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

Anatol Pomozov anatol.pomozov at gmail.com
Thu May 22 16:06:48 PDT 2014


Hi

On Tue, May 20, 2014 at 12:48 PM, Ady <ady-sf at hotmail.com> wrote:
>
>>
>> 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).

FYI: I compiled syslinux without DEBUG options - the sys file size
came down to 60K. Now I am able to boot from btrfs. Thanks for your
help!

I did not try the recent patches from Peter yet.

> 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.


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