[PATCH v2] qemuarm-trixie: Workaround with missing drivers in qemuarm-trixie initramfs

[Zhihang Wei]

This is a workaround to fix the current qemuarm-trixie image unbootable
issue.

Starting with Debian Trixie, update-initramfs invokes "dracut-install"
to collect and install required drivers into the generated initramfs.
"dracut-install" relies on fts_open() / fts_read() from glibc to
traverse directories and locate drivers.

Due to a long-standing bug [1] between qemu and glibc, the fts_*
functions may fail to find files on certain 32-bit architectures. As a
result, required modules such as virtio_blk are not detected and not
added to the initramfs. The produced image then fails to boot under
qemu because the block device driver is missing.

A similiar dracut bug report was filed in 2024 [2], pointing to this
upstream glibc issue reported in 2018 [1]. No upstream fix has been
applied, and the issue appears to affect only qemu builds for specific
32-bit targets.

As a temporary workaround, use a customized initramfs-hook to append
the neccessary drivers that are currently missed from the initramfs.

For a complete fix, we either need to push for an upstream glibc/qemu
fix, or convince dracut to avoid using these non-POSIX fts_* functions
and use opendir() / readdir() instead.

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=23960
[2] https://bugs-devel.debian.org/cgi-bin/bugreport.cgi?bug=1079443

Signed-off-by: Zhihang Wei <w...@ilbers.de>
---
Changes in v2:
- Use initramfs-hook to install the driver, instead of adding another
variable

meta-isar/conf/multiconfig/qemuarm-trixie.conf | 4 +++-
.../initramfs-virtio-blk-hook_0.1.bb | 8 ++++++++
2 files changed, 11 insertions(+), 1 deletion(-)
create mode 100644 meta/recipes-initramfs/initramfs-virtio-blk-hook/initramfs-virtio-blk-hook_0.1.bb

diff --git a/meta-isar/conf/multiconfig/qemuarm-trixie.conf b/meta-isar/conf/multiconfig/qemuarm-trixie.conf
index 5600ab23..20eecd92 100644
--- a/meta-isar/conf/multiconfig/qemuarm-trixie.conf
+++ b/meta-isar/conf/multiconfig/qemuarm-trixie.conf
@@ -1,7 +1,9 @@
# This software is a part of Isar.
-# Copyright (C) 2024 ilbers GmbH
+# Copyright (C) 2024-2026 ilbers GmbH
#
# SPDX-License-Identifier: MIT

MACHINE ?= "qemuarm"
DISTRO ?= "debian-trixie"
+
+IMAGE_INSTALL += "initramfs-virtio-blk-hook"
diff --git a/meta/recipes-initramfs/initramfs-virtio-blk-hook/initramfs-virtio-blk-hook_0.1.bb b/meta/recipes-initramfs/initramfs-virtio-blk-hook/initramfs-virtio-blk-hook_0.1.bb
new file mode 100644
index 00000000..229d91d6
--- /dev/null
+++ b/meta/recipes-initramfs/initramfs-virtio-blk-hook/initramfs-virtio-blk-hook_0.1.bb
@@ -0,0 +1,8 @@
+# This software is a part of Isar.
+# Copyright (C) 2026 ilbers GmbH
+#
+# SPDX-License-Identifier: MIT
+
+inherit initramfs-hook
+
+HOOK_ADD_MODULES = "virtio-blk"
--
2.39.5

[Jan Kiszka]

This covers the initramfs-tools based generation. What if someone
enables dracut (kas/opt/dracut.yaml)?

> diff --git a/meta/recipes-initramfs/initramfs-virtio-blk-hook/initramfs-virtio-blk-hook_0.1.bb b/meta/recipes-initramfs/initramfs-virtio-blk-hook/initramfs-virtio-blk-hook_0.1.bb
> new file mode 100644
> index 00000000..229d91d6
> --- /dev/null
> +++ b/meta/recipes-initramfs/initramfs-virtio-blk-hook/initramfs-virtio-blk-hook_0.1.bb
> @@ -0,0 +1,8 @@
> +# This software is a part of Isar.
> +# Copyright (C) 2026 ilbers GmbH
> +#
> +# SPDX-License-Identifier: MIT
> +
> +inherit initramfs-hook
> +
> +HOOK_ADD_MODULES = "virtio-blk"

Jan

--
Siemens AG, Foundational Technologies
Linux Expert Center

[Zhihang Wei]

A pure dracut generated initramfs for qemuarm-trixie cannot boot. It
surprisingly has virtio_blk, but still not bootable. Need to find the
reason.

Actually, there should be more drivers installed into initramfs by
initramfs-tools, but they are now missing due to the same bug. Adding
virtio-blk just makes this initramfs-tools generated initramfs
"minimally" bootable. My guess is that the dracut generated initramfs
is missing some other necessary drivers.

Zhihang

[Jan Kiszka]

initramfs and "necessary" drivers is tricky for us. Normally, those are
probed on the machine that will use the initramfs afterwards, but that
does not work with Isar. With trixie, some unconditionally installed
modules were dropped, and that already caused extra efforts downstream
(unless you are on Debian kernels, it's often best to simply compile
them in).

But maybe there is more involved with plain dracut, and Quirin has some
idea.