update QNX scripts to work with QEMU built from source by japaric · Pull Request #2422 · ferrocene/ferrocene

japaric · 2026-06-26T14:28:26Z

qemu-system-$ARCH -netdev bridge,(..) uses the qemu-bridge-helper script that was installed with qemu-system-$ARCH. However, to set up the bridge network in the QNX scripts, we are using the qemu-bridge-helper of the system installed QEMU.

When using a QEMU built from source, we have seen the VM fail to initialize due to a different version of qemu-bridge-helper being used to set up the network bridge. To ensure the right qemu-bridge-helper is using in the QNX script, we search for it using the absolute path of the qemu-system-$ARCH as the reference, instead of assuming it'll be in /usr as that only works when the system installed QEMU is used.

`qemu-system-$ARCH -netdev bridge,(..)` uses the qemu-bridge-helper script that was installed with `qemu-system-$ARCH`. However, to set up the bridge network in the QNX scripts, we are using the qemu-bridge-helper of the system installed QEMU. When using a QEMU built from source, we have seen the VM fail to initialize due to a different version of qemu-bridge-helper being used to set up the network bridge. To ensure the right qemu-bridge-helper is using in the QNX script, we search for it using the absolute path of the `qemu-system-$ARCH` as the reference, instead of assuming it'll be in `/usr` as that only works when the system installed QEMU is used.

jyn514

seems reasonable.

bors r+

bors-ferrocene · 2026-06-26T14:31:08Z

🕐 Waiting for PR status (Github check) to be set, probably by CI. Bors will automatically try to run when all required PR statuses are set.

bors-ferrocene · 2026-06-26T20:03:09Z

Build failed (retrying...):

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2422: update QNX scripts to work with QEMU built from source r=jyn514 a=japaric `qemu-system-$ARCH -netdev bridge,(..)` uses the qemu-bridge-helper script that was installed with `qemu-system-$ARCH`. However, to set up the bridge network in the QNX scripts, we are using the qemu-bridge-helper of the system installed QEMU. When using a QEMU built from source, we have seen the VM fail to initialize due to a different version of qemu-bridge-helper being used to set up the network bridge. To ensure the right qemu-bridge-helper is using in the QNX script, we search for it using the absolute path of the `qemu-system-$ARCH` as the reference, instead of assuming it'll be in `/usr` as that only works when the system installed QEMU is used. Co-authored-by: Jorge Aparicio <[email protected]>

bors-ferrocene · 2026-06-27T01:47:11Z

Build failed:

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jyn514 · 2026-06-29T08:49:32Z

seems like a real error.

^@^@QNX_SHARED_LICENSE_FILE=/home/ci/project/qnx710-472/license/licenses
QNX_HOST=/home/ci/project/qnx710-472/host/linux/x86_64
QNX_TARGET=/home/ci/project/qnx710-472/target/qnx7
MAKEFLAGS=-I/home/ci/project/qnx710-472/target/qnx7/usr/include

===> setting up QEMU bridge network
error: bridge.conf not found; update this search logic (helper=/usr/lib/qemu/qemu-bridge-helper)

japaric · 2026-06-29T13:25:22Z

seems like a real error.

yeah, bridge.conf does not exist in the Docker image as it is created in the container by the QNX SDP net.sh script so we cannot check for its presence to confirm that it is in one of the expected locations. I have changed the logic to extract the expected location from the bridge helper binary instead

jyn514 · 2026-06-30T15:59:58Z

+    # The location where `qemu-bridge-helper` expects `bride.conf` to be is
+    # different on a custom QEMU build vs on the Debian packaged QEMU. Also, the
+    # file is not contained in the Debian package not created by
+    # `make install` on a custom build; instead the QNX SDP's `net.sh` script
+    # will create it. As `bridge.conf` does not exist we cannot search for it
+    # using `find`. The most reliable way to get its expected location seems to
+    # be to extract the location directly from the helper binary itself
+    #
+    # Examples of bridge-qemu-helper and bridge.conf locations
+    # - Ubuntu/Debian package:
+    #   - `/usr/lib/qemu/qemu-bridge-helper`;
+    #   - `/etc/qemu/bridge.conf`
+    # - custom build:
+    #   - `$PREFIX/libexec/qemu-bridge-helper`;
+    #   - `$PREFIX/etc/qemu/bridge.conf`
+    strings "$qemu_bridge_helper" | grep '^/.*/bridge.conf$'


well this is a little terrifying 😆 is there any way we can run net.sh ahead of time so we can see where it actually puts the bridge?

net.sh takes the full path to bridge.conf as an argument and it will create/extend it there, where you tell it to put it even if it's wrong. you have to pass the full bridge.conf path that QEMU expects to net.sh or qemu-bridge-helper will fail later on. so, we cannot get the expected bridge.conf location from net.sh, only from QEMU itself, or rather, from qemu-bridge-helper.

the other option I can think of is running a dummy QEMU invocation first that tries to use the bridge network and helper, which will fail because bridge.conf does not exist, and then parse the error message. the expected bridge.conf location will be contained there

the expected bridge.conf appears to be in the --sysconfdir location you pass to QEMU's configure script but qemu-system-* --version does not print this (or any) configuration setting , like say gcc -v does.

qemu-bridge-helper itself has a very primitive command line parsing. it does not accept --help or --version flags; it only prints an "usage" one liner if the arguments are wrong.

this is so sad. i guess this is ok; you're the one using this script most often, if you're willing to maintain it i'm ok with the change.

jyn514

bors merge

bors-ferrocene · 2026-07-10T19:41:53Z

Build succeeded:

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setup

jyn514 approved these changes Jun 26, 2026

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jyn514 added the waiting-on-author If this PR was opened by an automation, the "author" is the assignee. label Jun 29, 2026

extract bridge.conf location from helper binary

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japaric added waiting-on-review and removed waiting-on-author If this PR was opened by an automation, the "author" is the assignee. labels Jun 29, 2026

jyn514 reviewed Jun 30, 2026

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jyn514 added waiting-on-author If this PR was opened by an automation, the "author" is the assignee. and removed waiting-on-review labels Jun 30, 2026

jyn514 approved these changes Jul 10, 2026

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jyn514 added waiting-on-ci and removed waiting-on-author If this PR was opened by an automation, the "author" is the assignee. labels Jul 10, 2026

bors-ferrocene Bot merged commit 31cd51a into main Jul 10, 2026
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github-actions Bot added the backport:maybe PR candidate for backport label Jul 10, 2026

bors-ferrocene Bot deleted the ja-qnx-with-custom-qnx-build branch July 10, 2026 19:42

github-actions Bot added the merged-in:1.98 label Jul 10, 2026

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update QNX scripts to work with QEMU built from source#2422

update QNX scripts to work with QEMU built from source#2422
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