linux-kernel - Re: [PATCH V3] rtla: Remove procps-ng dependency

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Message-ID: <20220510113033.auxhunymxbhioi4z@carbon.lan>
Date:   Tue, 10 May 2022 13:30:33 +0200
From:   Daniel Wagner <dwagner@...e.de>
To:     Daniel Bristot de Oliveira <bristot@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        linux-trace-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
        John Kacur <jkacur@...hat.com>, Tao Zhou <tao.zhou@...ux.dev>
Subject: Re: [PATCH V3] rtla: Remove procps-ng dependency

On Tue, May 10, 2022 at 11:57:04AM +0200, Daniel Bristot de Oliveira wrote:
> +static int procfs_is_workload_pid(const char *comm_prefix, struct dirent *proc_entry)
> +{
> +	char buffer[MAX_PATH];
> +	int comm_fd, retval;
> +	char *t_name;
> +
> +	if (proc_entry->d_type != DT_DIR)
> +		return 0;
> +
> +	if (*proc_entry->d_name == '.')
> +		return 0;
> +
> +	/* check if the string is a pid */
> +	for (t_name = proc_entry->d_name; t_name; t_name++) {
> +		if (!isdigit(*t_name))
> +			break;
> +	}
> +
> +	if (*t_name != '\0')
> +		return 0;
> +
> +	snprintf(buffer, MAX_PATH, "/proc/%s/comm", proc_entry->d_name);
> +	comm_fd = open(buffer, O_RDONLY);
> +	if (comm_fd < 0)
> +		return 0;
> +
> +	memset(buffer, 0, MAX_PATH);
> +	retval = read(comm_fd, buffer, MAX_PATH);
> +
> +	close(comm_fd);
> +
> +	if (retval <= 0)
> +		return 0;
> +
> +	retval = strncmp(comm_prefix, buffer, strlen(comm_prefix));
> +	if (retval)
> +		return 0;
> +
> +	/* comm already have \n */
> +	debug_msg("Found workload pid:%s comm:%s", proc_entry->d_name, buffer);
> +
> +	return 1;
> +}
> +
> +/*
> + * set_comm_sched_attr - set sched params to threads starting with char *comm_prefix
> + *
> + * This function uses /procfs to list the currently running threads and then set the
> + * sched_attr *attr to the threads that start with char *comm_prefix. It is
>   * mainly used to set the priority to the kernel threads created by the
>   * tracers.
>   */
> -int set_comm_sched_attr(const char *comm, struct sched_attr *attr)
> +int set_comm_sched_attr(const char *comm_prefix, struct sched_attr *attr)
>  {
> -	int flags = PROC_FILLCOM | PROC_FILLSTAT;
> -	PROCTAB *ptp;
> -	proc_t task;
> +	struct dirent *proc_entry;
> +	DIR *procfs;
>  	int retval;
>  
> -	ptp = openproc(flags);
> -	if (!ptp) {
> -		err_msg("error openproc()\n");
> -		return -ENOENT;
> +	if (strlen(comm_prefix) >= MAX_PATH) {
> +		err_msg("Command prefix is too long: %d < strlen(%s)\n",
> +			MAX_PATH, comm_prefix);
> +		exit(EINVAL);
>  	}
>  
> -	memset(&task, 0, sizeof(task));
> +	procfs = opendir("/proc");

Maybe you want to check if procfs is a valid handle before using it.

> +
> +	while ((proc_entry = readdir(procfs))) {
>  
> -	while (readproc(ptp, &task)) {
> -		retval = strncmp(comm, task.cmd, strlen(comm));
> -		if (retval)
> +		retval = procfs_is_workload_pid(comm_prefix, proc_entry);
> +		if (!retval)
>  			continue;
> -		retval = __set_sched_attr(task.tid, attr);
> -		if (retval)
> +
> +		/* procfs_is_workload_pid confirmed it is a pid */
> +		retval = __set_sched_attr(atoi(proc_entry->d_name), attr);
> +		if (retval) {
> +			err_msg("Error setting sched attributes for pid:%s\n", proc_entry->d_name);
>  			goto out_err;
> -	}
> +		}
>  
> -	closeproc(ptp);
> +		debug_msg("Set sched attributes for pid:%s\n", proc_entry->d_name);
> +	}
>  	return 0;
>  
>  out_err:
> -	closeproc(ptp);
> +	closedir(procfs);
>  	return 1;
>  }
>  
> diff --git a/tools/tracing/rtla/src/utils.h b/tools/tracing/rtla/src/utils.h
> index fa08e374870a..5571afd3b549 100644
> --- a/tools/tracing/rtla/src/utils.h
> +++ b/tools/tracing/rtla/src/utils.h
> @@ -6,6 +6,7 @@
>   * '18446744073709551615\0'
>   */
>  #define BUFF_U64_STR_SIZE	24
> +#define MAX_PATH		1024

linux/limits.h defined MAX_PATH as well, though as 4096. Maybe use that
definition? If you want to make it dynamic you could use fpathconf(fd,
_PC_PATH_MAX) but one could argue that is over engineering :)

Thanks for the fix. Anyway just nitpicking.

Reviewed-by: Daniel Wagner <dwagner@...e.de>