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From:   Ivan Babrou <ivan@cloudflare.com>
Date:   Tue, 18 Oct 2022 11:51:02 -0700
Message-ID: <CABWYdi37Ts7KDshSvwMf34EKuUrz25duL7W8hOO8t1Xm53t2rA@mail.gmail.com>
Subject: Re: [PATCH v3] proc: report open files as size in stat() for /proc/pid/fd
To:     Brian Foster <bfoster@redhat.com>
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@cloudflare.com, Alexey Dobriyan <adobriyan@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        "Theodore Ts'o" <tytso@mit.edu>,
        David Laight <David.Laight@aculab.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>,
        Mike Rapoport <rppt@kernel.org>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Kalesh Singh <kaleshsingh@google.com>
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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;
  }