Fix QEMU hanging when boot.sh --test output is piped#378
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boot.sh --test now redirects stdin from /dev/null before exec'ing QEMU, so QEMU's -nographic serial setup never calls tcsetattr() on a real terminal. When the caller pipes stdout (e.g., through tee) or wraps boot.sh with timeout(1), QEMU runs in a process group that is not the terminal's foreground group; a tcsetattr() call then receives SIGTTOU and stops the process (state Tl), producing no output. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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When I ran
devtools/test-modules.shfrom my terminal, it printed "Booting QEMU for testing" and then produced no further output. Inps aux, QEMU was stuck in stateTl(stopped).Root cause:
-nographicmakes QEMU calltcsetattr()to put the terminal in raw mode for serial input. That's fine when QEMU runs in the foreground, buttest-modules.shpipes stdout throughtee, andtimeout(1)moves the child into its own process group (so it can kill the whole group on timeout). Since that group isn't the terminal's foreground group,tcsetattr()receivesSIGTTOUand the kernel stops QEMU before it prints anything.The fix: redirect stdin from
/dev/nullinboot.sh --testmode. The guest never needs keyboard input during automated testing, so this is always safe, and it prevents QEMU from ever touching a real terminal.CI never hit this because GitHub Actions runners don't have a TTY —
tcsetattr()fails silently withENOTTYinside a container.Tested both
test-modules.sh(33 passed, 0 failed) and interactiveboot.shto confirm the fix doesn't break anything.Summary by cubic
Prevents QEMU from hanging in test mode when output is piped by redirecting stdin from
/dev/null. This avoidsSIGTTOUfromtcsetattr()under-nographicso tests print output and complete.boot.sh --test, exec QEMU with< /dev/nullto avoid touching the real TTY.teeandtimeout(1);devtools/test-modules.shpasses, and interactiveboot.shis unchanged.Written for commit 37cf3aa. Summary will update on new commits. Review in cubic