storage: Fix checking whether source filesystem is mounted

Right now, we use simple string comparison both on the source paths
(mount's output vs pool's source) and the target (mount's mnt_dir vs
pool's target). The problem are symlinks and mount indeed returns
symlinks in its output, e.g. /dev/mappper/lvm_symlink. The same goes for
the pool's source/target, so in order to successfully compare these two
replace plain string comparison with virFileComparePaths which will
resolve all symlinks and canonicalize the paths prior to comparison.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1417203Signed-off-by: NErik Skultety <eskultet@redhat.com>

src/storage/storage_backend_fs.c

@@ -301,6 +301,7 @@ virStorageBackendFileSystemIsMounted(virStoragePoolObjPtr pool)
     FILE *mtab;
     struct mntent ent;
     char buf[1024];
+    int rc1, rc2;
 
     if ((mtab = fopen(_PATH_MOUNTED, "r")) == NULL) {
         virReportSystemError(errno,
@@ -313,8 +314,15 @@ virStorageBackendFileSystemIsMounted(virStoragePoolObjPtr pool)
         if (!(src = virStorageBackendFileSystemGetPoolSource(pool)))
             goto cleanup;
 
-        if (STREQ(ent.mnt_dir, pool->def->target.path) &&
-            STREQ(ent.mnt_fsname, src)) {
+        /* compare both mount destinations and sources to be sure the mounted
+         * FS pool is really the one we're looking for
+         */
+        if ((rc1 = virFileComparePaths(ent.mnt_dir,
+                                       pool->def->target.path)) < 0 ||
+            (rc2 = virFileComparePaths(ent.mnt_fsname, src)) < 0)
+            goto cleanup;
+
+        if (rc1 && rc2) {
             ret = 1;
             goto cleanup;
         }