Re: [PATCH v2 2/2] alloc_tag: keep codetag iterator active between read() calls

Suren Baghdasaryan
2025-05-09T20:46:50Z

On Fri, May 9, 2025 at 12:46 PM Tim Chen <tim.c.chen@linux.intel.com> wrote:
>
> On Fri, 2025-05-09 at 12:36 -0700, Suren Baghdasaryan wrote:
> > On Fri, May 9, 2025 at 11:33 AM Tim Chen <tim.c.chen@linux.intel.com> wrote:
> > >
> > > On Sat, 2025-05-10 at 01:39 +0800, David Wang wrote:
> > > >
> > > >
> > > > Signed-off-by: David Wang <00107082@163.com>
> >
> > Acked-by: Suren Baghdasaryan <surenb@google.com>
> >
> > > > ---
> > > > lib/alloc_tag.c | 29 ++++++++++-------------------
> > > > 1 file changed, 10 insertions(+), 19 deletions(-)
> > > >
> > > > diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> > > > index 25ecc1334b67..fdd5887769a6 100644
> > > > --- a/lib/alloc_tag.c
> > > > +++ b/lib/alloc_tag.c
> > > > @@ -45,21 +45,16 @@ struct allocinfo_private {
> > > > static void *allocinfo_start(struct seq_file *m, loff_t *pos)
> > > > {
> > > > struct allocinfo_private *priv;
> > > > - struct codetag *ct;
> > > > loff_t node = *pos;
> > > >
> > > > - priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> > > > - m->private = priv;
> > > > - if (!priv)
> > > > - return NULL;
> > > > -
> > > > - priv->print_header = (node == 0);
> > > > + priv = (struct allocinfo_private *)m->private;
> > > > codetag_lock_module_list(alloc_tag_cttype, true);
> > > > - priv->iter = codetag_get_ct_iter(alloc_tag_cttype);
> > > > - while ((ct = codetag_next_ct(&priv->iter)) != NULL && node)
> > > > - node--;
> > > > -
> > > > - return ct ? priv : NULL;
> > > > + if (node == 0) {
> > > > + priv->print_header = true;
> > > > + priv->iter = codetag_get_ct_iter(alloc_tag_cttype);
> > > > + codetag_next_ct(&priv->iter);
> > > > + }
> > >
> > > Do you need to skip print header when *pos != 0? i.e add
> >
> > Technically not needed since proc_create_seq_private() allocates
> > seq->private using kzalloc(), so the initial value of
> > priv->print_header is always false.
>
> But we'll start with first call to allocinfo_start() with *pos == 0,

Usually but not always if we do lseek() to a non-zero position beforehand.

> then print_header will be initialized to true.

After the first call to allocinfo_show() print_header will be reset
back to false.

> Will there be subsequent calls of allocinfo_start() with *pos !=0,
> but priv->print_header stays at 0?

Yes, there will be subsequent calls to allocinfo_start() with *pos !=0
and priv->print_header=false, which is what we want, right? We want to
print the header only at the beginning of the file (node == 0).

>
> Tim
> >
> > >
> > > } else {
> > > priv->print_header = false;
> > > }
> > >
> > > Tim
> > >
> > > > + return priv->iter.ct ? priv : NULL;
> > > > }
> > > >
> > >
>