Command 'perf record' calls:

  cmd_report()
    record__auxtrace_init()
       auxtrace_record__init()

On s390 function auxtrace_record__init() returns random return value due
to missing initialization.

This sometime causes 'perf record' to exit immediately without error
message and creating a perf.data file.

Fix this by setting error the return code to zero before returning from
platform specific functions which may not set the error code in call
cases.
Signed-off-by: NThomas Richter <tmricht@linux.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Link: http://lkml.kernel.org/r/20180423142940.21143-1-tmricht@linux.ibm.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

Perf tool need implement a callback to enable using AUX buffer. Perf
will do another mmap() to trigger the setup of AUX buffer in kernel
if there is such callback. The default size of the AUX buffer is set
properly according to the sampling frequency to avoid overflow. It
could also be manually set by -m option of perf.

The interface of perf is not changed. Diagnostic mode sampling
could be started by `perf record -e rBD000` like before.
Signed-off-by: NPu Hou <bjhoupu@linux.vnet.ibm.com>
Reviewed-by: NHendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>