FreeLists / openbeosstorage / [openbeosstorage] Re: BDiskSystem::Supports*()/Validate*()

["Axel Dörfler" <axeld@xxxxxxxxxxxxxxxx>]

"Ingo Weinhold" <bonefish@xxxxxxxxxxxxxxx> wrote:
> On Thu, 24 Jul 2003 04:37:52 +0200 CEST "Axel Dörfler" <axeld@pinc-
> software.de> wrote:
> > If you enlarge an existing partition, BFS won't even notice it (it 
> > will still operate properly but ignore the extra space).
> The problem is, that we can't handle that in a consistent way, i.e. 
> shrinking the size will indeed corrupt the data. And when enlarging 
> first and shrinking then, we can't know and have to assume, that the 
> data are lost.

That's right, and it should be reflected by a warning along the lines 
"data on that partition is most probably destroyed" or similar.

> And I also wouldn't like to have e.g. a 1 GB FS residing on a 2 GB 
> partition without being able to get that info. What we could do, is 
> to 
> add a BPartition::ContentSize(). Then DriveSetup can give the user a 
> very good picture of the situation. Thoughts?

Might be a good idea, yes. OTOH some file systems might have size 
alignment requirements and cannot use the whole space - and if it 
always says something about 0.3% free on that partition it could be 
confusing for the user.
Also, that case should only very rarely happen, so it could be too much 
of a good thing as well.

> > >   bool CanResize(bool *canResizeContents, bool *whileMounted = 
> > > NULL);
> > 
> > I am not sure if I like that way of method calling, even if I might 
> > be a bit late :)
> > I think it's strange that a CanResize() call needs and changes 
> > boolean values.
> At least for all operations applicable on file systems the respective 
> Can*() methods takes a `whileMounted' parameter. Not required, but 
> optional. I think `canResizeContents' is not optional only for the 
> reason, that I can hardly imagine, why one would not be interested in 
> that info.

True enough, but it would always create the need to have another 
variable and check, even if what I want to know would be this:
bool canResizeContents;
if (CanResize(&canResizeContents) && canResizeContents) {
        ...
}

I think it would be clearer to write:
if ((ResizeCapabilities() & (CAN_RESIZE | CAN_RESIZE_CONTENTS)) != 0) {
        ...
}

But if the contents of the partition are supposed to be going away 
anyway, you could also just check:
if (CanResize()) {
        ...
}
without having to define an extra boolean parameter.

OTOH for DriveSetup its use would probably nice, I have to admit:

bool canResizeContents;
if (CanResize(&canResizeContents)) {
        if (!canResizeContents)
                warnUserAndAbortIfHeWantsTo();

        // resize the partition
        ...
}

> > I would understand a:
> > enum resize_capabilities {
> >     B_CAN_RESIZE_ITSELF = 1,
> >     B_CAN_RESIZE_CONTENTS = 2,
> >     B_RESIZE_WHILE_MOUNTED = 4
> > };
> > and:
> > bool CanResize();
> > resize_capabilities ResizeCapabilities();
> > 
> > better (or something to that extend). The functionality itself 
> > looks 
> > good, though :)
> In fact, CanResize() wouldn't be needed at all, since all information 
> would be provided by the second method. It is even less clear, what 
> it 
> would return here -- whether the partition can be resized, or it's 
> contents, or both?

True, CanResize() wouldn't be needed anymore - yet the value it returns 
is as confusing as in the current solution (IMO).

> > >   bool CanMove(bool *canMoveContents, bool *whileMounted = NULL);
> > 
> > same as above.
> 
> Now the method looks even as scary as this:
> 
>       bool CanMove(BObjectList<BPartition> *unmovableDescendants,
>                                BObjectList<BPartition> 
> *movableOnlyIfUnmounted) 
> const;
> 
> So you would think of a `bool CanMove() const' and a second method 
> (status_t GetMovingProperies(...)).
> 
> Looks OK in principle. I'm a bit undecided though. Tyler?

Oh, didn't know it's already that complicated :-)
But in which case does CanMove() return true? Only if 
unmovableDescendants is empty? In my understanding, you cannot move a 
partition when there is an unmovable descendant.

Adios...
   Axel.