[PATCH v5 08/11] tracing/user_events: Use write ABI in example

Beau Belgrave
2022-12-05T21:01:18Z

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.

Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
---
samples/user_events/example.c | 47 +++++++----------------------------
1 file changed, 9 insertions(+), 38 deletions(-)

diff --git a/samples/user_events/example.c b/samples/user_events/example.c
index d06dc24156ec..28165a096697 100644
--- a/samples/user_events/example.c
+++ b/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
+const char *data_file = "/sys/kernel/tracing/user_events_data";
+int enabled = 0;

-/* Assumes debugfs is mounted */
-const char *data_file = "/sys/kernel/debug/tracing/user_events_data";
-const char *status_file = "/sys/kernel/debug/tracing/user_events_status";
-
-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);

--
2.25.1