12 files changed, 687 insertions, 0 deletions

diff --git a/tools/testing/selftests/proc/.gitignore b/tools/testing/selftests/proc/.gitignore
new file mode 100644
index 000000000000..6c16f77c722c
--- /dev/null
+++ b/tools/testing/selftests/proc/.gitignore
@@ -0,0 +1,8 @@
+/proc-loadavg-001
+/proc-self-map-files-001
+/proc-self-map-files-002
+/proc-self-syscall
+/proc-self-wchan
+/proc-uptime-001
+/proc-uptime-002
+/read
diff --git a/tools/testing/selftests/proc/Makefile b/tools/testing/selftests/proc/Makefile
new file mode 100644
index 000000000000..dbb87e56264c
--- /dev/null
+++ b/tools/testing/selftests/proc/Makefile
@@ -0,0 +1,13 @@
+CFLAGS += -Wall -O2
+
+TEST_GEN_PROGS :=
+TEST_GEN_PROGS += proc-loadavg-001
+TEST_GEN_PROGS += proc-self-map-files-001
+TEST_GEN_PROGS += proc-self-map-files-002
+TEST_GEN_PROGS += proc-self-syscall
+TEST_GEN_PROGS += proc-self-wchan
+TEST_GEN_PROGS += proc-uptime-001
+TEST_GEN_PROGS += proc-uptime-002
+TEST_GEN_PROGS += read
+
+include ../lib.mk
diff --git a/tools/testing/selftests/proc/config b/tools/testing/selftests/proc/config
new file mode 100644
index 000000000000..68fbd2b35884
--- /dev/null
+++ b/tools/testing/selftests/proc/config
@@ -0,0 +1 @@
+CONFIG_PROC_FS=y
diff --git a/tools/testing/selftests/proc/proc-loadavg-001.c b/tools/testing/selftests/proc/proc-loadavg-001.c
new file mode 100644
index 000000000000..e38ad6d94d4b
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-loadavg-001.c
@@ -0,0 +1,83 @@
+/*
+ * Copyright _ 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/* Test that /proc/loadavg correctly reports last pid in pid namespace. */
+#define _GNU_SOURCE
+#include <errno.h>
+#include <sched.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/wait.h>
+
+int main(void)
+{
+	pid_t pid;
+	int wstatus;
+
+	if (unshare(CLONE_NEWPID) == -1) {
+		if (errno == ENOSYS || errno == EPERM)
+			return 2;
+		return 1;
+	}
+
+	pid = fork();
+	if (pid == -1)
+		return 1;
+	if (pid == 0) {
+		char buf[128], *p;
+		int fd;
+		ssize_t rv;
+
+		fd = open("/proc/loadavg" , O_RDONLY);
+		if (fd == -1)
+			return 1;
+		rv = read(fd, buf, sizeof(buf));
+		if (rv < 3)
+			return 1;
+		p = buf + rv;
+
+		/* pid 1 */
+		if (!(p[-3] == ' ' && p[-2] == '1' && p[-1] == '\n'))
+			return 1;
+
+		pid = fork();
+		if (pid == -1)
+			return 1;
+		if (pid == 0)
+			return 0;
+		if (waitpid(pid, NULL, 0) == -1)
+			return 1;
+
+		lseek(fd, 0, SEEK_SET);
+		rv = read(fd, buf, sizeof(buf));
+		if (rv < 3)
+			return 1;
+		p = buf + rv;
+
+		/* pid 2 */
+		if (!(p[-3] == ' ' && p[-2] == '2' && p[-1] == '\n'))
+			return 1;
+
+		return 0;
+	}
+
+	if (waitpid(pid, &wstatus, 0) == -1)
+		return 1;
+	if (WIFEXITED(wstatus) && WEXITSTATUS(wstatus) == 0)
+		return 0;
+	return 1;
+}
diff --git a/tools/testing/selftests/proc/proc-self-map-files-001.c b/tools/testing/selftests/proc/proc-self-map-files-001.c
new file mode 100644
index 000000000000..af1d0a6af810
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-self-map-files-001.c
@@ -0,0 +1,82 @@
+/*
+ * Copyright _ 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/* Test readlink /proc/self/map_files/... */
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <stdlib.h>
