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SubjectRe: [PATCH v12 12/17] tools/counter: Create Counter tools
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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@ucw.cz>
> Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.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errno is no longer valid after calling perror().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;
> +}
>

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