Change /etc/mtab to /proc/self/mounts

Misleading error message "The /dev/zfs device is missing and must be created.", if /etc/mtab is missing.

Signed-off-by: Eric Desrochers <eric.desrochers@canonical.com>

cmd/mount_zfs/mount_zfs.c

@@ -283,66 +283,6 @@ parse_dataset(char *dataset)
 	return (dataset);
 }
 
-/*
- * Update the mtab_* code to use the libmount library when it is commonly
- * available otherwise fallback to legacy mode.  The mount(8) utility will
- * manage the lock file for us to prevent racing updates to /etc/mtab.
- */
-static int
-mtab_is_writeable(void)
-{
-	struct stat st;
-	int error, fd;
-
-	error = lstat(MNTTAB, &st);
-	if (error || S_ISLNK(st.st_mode))
-		return (0);
-
-	fd = open(MNTTAB, O_RDWR | O_CREAT, 0644);
-	if (fd < 0)
-		return (0);
-
-	close(fd);
-	return (1);
-}
-
-static int
-mtab_update(char *dataset, char *mntpoint, char *type, char *mntopts)
-{
-	struct mntent mnt;
-	FILE *fp;
-	int error;
-
-	mnt.mnt_fsname = dataset;
-	mnt.mnt_dir = mntpoint;
-	mnt.mnt_type = type;
-	mnt.mnt_opts = mntopts ? mntopts : "";
-	mnt.mnt_freq = 0;
-	mnt.mnt_passno = 0;
-
-	fp = setmntent(MNTTAB, "a+");
-	if (!fp) {
-		(void) fprintf(stderr, gettext(
-		    "filesystem '%s' was mounted, but %s "
-		    "could not be opened due to error %d\n"),
-		    dataset, MNTTAB, errno);
-		return (MOUNT_FILEIO);
-	}
-
-	error = addmntent(fp, &mnt);
-	if (error) {
-		(void) fprintf(stderr, gettext(
-		    "filesystem '%s' was mounted, but %s "
-		    "could not be updated due to error %d\n"),
-		    dataset, MNTTAB, errno);
-		return (MOUNT_FILEIO);
-	}
-
-	(void) endmntent(fp);
-
-	return (MOUNT_SUCCESS);
-}
-
 static void
 append_mntopt(const char *name, const char *val, char *mntopts,
     char *mtabopt, boolean_t quote)
@@ -615,11 +555,5 @@ main(int argc, char **argv)
 		}
 	}
 
-	if (!nomtab && mtab_is_writeable()) {
-		error = mtab_update(dataset, mntpoint, MNTTYPE_ZFS, mtabopt);
-		if (error)
-			return (error);
-	}
-
 	return (MOUNT_SUCCESS);
 }

cmd/zfs/zfs_main.c

@@ -6116,9 +6116,10 @@ share_mount(int op, int argc, char **argv)
 		}
 
 		/*
-		 * When mount is given no arguments, go through /etc/mtab and
-		 * display any active ZFS mounts.  We hide any snapshots, since
-		 * they are controlled automatically.
+		 * When mount is given no arguments, go through
+		 * /proc/self/mounts and display any active ZFS mounts.
+		 * We hide any snapshots, since they are controlled
+		 * automatically.
 		 */
 
 		/* Reopen MNTTAB to prevent reading stale data from open file */
@@ -6198,8 +6199,8 @@ unshare_unmount_compare(const void *larg, const void *rarg, void *unused)
 
 /*
  * Convenience routine used by zfs_do_umount() and manual_unmount().  Given an
- * absolute path, find the entry /etc/mtab, verify that its a ZFS filesystem,
- * and unmount it appropriately.
+ * absolute path, find the entry /proc/self/mounts, verify that its a
+ * ZFS filesystems, and unmount it appropriately.
  */
 static int
 unshare_unmount_path(int op, char *path, int flags, boolean_t is_manual)
@@ -6212,7 +6213,7 @@ unshare_unmount_path(int op, char *path, int flags, boolean_t is_manual)
 	ino_t path_inode;
 
