Re: [OE-core] [RESEND PATCH 2/2] runqemu: resize rootfs image to power of 2 for SD or pflash

[Gyorgy Sarvari <skandigraun@gmail.com>]

On 10/1/25 19:57, Jon Mason via lists.openembedded.org wrote:
> QEMU requires that SD and pflash images are sized to be a power of 2
> (e.g., 32M, 64M, etc).  So, if the image being used is not a power of 2
> and it's being used for SD or pflash, increase it to the next power of 2
> size via the truncate command.
>
> This might not be an actual spec requirement, and is being investigated
> in https://gitlab.com/qemu-project/qemu/-/issues/1754
>
> Signed-off-by: Jon Mason <jon.mason@arm.com>
> ---
>  scripts/runqemu | 24 ++++++++++++++++++++++--
>  1 file changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/runqemu b/scripts/runqemu
> index a8144aa68c3d..cd2ded69916a 100755
> --- a/scripts/runqemu
> +++ b/scripts/runqemu
> @@ -421,7 +421,27 @@ class BaseConfig(object):
>          else:
>              raise RunQemuError("Unknown path arg %s" % p)
>  
> -    def uncompress_rootfs(self):
> +    def rootfs_fixups(self):
> +
> +        """Resize rootfs image if needed"""

Nit: the docstring now only describes the newly added behavior, but not
the original. The original docstring is also present, but it is now in
the middle of the method.

> +        qb_rootfs_opt = self.get('QB_ROOTFS_OPT')
> +
> +        # Check if sdcard size is a power of 2, as that is currently a requirement for qemu
> +        # See https://gitlab.com/qemu-project/qemu/-/issues/1754
> +        rootfs_size = os.path.getsize(self.rootfs)
> +        rootfs_size_pwr2 = 1 << (rootfs_size - 1).bit_length()
> +        if ("if=sd" in qb_rootfs_opt or "if=pflash" in qb_rootfs_opt) and rootfs_size != rootfs_size_pwr2:
> +            logger.info("Using sd-card or pflash and is not power of 2. File size %d, power of 2 size %d" %(rootfs_size, rootfs_size_pwr2))
> +            logger.info("Attempting to use truncate to correct this.")
> +
> +            # Ensure the 'truncate' tool is installed before attempting to make a power of 2.
> +            if not shutil.which('truncate'):
> +                raise RunQemuError(f"'truncate' is required to make {self.rootfs} a power of 2 in size but was not found in PATH")
> +            try:
> +                subprocess.check_call(['truncate', '-s', str(rootfs_size_pwr2), self.rootfs])
> +            except subprocess.CalledProcessError as e:
> +                raise RunQemuError(f"Failed to make {self.rootfs} power of 2 in size: {e}")
> +
>          """Decompress ZST rootfs image if needed"""
>          if not self.rootfs or not self.fstype.endswith('.zst'):
>              return
> @@ -1808,7 +1828,7 @@ def main():
>          config.check_args()
>          config.read_qemuboot()
>          config.check_and_set()
> -        config.uncompress_rootfs()
> +        config.rootfs_fixups()
>          # Check whether the combos is valid or not
>          config.validate_combos()
>          config.print_config()
>
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