Re: [dpdk-dev] Proposal: enable redirection of DPDK logs from the user app

[Olivier Matz <olivier.matz@6wind.com>]

Hi Francesco,

On 10/04/2016 02:28 PM, Montorsi, Francesco wrote:
> Hi Olivier,
> 
>> It seems the mailing list stripped your patch sent as attachment. 
>> Can you please resend it again in the body of the mail?
> You're right sorry. It's attached at the end of this mail.
> 
>> I think we can already redirect logs to a file by using
>> fopencookie() + rte_openlog_stream(). Did you already check these
>> functions?
> 
> Yes, but to be honest, that seems a troublesome solution for
> something as easy as logging a string; e.g. by using fopencookie()
> approach, you don't have the concept of "log message", you just
> provide a function that must write a block of bytes somewhere.
> Typically instead, you need to know where a log message starts and
> ends, to e.g., add prefixes/postfixes to it.

I'm not sure that true if you call setbuf(log_stream, NULL).

In that case, it looks easy to prefix / postfix messages with a
fopencookie callback like:

/* example on stdout */
ssize_t
simple_write(void *c, const char *buf, size_t size)
{
	ssize_t ret1, ret2, ret3;

	ret1 = fwrite("<", 1, 1, stdout);
	if (ret1 == 0)
		return 0;
	ret2 = fwrite(buf, size, 1, stdout);
	if (ret2 == 0)
		return 0;
	ret3 = fwrite(">", 1, 1, stdout);
	if (ret3 == 0)
		return 0;
	return ret1 + ret2 + ret3;
}


> Indeed, most of the C/C++ (open source) libraries have some simple
> hook that allows the user to have more control on logging... I think
> DPDK should be no exception... :)

I understand that the current API is a bit more complex, but I don't
feel there is any blocking issue to do what you want. What do you think?


Also, I know you've said your patch needs some rework, but as you've
also said you are using it, maybe it would be useful for you to know:
- it makes use of a global variable 'log_buffer', shared by all the
pthreads, which can lead to crashes
- it strips the log messages to 4095 chars

Regards,
Olivier