On 13/07/2023 15:16, Mark Brown wrote:
On Thu, Jul 13, 2023 at 02:54:32PM +0100, Ryan Roberts wrote:
The selftests runner pipes the test program's stdout to tap_prefix. The presence of the pipe means that the test program sets its stdout to be fully buffered (as aposed to line buffered when directly connected to the terminal). The block buffering means that there is often content in the buffer at fork() time, which causes the output to end up duplicated. This was causing problems for mm:cow where test results were duplicated 20-30x.
Solve this by using `stdbuf`, when available to force the test program to use line buffered mode. This means previously printf'ed results are flushed out of the program before any fork().
This is going to be useful in general since not all selftests use the kselftest helpers but it'd probably also be good to make ksft_print_header() also make the output unbuffered
Yeah sounds reasonable.
so that if setbuf isn't installed on the target system or the tests are run standalone we don't run into issues there. Even if the test isn't corrupting data having things unbuffered is going to be good for making sure we don't drop any output if the test dies.
Note that currently I've set stdbuf to encourage line buffering rather than no buffering. Are you saying no buffering is preferred? I took the view that line buffering is a good middle ground, and and aligns with what people see when developing and running the program manually in the terminal.
if [ -x /usr/bin/stdbuf ]; thenstdbuf="/usr/bin/stdbuf --output=L "fiMight be more robust to use type -p to find stdbuf in case it's in /bin or something?
Yep good idea.