mount: (new) be more pedantic about --make-*

Signed-off-by: Karel Zak <kzak@redhat.com>

2 files changed, 31 insertions, 11 deletions

diff --git a/sys-utils/mount.8 b/sys-utils/mount.8
index d18881b2c..5ec121092 100644
--- a/sys-utils/mount.8
+++ b/sys-utils/mount.8
@@ -398,6 +398,15 @@ command (then mount(8) does not read /etc/mtab), then you have to use bind flag
 .B mount -o remount,ro,bind
 .I olddir newdir
 .RE
+
+Note that
+.I remount,ro,bind
+will create a read-only mountpoint (VFS entry), but the original filesystem suberblock
+will be still writable, it means that the
+.I olddir
+will be writable, but the
+.I newdir
+will be read-only.
 .RE
 
 .B The move operation.
@@ -434,6 +443,11 @@ unbindable mount is a private mount which cannot be cloned through a bind
 operation. Detailed semantics is documented in Documentation/filesystems/sharedsubtree.txt
 file in the kernel source tree.
 
+Note that Linux kernel does not allow to change more propagation flags by one
+.B mount (2)
+syscall and the flags cannot be mixed with another mount options. It means that
+more --make-* options cannot be used together or with another mount options.
+
 .RS
 .nf
 .BI "mount --make-shared " mountpoint
diff --git a/sys-utils/mount.c b/sys-utils/mount.c
index d1e2e16c7..f5df087ea 100644
--- a/sys-utils/mount.c
+++ b/sys-utils/mount.c
@@ -789,37 +789,37 @@ int main(int argc, char **argv)
 			mnt_context_enable_sloppy(cxt, TRUE);
 			break;
 		case 'B':
-			oper = MS_BIND;
+			oper |= MS_BIND;
 			break;
 		case 'M':
-			oper = MS_MOVE;
+			oper |= MS_MOVE;
 			break;
 		case 'R':
-			oper = (MS_BIND | MS_REC);
+			oper |= (MS_BIND | MS_REC);
 			break;
 		case MOUNT_OPT_SHARED:
-			oper = MS_SHARED;
+			oper |= MS_SHARED;
 			break;
 		case MOUNT_OPT_SLAVE:
-			oper = MS_SLAVE;
+			oper |= MS_SLAVE;
 			break;
 		case MOUNT_OPT_PRIVATE:
-			oper = MS_PRIVATE;
+			oper |= MS_PRIVATE;
 			break;
 		case MOUNT_OPT_UNBINDABLE:
-			oper = MS_UNBINDABLE;
+			oper |= MS_UNBINDABLE;
 			break;
 		case MOUNT_OPT_RSHARED:
-			oper = (MS_SHARED | MS_REC);
+			oper |= (MS_SHARED | MS_REC);
 			break;
 		case MOUNT_OPT_RSLAVE:
-			oper = (MS_SLAVE | MS_REC);
+			oper |= (MS_SLAVE | MS_REC);
 			break;
 		case MOUNT_OPT_RPRIVATE:
-			oper = (MS_PRIVATE | MS_REC);
+			oper |= (MS_PRIVATE | MS_REC);
 			break;
 		case MOUNT_OPT_RUNBINDABLE:
-			oper = (MS_UNBINDABLE | MS_REC);
+			oper |= (MS_UNBINDABLE | MS_REC);
 			break;
 		default:
 			usage(stderr);
@@ -885,6 +885,12 @@ int main(int argc, char **argv)
 		usage(stderr);
 
 	if (oper) {
+		if (!is_power_of_2(oper))
+			errx(MOUNT_EX_USAGE, _("propagation flags (--make-* or --bind options) are mutually exclusive"));
+
+		if (oper != MS_BIND && mnt_context_get_options(cxt))
+			errx(MOUNT_EX_USAGE, _("propagation flags (--make-* options) cannot be mixed with another mount options"));
+
 		/* MS_PROPAGATION operations, let's set the mount flags */
 		mnt_context_set_mflags(cxt, oper);