Re: [QUERY] wic running in buildchroot-target

[Jan Kiszka <jan.kiszka@siemens.com>]

On 19.06.19 09:45, chombourger@gmail.com wrote:
> Hello all,
> 
> I am continuing my journey on the MIPS architecture.
> I wanted to add wks files for my MIPS target (Creator Ci40) and do_wic_image failed:
> 
> INFO: Creating image(s)...
> 
> -rw-r--r-- 1 root root 697932185 Jun 18 13:34 
> /tmp/development-image-mel-omni-img-creator-ci40.wic/tmp.wic.n3m8x3xo/rootfs_platforma.1.ext4
> Unsupported ioctl: cmd=0x0002
> Traceback (most recent call last):
>    File "/home/chombourger/Projects/isar/scripts/lib/wic/filemap.py", line 40, 
> in get_block_size
>      binary_data = fcntl.ioctl(file_obj, 2, struct.pack('I', 0))
> OSError: [Errno 89] Function not implemented
> 
> During handling of the above exception, another exception occurred:
> 
> Traceback (most recent call last):
>    File "/home/chombourger/Projects/isar/scripts/lib/wic/filemap.py", line 103, 
> in __init__
>      self.block_size = get_block_size(self._f_image)
>    File "/home/chombourger/Projects/isar/scripts/lib/wic/filemap.py", line 42, 
> in get_block_size
>      raise IOError("Unable to determine block size")
> OSError: Unable to determine block size
> 
> wic appears to be running from buildchroot-target and therefore under 
> qemu-<arch>-static
> evidently mips does not implement the FIGETBSZ ioctl
> 
> My options would be:
> 
> (1) check if a more recent version of qemu does implement this ioctl
> (2) add support for this ioctl in qemu-user

Support for that IOCTL seems arch-independent, but maybe the qemu-user build was 
just missing some define:

qemu/linux-user/ioctls.h
      /* emulated ioctl list */
...
#ifdef FIGETBSZ
      IOCTL(FIGETBSZ, IOC_R, MK_PTR(TYPE_LONG))
#endif

But this is better discussed on qemu-devel. You are using qemu from buster 
already, right?

> (3) work-around it in wic with something like:
> 
> diff --git a/scripts/lib/wic/filemap.py b/scripts/lib/wic/filemap.py
> index 080668e..1ce3ace 100644
> --- a/scripts/lib/wic/filemap.py
> +++ b/scripts/lib/wic/filemap.py
> @@ -40,8 +40,13 @@ def get_block_size(file_obj):
>       # Get the block size of the host file-system for the image file by calling
>       # the FIGETBSZ ioctl (number 2).
> -    binary_data = ioctl(file_obj, 2, struct.pack('I', 0))
> -    return struct.unpack('I', binary_data)[0]
> +    try:
> +        binary_data = ioctl(file_obj, 2, struct.pack('I', 0))
> +        return struct.unpack('I', binary_data)[0]
> +    except OSError as err:
> +        if err.errno == os.errno.ENOSYS:
> +            return 4096
> +        raise err
>   class ErrorNotSupp(Exception):
>       """
> 
> Ok.

wic patches should go upstream first. We avoid patching it.

> 
> But why are we running wic in buildchroot-target. Comments I have seen in the 
> code only say that it is a prerequisite but do not say why (I should probably 
> check git logs as well)
> I wonder if it should run in buildchroot-host context instead (so we still use a 
> host environment we control) but avoid the overhead of qemu emulation for 
> DISTRO_ARCH != amd64
> 
> What are your thoughts?

I do not remember all details, there might be technical difficulties, e.g. when 
you need to u-boot tools from a custom build, and that build is currently not 
generating native packages. But the killer argument is: CROSS_COMPILE is only 
optional. The default and production case is native (via qemu-user). Debian is 
not a fully cross-buildable distro, like most others.

Jan

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