Hi,
> >> - if the StartId is 0x55aa, then we need to look further, beause we
> >> can't decide yet. For example, if State is VAR_HEADER_VALID_ONLY (0x7f),
> >> then it might be fine for the variable header (at the very end of the
> >> varstore) *not* to be followed by payload bytes (name, data).
> >
> > Not sure this makes sense. VAR_HEADER_VALID_ONLY is a temporary state,
> > while the variable driver writes name and data just after the header,
> > to be updated to VAR_ADDED when the write completed successfully. So
> > I'd expect to never find a header without space for name + data.
>
> - Do we know for sure that VAR_HEADER_VALID_ONLY is never expected to be
> seen?
Writing goes like this:
(1) find free space
(2) write header, with VAR_HEADER_VALID_ONLY.
(3) write name + data
(4) update header, set state = VAR_ADDED.
> What if the variable update design defines VAR_HEADER_VALID_ONLY
> specifically so that the variable driver can recover from a power loss
> "in the middle"?
Power loss in step (3) can surely lead to variables in
VAR_HEADER_VALID_ONLY state, and I'd expect the variable driver can
actually recover from that.
[ side note: The (2) write should be small enough that it fits into the
flash block write buffer (128 bytes). Which could be
important to maintain variable store consistency. ]
Nevertheless we should never find a header at the end of the variable
store, without space allocated for name + date. Minimal space for the
name is 4 bytes (one char16 + '\0'), for the data 1 byte, alignment
rounds the latter to 4 bytes too, so this should be true:
VarOffset + sizeof(*VarHeader) + 8 <= VariableStoreHeader->Size
> So I figure, if we accept VAR_HEADER_VALID_ONLY in that logic, then we
> should also accept VAR_HEADER_VALID_ONLY if it's at the very end of
> the varstore.
Disagree, see above. Storing the header at a place which leaves no room
for name + data doesn't make sense to me.
We could go the extra mile and look at the next StartId location, verify
StartId != 0x55aa, in the no-space-left-for-header case.
take care,
Gerd
-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#113182): https://edk2.groups.io/g/devel/message/113182
Mute This Topic: https://groups.io/mt/103171811/21656
Group Owner: [email protected]
Unsubscribe: https://edk2.groups.io/g/devel/unsub [[email protected]]
-=-=-=-=-=-=-=-=-=-=-=-
