Reading while there is data to read in FIFO

Author: SuperStrongDinosaur

base/cvd/cuttlefish/common/libs/fs/shared_fd.cpp

@@ -518,17 +518,32 @@ int SharedFD::Fchdir(SharedFD shared_fd) {
 
 Result<SharedFD> SharedFD::Fifo(const std::string& path, mode_t mode) {
   struct stat st {};
+  bool existed = false;
   if (TEMP_FAILURE_RETRY(stat(path.c_str(), &st)) != 0) {
     CF_EXPECTF(TEMP_FAILURE_RETRY(mkfifo(path.c_str(), mode)) == 0,
                "Failed to mkfifo('{}', {:o}): {}", path, mode,
                ::cuttlefish::StrError(errno));
   } else {
     CF_EXPECTF(S_ISFIFO(st.st_mode),
                "File at '{}' exists but is not a FIFO", path);
+    existed = true;
   }
 
   auto ret = Open(path, O_RDWR);
   CF_EXPECTF(ret->IsOpen(), "Failed to open '{}': '{}'", path, ret->StrError());
+
+  if (existed) {
+    int flags = ret->Fcntl(F_GETFL, 0);
+    if (flags >= 0) {
+      ret->Fcntl(F_SETFL, flags | O_NONBLOCK);
+      char buf[4096];
+      while (ret->Read(buf, sizeof(buf)) > 0) {
+        // Reading while there is data to read
+      }
+      ret->Fcntl(F_SETFL, flags);
+    }
+  }
+
   return ret;
 }