tools/testing/selftests/proc/fd-003-kthread.c

Source file repositories/reference/linux-study-clean/tools/testing/selftests/proc/fd-003-kthread.c

File Facts

System
Linux kernel
Corpus path
tools/testing/selftests/proc/fd-003-kthread.c
Extension
.c
Size
3993 bytes
Lines
179
Domain
Support Tooling And Documentation
Bucket
tools
Inferred role
Support Tooling And Documentation: implementation source
Status
source implementation candidate

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

// Test that /proc/$KERNEL_THREAD/fd/ is empty.

#undef NDEBUG
#include <sys/syscall.h>
#include <assert.h>
#include <dirent.h>
#include <limits.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#include "proc.h"

#define PF_KHTREAD 0x00200000

/*
 * Test for kernel threadness atomically with openat().
 *
 * Return /proc/$PID/fd descriptor if process is kernel thread.
 * Return -1 if a process is userspace process.
 */
static int kernel_thread_fd(unsigned int pid)
{
	unsigned int flags = 0;
	char buf[4096];
	int dir_fd, fd;
	ssize_t rv;

	snprintf(buf, sizeof(buf), "/proc/%u", pid);
	dir_fd = open(buf, O_RDONLY|O_DIRECTORY);
	if (dir_fd == -1)
		return -1;

	/*
	 * Believe it or not, struct task_struct::flags is directly exposed
	 * to userspace!
	 */
	fd = openat(dir_fd, "stat", O_RDONLY);
	if (fd == -1) {
		close(dir_fd);
		return -1;
	}
	rv = read(fd, buf, sizeof(buf));
	close(fd);
	if (0 < rv && rv <= sizeof(buf)) {
		unsigned long long flags_ull;
		char *p, *end;
		int i;

		assert(buf[rv - 1] == '\n');
		buf[rv - 1] = '\0';

		/* Search backwards: ->comm can contain whitespace and ')'. */
		for (i = 0; i < 43; i++) {
			p = strrchr(buf, ' ');
			assert(p);
			*p = '\0';
		}

		p = strrchr(buf, ' ');
		assert(p);

		flags_ull = xstrtoull(p + 1, &end);
		assert(*end == '\0');
		assert(flags_ull == (unsigned int)flags_ull);

		flags = flags_ull;
	}

	fd = -1;
	if (flags & PF_KHTREAD) {
		fd = openat(dir_fd, "fd", O_RDONLY|O_DIRECTORY);
	}
	close(dir_fd);
	return fd;
}

static void test_readdir(int fd)
{
	DIR *d;
	struct dirent *de;

	d = fdopendir(fd);
	assert(d);

	de = xreaddir(d);
	assert(streq(de->d_name, "."));

Annotation

Implementation Notes