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-rw-r--r--arch/arm/kvm/Kconfig1
-rw-r--r--arch/arm64/kvm/Kconfig1
-rw-r--r--arch/mips/kvm/Kconfig1
-rw-r--r--arch/powerpc/kvm/Kconfig1
-rw-r--r--arch/s390/kvm/Kconfig1
-rw-r--r--arch/x86/Kconfig1
-rw-r--r--arch/x86/kvm/Kconfig1
-rw-r--r--drivers/base/Kconfig1
-rw-r--r--drivers/char/tpm/Kconfig1
-rw-r--r--drivers/dma-buf/Kconfig1
-rw-r--r--drivers/gpio/Kconfig1
-rw-r--r--drivers/iio/Kconfig1
-rw-r--r--drivers/infiniband/Kconfig1
-rw-r--r--drivers/vfio/Kconfig1
-rw-r--r--fs/Makefile2
-rw-r--r--fs/notify/fanotify/Kconfig1
-rw-r--r--fs/notify/inotify/Kconfig1
-rw-r--r--include/linux/pid.h2
-rw-r--r--include/uapi/linux/sched.h1
-rw-r--r--init/Kconfig10
-rw-r--r--kernel/fork.c107
-rw-r--r--kernel/signal.c12
-rw-r--r--kernel/sys_ni.c3
-rw-r--r--samples/Makefile2
-rw-r--r--samples/pidfd/Makefile6
-rw-r--r--samples/pidfd/pidfd-metadata.c112
26 files changed, 235 insertions, 38 deletions
diff --git a/arch/arm/kvm/Kconfig b/arch/arm/kvm/Kconfig
index 3f5320f46de2..f591026347a5 100644
--- a/arch/arm/kvm/Kconfig
+++ b/arch/arm/kvm/Kconfig
@@ -22,7 +22,6 @@ config KVM
bool "Kernel-based Virtual Machine (KVM) support"
depends on MMU && OF
select PREEMPT_NOTIFIERS
- select ANON_INODES
select ARM_GIC
select ARM_GIC_V3
select ARM_GIC_V3_ITS
diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index a3f85624313e..a67121d419a2 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -23,7 +23,6 @@ config KVM
depends on OF
select MMU_NOTIFIER
select PREEMPT_NOTIFIERS
- select ANON_INODES
select HAVE_KVM_CPU_RELAX_INTERCEPT
select HAVE_KVM_ARCH_TLB_FLUSH_ALL
select KVM_MMIO
diff --git a/arch/mips/kvm/Kconfig b/arch/mips/kvm/Kconfig
index 4528bc9c3cb1..eac25aef21e0 100644
--- a/arch/mips/kvm/Kconfig
+++ b/arch/mips/kvm/Kconfig
@@ -21,7 +21,6 @@ config KVM
depends on MIPS_FP_SUPPORT
select EXPORT_UASM
select PREEMPT_NOTIFIERS
- select ANON_INODES
select KVM_GENERIC_DIRTYLOG_READ_PROTECT
select HAVE_KVM_VCPU_ASYNC_IOCTL
select KVM_MMIO
diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
index bfdde04e4905..f53997a8ca62 100644
--- a/arch/powerpc/kvm/Kconfig
+++ b/arch/powerpc/kvm/Kconfig
@@ -20,7 +20,6 @@ if VIRTUALIZATION
config KVM
bool
select PREEMPT_NOTIFIERS
- select ANON_INODES
select HAVE_KVM_EVENTFD
select HAVE_KVM_VCPU_ASYNC_IOCTL
select SRCU
diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig
index 767453faacfc..1816ee48eadd 100644
--- a/arch/s390/kvm/Kconfig
+++ b/arch/s390/kvm/Kconfig
@@ -21,7 +21,6 @@ config KVM
prompt "Kernel-based Virtual Machine (KVM) support"
depends on HAVE_KVM
select PREEMPT_NOTIFIERS
- select ANON_INODES
select HAVE_KVM_CPU_RELAX_INTERCEPT
select HAVE_KVM_VCPU_ASYNC_IOCTL
select HAVE_KVM_EVENTFD
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 0a3cc347143f..e7212731cffb 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -44,7 +44,6 @@ config X86
#
select ACPI_LEGACY_TABLES_LOOKUP if ACPI
select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
- select ANON_INODES
select ARCH_32BIT_OFF_T if X86_32
