tracing/user_events: Use write ABI in example

The ABI has changed to use a remote write approach. Update the example
to show the expected use of this new ABI. Also remove debugfs
path and use tracefs to ensure example works in more environments.

Link: https://lkml.kernel.org/r/20230328235219.203-9-beaub@linux.microsoft.comSigned-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

samples/user_events/example.c

@@ -9,51 +9,28 @@
 #include <errno.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
+#include <sys/uio.h>
 #include <fcntl.h>
 #include <stdio.h>
 #include <unistd.h>
-#include <asm/bitsperlong.h>
-#include <endian.h>
 #include <linux/user_events.h>
 
-#if __BITS_PER_LONG == 64
-#define endian_swap(x) htole64(x)
-#else
-#define endian_swap(x) htole32(x)
-#endif
-
-/* Assumes debugfs is mounted */
 const char *data_file = "/sys/kernel/tracing/user_events_data";
-const char *status_file = "/sys/kernel/tracing/user_events_status";
+int enabled = 0;
 
-static int event_status(long **status)
-{
-	int fd = open(status_file, O_RDONLY);
-
-	*status = mmap(NULL, sysconf(_SC_PAGESIZE), PROT_READ,
-		       MAP_SHARED, fd, 0);
-
-	close(fd);
-
-	if (*status == MAP_FAILED)
-		return -1;
-
-	return 0;
-}
-
-static int event_reg(int fd, const char *command, long *index, long *mask,
-		     int *write)
+static int event_reg(int fd, const char *command, int *write, int *enabled)
 {
 	struct user_reg reg = {0};
 
 	reg.size = sizeof(reg);
+	reg.enable_bit = 31;
+	reg.enable_size = sizeof(*enabled);
+	reg.enable_addr = (__u64)enabled;
 	reg.name_args = (__u64)command;
 
 	if (ioctl(fd, DIAG_IOCSREG, &reg) == -1)
 		return -1;
 
-	*index = reg.status_bit / __BITS_PER_LONG;
-	*mask = endian_swap(1L << (reg.status_bit % __BITS_PER_LONG));
 	*write = reg.write_index;
 
 	return 0;
@@ -62,17 +39,12 @@ static int event_reg(int fd, const char *command, long *index, long *mask,
 int main(int argc, char **argv)
 {
 	int data_fd, write;
-	long index, mask;
-	long *status_page;
 	struct iovec io[2];
 	__u32 count = 0;
 
-	if (event_status(&status_page) == -1)
-		return errno;
-
 	data_fd = open(data_file, O_RDWR);
 
-	if (event_reg(data_fd, "test u32 count", &index, &mask, &write) == -1)
+	if (event_reg(data_fd, "test u32 count", &write, &enabled) == -1)
 		return errno;
 
 	/* Setup iovec */
@@ -80,13 +52,12 @@ int main(int argc, char **argv)
 	io[0].iov_len = sizeof(write);
 	io[1].iov_base = &count;
 	io[1].iov_len = sizeof(count);
-
 ask:
 	printf("Press enter to check status...\n");
 	getchar();
 
 	/* Check if anyone is listening */
-	if (status_page[index] & mask) {
+	if (enabled) {
 		/* Yep, trace out our data */
 		writev(data_fd, (const struct iovec *)io, 2);