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

Alexey Budankov
2020-07-13T08:24:59Z

On 13.07.2020 6:20, Namhyung Kim wrote:
> On Wed, Jul 8, 2020 at 4:50 PM Alexey Budankov
> <alexey.budankov@linux.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@linux.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?

If it wants to be more explicit then it could possibly be implemented
like this:

memset(cmd_data, 0, data_size);
data_size--;

>
>> +
>> + 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?

That was the explicit request to support commands of variable
length so it implements it like that.

Alexei

>
> 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;
>> +}