select ARCH_CLOCKSOURCE_DATA
select ARCH_CLOCKSOURCE_INIT
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 72fa955f4a15..fc042419e670 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -27,7 +27,6 @@ config KVM
depends on X86_LOCAL_APIC
select PREEMPT_NOTIFIERS
select MMU_NOTIFIER
- select ANON_INODES
select HAVE_KVM_IRQCHIP
select HAVE_KVM_IRQFD
select IRQ_BYPASS_MANAGER
diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index 059700ea3521..03f067da12ee 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -174,7 +174,6 @@ source "drivers/base/regmap/Kconfig"
config DMA_SHARED_BUFFER
bool
default n
- select ANON_INODES
select IRQ_WORK
help
This option enables the framework for buffer-sharing between
diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
index 536e55d3919f..f3e4bc490cf0 100644
--- a/drivers/char/tpm/Kconfig
+++ b/drivers/char/tpm/Kconfig
@@ -157,7 +157,6 @@ config TCG_CRB
config TCG_VTPM_PROXY
tristate "VTPM Proxy Interface"
depends on TCG_TPM
- select ANON_INODES
---help---
This driver proxies for an emulated TPM (vTPM) running in userspace.
A device /dev/vtpmx is provided that creates a device pair
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
index 2e5a0faa2cb1..3fc9c2efc583 100644
--- a/drivers/dma-buf/Kconfig
+++ b/drivers/dma-buf/Kconfig
@@ -3,7 +3,6 @@ menu "DMABUF options"
config SYNC_FILE
bool "Explicit Synchronization Framework"
default n
- select ANON_INODES
select DMA_SHARED_BUFFER
---help---
The Sync File Framework adds explicit syncronization via
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 3f50526a771f..0f91600c27ae 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -12,7 +12,6 @@ config ARCH_HAVE_CUSTOM_GPIO_H
menuconfig GPIOLIB
bool "GPIO Support"
- select ANON_INODES
help
This enables GPIO support through the generic GPIO library.
You only need to enable this, if you also want to enable
diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
index d08aeb41cd07..1dec0fecb6ef 100644
--- a/drivers/iio/Kconfig
+++ b/drivers/iio/Kconfig
@@ -4,7 +4,6 @@
menuconfig IIO
tristate "Industrial I/O support"
- select ANON_INODES
help
The industrial I/O subsystem provides a unified framework for
drivers for many different types of embedded sensors using a
diff --git a/drivers/infiniband/Kconfig b/drivers/infiniband/Kconfig
index a1fb840de45d..d318bab25860 100644
--- a/drivers/infiniband/Kconfig
+++ b/drivers/infiniband/Kconfig
@@ -25,7 +25,6 @@ config INFINIBAND_USER_MAD
config INFINIBAND_USER_ACCESS
tristate "InfiniBand userspace access (verbs and CM)"
- select ANON_INODES
depends on MMU
---help---
Userspace InfiniBand access support. This enables the
diff --git a/drivers/vfio/Kconfig b/drivers/vfio/Kconfig
index 9de5ed38da83..3798d77d131c 100644
--- a/drivers/vfio/Kconfig
+++ b/drivers/vfio/Kconfig
@@ -22,7 +22,6 @@ menuconfig VFIO
tristate "VFIO Non-Privileged userspace driver framework"
depends on IOMMU_API
select VFIO_IOMMU_TYPE1 if (X86 || S390 || ARM || ARM64)
- select ANON_INODES
help
VFIO provides a framework for secure userspace device drivers.
