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 ]; then >> + stdbuf="/usr/bin/stdbuf --output=L " >> + fi > > Might be more robust to use type -p to find stdbuf in case it's in /bin > or something? Yep good idea.
