UEFI: caveats about not utf-8 dir entries

[tlaronde%polynum.com@localhost]

I don't know if this is for tech-kern or tech-userlevel (perhaps the
two).

I just read today, on the devel UEFI edk2 devel list, from patches for
ext4, a comment on the problem of the encoding of dir entries.

The problem is that, generally in fs, no encoding is specified: dir
entries are just a sequence of bytes, whether nul byte terminated or
with the length of the entry given (the later for ext4).

UEFI (edk2) deals, internally, with UCS-2 strings.

With ext4 (and I expect this is the same for other fs drivers),
conversion is attempted from utf-8. Here, if the "from utf-8" conversion
errors (not utf-8), the dir entry is skipped, meaning that not anything
on a fs read can be reached by the UEFI code.

This has to be kept in mind when populating a msdos partition for
booting and for people wandering in a filesystem using the UEFI shell:
even if the fs is readable, perhaps not everything will be accessible.

FWIW,
-- 
        Thierry Laronde <tlaronde +AT+ polynum +dot+ com>
                     http://www.kergis.com/
                    http://kertex.kergis.com/
Key fingerprint = 0FF7 E906 FBAF FE95 FD89  250D 52B1 AE95 6006 F40C