 	/*
-	 * Search for the path in /etc/mtab.  Rather than looking for the
+	 * Search for the path in /proc/self/mounts. Rather than looking for the
 	 * specific path, which can be fooled by non-standard paths (i.e. ".."
 	 * or "//"), we stat() the path and search for the corresponding
 	 * (major,minor) device pair.
@@ -6243,8 +6244,8 @@ unshare_unmount_path(int op, char *path, int flags, boolean_t is_manual)
 			    "currently mounted\n"), cmdname, path);
 			return (1);
 		}
-		(void) fprintf(stderr, gettext("warning: %s not in mtab\n"),
-		    path);
+		(void) fprintf(stderr, gettext("warning: %s not in"
+		    "/proc/self/mounts\n"), path);
 		if ((ret = umount2(path, flags)) != 0)
 			(void) fprintf(stderr, gettext("%s: %s\n"), path,
 			    strerror(errno));
@@ -6355,9 +6356,9 @@ unshare_unmount(int op, int argc, char **argv)
 		/*
 		 * We could make use of zfs_for_each() to walk all datasets in
 		 * the system, but this would be very inefficient, especially
-		 * since we would have to linearly search /etc/mtab for each
-		 * one.  Instead, do one pass through /etc/mtab looking for
-		 * zfs entries and call zfs_unmount() for each one.
+		 * since we would have to linearly search /proc/self/mounts for
+		 * each one. Instead, do one pass through /proc/self/mounts
+		 * looking for zfs entries and call zfs_unmount() for each one.
 		 *
 		 * Things get a little tricky if the administrator has created
 		 * mountpoints beneath other ZFS filesystems.  In this case, we

cmd/zinject/translate.c

@@ -120,7 +120,7 @@ parse_pathname(const char *inpath, char *dataset, char *relpath,
 #else
 	if ((fp = fopen(MNTTAB, "r")) == NULL) {
 #endif
-		(void) fprintf(stderr, "cannot open /etc/mtab\n");
+		(void) fprintf(stderr, "cannot open /proc/self/mounts\n");
 		return (-1);
 	}
 

config/user-commands.m4

@@ -118,7 +118,7 @@ AC_DEFUN([ZFS_AC_CONFIG_USER_COMMANDS_LINUX], [
 	PAGESIZE=$($GETCONF PAGESIZE)
 	AC_SUBST(PAGESIZE)
 
-	MNTTAB=/etc/mtab
+	MNTTAB=/proc/self/mounts
 	AC_SUBST(MNTTAB)
 ])
 

contrib/initramfs/scripts/zfs

@@ -288,9 +288,8 @@ load_module_initrd()
 		wait_for_dev
 	fi
 
-	# zpool import refuse to import without a valid mtab
-	[ ! -f /proc/mounts ] && mount proc /proc
-	[ ! -f /etc/mtab ] && cat /proc/mounts > /etc/mtab
+	# zpool import refuse to import without a valid /proc/self/mounts
+	[ ! -f /proc/self/mounts ] && mount proc /proc
 
 	# Load the module
 	load_module "zfs" || return 1
@@ -919,7 +918,7 @@ mountroot()
 	#
 	#   but the MOUNTPOINT prefix is preserved on descendent filesystem
 	#   after the pivot into the regular root, which later breaks things
-	#   like `zfs mount -a` and the /etc/mtab refresh.
+	#   like `zfs mount -a` and the /proc/self/mounts refresh.
 	#
 	# * Mount additional filesystems required
 	#   Such as /usr, /var, /usr/local etc.

etc/init.d/zfs-functions.in

@@ -368,7 +368,7 @@ read_mtab()
 			# Set the variable.
 			eval export MTAB_$mntpnt=\"$fs\"
 		fi
-	done < /proc/mounts
+	done < /proc/self/mounts
 }
 
 in_mtab()

etc/init.d/zfs-mount.in

@@ -39,7 +39,7 @@ chkroot() {
 		if [ "$2" = "/" ]; then
 			return 0
 		fi
-	done < /etc/mtab
+	done < /proc/self/mounts
 
 	return 1
 }
@@ -178,7 +178,7 @@ do_start()
 
 	check_module_loaded "zfs" || exit 0
 
-	# Ensure / exists in /etc/mtab, if not update mtab accordingly.
+	# Ensure / exists in /proc/self/mounts.
 	# This should be handled by rc.sysinit but lets be paranoid.
 	if ! chkroot
 	then

include/sys/mntent.h

@@ -36,7 +36,6 @@
 #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	MOUNT_BUSY	0x80		/* Mount failed due to EBUSY */

lib/libspl/include/sys/mnttab.h

@@ -38,7 +38,7 @@
 #undef MNTTAB
 #endif /* MNTTAB */
 
-#define	MNTTAB		"/etc/mtab"
+#define	MNTTAB		"/proc/self/mounts"
 #define	MNT_LINE_MAX	4096
 
