Re: [Xen-users] Problems with pygrub: ValueError: unable to open file

[Michael Paesold <mpaesold@xxxxxx>]

I wrote:
> I am currently struggling with getting pygrub to work. I am using unstable
> 9327:cf89e8f0831b with 2.6.16-rc6-git3 on CentOS 4 (although the kernel
> version should not matter here).
...

> Traceback (most recent call last):
>  File "/root/pygrub", line 258, in ?
>    cf = get_config(file, isconfig)
>  File "/root/pygrub", line 121, in get_config
>    fs = fstype.open_fs(fn, offset)
>  File "/usr/lib/python2.3/site-packages/grub/fsys/ext2/__init__.py", line
> 35, in open_fs
>    return Ext2Fs(fn, offset = offset)
> ValueError: unable to open file
> Error: Boot loader didn't return any data!
>
> I checked the values of fn and offset:
> fn = /dev/sdb1
> offset = 512
>
> This seems perfectly ok, considering the output of fdisk:
...

Well, after further investigation, the problem is that the CentOS/RHEL 4
version of e2fsprogs does not have a ext2fs_open2 that allows to use the
offset. The "bug" is that this is not reported at all.

    if (offset != 0) {
        snprintf(offsetopt, 29, "offset=%d", offset);
    }

#ifdef HAVE_EXT2FS_OPEN2
    err = ext2fs_open2(name, offsetopt, flags, superblock, block_size,
                       unix_io_manager, &efs);
#else
    err = ext2fs_open(name, flags, superblock, block_size,
                      unix_io_manager, &efs);
#endif


Here, HAVE_EXT2FS_OPEN2 is not defined. An offset cannot be used if 
ext2fs_open2 is not available. Does anyone see a way to work around this 
issue other than either update e2fsprogs or otherwise teach pygrub to use 
devicemapper or similar to be able to open an ext2 filesystem in a 
partition that is not directly accessible to the host (e.g. in a 
partitioned image)?
Best Regards,
Michael Paesold

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