+
+static void pass(const char *fmt, unsigned long a, unsigned long b)
+{
+	char name[64];
+	char buf[64];
+
+	snprintf(name, sizeof(name), fmt, a, b);
+	if (readlink(name, buf, sizeof(buf)) == -1)
+		exit(1);
+}
+
+static void fail(const char *fmt, unsigned long a, unsigned long b)
+{
+	char name[64];
+	char buf[64];
+
+	snprintf(name, sizeof(name), fmt, a, b);
+	if (readlink(name, buf, sizeof(buf)) == -1 && errno == ENOENT)
+		return;
+	exit(1);
+}
+
+int main(void)
+{
+	const unsigned int PAGE_SIZE = sysconf(_SC_PAGESIZE);
+	void *p;
+	int fd;
+	unsigned long a, b;
+
+	fd = open("/dev/zero", O_RDONLY);
+	if (fd == -1)
+		return 1;
+
+	p = mmap(NULL, PAGE_SIZE, PROT_NONE, MAP_PRIVATE|MAP_FILE, fd, 0);
+	if (p == MAP_FAILED)
+		return 1;
+
+	a = (unsigned long)p;
+	b = (unsigned long)p + PAGE_SIZE;
+
+	pass("/proc/self/map_files/%lx-%lx", a, b);
+	fail("/proc/self/map_files/ %lx-%lx", a, b);
+	fail("/proc/self/map_files/%lx -%lx", a, b);
+	fail("/proc/self/map_files/%lx- %lx", a, b);
+	fail("/proc/self/map_files/%lx-%lx ", a, b);
+	fail("/proc/self/map_files/0%lx-%lx", a, b);
+	fail("/proc/self/map_files/%lx-0%lx", a, b);
+	if (sizeof(long) == 4) {
+		fail("/proc/self/map_files/100000000%lx-%lx", a, b);
+		fail("/proc/self/map_files/%lx-100000000%lx", a, b);
+	} else if (sizeof(long) == 8) {
+		fail("/proc/self/map_files/10000000000000000%lx-%lx", a, b);
+		fail("/proc/self/map_files/%lx-10000000000000000%lx", a, b);
+	} else
+		return 1;
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-self-map-files-002.c b/tools/testing/selftests/proc/proc-self-map-files-002.c
new file mode 100644
index 000000000000..aebf4be56111
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-self-map-files-002.c
@@ -0,0 +1,85 @@
+/*
+ * Copyright _ 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+/* Test readlink /proc/self/map_files/... with address 0. */
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <stdlib.h>
+
+static void pass(const char *fmt, unsigned long a, unsigned long b)
+{
+	char name[64];
+	char buf[64];
+
+	snprintf(name, sizeof(name), fmt, a, b);
+	if (readlink(name, buf, sizeof(buf)) == -1)
+		exit(1);
+}
+
+static void fail(const char *fmt, unsigned long a, unsigned long b)
+{
+	char name[64];
+	char buf[64];
+
+	snprintf(name, sizeof(name), fmt, a, b);
+	if (readlink(name, buf, sizeof(buf)) == -1 && errno == ENOENT)
+		return;
+	exit(1);
+}
+
+int main(void)
+{
+	const unsigned int PAGE_SIZE = sysconf(_SC_PAGESIZE);
+	void *p;
+	int fd;
+	unsigned long a, b;
+
+	fd = open("/dev/zero", O_RDONLY);
+	if (fd == -1)
+		return 1;
+
+	p = mmap(NULL, PAGE_SIZE, PROT_NONE, MAP_PRIVATE|MAP_FILE|MAP_FIXED, fd, 0);
+	if (p == MAP_FAILED) {
+		if (errno == EPERM)
+			return 2;
+		return 1;
+	}
+
+	a = (unsigned long)p;
+	b = (unsigned long)p + PAGE_SIZE;
+
+	pass("/proc/self/map_files/%lx-%lx", a, b);
+	fail("/proc/self/map_files/ %lx-%lx", a, b);
+	fail("/proc/self/map_files/%lx -%lx", a, b);
+	fail("/proc/self/map_files/%lx- %lx", a, b);
+	fail("/proc/self/map_files/%lx-%lx ", a, b);
+	fail("/proc/self/map_files/0%lx-%lx", a, b);
+	fail("/proc/self/map_files/%lx-0%lx", a, b);
+	if (sizeof(long) == 4) {
