[openbeosstorage] Re: Kernel Interface Design


> My attempt at the emulator code (haven't had chance to try it under BeOS 
> yet - but it compiles under gcc).  Any comments on this one?

That's not bad. I don't think we need to manage our own file descriptors
now (see my comment in the next paragraph). Combining read and
readdir into one function is an interesting idea. 

> Data types - open modes are ints if you use open rather than fopen 
> (O_CREAT, etc) - see the attached example

Hmm, good observation. That's what I get for not actually using
POSIX funtions ;-). In light of that, I'm thinking we ought to just
pass the ints returned by POSIX-open() and kernel-open() then,
instead of managing our own file descriptors. The less code
between us and the architecture below us, the better.

> I think Tyler's right about throwing exceptions - this version doesn't, 
> but it would make the code clearer if it did.

I wrote up the beginnings of an exception class we can use as
the basis for our error handling. It takes an integer error code and
a string error message. If you compile it with debug support in,
it automatically prints out the error message to stdout when an
exception is created. 

I put it in CVS at /storage_kit/source/lib. SKError.cpp and SKError.h 
are the files. Test.SKError.cpp just shows an example of using it. 

Since catching by value or by reference seemed to involve the copy 
constructor being called a couple of times (which meant a lot of 
unnecessary string allocation and copying), I decided to make the
copy constructor private so you're required to throw dynamically 
allocated exceptions. That means any time you catch an *SKError 
pointer and don't raise it again, you have to delete it. Doing it that
way means the constructor only gets called once for each exception.

-Tyler

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