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

David Wang
2025-05-10T03:35:59Z

At 2025-05-10 03:46:06, "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,
>then print_header will be initialized to true.
>Will there be subsequent calls of allocinfo_start() with *pos !=0,
>but priv->print_header stays at 0?

Header only needs to be printed at line #0:
Normal seq_file operates;
start(0)
show(0) <---print header here
show(1)
stop()
start(2) <----no need to print header
show(2)
show(3)
...

If start(0)/show(0) happened twice, two header would be printed; or if there is no start(0) nothing would be printed.
If those two scenario happens, I think it is a bug in seq_file.

Thanks
David

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