See Documentation/vfio.txt for more details.
diff --git a/fs/Makefile b/fs/Makefile
index 427fec226fae..35945f8139e6 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -25,7 +25,7 @@ obj-$(CONFIG_PROC_FS) += proc_namespace.o
obj-y += notify/
obj-$(CONFIG_EPOLL) += eventpoll.o
-obj-$(CONFIG_ANON_INODES) += anon_inodes.o
+obj-y += anon_inodes.o
obj-$(CONFIG_SIGNALFD) += signalfd.o
obj-$(CONFIG_TIMERFD) += timerfd.o
obj-$(CONFIG_EVENTFD) += eventfd.o
diff --git a/fs/notify/fanotify/Kconfig b/fs/notify/fanotify/Kconfig
index 735bfb2e9190..521dc91d2cb5 100644
--- a/fs/notify/fanotify/Kconfig
+++ b/fs/notify/fanotify/Kconfig
@@ -1,7 +1,6 @@
config FANOTIFY
bool "Filesystem wide access notification"
select FSNOTIFY
- select ANON_INODES
select EXPORTFS
default n
---help---
diff --git a/fs/notify/inotify/Kconfig b/fs/notify/inotify/Kconfig
index b981fc0c8379..0161c74e76e2 100644
--- a/fs/notify/inotify/Kconfig
+++ b/fs/notify/inotify/Kconfig
@@ -1,6 +1,5 @@
config INOTIFY_USER
bool "Inotify support for userspace"
- select ANON_INODES
select FSNOTIFY
default y
---help---
diff --git a/include/linux/pid.h b/include/linux/pid.h
index b6f4ba16065a..3c8ef5a199ca 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -66,6 +66,8 @@ struct pid
extern struct pid init_struct_pid;
+extern const struct file_operations pidfd_fops;
+
static inline struct pid *get_pid(struct pid *pid)
{
if (pid)
diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index 22627f80063e..ed4ee170bee2 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -10,6 +10,7 @@
#define CLONE_FS 0x00000200 /* set if fs info shared between processes */
#define CLONE_FILES 0x00000400 /* set if open files shared between processes */
#define CLONE_SIGHAND 0x00000800 /* set if signal handlers and blocked signals shared */
+#define CLONE_PIDFD 0x00001000 /* set if a pidfd should be placed in parent */
#define CLONE_PTRACE 0x00002000 /* set if we want to let tracing continue on the child too */
#define CLONE_VFORK 0x00004000 /* set if the parent wants the child to wake it up on mm_release */
#define CLONE_PARENT 0x00008000 /* set if we want to have the same parent as the cloner */
diff --git a/init/Kconfig b/init/Kconfig
index 4592bf7997c0..be8f97e37a76 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1171,9 +1171,6 @@ config LD_DEAD_CODE_DATA_ELIMINATION
config SYSCTL
bool
-config ANON_INODES
- bool
-
config HAVE_UID16
bool
@@ -1378,14 +1375,12 @@ config HAVE_FUTEX_CMPXCHG
config EPOLL
bool "Enable eventpoll support" if EXPERT
default y
- select ANON_INODES
help
Disabling this option will cause the kernel to be built without
support for epoll family of system calls.
config SIGNALFD
bool "Enable signalfd() system call" if EXPERT
- select ANON_INODES
default y
help
Enable the signalfd() system call that allows to receive signals
@@ -1395,7 +1390,6 @@ config SIGNALFD
config TIMERFD
bool "Enable timerfd() system call" if EXPERT
- select ANON_INODES
default y
help
Enable the timerfd() system call that allows to receive timer
@@ -1405,7 +1399,6 @@ config TIMERFD
config EVENTFD
bool "Enable eventfd() system call" if EXPERT
- select ANON_INODES
default y
help
Enable the eventfd() system call that allows to receive both
@@ -1516,7 +1509,6 @@ config KALLSYMS_BASE_RELATIVE
# syscall, maps, verifier
config BPF_SYSCALL
bool "Enable bpf() system call"
- select ANON_INODES
select BPF
select IRQ_WORK
default n
@@ -1533,7 +1525,6 @@ config BPF_JIT_ALWAYS_ON
config USERFAULTFD
bool "Enable userfaultfd() system call"
- select ANON_INODES
depends on MMU
help
Enable the userfaultfd() system call that allows to intercept and
@@ -1600,7 +1591,6 @@ config PERF_EVENTS
