tree-wide: drop support for kernels without pidfd_open() and pidfd_send_signal()

Our baseline is v5.4 now.

src/basic/missing_syscall.h

@@ -299,12 +299,7 @@ static inline long missing_get_mempolicy(int *mode, unsigned long *nodemask,
 
 #if !HAVE_PIDFD_SEND_SIGNAL
 static inline int missing_pidfd_send_signal(int fd, int sig, siginfo_t *info, unsigned flags) {
-#  ifdef __NR_pidfd_send_signal
         return syscall(__NR_pidfd_send_signal, fd, sig, info, flags);
-#  else
-        errno = ENOSYS;
-        return -1;
-#  endif
 }
 
 #  define pidfd_send_signal missing_pidfd_send_signal
@@ -312,12 +307,7 @@ static inline int missing_pidfd_send_signal(int fd, int sig, siginfo_t *info, un
 
 #if !HAVE_PIDFD_OPEN
 static inline int missing_pidfd_open(pid_t pid, unsigned flags) {
-#  ifdef __NR_pidfd_open
         return syscall(__NR_pidfd_open, pid, flags);
-#  else
-        errno = ENOSYS;
-        return -1;
-#  endif
 }
 
 #  define pidfd_open missing_pidfd_open

src/basic/pidfd-util.c

@@ -24,12 +24,8 @@ static int pidfd_check_pidfs(void) {
                 return have_pidfs;
 
         _cleanup_close_ int fd = pidfd_open(getpid_cached(), 0);
-        if (fd < 0) {
-                if (ERRNO_IS_NOT_SUPPORTED(errno))
-                        return (have_pidfs = false);
-
+        if (fd < 0)
                 return -errno;
-        }
 
         return (have_pidfs = fd_is_fs_type(fd, PID_FS_MAGIC));
 }

src/basic/pidref.c

@@ -84,8 +84,8 @@ int pidref_set_pid(PidRef *pidref, pid_t pid) {
 
         fd = pidfd_open(pid, 0);
         if (fd < 0) {
-                /* Graceful fallback in case the kernel doesn't support pidfds or is out of fds */
-                if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno) && !ERRNO_IS_RESOURCE(errno))
+                /* Graceful fallback in case the kernel is out of fds */
+                if (!ERRNO_IS_RESOURCE(errno))
                         return log_debug_errno(errno, "Failed to open pidfd for pid " PID_FMT ": %m", pid);
 
                 fd = -EBADF;