On Wed, May 10, 2017 at 3:48 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> I was thinking that you'd need some well-defined way to tell whether the
> string should be replaced. If the thing just hangs out across syscalls,
> then you don't know when it got put there. Is it a leftover from a
> previous syscall or did a lower layer just put it there?
Example userspace code:
/* Throw away previous error string */
get_detailed_error(NULL, 0);
ret = somesyscall(...);
if (ret == -1) {
char errbuf[1024];
/* Get detailed error string for somesyscall */
get_detailed_error(errbuf, sizeof(errbuf));
err(1, errbuf);
}
>> That's why I liked the static string thing. It's just one assignment
>> and no worries about freeing. Not sure what to do about modules,
>> though. Can we somehow move the cost of checking the validity to the
>> place where the error is retrieved?
>>
>
> Seems a little dangerous,
True.
> and could be limiting. Dynamically allocated
> strings seem like they could be more useful.
Overdesign always starts with that. A static string is infinitely
more descriptive than an error num, and we've done pretty well with
the latter, so I'm not convinced that we really need a formatted
string.
Maybe just use kstrdup_const() if CONFIG_MODULE_UNLOAD is set,
otherwise plain assignment. Then free the string when retrieving and
on task exit.
Thanks,
Miklos
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