[lttng-dev] ERROR: No buffer space available

[Mathieu Desnoyers]

CCing lttng-dev, as other people might want to help.

Please be aware that the TRACE_EVENT LTTng implementation is slightly
different from the mainline kernel implementation, so the documentation
you refer to is not a perfect fit.

Thanks,

Mathieu

* Rui Han (r.han at umiami.edu) wrote:
> Hi Mathieu,
> 
> I did reboot the system. I am wondering if it is because the header file
> need to be modified. I am not quite understand how the headers worked. I
> read the article at http://lwn.net/Articles/383362/, but I am not
> completely understand the essence of the discussion about the header. Could
> you give me some hint that I can understand lttng and debug the code to get
> what I wanted?
> 
> Thank you very much.
> 
> Regards,
> Rui
> 
> On Sun, Aug 5, 2012 at 1:03 PM, Mathieu Desnoyers <
> mathieu.desnoyers at efficios.com> wrote:
> 
> > * Rui Han (r.han at umiami.edu) wrote:
> > > Hi,
> > >
> > > I try to modified the lttng2.0 source code for my research. For example,
> > I
> > > try to log the "comm" for the write system call, I add the following
> > filed
> > > in the file x86-64-syscalls-3.0.4_pointers.h located at the path
> > > lttng-modules-2.0.3/instrumentation/syscalls/headers. I modify the
> > > TRACE_EVENTS() macro from the original one:
> > >
> > > #ifndef OVERRIDE_64_sys_write
> > > SC_TRACE_EVENT(sys_write,
> > > TP_PROTO(unsigned int fd, const char * buf, size_t count),
> > > TP_ARGS(fd, buf, count),
> > > TP_STRUCT__entry(__field(unsigned int, fd) __field_hex(const char *, buf)
> > > __field(size_t, count)),
> > > TP_fast_assign(tp_assign(fd, fd) tp_assign(buf, buf) tp_assign(count,
> > > count)),
> > > TP_printk()
> > > )
> > > #endif
> > >
> > > to the following one:
> > >
> > > #ifndef OVERRIDE_64_sys_write
> > > SC_TRACE_EVENT(sys_write,
> > > TP_PROTO(unsigned int fd, const char * buf, size_t count, struct
> > > task_struct *p),
> > > TP_ARGS(fd, buf, count, p),
> > > TP_STRUCT__entry( __field(unsigned int, fd) __field_hex(const char *,
> > > buf) __field(size_t,
> > > count) __array_text(char, comm, TASK_COMM_LEN)),
> > > TP_fast_assign( tp_assign(fd, fd) tp_assign(buf, buf) tp_assign(count,
> > > 2064) tp_memcpy(comm,
> > > p->comm, TASK_COMM_LEN)),
> > > TP_printk()
> > > )
> > > #endif
> > >
> > > I add one argument *p and one filed "comm"  for the macro. It was able to
> > > be compiled, however, after reload the lttng modules, It will show the
> > > following error messages when I start lttng.
> > >
> > > PERROR: ioctl start session: No buffer space available [in
> > > kernel_start_session() at kernel.c:397]
> > > Error: Starting kernel trace failed
> >
> > I don't see how modifying the system call tracing macro would trigger
> > this error at start. Try restarting lttng-sessiond. Try unloading the
> > lttng modules, and, maybe, as last resort, rebooting your system.
> >
> > Thanks,
> >
> > Mathieu
> >
> > >
> > > It won't work. Please help me out with this. My next step is try to add
> > > extra fields in the sys_connect macros to enable the logging of the
> > > connected IP/port from the socket. Is this method right? what are other
> > > possible solutions in order to logging the details of the socket
> > > information?
> > >
> > > Thank you very much.
> > >
> > > Regards,
> > > Rui
> >
> > --
> > Mathieu Desnoyers
> > Operating System Efficiency R&D Consultant
> > EfficiOS Inc.
> > http://www.efficios.com
> >

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com