bool "Kernel performance events and counters"
default y if PROFILING
depends on HAVE_PERF_EVENTS
- select ANON_INODES
select IRQ_WORK
select SRCU
help
diff --git a/kernel/fork.c b/kernel/fork.c
index fbe9dfcd8680..8b03d93ba068 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -11,6 +11,7 @@
* management can be a bitch. See 'mm/memory.c': 'copy_page_range()'
*/
+#include <linux/anon_inodes.h>
#include <linux/slab.h>
#include <linux/sched/autogroup.h>
#include <linux/sched/mm.h>
@@ -21,6 +22,7 @@
#include <linux/sched/task.h>
#include <linux/sched/task_stack.h>
#include <linux/sched/cputime.h>
+#include <linux/seq_file.h>
#include <linux/rtmutex.h>
#include <linux/init.h>
#include <linux/unistd.h>
@@ -1670,6 +1672,58 @@ static inline void rcu_copy_process(struct task_struct *p)
#endif /* #ifdef CONFIG_TASKS_RCU */
}
+static int pidfd_release(struct inode *inode, struct file *file)
+{
+ struct pid *pid = file->private_data;
+
+ file->private_data = NULL;
+ put_pid(pid);
+ return 0;
+}
+
+#ifdef CONFIG_PROC_FS
+static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
+{
+ struct pid_namespace *ns = proc_pid_ns(file_inode(m->file));
+ struct pid *pid = f->private_data;
+
+ seq_put_decimal_ull(m, "Pid:\t", pid_nr_ns(pid, ns));
+ seq_putc(m, '\n');
+}
+#endif
+
+const struct file_operations pidfd_fops = {
+ .release = pidfd_release,
+#ifdef CONFIG_PROC_FS
+ .show_fdinfo = pidfd_show_fdinfo,
+#endif
+};
+
+/**
+ * pidfd_create() - Create a new pid file descriptor.
+ *
+ * @pid: struct pid that the pidfd will reference
+ *
+ * This creates a new pid file descriptor with the O_CLOEXEC flag set.
+ *
+ * Note, that this function can only be called after the fd table has
+ * been unshared to avoid leaking the pidfd to the new process.
+ *
+ * Return: On success, a cloexec pidfd is returned.
+ * On error, a negative errno number will be returned.
+ */
+static int pidfd_create(struct pid *pid)
+{
+ int fd;
+
+ fd = anon_inode_getfd("[pidfd]", &pidfd_fops, get_pid(pid),
+ O_RDWR | O_CLOEXEC);
+ if (fd < 0)
+ put_pid(pid);
+
+ return fd;
+}
+
/*
* This creates a new process as a copy of the old one,
* but does not actually start it yet.
@@ -1682,13 +1736,14 @@ static __latent_entropy struct task_struct *copy_process(
unsigned long clone_flags,
unsigned long stack_start,
unsigned long stack_size,
+ int __user *parent_tidptr,
int __user *child_tidptr,
struct pid *pid,
int trace,
unsigned long tls,
int node)
{
- int retval;
+ int pidfd = -1, retval;
struct task_struct *p;
struct multiprocess_signals delayed;
@@ -1738,6 +1793,31 @@ static __latent_entropy struct task_struct *copy_process(
return ERR_PTR(-EINVAL);
}
+ if (clone_flags & CLONE_PIDFD) {
+ int reserved;
+
+ /*
+ * - CLONE_PARENT_SETTID is useless for pidfds and also
+ * parent_tidptr is used to return pidfds.
+ * - CLONE_DETACHED is blocked so that we can potentially
+ * reuse it later for CLONE_PIDFD.
+ * - CLONE_THREAD is blocked until someone really needs it.
+ */
+ if (clone_flags &
+ (CLONE_DETACHED | CLONE_PARENT_SETTID | CLONE_THREAD))
+ return ERR_PTR(-EINVAL);
+
+ /*
+ * Verify that parent_tidptr is sane so we can potentially
+ * reuse it later.
+ */
+ if (get_user(reserved, parent_tidptr))
+ return ERR_PTR(-EFAULT);
+
+ if (reserved != 0)
+ return ERR_PTR(-EINVAL);
+ }
+
/*
* Force any signals received before this point to be delivered
* before the fork happens. Collect up signals sent to multiple
@@ -1944,6 +2024,22 @@ static __latent_entropy struct task_struct *copy_process(
}
}
+ /*
+ * This has to happen after we've potentially unshared the file
+ * descriptor table (so that the pidfd doesn't leak into the child
+ * if the fd table isn't shared).
