linux-kernel - Re: [PATCH v10 05/15] perf evlist: implement control command handling functions

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Date:   Mon, 13 Jul 2020 12:20:59 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        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 v10 05/15] perf evlist: implement control command handling functions

On Wed, Jul 8, 2020 at 4:50 PM Alexey Budankov
<alexey.budankov@...ux.intel.com> wrote:
>
>
> Implement functions of initialization, finalization and processing
> of control command messages coming from control file descriptors.
> Allocate control file descriptor as descriptor at struct pollfd
> object of evsel_list for atomic poll() operation.
>
> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
> ---
[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--);

I overlooked the '--' at the end and thought there might be
buffer overflow..  Care to add a comment?

> +
> +       do {
> +               err = read(evlist->ctl_fd.fd, &c, 1);

Maybe I missed earlier discussion, but do we really want
this 1 byte read in a loop?

Thanks
Namhyung


> +               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");
> +
> +       if (err > 0) {
> +               if (!strncmp(cmd_data, EVLIST_CTL_CMD_ENABLE_TAG,
> +                            (sizeof(EVLIST_CTL_CMD_ENABLE_TAG)-1))) {
> +                       *cmd = EVLIST_CTL_CMD_ENABLE;
> +               } else if (!strncmp(cmd_data, EVLIST_CTL_CMD_DISABLE_TAG,
> +                                   (sizeof(EVLIST_CTL_CMD_DISABLE_TAG)-1))) {
> +                       *cmd = EVLIST_CTL_CMD_DISABLE;
> +               }
> +       }
> +
> +       return err;
> +}