[UR] Add ur_close_fd and ur_duplicate_fd to utils

Author: kswiecicki

source/common/ur_util.cpp

@@ -9,15 +9,63 @@
  */
 
 #include "ur_util.hpp"
+#include "logger/ur_logger.hpp"
 
 #ifdef _WIN32
 #include <windows.h>
 int ur_getpid(void) { return static_cast<int>(GetCurrentProcessId()); }
+
+int ur_close_fd(int fd) { return -1; }
+
+int ur_duplicate_fd(int pid, int fd_in) {
+    // TODO: find another way to obtain a duplicate of another process's file descriptor
+    (void)pid;   // unused
+    (void)fd_in; // unused
+    return -1;
+}
+
 #else
 
+#include <sys/syscall.h>
 #include <unistd.h>
 int ur_getpid(void) { return static_cast<int>(getpid()); }
-#endif
+
+int ur_close_fd(int fd) { return close(fd); }
+
+int ur_duplicate_fd(int pid, int fd_in) {
+// pidfd_getfd(2) is used to obtain a duplicate of another process's file descriptor.
+// Permission to duplicate another process's file descriptor
+// is governed by a ptrace access mode PTRACE_MODE_ATTACH_REALCREDS check (see ptrace(2))
+// that can be changed using the /proc/sys/kernel/yama/ptrace_scope interface.
+// pidfd_getfd(2) is supported since Linux 5.6
+// pidfd_open(2) is supported since Linux 5.3
+#if defined(__NR_pidfd_open) && defined(__NR_pidfd_getfd)
+    errno = 0;
+    int pid_fd = syscall(SYS_pidfd_open, pid, 0);
+    if (pid_fd == -1) {
+        logger::error("SYS_pidfd_open");
+        return -1;
+    }
+
+    int fd_dup = syscall(SYS_pidfd_getfd, pid_fd, fd_in, 0);
+    close(pid_fd);
+    if (fd_dup == -1) {
+        logger::error("SYS_pidfd_getfd");
+        return -1;
+    }
+
+    return fd_dup;
+#else
+    // TODO: find another way to obtain a duplicate of another process's file descriptor
+    (void)pid;       // unused
+    (void)fd_in;     // unused
+    errno = ENOTSUP; // unsupported
+    logger::error("__NR_pidfd_open or __NR_pidfd_getfd not available");
+    return -1;
+#endif /* defined(__NR_pidfd_open) && defined(__NR_pidfd_getfd) */
+}
+
+#endif /* _WIN32 */
 
 std::optional<std::string> ur_getenv(const char *name) {
 #if defined(_WIN32)

source/common/ur_util.hpp

@@ -27,6 +27,8 @@
 #include <vector>
 
 int ur_getpid(void);
+int ur_close_fd(int fd);
+int ur_duplicate_fd(int pid, int fd_in);
 
 /* for compatibility with non-clang compilers */
 #if defined(__has_feature)