Re: [RFC 0/6] Backing Store for sysfs

[Dipankar Sarma <dipankar@in.ibm.com>]

On Mon, Oct 06, 2003 at 08:30:50PM +0100, viro@parcelfarce.linux.theplanet.co.uk wrote:
> On Tue, Oct 07, 2003 at 12:57:13AM +0530, Dipankar Sarma wrote:
> > sysfs currently uses dentries to represent filesystem hierarchy.
> > We want to create the dentries on the fly and age them out.
> > So, we can no longer use dentries to represent filesystem hierarchy.
> > Now, *something* has to represent the actual filesystem
> > hierarchy, so that dentries/inodes can be created on a lookup
> > miss based on that. So, what do you do here ? kobject and
> > its associates already represent most of the information necessary
> > for a backing store. Maneesh just added a little more to complete
> > what is equivalent of a on-disk filesystem. This allows vfs to
> > create dentries and inodes on the fly and age later on. Granted
> > that there are probably ugliness in the design to be sorted out
> > and it may have taken kobjects in a slightly different direction
> > than earlier, but it is not that odd when you look at it
> > from the VFS point of view.
> 
> Rot.  First of all, *not* *all* *kobjects* *are* *in* *sysfs*.  And these
> are pure loss in your case.

gregkh pointed out this as well and that is why I said that Maneesh's
patch may have taken kobjects in a different direction than what
it was intended earlier. I don't disagree with this and it may
very well be that dentry ageing will have to be done differently.

> 
> What's more important, for leaves of the sysfs tree your overhead is also
> a loss - we don't need to pin dentry down for them even with current sysfs
> design.   And that can be done with minimal code changes and no data changes
> at all.  Your patch will have to be more attractive than that.  What's the
> expected ratio of directories to non-directories in sysfs?

ISTR, a large number of files in sysfs are attributes which are leaves.
So, keeping a kobject tree partially connected using dentries as backing 
store as opposed to having everything connected might just be enough.
It will be looked into.

Thanks
Dipankar