+ */
+ if (clone_flags & CLONE_PIDFD) {
+ retval = pidfd_create(pid);
+ if (retval < 0)
+ goto bad_fork_free_pid;
+
+ pidfd = retval;
+ retval = put_user(pidfd, parent_tidptr);
+ if (retval)
+ goto bad_fork_put_pidfd;
+ }
+
#ifdef CONFIG_BLOCK
p->plug = NULL;
#endif
@@ -2004,7 +2100,7 @@ static __latent_entropy struct task_struct *copy_process(
*/
retval = cgroup_can_fork(p);
if (retval)
- goto bad_fork_free_pid;
+ goto bad_fork_put_pidfd;
/*
* From this point on we must avoid any synchronous user-space
@@ -2119,6 +2215,9 @@ bad_fork_cancel_cgroup:
spin_unlock(&current->sighand->siglock);
write_unlock_irq(&tasklist_lock);
cgroup_cancel_fork(p);
+bad_fork_put_pidfd:
+ if (clone_flags & CLONE_PIDFD)
+ ksys_close(pidfd);
bad_fork_free_pid:
cgroup_threadgroup_change_end(current);
if (pid != &init_struct_pid)
@@ -2184,7 +2283,7 @@ static inline void init_idle_pids(struct task_struct *idle)
struct task_struct *fork_idle(int cpu)
{
struct task_struct *task;
- task = copy_process(CLONE_VM, 0, 0, NULL, &init_struct_pid, 0, 0,
+ task = copy_process(CLONE_VM, 0, 0, NULL, NULL, &init_struct_pid, 0, 0,
cpu_to_node(cpu));
if (!IS_ERR(task)) {
init_idle_pids(task);
@@ -2236,7 +2335,7 @@ long _do_fork(unsigned long clone_flags,
trace = 0;
}
- p = copy_process(clone_flags, stack_start, stack_size,
+ p = copy_process(clone_flags, stack_start, stack_size, parent_tidptr,
child_tidptr, NULL, trace, tls, NUMA_NO_NODE);
add_latent_entropy();
diff --git a/kernel/signal.c b/kernel/signal.c
index 227ba170298e..cd83cc376767 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3513,7 +3513,6 @@ SYSCALL_DEFINE2(kill, pid_t, pid, int, sig)
return kill_something_info(sig, &info, pid);
}
-#ifdef CONFIG_PROC_FS
/*
* Verify that the signaler and signalee either are in the same pid namespace
* or that the signaler's pid namespace is an ancestor of the signalee's pid
@@ -3550,6 +3549,14 @@ static int copy_siginfo_from_user_any(kernel_siginfo_t *kinfo, siginfo_t *info)
return copy_siginfo_from_user(kinfo, info);
}
+static struct pid *pidfd_to_pid(const struct file *file)
+{
+ if (file->f_op == &pidfd_fops)
+ return file->private_data;
+
+ return tgid_pidfd_to_pid(file);
+}
+
/**
* sys_pidfd_send_signal - send a signal to a process through a task file
* descriptor
@@ -3586,7 +3593,7 @@ SYSCALL_DEFINE4(pidfd_send_signal, int, pidfd, int, sig,
return -EBADF;
/* Is this a pidfd? */
- pid = tgid_pidfd_to_pid(f.file);
+ pid = pidfd_to_pid(f.file);
if (IS_ERR(pid)) {
ret = PTR_ERR(pid);
goto err;
@@ -3620,7 +3627,6 @@ err:
fdput(f);
return ret;
}
-#endif /* CONFIG_PROC_FS */
static int
do_send_specific(pid_t tgid, pid_t pid, int sig, struct kernel_siginfo *info)
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index d21f4befaea4..4d9ae5ea6caf 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -167,9 +167,6 @@ COND_SYSCALL(syslog);
/* kernel/sched/core.c */
-/* kernel/signal.c */
-COND_SYSCALL(pidfd_send_signal);
-
/* kernel/sys.c */
COND_SYSCALL(setregid);
COND_SYSCALL(setgid);
