Re: [PATCH v4 05/13] tools/xenstore: use accounting buffering for node accounting

[Julien Grall <julien@xxxxxxx>]

Hi Juergen,

On 03/05/2023 06:13, Juergen Gross wrote:
> On 02.05.23 20:55, Julien Grall wrote:
> > Hi Juergen,
> >
> > On 05/04/2023 08:03, Juergen Gross wrote:
> > > Add the node accounting to the accounting information buffering in
> > > order to avoid having to undo it in case of failure.
> > >
> > > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > > ---
> > >   tools/xenstore/xenstored_core.c   | 21 ++-------------------
> > >   tools/xenstore/xenstored_domain.h |  4 ++--
> > >   2 files changed, 4 insertions(+), 21 deletions(-)
> > >
> > > diff --git a/tools/xenstore/xenstored_core.c 
> > > b/tools/xenstore/xenstored_core.c
> > > index 84335f5f3d..92a40ccf3f 100644
> > > --- a/tools/xenstore/xenstored_core.c
> > > +++ b/tools/xenstore/xenstored_core.c
> > > @@ -1452,7 +1452,6 @@ static void destroy_node_rm(struct connection 
> > > *conn, struct node *node)
> > >   static int destroy_node(struct connection *conn, struct node *node)
> > >   {
> > >       destroy_node_rm(conn, node);
> > > -    domain_nbentry_dec(conn, get_node_owner(node));
> > >       /*
> > >        * It is not possible to easily revert the changes in a 
> > > transaction.
> > > @@ -1797,27 +1796,11 @@ static int do_set_perms(const void *ctx, 
> > > struct connection *conn,
> > >       old_perms = node->perms;
> > >       domain_nbentry_dec(conn, get_node_owner(node));
> > IIRC, we originally said that domain_nbentry_dec() could never fail in 
> > a non-transaction case. But with your current rework, the function can 
> > now fail because of an allocation failure.
> How would that be possible to happen?
>
> domain_nbentry_dec() can only be called if a node is being owned by an 
> already
> known domain. So allocation is impossible to happen, as this would be a 
> major
> error in xenstored.
From my understanding, the nodes accounting will be temporary and then 
committed at the end of the request.
So we would call acc_add_changed_dom() which may require allocation to 
hold the temporary accounting.
> > Therefore, shouldn't we now check the error? (Possibly in a patch 
> > beforehand).
> I don't think so. I can add a comment if you want.
See above.

Cheers,

--
Julien Grall