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Subject[PATCH 2/2] samples: make pidfd-metadata fail gracefully on older kernels
Initialize pidfd to an invalid descriptor, to fail gracefully on
those kernels that do not implement CLONE_PIDFD and leave pidfd
unchanged.

Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
---
samples/pidfd/pidfd-metadata.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/samples/pidfd/pidfd-metadata.c b/samples/pidfd/pidfd-metadata.c
index 14b454448429..c459155daf9a 100644
--- a/samples/pidfd/pidfd-metadata.c
+++ b/samples/pidfd/pidfd-metadata.c
@@ -83,7 +83,7 @@ static int pidfd_metadata_fd(pid_t pid, int pidfd)

int main(int argc, char *argv[])
{
- int pidfd = 0, ret = EXIT_FAILURE;
+ int pidfd = -1, ret = EXIT_FAILURE;
char buf[4096] = { 0 };
pid_t pid;
int procfd, statusfd;
@@ -91,7 +91,11 @@ int main(int argc, char *argv[])

pid = pidfd_clone(CLONE_PIDFD, &pidfd);
if (pid < 0)
- exit(ret);
+ err(ret, "CLONE_PIDFD");
+ if (pidfd == -1) {
+ warnx("CLONE_PIDFD is not supported by the kernel");
+ goto out;
+ }

procfd = pidfd_metadata_fd(pid, pidfd);
close(pidfd);
--
ldv
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