+		fail("/proc/self/map_files/100000000%lx-%lx", a, b);
+		fail("/proc/self/map_files/%lx-100000000%lx", a, b);
+	} else if (sizeof(long) == 8) {
+		fail("/proc/self/map_files/10000000000000000%lx-%lx", a, b);
+		fail("/proc/self/map_files/%lx-10000000000000000%lx", a, b);
+	} else
+		return 1;
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-self-syscall.c b/tools/testing/selftests/proc/proc-self-syscall.c
new file mode 100644
index 000000000000..05eb6f91f1e9
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-self-syscall.c
@@ -0,0 +1,45 @@
+#define _GNU_SOURCE
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <unistd.h>
+#include <string.h>
+#include <stdio.h>
+
+static inline ssize_t sys_read(int fd, void *buf, size_t len)
+{
+	return syscall(SYS_read, fd, buf, len);
+}
+
+int main(void)
+{
+	char buf1[64];
+	char buf2[64];
+	int fd;
+	ssize_t rv;
+
+	fd = open("/proc/self/syscall", O_RDONLY);
+	if (fd == -1) {
+		if (errno == ENOENT)
+			return 2;
+		return 1;
+	}
+
+	/* Do direct system call as libc can wrap anything. */
+	snprintf(buf1, sizeof(buf1), "%ld 0x%lx 0x%lx 0x%lx",
+		 (long)SYS_read, (long)fd, (long)buf2, (long)sizeof(buf2));
+
+	memset(buf2, 0, sizeof(buf2));
+	rv = sys_read(fd, buf2, sizeof(buf2));
+	if (rv < 0)
+		return 1;
+	if (rv < strlen(buf1))
+		return 1;
+	if (strncmp(buf1, buf2, strlen(buf1)) != 0)
+		return 1;
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-self-wchan.c b/tools/testing/selftests/proc/proc-self-wchan.c
new file mode 100644
index 000000000000..b8d8728a6869
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-self-wchan.c
@@ -0,0 +1,25 @@
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <unistd.h>
+
+int main(void)
+{
+	char buf[64];
+	int fd;
+
+	fd = open("/proc/self/wchan", O_RDONLY);
+	if (fd == -1) {
+		if (errno == ENOENT)
+			return 2;
+		return 1;
+	}
+
+	buf[0] = '\0';
+	if (read(fd, buf, sizeof(buf)) != 1)
+		return 1;
+	if (buf[0] != '0')
+		return 1;
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-uptime-001.c b/tools/testing/selftests/proc/proc-uptime-001.c
new file mode 100644
index 000000000000..303f26092306
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-uptime-001.c
@@ -0,0 +1,45 @@
+/*
+ * Copyright _ 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+// Test that values in /proc/uptime increment monotonically.
+#undef NDEBUG
+#include <assert.h>
+#include <stdint.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "proc-uptime.h"
+
+int main(void)
+{
+	uint64_t start, u0, u1, i0, i1;
+	int fd;
+
+	fd = open("/proc/uptime", O_RDONLY);
+	assert(fd >= 0);
+
+	proc_uptime(fd, &u0, &i0);
+	start = u0;
+	do {
+		proc_uptime(fd, &u1, &i1);
+		assert(u1 >= u0);
+		assert(i1 >= i0);
+		u0 = u1;
+		i0 = i1;
+	} while (u1 - start < 100);
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-uptime-002.c b/tools/testing/selftests/proc/proc-uptime-002.c
new file mode 100644
index 000000000000..0cb79e1f1674
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-uptime-002.c
@@ -0,0 +1,79 @@
+/*
+ * Copyright _ 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+// Test that values in /proc/uptime increment monotonically
+// while shifting across CPUs.
