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

[Jan Beulich <jbeulich@xxxxxxxx>]

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
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.

> - 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.

Jan