pidfd fixes for v5.2-rc4

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Merge tag 'pidfd-fixes-v5.2-rc4' of gitolite.kernel.org:pub/scm/linux/kernel/git/brauner/linux

Pull pidfd fixes from Christian Brauner:
 "The contains two small patches to the pidfd samples and test binaries
  respectively.

  They were lacking appropriate ifdefines for __NR_pidfd_send_signal and
  could hence lead to compilation errors when that was not defined.

  This was spotted on mips independently by Guenter Roeck (who was kind
  enough to send a fix for the samples binary) and Arnd who spotted it
  in linux-next.

  Apart from these two patches, there's also a patch to update the
  comments for the pidfd_send_signal() syscall which were slightly
  wrong/inconsistenly worded"

* tag 'pidfd-fixes-v5.2-rc4' of gitolite.kernel.org:pub/scm/linux/kernel/git/brauner/linux:
  tests: fix pidfd-test compilation
  signal: improve comments
  samples: fix pidfd-metadata compilation

kernel/signal.c

@@ -3621,12 +3621,11 @@ static struct pid *pidfd_to_pid(const struct file *file)
 }
 
 /**
- * sys_pidfd_send_signal - send a signal to a process through a task file
- *                          descriptor
- * @pidfd:  the file descriptor of the process
- * @sig:    signal to be sent
- * @info:   the signal info
- * @flags:  future flags to be passed
+ * sys_pidfd_send_signal - Signal a process through a pidfd
+ * @pidfd:  file descriptor of the process
+ * @sig:    signal to send
+ * @info:   signal info
+ * @flags:  future flags
  *
  * The syscall currently only signals via PIDTYPE_PID which covers
  * kill(<positive-pid>, <signal>. It does not signal threads or process

samples/pidfd/pidfd-metadata.c

@@ -21,6 +21,10 @@
 #define CLONE_PIDFD 0x00001000
 #endif
 
+#ifndef __NR_pidfd_send_signal
+#define __NR_pidfd_send_signal -1
+#endif
+
 static int do_child(void *args)
 {
 	printf("%d\n", getpid());

tools/testing/selftests/pidfd/pidfd_test.c

@@ -16,6 +16,10 @@
 
 #include "../kselftest.h"
 
+#ifndef __NR_pidfd_send_signal
+#define __NR_pidfd_send_signal -1
+#endif
+
 static inline int sys_pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
 					unsigned int flags)
 {