[PATCH 02/13] Update PIDFD_* constants for Linux 6.17
Adhemerval Zanella
adhemerval.zanella@linaro.org
Fri Oct 3 19:38:53 GMT 2025
The pidfd interface was extended with:
* PIDFD_GET_INFO and pidfd_info (along with related extra flags) to
allow get information about the process without the need to parse
/proc (commit cdda1f26e74ba, Linux 6.13).
* PIDFD_SELF_{THREAD,THREAD_GROUP,SELF,SELF_PROCESS} to allow
pidfd_send_signal refer to the own process or thread lead groups
without the need of allocating a file descriptor (commit f08d0c3a71114,
Linux 6.15).
* PIDFD_INFO_COREDUMP that extends PIDFD_GET_INFO to obtain coredump
information.
Linux uAPI header defines both PIDFD_SELF_THREAD and
PIDFD_SELF_THREAD_GROUP on linux/fcntl.h (since they reserve part of the
AT_* values), however for glibc I do not see any good reason to add pidfd
definitions on fcntl-linux.h.
The tst-pidfd.c is extended with some PIDFD_SELF_* tests and a new
‘tst-pidfd_getinfo.c’ test is added to check PIDFD_GET_INFO. The
PIDFD_INFO_COREDUMP tests would require very large and complex tests
that are already covered by kernel tests.
Checked on aarch64-linux-gnu and x86_64-linux-gnu on kernels 6.8 and
6.17.
---
sysdeps/unix/sysv/linux/Makefile | 1 +
sysdeps/unix/sysv/linux/sys/pidfd.h | 58 +++++++++++++++++
sysdeps/unix/sysv/linux/tst-pidfd-consts.py | 2 +-
sysdeps/unix/sysv/linux/tst-pidfd.c | 44 ++++++++++++-
sysdeps/unix/sysv/linux/tst-pidfd_getinfo.c | 71 +++++++++++++++++++++
5 files changed, 172 insertions(+), 4 deletions(-)
create mode 100644 sysdeps/unix/sysv/linux/tst-pidfd_getinfo.c
diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index 2c5bf42236..642bcc7d66 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -211,6 +211,7 @@ tests += \
tst-ofdlocks \
tst-personality \
tst-pidfd \
+ tst-pidfd_getinfo \
tst-pidfd_getpid \
tst-pkey \
tst-ppoll \
diff --git a/sysdeps/unix/sysv/linux/sys/pidfd.h b/sysdeps/unix/sysv/linux/sys/pidfd.h
index e6fc024f96..1e6da6e553 100644
--- a/sysdeps/unix/sysv/linux/sys/pidfd.h
+++ b/sysdeps/unix/sysv/linux/sys/pidfd.h
@@ -42,6 +42,64 @@
#define PIDFD_GET_USER_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 9)
#define PIDFD_GET_UTS_NAMESPACE _IO(PIDFS_IOCTL_MAGIC, 10)
+/* Sentinels to avoid allocating a file descriptor to refer to own process. */
+#define PIDFD_SELF_THREAD -10000
+#define PIDFD_SELF_THREAD_GROUP -10001
+#define PIDFD_SELF PIDFD_SELF_THREAD
+#define PIDFD_SELF_PROCESS PIDFD_SELF_THREAD_GROUP
+
+
+/* Flags for pidfd_info. */
+
+/* Always returned, even if not requested */
+#define PIDFD_INFO_PID (1UL << 0)
+/* Always returned, even if not requested */
+#define PIDFD_INFO_CREDS (1UL << 1)
+/* Always returned if available, even if not requested */
+#define PIDFD_INFO_CGROUPID (1UL << 2)
+/* Only returned if requested. */
+#define PIDFD_INFO_EXIT (1UL << 3)
+/* Only returned if requested. */
+#define PIDFD_INFO_COREDUMP (1UL << 4)
+
+
+/* Value for coredump_mask in pidfd_info. Only valid if PIDFD_INFO_COREDUMP
+ is set in mask. */
+
+/* Did crash and... */
+#define PIDFD_COREDUMPED (1U << 0)
+/* coredumping generation was skipped. */
+#define PIDFD_COREDUMP_SKIP (1U << 1)
+/* coredump was done as the user. */
+#define PIDFD_COREDUMP_USER (1U << 2)
+/* coredump was done as root. */
+#define PIDFD_COREDUMP_ROOT (1U << 3)
+
+struct pidfd_info
+{
+ __uint64_t mask;
+ __uint64_t cgroupid;
+ __uint32_t pid;
+ __uint32_t tgid;
+ __uint32_t ppid;
+ __uint32_t ruid;
+ __uint32_t rgid;
+ __uint32_t euid;
+ __uint32_t egid;
+ __uint32_t suid;
+ __uint32_t sgid;
+ __uint32_t fsuid;
+ __uint32_t fsgid;
+ __int32_t exit_code;
+ __uint32_t coredump_mask;
+ __uint32_t __spare1;
+};
+
+/* sizeof first published struct */
+#define PIDFD_INFO_SIZE_VER0 64
+
+#define PIDFD_GET_INFO _IOWR(PIDFS_IOCTL_MAGIC, 11, struct pidfd_info)
+
/* Returns a file descriptor that refers to the process PID. The
close-on-exec is set on the file descriptor. */
extern int pidfd_open (__pid_t __pid, unsigned int __flags) __THROW;
diff --git a/sysdeps/unix/sysv/linux/tst-pidfd-consts.py b/sysdeps/unix/sysv/linux/tst-pidfd-consts.py
index 18010fe0e6..6dc678380c 100644
