* Stephane Eranian <eran...@google.com> wrote: > On Sun, Oct 21, 2012 at 6:55 PM, Ingo Molnar <mi...@kernel.org> wrote: > > > > * Andi Kleen <a...@linux.intel.com> wrote: > > > >> > > > This isn't limited to admin, right? So the above turns into a DoS on > >> > > > the > >> > > > console. > >> > > > > >> > > Ok, so how about a WARN_ON_ONCE() instead? > >> > > >> > That should be fine I guess ;-) > >> > >> imho there is need for a generic mechanism to return an error > >> string to the user program without such hacks. > > > > Agreed - we could return an 'extended errno' long error return > > value, which in reality is a pointer to an error string (in > > perf_attr::error_str), and copy that string to user-space at > > perf syscall return time. > > > I assume by perf_attr:error_str, you actually mean: > > struct perf_event_attr { > char error_str[PERF_ERR_LEN]; > }; > > Right?
I don't think we should allocate space in the attr, instead we should use something like: u8 __user *err_str; u32 err_str_len; which would be filled in by tooling with a string and a max_len value, and strncpy_to_user() could do the rest on the kernel side. [ A minor complication is that we don't have a strncpy_to_user() method at the moment. ] Static strings could be handled this way. [ Dynamic strings could be supported too with a few tricks, although I doubt it matters in practice. ] > > Thus error-string aware tooling could print the error string. > > > > So PMU drivers could do something obvious like: > > > > return (long)"perf: INST_RETIRED.PREC_DIST only works in exclusive > > mode"; > > > > The perf syscall notices these pointers by noticing that the > > error code returned is outside the errno range. > > Is that always the case on all archs? I think yes - and if not then it can be solved via some trivial offset value added to it on such an architecture, without complicating the code on normal architectures. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/