 #define	MNT_TOOLONG	1	/* entry exceeds MNT_LINE_MAX */

lib/libzfs/libzfs_dataset.c

@@ -1911,9 +1911,9 @@ zfs_unset_recvd_props_mode(zfs_handle_t *zhp, uint64_t *cookie)
  * zfs_prop_get_int() are built using this interface.
  *
  * Certain properties can be overridden using 'mount -o'.  In this case, scan
- * the contents of the /etc/mtab entry, searching for the appropriate options.
- * If they differ from the on-disk values, report the current values and mark
- * the source "temporary".
+ * the contents of the /proc/self/mounts entry, searching for the
+ * appropriate options. If they differ from the on-disk values, report the
+ * current values and mark the source "temporary".
  */
 static int
 get_numeric_property(zfs_handle_t *zhp, zfs_prop_t prop, zprop_source_t *src,
@@ -1984,8 +1984,9 @@ get_numeric_property(zfs_handle_t *zhp, zfs_prop_t prop, zprop_source_t *src,
 
 	/*
 	 * Because looking up the mount options is potentially expensive
-	 * (iterating over all of /etc/mtab), we defer its calculation until
-	 * we're looking up a property which requires its presence.
+	 * (iterating over all of /proc/self/mounts), we defer its
+	 * calculation until we're looking up a property which requires
+	 * its presence.
 	 */
 	if (!zhp->zfs_mntcheck &&
 	    (mntopt_on != NULL || prop == ZFS_PROP_MOUNTED)) {

lib/libzfs/libzfs_mount.c

@@ -259,9 +259,9 @@ 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
+ * than by the system call mount(2).  This ensures that the /proc/self/mounts
  * file is correctly locked for the update.  Performing our own locking
- * and /etc/mtab update requires making an unsafe assumption about how
+ * and /proc/self/mounts 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.
@@ -289,8 +289,6 @@ do_mount(const char *src, const char *mntpt, char *opts)
 	/* Return only the most critical mount error */
 	rc = libzfs_run_process(argv[0], argv, STDOUT_VERBOSE|STDERR_VERBOSE);
 	if (rc) {
-		if (rc & MOUNT_FILEIO)
-			return (EIO);
 		if (rc & MOUNT_USER)
 			return (EINTR);
 		if (rc & MOUNT_SOFTWARE)
@@ -348,7 +346,7 @@ zfs_add_option(zfs_handle_t *zhp, char *options, int len,
 
 	/*
 	 * zfs_prop_get_int() to not used to ensure our mount options
-	 * are not influenced by the current /etc/mtab contents.
+	 * are not influenced by the current /proc/self/mounts contents.
 	 */
 	value = getprop_uint64(zhp, prop, &source);
 
@@ -1182,8 +1180,8 @@ mountpoint_compare(const void *a, const void *b)
  * Unshare and unmount all datasets within the given pool.  We don't want to
  * rely on traversing the DSL to discover the filesystems within the pool,
  * because this may be expensive (if not all of them are mounted), and can fail
- * arbitrarily (on I/O error, for example).  Instead, we walk /etc/mtab and
- * gather all the filesystems that are currently mounted.
+ * arbitrarily (on I/O error, for example).  Instead, we walk /proc/self/mounts
+ * and gather all the filesystems that are currently mounted.
  */
 int
 zpool_disable_datasets(zpool_handle_t *zhp, boolean_t force)

scripts/ziltest.sh

@@ -185,7 +185,7 @@ CHECKSUM_BEFORE=$(sha256sum -b "$PAYLOAD")
 #
 # TX_WRITE (small file with ordering)
 #
-cp /etc/mtab $ROOT/small_file
+cp /proc/self/mounts $ROOT/small_file
 cp /etc/profile $ROOT/small_file
 
 #