linux-kernel - Re: [PATCH v8 03/13] perf evlist: implement control command handling functions

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Date:   Tue, 23 Jun 2020 16:56:13 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 03/13] perf evlist: implement control command handling
 functions

On Wed, Jun 17, 2020 at 11:36:46AM +0300, Alexey Budankov wrote:

SNIP

> +static int evlist__ctlfd_recv(struct evlist *evlist, enum evlist_ctl_cmd *cmd,
> +			      char *cmd_data, size_t data_size)
> +{
> +	int err;
> +	char c;
> +	size_t bytes_read = 0;
> +
> +	memset(cmd_data, 0, data_size--);
> +
> +	do {
> +		err = read(evlist->ctl_fd.fd, &c, 1);
> +		if (err > 0) {
> +			if (c == '\n' || c == '\0')
> +				break;
> +			cmd_data[bytes_read++] = c;
> +			if (bytes_read == data_size)
> +				break;
> +		} else {
> +			if (err == -1)
> +				pr_err("Failed to read from ctlfd %d: %m\n", evlist->ctl_fd.fd);
> +			break;
> +		}
> +	} while (1);
> +
> +	pr_debug("Message from ctl_fd: \"%s%s\"\n", cmd_data,
> +		 bytes_read == data_size ? "" : c == '\n' ? "\\n" : "\\0");

do you want to display the message above only if (err > 0) ?

> +
> +	if (err > 0) {
> +		if (!strncmp(cmd_data, EVLIST_CTL_CMD_ENABLE_TAG,
> +			     strlen(EVLIST_CTL_CMD_ENABLE_TAG))) {
> +			*cmd = EVLIST_CTL_CMD_ENABLE;
> +		} else if (!strncmp(cmd_data, EVLIST_CTL_CMD_DISABLE_TAG,
> +				    strlen(EVLIST_CTL_CMD_DISABLE_TAG))) {
> +			*cmd = EVLIST_CTL_CMD_DISABLE;
> +		}
> +	}
> +
> +	return err;
> +}

SNIP

> +	int ctlfd_pos = evlist->ctl_fd.pos;
> +	struct pollfd *entries = evlist->core.pollfd.entries;
> +
> +	if (ctlfd_pos == -1 || !entries[ctlfd_pos].revents)
> +		return 0;
> +
> +	if (entries[ctlfd_pos].revents & POLLIN) {
> +		err = evlist__ctlfd_recv(evlist, cmd, cmd_data,
> +					 EVLIST_CTL_CMD_MAX_LEN);
> +		if (err > 0) {
> +			switch (*cmd) {
> +			case EVLIST_CTL_CMD_ENABLE:
> +				evlist__enable(evlist);
> +				break;
> +			case EVLIST_CTL_CMD_DISABLE:
> +				evlist__disable(evlist);
> +				break;
> +			case EVLIST_CTL_CMD_ACK:
> +			case EVLIST_CTL_CMD_UNSUPPORTED:
> +			default:
> +				pr_debug("ctlfd: unsupported %d\n", *cmd);
> +				break;
> +			}
> +			if (!(*cmd == EVLIST_CTL_CMD_ACK || *cmd == EVLIST_CTL_CMD_UNSUPPORTED))
> +				evlist__ctlfd_ack(evlist);
> +		}
> +	}
> +
> +	if (entries[ctlfd_pos].revents & (POLLHUP | POLLERR))
> +		evlist__finalize_ctlfd(evlist);

should this error be propagated via err?

jirka