[syslinux] "EDD Load error" on btrfs, how to debug?

[Ady]

> 
> On Tue, May 20, 2014 1:52 pm, Anatol Pomozov wrote:
> 
> > Ok, we've figured out potential cause of the problem. The next
> > question how to minimize the size of ldlinux.sys?
> >
> > BTW looking at official (?) binary
> > https://www.kernel.org/pub/linux/utils/boot/syslinux/Testing/6.03/syslinux-6.03-pre11.tar.xz
> > I see that their size is also more than 64K
> 
> Actually, there is *no* 64KiB limit on btrfs. Look at btrfs-progs
> (ctree.h:830):
> 
> "
> /*
>  * We don't want to overwrite 1M at the beginning of device, even though
>  * there is our 1st superblock at 64k. Some possible reasons:
>  *  - the first 64k blank is useful for some boot loader/manager
>  *  - the first 1M could be scratched by buggy partitioner or somesuch
>  */
> #define BTRFS_BLOCK_RESERVED_1M_FOR_SUPER	((u64)1024 * 1024)
> "
> 
> 1MiB seems to be a reasonable size to fit bootsector + LDLINUX.SYS in. I
> don't know exactly how Syslinux is handling this, but it should be using
> the whole available space (1MiB instead).
> 
> -- 
> Paulo Alcantara, C.E.S.A.R
> Speaking for myself only.
 
The issue about the 64KB size (for bootsector + ADV + ldlinux.sys) is 
that *Syslinux* (as of 6.03-pre11) doesn't know _yet_ how to take 
advantage of the additional available space in Btrfs (patches are 
welcome).

That's the reason for suggesting workarounds instead of real 
solutions.

At any rate, the 64KB issue doesn't explain every and all the 
problems reported about Syslinux in Btrfs.

Regards,
Ady.