Re: [PATCH v2 13/17] xen/hypfs: support dynamic hypfs nodes

[Jürgen Groß <jgross@xxxxxxxx>]

On 03.12.20 16:08, Jan Beulich wrote:
> On 01.12.2020 09:21, Juergen Gross wrote:
> > Add a HYPFS_VARDIR_INIT() macro for initializing such a directory
> > statically, taking a struct hypfs_funcs pointer as parameter additional
> > to those of HYPFS_DIR_INIT().
> >
> > Modify HYPFS_VARSIZE_INIT() to take the function vector pointer as an
> > additional parameter as this will be needed for dynamical entries.
> >
> > For being able to let the generic hypfs coding continue to work on
> > normal struct hypfs_entry entities even for dynamical nodes add some
> > infrastructure for allocating a working area for the current hypfs
> > request in order to store needed information for traversing the tree.
> > This area is anchored in a percpu pointer and can be retrieved by any
> > level of the dynamic entries. The normal way to handle allocation and
> > freeing is to allocate the data in the enter() callback of a node and
> > to free it in the related exit() callback.
> >
> > Add a hypfs_add_dyndir() function for adding a dynamic directory
> > template to the tree, which is needed for having the correct reference
> > to its position in hypfs.
> >
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > ---
> > V2:
> > - switch to xzalloc_bytes() in hypfs_alloc_dyndata() (Jan Beulich)
> > - carved out from previous patch
> > - use enter() and exit() callbacks for allocating and freeing
> >    dyndata memory
> I can't seem to be able to spot what this describes, and the
> respective part of the description therefore also remains unclear
I think all pieces are coming together with patch 15.

> to me. Not the least again when considering multi-level templates,
> where potentially each of the handlers may want to allocate dyndata,
> yet only one party can at a time.
Right now: yes.

In case needed it will be rather easy to have a linked list of dyndata
entities, with the percpu dyndata variable pointing to the most recent
one (the one of the currently deepest nesting level).

> > - add hypfs_add_dyndir()
> Overall this patch adds a lot of (for now) dead code, which makes it
> hard to judge whether this is what's needed. I guess I'll again
> learn more by reding further patches.
I hope so.

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