user_events: Add sample code for typical usage

Add sample code for user_events typical usage to show how to register
and monitor status, as well as to write out data.

Link: https://lkml.kernel.org/r/20220118204326.2169-12-beaub@linux.microsoft.com
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/samples/user_events/Makefile b/samples/user_events/Makefile
new file mode 100644 (file)
index 0000000..7252b58
--- /dev/null
+++ b/samples/user_events/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+CFLAGS += -Wl,-no-as-needed -Wall -I../../usr/include
+
+example: example.o
+example.o: example.c

diff --git a/samples/user_events/example.c b/samples/user_events/example.c
new file mode 100644 (file)
index 0000000..4f5778e
--- /dev/null
+++ b/samples/user_events/example.c
@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2021, Microsoft Corporation.
+ *
+ * Authors:
+ *   Beau Belgrave <beaub@linux.microsoft.com>
+ */
+
+#include <errno.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <linux/user_events.h>
+
+/* 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(char **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, int *status, int *write)
+{
+       struct user_reg reg = {0};
+
+       reg.size = sizeof(reg);
+       reg.name_args = (__u64)command;
+
+       if (ioctl(fd, DIAG_IOCSREG, &reg) == -1)
+               return -1;
+
+       *status = reg.status_index;
+       *write = reg.write_index;
+
+       return 0;
+}
+
+int main(int argc, char **argv)
+{
+       int data_fd, status, write;
+       char *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", &status, &write) == -1)
+               return errno;
+
+       /* Setup iovec */
+       io[0].iov_base = &write;
+       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[status]) {
+               /* Yep, trace out our data */
+               writev(data_fd, (const struct iovec *)io, 2);
+
+               /* Increase the count */
+               count++;
+
+               printf("Something was attached, wrote data\n");
+       }
+
+       goto ask;
+
+       return 0;
+}