The commit 2433d39b69, which added time64 support to select, changed
the function to use __NR_pselect6 (or __NR_pelect6_time64) on all
architectures. However, on architectures where the symbol was
implemented with __NR_select the kernel normalizes the passed timeout
instead of return EINVAL. For instance, the input timeval
{ 0, 5000000 } is interpreted as { 5, 0 }.
And as indicated by BZ #27651, this semantic seems to be expected
and changing it results in some performance issues (most likely
the program does not check the return code and keeps issuing
select with unormalized tv_usec argument).
To avoid a different semantic depending whether which syscall the
architecture used to issue, select now always normalize the timeout
input. This is a slight change for some ABIs (for instance aarch64).
Checked on x86_64-linux-gnu and i686-linux-gnu.
Instead of polling the stderr, create two pipes and fork to check
if child timeout as expected similar to tst-pselect.c. Also lower
the timeout value.
Checked on x86_64-linux-gnu.
This change adds new test to assess select()'s timeout related
functionality (the rdfs set provides valid fd - stderr - but during
normal program operation there is no data to be read, so one just
waits for timeout).
To be more specific - two use cases are checked:
- if select() times out immediately when passed struct timeval has
zero values of tv_usec and tv_sec.
- if select() times out after timeout specified in passed argument
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Adhemerval Zanella
Lukasz Majewski