiet mount */
+#define	MNTOPT_LOUD	"loud"		/* verbose mount */
+#define	MNTOPT_BIND	"bind"		/* remount part of a tree */
+#define	MNTOPT_RBIND	"rbind"		/* include subtrees */
+#define	MNTOPT_XATTR	"user_xattr"	/* enable extended attributes */
+#define	MNTOPT_NOXATTR	"nouser_xattr"	/* disable extended attributes */
+#define	MNTOPT_COMMENT	"comment"	/* comment */
+#define	MNTOPT_BOOTWAIT	"bootwait"
+#define	MNTOPT_NOBOOTWAIT "nobootwait"
+#define	MNTOPT_OPTIONAL	"optional"
+#define	MNTOPT_SHOWTHROUGH "showthrough"
+#define	MNTOPT_ZFSUTIL	"zfsutil"	/* called by zfs utility */
 
 #endif	/* _SYS_MNTENT_H */
diff --git a/lib/libspl/include/sys/mnttab.h b/lib/libspl/include/sys/mnttab.h
index 70f144967..a30549a72 100644
--- a/lib/libspl/include/sys/mnttab.h
+++ b/lib/libspl/include/sys/mnttab.h
@@ -36,14 +36,14 @@
 
 #ifdef MNTTAB
 #undef MNTTAB
-#endif
+#endif /* MNTTAB */
 
-#define MNTTAB "/proc/mounts"
-#define MNT_LINE_MAX 1024
+#define	MNTTAB		"/etc/mtab"
+#define	MNT_LINE_MAX	1024
 
-#define MNT_TOOLONG 1    /* entry exceeds MNT_LINE_MAX */
-#define MNT_TOOMANY 2    /* too many fields in line */
-#define MNT_TOOFEW  3    /* too few fields in line */
+#define	MNT_TOOLONG	1	/* entry exceeds MNT_LINE_MAX */
+#define	MNT_TOOMANY	2	/* too many fields in line */
+#define	MNT_TOOFEW	3	/* too few fields in line */
 
 struct mnttab {
 	char *mnt_special;
diff --git a/lib/libspl/include/sys/mount.h b/lib/libspl/include/sys/mount.h
index 144f915d2..f6a67c6a0 100644
--- a/lib/libspl/include/sys/mount.h
+++ b/lib/libspl/include/sys/mount.h
@@ -42,9 +42,11 @@
 #define BLKGETSIZE64		_IOR(0x12, 114, size_t)
 #endif
 
-#define MS_FORCE		MNT_FORCE
-#define MS_OVERLAY		32768
-#define MS_NOMNTTAB		0         /* Not supported in Linux */
-#define MS_OPTIONSTR		0         /* Not necessary in Linux */
+#define	MS_USERS	0x40000000
+#define	MS_OWNER	0x10000000
+#define	MS_GROUP	0x08000000
+#define	MS_COMMENT	0x02000000
+#define	MS_FORCE	MNT_FORCE
+#define	MS_DETACH	MNT_DETACH
 
 #endif /* _LIBSPL_SYS_MOUNT_H */
diff --git a/lib/libzfs/libzfs_mount.c b/lib/libzfs/libzfs_mount.c
index 9950bf967..75ce3676f 100644
--- a/lib/libzfs/libzfs_mount.c
+++ b/lib/libzfs/libzfs_mount.c
@@ -259,6 +259,82 @@ zfs_is_mountable(zfs_handle_t *zhp, char *buf, size_t buflen,
 }
 
 /*
+ * The filesystem is mounted by invoking the system mount utility rather
+ * than by the system call mount(2).  This ensures that the /etc/mtab
+ * file is correctly locked for the update.  Performing our own locking
+ * and /etc/mtab update requires making an unsafe assumption about how
+ * the mount utility performs its locking.  Unfortunately, this also means
+ * in the case of a mount failure we do not have the exact errno.  We must
+ * make due with return value from the mount process.
+ *
+ * In the long term a shared library called libmount is under development
+ * which provides a common API to address the locking and errno issues.
+ * Once the standard mount utility has been updated to use this library
+ * we can add an autoconf check to conditionally use it.
+ *
+ * http://www.kernel.org/pub/linux/utils/util-linux/libmount-docs/index.html
+ */
+
+static int
+do_mount(const char *src, const char *mntpt, char *opts)
+{
+	char *argv[8] = {
+	    "/bin/mount",
+	    "-t", MNTTYPE_ZFS,
+	    "-o", opts,
+	    (char *)src,
+            (char *)mntpt,
+	    (char *)NULL };
+	int rc;
+
+	/* Return only the most critical mount error */
+	rc = libzfs_run_process(argv[0], argv);
+	if (rc) {
+		if (rc & MOUNT_FILEIO)
+			return EIO;
+		if (rc & MOUNT_USER)
+			return EINTR;
+		if (rc & MOUNT_SOFTWARE)
+			return EPIPE;
+		if (rc & MOUNT_SYSERR)
+			return EAGAIN;
+		if (rc & MOUNT_USAGE)
+			return EINVAL;
+
+		return ENXIO; /* Generic error */
+	}
+
+	return 0;
+}
+
+static int
+do_unmount(const char *mntpt, int flags)
+{
+	char force_opt[] = "-f";
+	char lazy_opt[] = "-l";
+	char *argv[7] = {
+	    "/bin/umount",
+	    "-t", MNTTYPE_ZFS,
+	    NULL, NULL, NULL, NULL };
+	int rc, count = 3;
+
+	if (flags & MS_FORCE) {
+		argv[count] = force_opt;
+		count++;
+	}
+
+	if (flags & MS_DETACH) {
+		argv[count] = lazy_opt;
+		count++;
+	}
+
+	argv[count] = (char *)mntpt;
+	rc = libzfs_run_process(argv[0], argv);
+
+	return (rc ? EINVAL : 0);
+}
+
+/*
  * Mount the given filesystem.
  */
 int
@@ -268,9 +344,10 @@ zfs_mount(zfs_handle_t *zhp, const char *options, int flags)
 	char mountpoint[ZFS_MAXPROPLEN];
 	char mntopts[MNT_LINE_MAX];
 	libzfs_handle_t *hdl = zhp->zfs_hdl;
+	int rc;
 