+#define _GNU_SOURCE
+#undef NDEBUG
+#include <assert.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <stdint.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "proc-uptime.h"
+
+static inline int sys_sched_getaffinity(pid_t pid, unsigned int len, unsigned long *m)
+{
+	return syscall(SYS_sched_getaffinity, pid, len, m);
+}
+
+static inline int sys_sched_setaffinity(pid_t pid, unsigned int len, unsigned long *m)
+{
+	return syscall(SYS_sched_setaffinity, pid, len, m);
+}
+
+int main(void)
+{
+	unsigned int len;
+	unsigned long *m;
+	unsigned int cpu;
+	uint64_t u0, u1, i0, i1;
+	int fd;
+
+	/* find out "nr_cpu_ids" */
+	m = NULL;
+	len = 0;
+	do {
+		len += sizeof(unsigned long);
+		free(m);
+		m = malloc(len);
+	} while (sys_sched_getaffinity(0, len, m) == -EINVAL);
+
+	fd = open("/proc/uptime", O_RDONLY);
+	assert(fd >= 0);
+
+	proc_uptime(fd, &u0, &i0);
+	for (cpu = 0; cpu < len * 8; cpu++) {
+		memset(m, 0, len);
+		m[cpu / (8 * sizeof(unsigned long))] |= 1UL << (cpu % (8 * sizeof(unsigned long)));
+
+		/* CPU might not exist, ignore error */
+		sys_sched_setaffinity(0, len, m);
+
+		proc_uptime(fd, &u1, &i1);
+		assert(u1 >= u0);
+		assert(i1 >= i0);
+		u0 = u1;
+		i0 = i1;
+	}
+
+	return 0;
+}
diff --git a/tools/testing/selftests/proc/proc-uptime.h b/tools/testing/selftests/proc/proc-uptime.h
new file mode 100644
index 000000000000..d584419f50a7
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-uptime.h
@@ -0,0 +1,74 @@
+/*
+ * Copyright _ 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+#undef NDEBUG
+#include <assert.h>
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+static unsigned long long xstrtoull(const char *p, char **end)
+{
+	if (*p == '0') {
+		*end = (char *)p + 1;
+		return 0;
+	} else if ('1' <= *p && *p <= '9') {
+		unsigned long long val;
+
+		errno = 0;
+		val = strtoull(p, end, 10);
+		assert(errno == 0);
+		return val;
+	} else
+		assert(0);
+}
+
+static void proc_uptime(int fd, uint64_t *uptime, uint64_t *idle)
+{
+	uint64_t val1, val2;
+	char buf[64], *p;
+	ssize_t rv;
+
+	/* save "p < end" checks */
+	memset(buf, 0, sizeof(buf));
+	rv = pread(fd, buf, sizeof(buf), 0);
+	assert(0 <= rv && rv <= sizeof(buf));
+	buf[sizeof(buf) - 1] = '\0';
+
+	p = buf;
+
+	val1 = xstrtoull(p, &p);
+	assert(p[0] == '.');
+	assert('0' <= p[1] && p[1] <= '9');
+	assert('0' <= p[2] && p[2] <= '9');
+	assert(p[3] == ' ');
+
+	val2 = (p[1] - '0') * 10 + p[2] - '0';
+	*uptime = val1 * 100 + val2;
+
+	p += 4;
+
+	val1 = xstrtoull(p, &p);
+	assert(p[0] == '.');
+	assert('0' <= p[1] && p[1] <= '9');
+	assert('0' <= p[2] && p[2] <= '9');
+	assert(p[3] == '\n');
+
+	val2 = (p[1] - '0') * 10 + p[2] - '0';
+	*idle = val1 * 100 + val2;
+
+	assert(p + 4 == buf + rv);
+}
diff --git a/tools/testing/selftests/proc/read.c b/tools/testing/selftests/proc/read.c
new file mode 100644
