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s390_runtime_instr.2: Document signum argument behavior change 

Document that the signum argument is ignored in newer kernels, but
that user space should pass a valid real-time signal number for
backwards compatibility.

Cowritten-by: Eugene Syromyatnikov <evgsyr@gmail.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Eugene Syromyatnikov <evgsyr@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Heiko Carstens 2020-04-16 12:10:07 +02:00 committed by Michael Kerrisk
parent bff15b74e0
commit cca27058b7
1 changed files with 20 additions and 4 deletions
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24
man2/s390_runtime_instr.2
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@ -48,9 +48,11 @@ argument controls whether run-time instrumentation is started
The
.IR signum
argument specifies the number of a real-time signal.
The real-time signal is sent to the thread if the run-time instrumentation
buffer is full or if the run-time-instrumentation-halted interrupt
occurred.
This argument was used to specify a signal number that should be delivered
to the thread if the run-time instrumentation buffer was full or if
the run-time-instrumentation-halted interrupt had occurred.
It has no effect beginning with Linux 4.4, since support for signalling
was never used and kernel support was removed.
.SH RETURN VALUE
On success,
.BR s390_runtime_instr ()
@ -67,9 +69,16 @@ is set to one of the error codes listed below.
.B EINVAL
The value specified in
.IR command
is not a valid command or the value specified in
is not a valid command.
.TP
.B EINVAL
The value specified in
.IR signum
is not a real-time signal number.
From Linux 4.4 onwards, the
.IR signum
argument has no effect, so that an invalid signal number will not result in an
error.
.TP
.B ENOMEM
Allocating memory for the run-time instrumentation control block failed.
@ -91,6 +100,13 @@ The
header file is available
.\" commit df2f815a7df7edb5335a3bdeee6a8f9f6f9c35c4
since Linux 4.16.
.PP
Support for signalling was removed with Linux 4.4.
With Linux 4.4 also the check whether
.IR signum
is a valid real-time signal was removed.
For backwards compatibility with old kernels it is recommended to pass a valid
real-time signal number and install a handler for it.
.SH SEE ALSO
.BR syscall (2),
.BR signal (7)