--- a/sysdeps/unix/sysv/linux/tst-pidfd-consts.py
+++ b/sysdeps/unix/sysv/linux/tst-pidfd-consts.py
@@ -39,7 +39,7 @@ def main():
sys.exit (77)
linux_version_headers = glibcsyscalls.linux_kernel_version(args.cc)
- linux_version_glibc = (6, 12)
+ linux_version_glibc = (6, 17)
sys.exit(glibcextract.compare_macro_consts(
'#include <sys/pidfd.h>\n',
'#include <asm/fcntl.h>\n'
diff --git a/sysdeps/unix/sysv/linux/tst-pidfd.c b/sysdeps/unix/sysv/linux/tst-pidfd.c
index f7e0c5d9fa..4e4591f6c8 100644
--- a/sysdeps/unix/sysv/linux/tst-pidfd.c
+++ b/sysdeps/unix/sysv/linux/tst-pidfd.c
@@ -16,6 +16,7 @@
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
+#include <array_length.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
@@ -41,15 +42,23 @@ static pid_t ppid;
static uid_t puid;
static void
-sighandler (int sig)
+sighandler_subprocess (int sig)
{
}
+static sig_atomic_t pidfd_self_flag;
+
+static void
+sighandler_parent (int sig)
+{
+ pidfd_self_flag = 1;
+}
+
static void
subprocess (void)
{
- xsignal (SIGUSR1, sighandler);
- xsignal (SIGUSR2, sighandler);
+ xsignal (SIGUSR1, sighandler_subprocess);
+ xsignal (SIGUSR2, sighandler_subprocess);
/* Check first pidfd_send_signal with default NULL siginfo_t argument. */
{
@@ -102,6 +111,7 @@ do_test (void)
FAIL_UNSUPPORTED ("kernel does not support pidfd_getfd, skipping test");
}
+
ppid = getpid ();
puid = getuid ();
@@ -115,6 +125,34 @@ do_test (void)
TEST_COMPARE (errno, EBADF);
}
+ xsignal (SIGUSR1, sighandler_parent);
+
+ {
+ sigset_t mask, oldmask;
+ sigemptyset (&mask);
+ sigaddset (&mask, SIGUSR1);
+ TEST_COMPARE (sigprocmask (SIG_BLOCK, &mask, &oldmask), 0);
+
+ /* PIDFD_SELF_{THREAD,THREAD_GROUP} were added on Linux 6.15. On older
+ kernels pidfd_send_signal should return -1/EBADF. */
+ const int pidfd_selfs[] = { PIDFD_SELF, PIDFD_SELF_PROCESS };
+ for (int i = 0; i < array_length (pidfd_selfs); i++)
+ {
+ pidfd_self_flag = 0;
+ int r = pidfd_send_signal (pidfd_selfs[i], SIGUSR1, NULL, 0);
+ if (r == -1)
+ TEST_COMPARE (errno, EBADF);
+ else
+ {
+ while (pidfd_self_flag == 0)
+ sigsuspend (&oldmask);
+ TEST_COMPARE (pidfd_self_flag, 1);
+ }
+ }
+
+ TEST_COMPARE (sigprocmask (SIG_SETMASK, &oldmask, NULL), 0);
+ }
+
/* Check if pidfd_getpid returns ESRCH for exited subprocess. */
{
pid_t pidfork = xfork ();
diff --git a/sysdeps/unix/sysv/linux/tst-pidfd_getinfo.c b/sysdeps/unix/sysv/linux/tst-pidfd_getinfo.c
new file mode 100644
index 0000000000..948a7cdb6b
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/tst-pidfd_getinfo.c
@@ -0,0 +1,71 @@
+/* Basic tests for Linux PID_GET_INFO interfaces.
+ Copyright (C) 2022-2025 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#include <errno.h>
+#include <stdint.h>
+#include <sys/pidfd.h>
+#include <support/check.h>
+#include <support/xunistd.h>
+
+static int
+do_test (void)
+{
+ {
+ /* The pidfd_getfd syscall was the last in the set of pidfd related
+ syscalls added to the kernel. Use pidfd_getfd to decide if this
+ kernel has pidfd support that we can test. */
+ int r = pidfd_getfd (0, 0, 1);
+ TEST_VERIFY_EXIT (r == -1);
+ if (errno == ENOSYS)
+ FAIL_UNSUPPORTED ("kernel does not support pidfd_getfd, skipping test");
+ }
+
+ int pidfd = pidfd_open (getpid(), 0);
+ TEST_VERIFY (pidfd >= 0);
+
+ int pid = pidfd_getpid (pidfd);
+ TEST_VERIFY (pid >= 0);
+
+ struct pidfd_info info = {
+ .mask = PIDFD_INFO_CGROUPID,
+ };
+ if (ioctl (pidfd, PIDFD_GET_INFO, &info) != 0)
+ {
+ if (errno == ENOTTY)
+ FAIL_UNSUPPORTED ("kernel does not support PIDFD_GET_INFO");
+ else
+ FAIL_EXIT1 ("ioctl (PIDFD_GET_INFO) failed: %m");
+ }
+
+ TEST_COMPARE (info.pid, pid);
+ TEST_COMPARE (info.ppid, getppid ());
+ TEST_COMPARE (info.ruid, getuid ());
+ TEST_COMPARE (info.rgid, getgid ());
+ TEST_COMPARE (info.euid, geteuid ());
+ TEST_COMPARE (info.egid, getegid ());
+ TEST_COMPARE (info.suid, geteuid ());
+ TEST_COMPARE (info.sgid, getegid ());
+ if (info.mask & PIDFD_INFO_CGROUPID)
+ TEST_VERIFY (info.cgroupid != 0);
+
+ xclose (pidfd);
+
+ return 0;
+}
+
+#include <support/test-driver.c>
--
2.43.0
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