index 000000000000..12e397f78592
--- /dev/null
+++ b/tools/testing/selftests/proc/read.c
@@ -0,0 +1,147 @@
+/*
+ * Copyright _ 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+// Test
+// 1) read of every file in /proc
+// 2) readlink of every symlink in /proc
+// 3) recursively (1) + (2) for every directory in /proc
+// 4) write to /proc/*/clear_refs and /proc/*/task/*/clear_refs
+// 5) write to /proc/sysrq-trigger
+#undef NDEBUG
+#include <assert.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <dirent.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+static inline bool streq(const char *s1, const char *s2)
+{
+	return strcmp(s1, s2) == 0;
+}
+
+static struct dirent *xreaddir(DIR *d)
+{
+	struct dirent *de;
+
+	errno = 0;
+	de = readdir(d);
+	if (!de && errno != 0) {
+		exit(1);
+	}
+	return de;
+}
+
+static void f_reg(DIR *d, const char *filename)
+{
+	char buf[4096];
+	int fd;
+	ssize_t rv;
+
+	/* read from /proc/kmsg can block */
+	fd = openat(dirfd(d), filename, O_RDONLY|O_NONBLOCK);
+	if (fd == -1)
+		return;
+	rv = read(fd, buf, sizeof(buf));
+	assert((0 <= rv && rv <= sizeof(buf)) || rv == -1);
+	close(fd);
+}
+
+static void f_reg_write(DIR *d, const char *filename, const char *buf, size_t len)
+{
+	int fd;
+	ssize_t rv;
+
+	fd = openat(dirfd(d), filename, O_WRONLY);
+	if (fd == -1)
+		return;
+	rv = write(fd, buf, len);
+	assert((0 <= rv && rv <= len) || rv == -1);
+	close(fd);
+}
+
+static void f_lnk(DIR *d, const char *filename)
+{
+	char buf[4096];
+	ssize_t rv;
+
+	rv = readlinkat(dirfd(d), filename, buf, sizeof(buf));
+	assert((0 <= rv && rv <= sizeof(buf)) || rv == -1);
+}
+
+static void f(DIR *d, unsigned int level)
+{
+	struct dirent *de;
+
+	de = xreaddir(d);
+	assert(de->d_type == DT_DIR);
+	assert(streq(de->d_name, "."));
+
+	de = xreaddir(d);
+	assert(de->d_type == DT_DIR);
+	assert(streq(de->d_name, ".."));
+
+	while ((de = xreaddir(d))) {
+		assert(!streq(de->d_name, "."));
+		assert(!streq(de->d_name, ".."));
+
+		switch (de->d_type) {
+			DIR *dd;
+			int fd;
+
+		case DT_REG:
+			if (level == 0 && streq(de->d_name, "sysrq-trigger")) {
+				f_reg_write(d, de->d_name, "h", 1);
+			} else if (level == 1 && streq(de->d_name, "clear_refs")) {
+				f_reg_write(d, de->d_name, "1", 1);
+			} else if (level == 3 && streq(de->d_name, "clear_refs")) {
+				f_reg_write(d, de->d_name, "1", 1);
+			} else {
+				f_reg(d, de->d_name);
+			}
+			break;
+		case DT_DIR:
+			fd = openat(dirfd(d), de->d_name, O_DIRECTORY|O_RDONLY);
+			if (fd == -1)
+				continue;
+			dd = fdopendir(fd);
+			if (!dd)
+				continue;
+			f(dd, level + 1);
+			closedir(dd);
+			break;
+		case DT_LNK:
+			f_lnk(d, de->d_name);
+			break;
+		default:
+			assert(0);
+		}
+	}
+}
+
+int main(void)
+{
+	DIR *d;
+
+	d = opendir("/proc");
+	if (!d)
+		return 2;
+	f(d, 0);
+	return 0;
+}