linux-kernel - Re: [PATCH 4/6] perf tools: Add FIFO file names as alternative options to --control

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Date:   Mon, 31 Aug 2020 15:19:27 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/6] perf tools: Add FIFO file names as alternative
 options to --control

On Sat, Aug 29, 2020 at 01:50:13PM +0300, Adrian Hunter wrote:

SNIP

> +		*p = '\0';
> +
> +	/*
> +	 * O_RDWR avoids POLLHUPs which is necessary to allow the other
> +	 * end of a FIFO to be repeatedly opened and closed.
> +	 */
> +	fd = open(s, O_RDWR | O_NONBLOCK | O_CLOEXEC);
> +	if (fd < 0) {
> +		pr_err("Failed to open '%s'\n", s);
> +		ret = -errno;
> +		goto out_free;
> +	}
> +	*ctl_fd = fd;
> +	*ctl_fd_close = true;
> +
> +	if (p && *++p) {
> +		/* O_RDWR | O_NONBLOCK means the other end need not be open */
> +		fd = open(p, O_RDWR | O_NONBLOCK | O_CLOEXEC);
> +		if (fd < 0) {
> +			pr_err("Failed to open '%s'\n", p);
> +			ret = -errno;
> +			goto out_free;
> +		}
> +		*ctl_fd_ack = fd;
> +	}
> +
> +out_free:
> +	free(s);
> +	return ret;
> +}
> +
> +int evlist__parse_control(const char *str, int *ctl_fd, int *ctl_fd_ack, bool *ctl_fd_close)
>  {
>  	char *comma = NULL, *endptr = NULL;
>  
>  	if (strncmp(str, "fd:", 3))
> -		return -EINVAL;
> +		return evlist__parse_control_names(str, ctl_fd, ctl_fd_ack, ctl_fd_close);

do we want to mention somewhere that the fifo name is everything
except for 'fd:' ?

also how likely is that we will add another channel type that
will need another keyword (likd 'fd:')? I originaly thought
we'd use 'fifo:filename' for this ... would be great to somehow
avoid future confusions

thanks,
jirka