[RFC PATCH] Sector 2 of non-embedded core.img: write early or patch later?

[Pavel Roskin]

Hello!

We have a serious problem with installing onto partitions (e.g.
grub-install /dev/sda1) and drives with geometry that doesn't leave
enough space for core.img to be embedded before the first partition.
While it's not a desirable configuration, it should work, but it
doesn't.

Either we should write sector 2 before the core.img is checked for
readability or we should delay patching sector 2 in memory until the
verification is done.  Otherwise, the verification will fail.

Delayed patching changes nothing in terms of I/O but needs a longer
patch and won't scale well if we want to put more information into
sector 2, as we'll need to cache more data.

Writing sector 2 early is less intrusive in terms of code, but may be
slower e.g. on floppies.  It's probably more reliable because we verify
that the modified sector 2 made it to the filesystem.

I tend to prefer the later ("write early") approach, but I'd like to see
some feedback before I commit it.

Both proposed patches are attached.

-- 
Regards,
Pavel Roskin

01-patch-later.patch
Description: Text Data

01-write-early.patch
Description: Text Data