Its API is similar to support_capture_subprocess, but rather creates a
new process based on the input path and arguments. Under the hoods it
uses posix_spawn to create the new process.
It also allows the use of other support_capture_* functions to check
for expected results and free the resources.
Checked on x86_64-linux-gnu.
* support/Makefile (libsupport-routines): Add support_subprocess,
xposix_spawn, xposix_spawn_file_actions_addclose, and
xposix_spawn_file_actions_adddup2.
(tst-support_capture_subprocess-ARGS): New rule.
* support/capture_subprocess.h (support_capture_subprogram): New
prototype.
* support/support_capture_subprocess.c (support_capture_subprocess):
Refactor to use support_subprocess and support_capture_poll.
(support_capture_subprogram): New function.
* support/tst-support_capture_subprocess.c (write_mode_to_str,
str_to_write_mode, test_common, parse_int, handle_restart,
do_subprocess, do_subprogram, do_multiple_tests): New functions.
(do_test): Add support_capture_subprogram tests.
* support/subprocess.h: New file.
* support/support_subprocess.c: Likewise.
* support/xposix_spawn.c: Likewise.
* support/xposix_spawn_file_actions_addclose.c: Likewise.
* support/xposix_spawn_file_actions_adddup2.c: Likewise.
* support/xspawn.h: Likewise.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
