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

[Zhihang Wei <wzh@ilbers.de>]

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 initrd.
"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 initrd. 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, introduce INITRAMFS_EXTRA_DRIVERS and use it
to append the neccessary drivers that are currently missed from the
initrd.

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 <wzh@ilbers.de>
---
 meta-isar/conf/multiconfig/qemuarm-trixie.conf | 2 ++
 meta/classes-recipe/rootfs.bbclass             | 9 ++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/meta-isar/conf/multiconfig/qemuarm-trixie.conf b/meta-isar/conf/multiconfig/qemuarm-trixie.conf
index 5600ab23..dcf0b839 100644
--- a/meta-isar/conf/multiconfig/qemuarm-trixie.conf
+++ b/meta-isar/conf/multiconfig/qemuarm-trixie.conf
@@ -5,3 +5,5 @@
 
 MACHINE ?= "qemuarm"
 DISTRO ?= "debian-trixie"
+
+INITRAMFS_EXTRA_DRIVERS += "virtio_blk"
diff --git a/meta/classes-recipe/rootfs.bbclass b/meta/classes-recipe/rootfs.bbclass
index 8485b32f..65843f61 100644
--- a/meta/classes-recipe/rootfs.bbclass
+++ b/meta/classes-recipe/rootfs.bbclass
@@ -12,12 +12,19 @@ ROOTFS_DISTRO ?= "${DISTRO}"
 # the default initramfs generator and it is not
 # possible to derive the value in another way
 ROOTFS_USE_DRACUT ??= ""
+INITRAMFS_EXTRA_DRIVERS ?= ""
 
 def initramfs_generator_cmdline(d):
     rootfs_packages =  d.getVar('ROOTFS_PACKAGES') or ''
+    extra_drivers = d.getVar('INITRAMFS_EXTRA_DRIVERS') or ''
     if 'dracut' in rootfs_packages or bb.utils.to_boolean(d.getVar('ROOTFS_USE_DRACUT')):
         return "dracut --force --kver \"$kernel_version\""
-    return "update-initramfs -u -v -k \"$kernel_version\""
+    cmds = []
+    if extra_drivers:
+        for drv in extra_drivers.split():
+            cmds.append(f'echo {drv} | tee -a /etc/initramfs-tools/modules')
+    cmds.append('update-initramfs -u -v -k "$kernel_version"')
+    return " && ".join(cmds)
 
 ROOTFS_PACKAGES ?= ""
 ROOTFS_VARDEPS ?= ""
-- 
2.39.5

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