linux-kernel - Re: [PATCH v12 12/17] tools/counter: Create Counter tools

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Message-ID: <343a2bd3-38b7-7462-bc52-d3f6493bede0@lechnology.com>
Date:   Sat, 10 Jul 2021 11:53:35 -0500
From:   David Lechner <david@...hnology.com>
To:     William Breathitt Gray <vilhelm.gray@...il.com>, jic23@...nel.org
Cc:     linux-stm32@...md-mailman.stormreply.com, kernel@...gutronix.de,
        a.fatoum@...gutronix.de, kamel.bouhara@...tlin.com,
        gwendal@...omium.org, alexandre.belloni@...tlin.com,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, syednwaris@...il.com,
        patrick.havelange@...ensium.com, fabrice.gasnier@...com,
        mcoquelin.stm32@...il.com, alexandre.torgue@...com,
        o.rempel@...gutronix.de, jarkko.nikula@...ux.intel.com,
        Pavel Machek <pavel@....cz>
Subject: Re: [PATCH v12 12/17] tools/counter: Create Counter tools

On 7/5/21 3:19 AM, William Breathitt Gray wrote:
> This creates an example Counter program under tools/counter/*
> to exemplify the Counter character device interface.
> 
> Cc: Pavel Machek <pavel@....cz>
> Signed-off-by: William Breathitt Gray <vilhelm.gray@...il.com>
> ---


> --- a/tools/Makefile
> +++ b/tools/Makefile
> @@ -12,6 +12,7 @@ help:
>   	@echo '  acpi                   - ACPI tools'
>   	@echo '  bpf                    - misc BPF tools'
>   	@echo '  cgroup                 - cgroup tools'
> +	@echo '  counter                - Counter tools'

nit: other descriptions start with lower case letter, so to be
consistent, this should too


> --- /dev/null
> +++ b/tools/counter/counter_example.c
> @@ -0,0 +1,95 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Counter - example userspace application
> + *
> + * The userspace application opens /dev/counter0, configures the
> + * COUNTER_EVENT_INDEX event channel 0 to gather Count 0 count and Count
> + * 1 count, and prints out the data as it becomes available on the
> + * character device node.
> + *
> + * Copyright (C) 2021 William Breathitt Gray
> + */
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <linux/counter.h>
> +#include <stdio.h>
> +#include <string.h>
> +#include <sys/ioctl.h>
> +#include <unistd.h>
> +
> +struct counter_watch watches[2] = {

nit: this can be static

> +	{
> +		/* Component data: Count 0 count */
> +		.component.type = COUNTER_COMPONENT_COUNT,
> +		.component.scope = COUNTER_SCOPE_COUNT,
> +		.component.parent = 0,
> +		/* Event type: Index */
> +		.event = COUNTER_EVENT_INDEX,
> +		/* Device event channel 0 */
> +		.channel = 0,
> +	},
> +	{
> +		/* Component data: Count 1 count */
> +		.component.type = COUNTER_COMPONENT_COUNT,
> +		.component.scope = COUNTER_SCOPE_COUNT,
> +		.component.parent = 1,
> +		/* Event type: Index */
> +		.event = COUNTER_EVENT_INDEX,
> +		/* Device event channel 0 */
> +		.channel = 0,
> +	},
> +};
> +
> +int main(void)
> +{
> +	int fd;
> +	int ret;
> +	struct counter_event event_data[2];
> +
> +	fd = open("/dev/counter0", O_RDWR);
> +	if (fd == -1) {
> +		perror("Unable to open /dev/counter0");
> +		return -errno;

errno is no longer valid after calling perror(). Since this
is example code, we can just return 1 instead (exit codes
positive number between 0 and 255 so -1 would be 255).

> +	}
> +
> +	ret = ioctl(fd, COUNTER_ADD_WATCH_IOCTL, watches);
> +	if (ret == -1) {
> +		perror("Error adding watches[0]");
> +		return -errno;
> +	}
> +	ret = ioctl(fd, COUNTER_ADD_WATCH_IOCTL, watches + 1);
> +	if (ret == -1) {
> +		perror("Error adding watches[1]");
> +		return -errno;
> +	}
> +	ret = ioctl(fd, COUNTER_ENABLE_EVENTS_IOCTL);
> +	if (ret == -1) {
> +		perror("Error enabling events");
> +		return -errno;
> +	}
> +
> +	for (;;) {
> +		ret = read(fd, event_data, sizeof(event_data));
> +		if (ret == -1) {
> +			perror("Failed to read event data");
> +			return -errno;
> +		}
> +
> +		if (ret != sizeof(event_data)) {
> +			fprintf(stderr, "Failed to read event data\n");
> +			return -EIO;
> +		}
> +
> +		printf("Timestamp 0: %llu\tCount 0: %llu\n"
> +		       "Error Message 0: %s\n"
> +		       "Timestamp 1: %llu\tCount 1: %llu\n"
> +		       "Error Message 1: %s\n",
> +		       (unsigned long long)event_data[0].timestamp,
> +		       (unsigned long long)event_data[0].value,
> +		       strerror(event_data[0].status),
> +		       (unsigned long long)event_data[1].timestamp,
> +		       (unsigned long long)event_data[1].value,
> +		       strerror(event_data[1].status));
> +	}

Aren't the Count 0 and Count 1 events independent? Why should we expect to
always get both events at the same time in the same order?

> +
> +	return 0;
> +}
>