Fix stale errno in listDir causing spurious ENOMEM crash

gloo/common/linux.cc

@@ -74,6 +74,7 @@ static std::vector<std::string> listDir(const std::string& path) {
       continue;
     }
     result.push_back(dirent->d_name);
+    errno = 0;
   }
   GLOO_ENFORCE(errno == 0, strerror(errno));
   auto rv = closedir(dirp);

gloo/test/linux_test.cc

@@ -6,6 +6,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+#include <errno.h>
+
 #include <functional>
 #include <thread>
 #include <vector>
@@ -45,6 +47,15 @@ TEST_F(LinuxTest, PCIDistance) {
   }
 }
 
+// Verify that listDir (called by pciDevices) tolerates stale errno left by
+// prior allocations. Before the fix, vector::push_back inside the readdir
+// loop could leave errno=ENOMEM from a transient mmap failure, causing
+// GLOO_ENFORCE(errno == 0) to crash after readdir returns NULL at EOF.
+TEST_F(LinuxTest, PciDevicesDoesNotCrashWithStaleErrno) {
+  errno = ENOMEM;
+  ASSERT_NO_THROW(pciDevices(kPCIClassNetwork));
+}
+
 } // namespace
 } // namespace test
 } // namespace gloo