libmount: improve MS_REC usage

libmount allows to split one library (mount(8)) call to multiple mount(2)
syscalls, for example

   --rbind --make-rslave

in this case we have to be careful with MS_REC because the flag is
applied to multiple operations.

 # strace -e mount mount --rbind --make-rslave /mnt/A /mnt/B

Old version:

 mount("/mnt/A", "/mnt/B", 0x13ecac0, MS_MGC_VAL|MS_BIND, NULL) = 0
 mount("none", "/mnt/B", NULL, MS_REC|MS_SLAVE, NULL) = 0

Fixed version:

 mount("/mnt/A", "/mnt/B", 0x1f22ac0, MS_MGC_VAL|MS_BIND|MS_REC, NULL) = 0
 mount("none", "/mnt/B", NULL, MS_REC|MS_SLAVE, NULL) = 0

Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=1584443
Signed-off-by: Karel Zak <kzak@redhat.com>

3 files changed, 33 insertions, 6 deletions

diff --git a/libmount/src/context.c b/libmount/src/context.c
index e7f1ee934..8e00b75a9 100644
--- a/libmount/src/context.c
+++ b/libmount/src/context.c
@@ -1375,6 +1375,11 @@ struct libmnt_lock *mnt_context_get_lock(struct libmnt_context *cxt)
  *
  * both of these calls have the same effect.
  *
+ * Be careful if you want to use MS_REC flag -- in this case the bit is applied
+ * to all bind/slave/etc. options. If you want to mix more propadation flags
+ * and/or bind, move operations than it's better to specify mount options by
+ * strings.
+ *
  * Returns: 0 on success, negative number in case of error.
  */
 int mnt_context_set_mflags(struct libmnt_context *cxt, unsigned long flags)
diff --git a/libmount/src/context_mount.c b/libmount/src/context_mount.c
index b88e60507..a8e84127c 100644
--- a/libmount/src/context_mount.c
+++ b/libmount/src/context_mount.c
@@ -73,6 +73,7 @@ static int init_propagation(struct libmnt_context *cxt)
 	char *opts = (char *) mnt_fs_get_vfs_options(cxt->fs);
 	size_t namesz;
 	struct libmnt_optmap const *maps[1];
+	int rec_count = 0;
 
 	if (!opts)
 		return 0;
@@ -86,9 +87,19 @@ static int init_propagation(struct libmnt_context *cxt)
 		struct libmnt_addmount *ad;
 		int rc;
 
-		if (!mnt_optmap_get_entry(maps, 1, name, namesz, &ent)
-		    || !ent
-		    || !(ent->id & MS_PROPAGATION))
+		if (!mnt_optmap_get_entry(maps, 1, name, namesz, &ent) || !ent)
+			continue;
+
+		DBG(CXT, ul_debugobj(cxt, " checking %s", ent->name));
+
+		/* Note that MS_REC may be used for more flags, so we have to keep
+		 * track about number of recursive options to keep the MS_REC in the
+		 * mountflags if necessary.
+		 */
+		if (ent->id & MS_REC)
+			rec_count++;
+
+		if (!(ent->id & MS_PROPAGATION))
 			continue;
 
 		ad = mnt_new_addmount();
@@ -96,13 +107,21 @@ static int init_propagation(struct libmnt_context *cxt)
 			return -ENOMEM;
 
 		ad->mountflags = ent->id;
+		DBG(CXT, ul_debugobj(cxt, " adding extra mount(2) call for %s", ent->name));
 		rc = mnt_context_append_additional_mount(cxt, ad);
 		if (rc)
 			return rc;
 
+		DBG(CXT, ul_debugobj(cxt, " removing %s from primary mount(2) call", ent->name));
 		cxt->mountflags &= ~ent->id;
+
+		if (ent->id & MS_REC)
+			rec_count--;
 	}
 
+	if (rec_count)
+		cxt->mountflags |= MS_REC;
+
 	return 0;
 }
 
diff --git a/libmount/src/optstr.c b/libmount/src/optstr.c
index 8248f0dee..cc077ffd9 100644
--- a/libmount/src/optstr.c
+++ b/libmount/src/optstr.c
@@ -800,14 +800,17 @@ int mnt_optstr_apply_flags(char **optstr, unsigned long flags,
 					if (rc)
 						goto err;
 				}
-				if (!(ent->mask & MNT_INVERT))
+				if (!(ent->mask & MNT_INVERT)) {
 					fl &= ~ent->id;
+					if (ent->id & MS_REC)
+						fl |= MS_REC;
+				}
 			}
 		}
 	}
 
-	/* add missing options */
-	if (fl) {
+	/* add missing options (but ignore fl if contains MS_REC only) */
+	if (fl && fl != MS_REC) {
 		const struct libmnt_optmap *ent;
 		char *p;