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>

diff --git a/libmount/src/context.c b/libmount/src/context.c
index e7f1ee9348fc2c4829b1f5d91482aeeb0301292c..8e00b75a9e70f098d0a4889eec379cf47f8b02ac 100644 (file)
--- 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 b88e605071c479f4d9c52153eacfcd02d0b1db6c..a8e84127cfe6352bc4f283394d6fa53137dc09e9 100644 (file)
--- 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 8248f0dee8c26245691c7c87e953336195c8b869..cc077ffd94d13a8571100e0944ae84286fffe619 100644 (file)
--- 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;