linux-kernel - Re: [PATCH 1/1] cgroups: introduce cft->read

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Date:	Wed, 2 Apr 2008 23:53:03 -0500
From:	serge@...lyn.com
To:	Paul Menage <menage@...gle.com>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] cgroups: introduce cft->read_seq()

Quoting Paul Menage (menage@...gle.com):
> On Wed, Apr 2, 2008 at 6:01 PM, Serge E. Hallyn <serue@...ibm.com> wrote:
> >  +       /*
> >  +        * read_seq() is used for outputting a simple sequence
> >  +        * using seqfile.
> >  +        */
> >  +       int (*read_seq) (struct cgroup *cont, struct cftype *cft,
> >  +                        struct seq_file *m);
> 
> Maybe make it read_seq_string() to emphasise that it's not intended
> for structured data?
> 
> >
> >  -static int cgroup_seqfile_show(struct seq_file *m, void *arg)
> >  +static int cgroup_map_seqfile_show(struct seq_file *m, void *arg)
> >   {
> >         struct cgroup_seqfile_state *state = m->private;
> >         struct cftype *cft = state->cft;
> >  @@ -1529,6 +1529,13 @@ static int cgroup_seqfile_show(struct seq_file *m, void *arg)
> >         return cft->read_map(state->cgroup, cft, &cb);
> >   }
> 
> I think you can make this simpler - have cgroup_seqfile_show() switch
> based on whether the cft has a read_seq_string or a read_map, and then
> you only need one function.
> 
> >
> >  +static int cgroup_simple_seqfile_show(struct seq_file *m, void *arg)
> >  +{
> >  +       struct cgroup_seqfile_state *state = m->private;
> >  +       struct cftype *cft = state->cft;
> >  +       return cft->read_seq(state->cgroup, cft, m);
> >  +}
> >  +
> >   int cgroup_seqfile_release(struct inode *inode, struct file *file)
> >   {
> >         struct seq_file *seq = file->private_data;
> >  @@ -1562,7 +1569,18 @@ static int cgroup_file_open(struct inode *inode, struct file *file)
> >                 state->cft = cft;
> >                 state->cgroup = __d_cgrp(file->f_dentry->d_parent);
> >                 file->f_op = &cgroup_seqfile_operations;
> >  -               err = single_open(file, cgroup_seqfile_show, state);
> >  +               err = single_open(file, cgroup_map_seqfile_show, state);
> >  +               if (err < 0)
> >  +                       kfree(state);
> >  +       } else if (cft->read_seq) {
> >  +               struct cgroup_seqfile_state *state =
> >  +                       kzalloc(sizeof(*state), GFP_USER);
> >  +               if (!state)
> >  +                       return -ENOMEM;
> >  +               state->cft = cft;
> >  +               state->cgroup = __d_cgrp(file->f_dentry->d_parent);
> >  +               file->f_op = &cgroup_seqfile_operations;
> >  +               err = single_open(file, cgroup_simple_seqfile_show, state);
> >                 if (err < 0)
> >                         kfree(state);
> 
> and this arm can just be eliminated, by adding "||
> cft->read_seq_string" to the test for cft_read_seq_map above.
> 
> It was always my intention that cgroup_seqfile_show() be able to
> handle multiple data types, but up until now we only had one.

Thanks Paul, will do each of these.

-serge
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