 	if (options == NULL)
-		mntopts[0] = '\0';
+		(void) strlcpy(mntopts, MNTOPT_DEFAULTS, sizeof (mntopts));
 	else
 		(void) strlcpy(mntopts, options, sizeof (mntopts));
 
@@ -278,7 +355,12 @@ zfs_mount(zfs_handle_t *zhp, const char *options, int flags)
 	 * If the pool is imported read-only then all mounts must be read-only
 	 */
 	if (zpool_get_prop_int(zhp->zpool_hdl, ZPOOL_PROP_READONLY, NULL))
-		flags |= MS_RDONLY;
+		(void) strlcat(mntopts, "," MNTOPT_RO, sizeof (mntopts));
+
+	/*
+	 * Append zfsutil option so the mount helper allow the mount
+	 */
+	strlcat(mntopts, "," MNTOPT_ZFSUTIL, sizeof (mntopts));
 
 #ifdef HAVE_LIBSELINUX
 	if (is_selinux_enabled())
@@ -302,12 +384,9 @@ zfs_mount(zfs_handle_t *zhp, const char *options, int flags)
 
 	/*
 	 * Determine if the mountpoint is empty.  If so, refuse to perform the
-	 * mount.  We don't perform this check if MS_OVERLAY is specified, which
-	 * would defeat the point.  We also avoid this check if 'remount' is
-	 * specified.
+	 * mount.  We don't perform this check if 'remount' is specified.
 	 */
-	if ((flags & MS_OVERLAY) == 0 &&
-	    strstr(mntopts, MNTOPT_REMOUNT) == NULL &&
+	if (strstr(mntopts, MNTOPT_REMOUNT) == NULL &&
 	    !dir_is_empty(mountpoint)) {
 		zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
 		    "directory is not empty"));
@@ -316,20 +395,20 @@ zfs_mount(zfs_handle_t *zhp, const char *options, int flags)
 	}
 
 	/* perform the mount */
-	if (mount(zfs_get_name(zhp), mountpoint, MS_OPTIONSTR | flags,
-	    MNTTYPE_ZFS, NULL, 0, mntopts, sizeof (mntopts)) != 0) {
+	rc = do_mount(zfs_get_name(zhp), mountpoint, mntopts);
+	if (rc) {
 		/*
 		 * Generic errors are nasty, but there are just way too many
 		 * from mount(), and they're well-understood.  We pick a few
 		 * common ones to improve upon.
 		 */
-		if (errno == EBUSY) {
+		if (rc == EBUSY) {
 			zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
 			    "mountpoint or dataset is busy"));
-		} else if (errno == EPERM) {
+		} else if (rc == EPERM) {
 			zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
 			    "Insufficient privileges"));
-		} else if (errno == ENOTSUP) {
+		} else if (rc == ENOTSUP) {
 			char buf[256];
 			int spa_version;
 
@@ -342,7 +421,7 @@ zfs_mount(zfs_handle_t *zhp, const char *options, int flags)
 			    ZFS_PROP_VERSION), spa_version);
 			zfs_error_aux(hdl, dgettext(TEXT_DOMAIN, buf));
 		} else {
-			zfs_error_aux(hdl, strerror(errno));
+			zfs_error_aux(hdl, strerror(rc));
 		}
 		return (zfs_error_fmt(hdl, EZFS_MOUNTFAILED,
 		    dgettext(TEXT_DOMAIN, "cannot mount '%s'"),
@@ -350,8 +429,7 @@ zfs_mount(zfs_handle_t *zhp, const char *options, int flags)
 	}
 
 	/* add the mounted entry into our cache */
-	libzfs_mnttab_add(hdl, zfs_get_name(zhp), mountpoint,
-	    mntopts);
+	libzfs_mnttab_add(hdl, zfs_get_name(zhp), mountpoint, mntopts);
 	return (0);
 }
 
@@ -361,7 +439,7 @@ zfs_mount(zfs_handle_t *zhp, const char *options, int flags)
 static int
 unmount_one(libzfs_handle_t *hdl, const char *mountpoint, int flags)
 {
-	if (umount2(mountpoint, flags) != 0) {
+	if (do_unmount(mountpoint, flags) != 0) {
 		zfs_error_aux(hdl, strerror(errno));
 		return (zfs_error_fmt(hdl, EZFS_UMOUNTFAILED,
 		    dgettext(TEXT_DOMAIN, "cannot unmount '%s'"),