linux-kernel - Re: [PATCH v8 10/12] user_events: Add sample code for typical usage

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Date:   Thu, 23 Dec 2021 08:18:14 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Beau Belgrave <beaub@...ux.microsoft.com>
Cc:     rostedt@...dmis.org, linux-trace-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 10/12] user_events: Add sample code for typical usage

On Thu, 16 Dec 2021 09:35:09 -0800
Beau Belgrave <beaub@...ux.microsoft.com> wrote:

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

Ah, here is the sample code. OK.

Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>

Thanks!

> 
> Signed-off-by: Beau Belgrave <beaub@...ux.microsoft.com>
> ---
>  samples/user_events/Makefile  |  5 ++
>  samples/user_events/example.c | 91 +++++++++++++++++++++++++++++++++++
>  2 files changed, 96 insertions(+)
>  create mode 100644 samples/user_events/Makefile
>  create mode 100644 samples/user_events/example.c
> 
> diff --git a/samples/user_events/Makefile b/samples/user_events/Makefile
> new file mode 100644
> index 000000000000..7252b589db57
> --- /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
> index 000000000000..4f5778e441c0
> --- /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@...ux.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;
> +}
> -- 
> 2.17.1
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>