cmdlib.sh: feed /dev/zero as qemu stdin#3793
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jlebon merged 2 commits intocoreos:mainfrom May 8, 2024
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Skipping CI for Draft Pull Request. |
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/test all |
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/test rhcos |
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This reverts commit 79b15c8. I found a workaround for the issue that prompted that commit. See next commit.
This is a follow-up to 79b15c8 ("cmdlib.sh: go back to using `tail -F` for command output") which was subsequently reverted. To summarize, it seems like in QEMU v8.2 (in f40), the guest sometimes would hang when writing over virtio-serial if the device is hooked up to the QEMU's stdio. In testing, removing the `<&-` hack to close QEMU's stdin fixed it for CoreOS CI but not Prow: coreos#3785 (comment) I think I've narrowed it down to CoreOS CI (i.e. Jenkins) allocating a tty and Prow not. When stdin is not a tty, QEMU would immediately gets EOF if it tries to read anything. I'm not sure exactly what happens, but I think the virtio-serial hang is linked to this (even though there's no userspace code in the guest trying to read from the virtio-serial port). Work around this by explicitly feeding `/dev/zero` to QEMU's stdin.
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jlebon
changed the title
tail -F for command output"/dev/zero as qemu stdin
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OK sweet! CI is happy. 🎉 Yes, I should try to get a minimal reproducer of the underlying issue and file a bug at some point, but... time. :( |
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This is a follow-up to 79b15c8 ("cmdlib.sh: go back to using
tail -Ffor command output") which was subsequently reverted.
To summarize, it seems like in QEMU v8.2 (in f40), the guest sometimes
would hang when writing over virtio-serial if the device is hooked up to
the QEMU's stdio.
In testing, removing the
<&-hack to close QEMU's stdin fixed it forCoreOS CI but not Prow:
#3785 (comment)
I think I've narrowed it down to CoreOS CI (i.e. Jenkins) allocating a
tty and Prow not. When stdin is not a tty, QEMU would immediately gets
EOF if it tries to read anything. I'm not sure exactly what happens, but
I think the virtio-serial hang is linked to this (even though there's no
userspace code in the guest trying to read from the virtio-serial port).
Work around this by explicitly feeding
/dev/zeroto QEMU's stdin.