Fix/command read busy loop - #5259
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fgets() returns nullptr on both a read error and at end-of-file and an
error sets ferror(), never feof().
The first failed read therefore spins the thread at 100% CPU for good,
because read() looped only on feof() and never returns.
(command::close() also never never reaps the child, nothing else does,
as the SIGCHLD handler only drains the list forkExec() fills).
Loop on fgets() which stops on both end-of-file and error, then check
ferror() so a failed read is not silently a truncated module output.
Reproduced by calling read() under a watchdog on a directory fd, whose
reads fail with EISDIR:
before: WATCHDOG: read() did not return after 3s -- SPINNING
after: [error] Error reading command output: Is a directory
read() RETURNED, 0 bytes
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com>
The regression this guards against does not fail a run, it wedges one, so the call goes in a child with a 5s watchdog and a return to the old behaviour is reported as a failure instead of a hang. Passes on the current code; with read() put back the way it was it fails with "command::read did not return within 5s". Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Signed-off-by: Adrian Ratiu <adrian.ratiu@collabora.com>
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What does this PR do?
It fixes a busyloop at 100% cpu I noticed and adds a regresion test.
More details in the commit messages.
Related issues
No issue.
Checklist
clang-formatninja -C build)- [ ] Man page updated for any new/changed user-facing option (man/)