diff --git a/samples/Makefile b/samples/Makefile
index b1142a958811..fadadb1c3b05 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -3,4 +3,4 @@
obj-$(CONFIG_SAMPLES) += kobject/ kprobes/ trace_events/ livepatch/ \
hw_breakpoint/ kfifo/ kdb/ hidraw/ rpmsg/ seccomp/ \
configfs/ connector/ v4l/ trace_printk/ \
- vfio-mdev/ statx/ qmi/ binderfs/
+ vfio-mdev/ statx/ qmi/ binderfs/ pidfd/
diff --git a/samples/pidfd/Makefile b/samples/pidfd/Makefile
new file mode 100644
index 000000000000..0ff97784177a
--- /dev/null
+++ b/samples/pidfd/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+
+hostprogs-y := pidfd-metadata
+always := $(hostprogs-y)
+HOSTCFLAGS_pidfd-metadata.o += -I$(objtree)/usr/include
+all: pidfd-metadata
diff --git a/samples/pidfd/pidfd-metadata.c b/samples/pidfd/pidfd-metadata.c
new file mode 100644
index 000000000000..640f5f757c57
--- /dev/null
+++ b/samples/pidfd/pidfd-metadata.c
@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#define _GNU_SOURCE
+#include <err.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <inttypes.h>
+#include <limits.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#ifndef CLONE_PIDFD
+#define CLONE_PIDFD 0x00001000
+#endif
+
+static int do_child(void *args)
+{
+ printf("%d\n", getpid());
+ _exit(EXIT_SUCCESS);
+}
+
+static pid_t pidfd_clone(int flags, int *pidfd)
+{
+ size_t stack_size = 1024;
+ char *stack[1024] = { 0 };
+
+#ifdef __ia64__
+ return __clone2(do_child, stack, stack_size, flags | SIGCHLD, NULL, pidfd);
+#else
+ return clone(do_child, stack + stack_size, flags | SIGCHLD, NULL, pidfd);
+#endif
+}
+
+static inline int sys_pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
+ unsigned int flags)
+{
+ return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
+}
+
+static int pidfd_metadata_fd(pid_t pid, int pidfd)
+{
+ int procfd, ret;
+ char path[100];
+
+ snprintf(path, sizeof(path), "/proc/%d", pid);
+ procfd = open(path, O_DIRECTORY | O_RDONLY | O_CLOEXEC);
+ if (procfd < 0) {
+ warn("Failed to open %s\n", path);
+ return -1;
+ }
+
+ /*
+ * Verify that the pid has not been recycled and our /proc/<pid> handle
+ * is still valid.
+ */
+ ret = sys_pidfd_send_signal(pidfd, 0, NULL, 0);
+ if (ret < 0) {
+ switch (errno) {
+ case EPERM:
+ /* Process exists, just not allowed to signal it. */
+ break;
+ default:
+ warn("Failed to signal process\n");
+ close(procfd);
+ procfd = -1;
+ }
+ }
+
+ return procfd;
+}
+
+int main(int argc, char *argv[])
+{
+ int pidfd = 0, ret = EXIT_FAILURE;
+ char buf[4096] = { 0 };
+ pid_t pid;
+ int procfd, statusfd;
+ ssize_t bytes;
+
+ pid = pidfd_clone(CLONE_PIDFD, &pidfd);
+ if (pid < 0)
+ exit(ret);
+
+ procfd = pidfd_metadata_fd(pid, pidfd);
+ close(pidfd);
+ if (procfd < 0)
+ goto out;
+
+ statusfd = openat(procfd, "status", O_RDONLY | O_CLOEXEC);
+ close(procfd);
+ if (statusfd < 0)
+ goto out;
+
+ bytes = read(statusfd, buf, sizeof(buf));
+ if (bytes > 0)
+ bytes = write(STDOUT_FILENO, buf, bytes);
+ close(statusfd);
+ ret = EXIT_SUCCESS;
+
+out:
+ (void)wait(NULL);
+
+ exit(ret);
+}