Re: [PATCH v3] proc: report open files as size in stat() for /proc/pid/fd

[Brian Foster <bfoster@redhat.com>]

On Tue, Oct 18, 2022 at 11:51:02AM -0700, Ivan Babrou wrote:
> On Tue, Oct 18, 2022 at 11:16 AM Brian Foster <bfoster@redhat.com> wrote:
> > > +static int proc_readfd_count(struct inode *inode)
> > > +{
> > > +     struct task_struct *p = get_proc_task(inode);
> > > +     struct fdtable *fdt;
> > > +     unsigned int open_fds = 0;
> > > +
> > > +     if (!p)
> > > +             return -ENOENT;
> >
> > Maybe this shouldn't happen, but do you mean to assign the error code to
> > stat->size in the caller? Otherwise this seems reasonable to me.
> 
> You are right. As unlikely as it is to happen, we shouldn't return
> negative size.
> 
> What's the idiomatic way to make this work? My two options are:
> 
> 1. Pass &stat->size into proc_readfd_count:
> 
>   if (S_ISDIR(inode->i_mode)) {
>     rv = proc_readfd_count(inode, &stat->size);
>     if (rv < 0)
>       goto out;
>   }
> 
> out:
>   return rv;
> 
> OR without a goto:
> 
>   if (S_ISDIR(inode->i_mode)) {
>     rv = proc_readfd_count(inode, &stat->size));
>     if (rv < 0)
>       return rv;
>   }
> 
>   return rv;
> 
> 2. Return negative count as error (as we don't expect negative amount
> of files open):
> 
>   if (S_ISDIR(inode->i_mode)) {
>     size = proc_readfd_count(inode);
>     if (size < 0)
>       return size;
>     stat->size = size;
>   }
> 

I suppose the latter is less of a change to the original patch..? Either
way seems reasonable to me. I have no strong preference FWIW.

Brian