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

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Message-ID: <3ab05af5-b882-ffde-8311-307b6c373fd3@linux.intel.com>
Date:   Wed, 24 Jun 2020 16:20:51 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.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 23.06.2020 17:56, Jiri Olsa wrote:
> 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) ?

I do, only for err >= 0. For err == -1 there is already the error message.

> 
>> +
>> +	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?

I don't think so. Currently it returns 0 only and there is no need to 
stop collection or skip processing in caller in this case.

~Alexey

> 
> jirka
>