linux-kernel - Re: [PATCH v3 2/2] dmabuf: Add dmabuf inode number to /proc/*/fdinfo

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Date:   Fri, 5 Feb 2021 10:13:43 -0500
From:   Kalesh Singh <kaleshsingh@...gle.com>
To:     Christian König <christian.koenig@....com>
Cc:     Jann Horn <jannh@...gle.com>,
        Jeffrey Vander Stoep <jeffv@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Michal Hocko <mhocko@...e.com>,
        Alexey Gladkov <gladkov.alexey@...il.com>,
        Anand K Mistry <amistry@...gle.com>,
        NeilBrown <neilb@...e.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Michel Lespinasse <walken@...gle.com>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        Andrei Vagin <avagin@...il.com>,
        Yafang Shao <laoar.shao@...il.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        DRI mailing list <dri-devel@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>
Subject: Re: [PATCH v3 2/2] dmabuf: Add dmabuf inode number to /proc/*/fdinfo

On Fri, Feb 5, 2021 at 2:56 AM Christian König <christian.koenig@....com> wrote:
>
> Am 05.02.21 um 03:23 schrieb Kalesh Singh:
> > If a FD refers to a DMA buffer add the DMA buffer inode number to
> > /proc/<pid>/fdinfo/<FD> and /proc/<pid>/task/<tid>/fdindo/<FD>.
> >
> > The dmabuf inode number allows userspace to uniquely identify the buffer
> > and avoids a dependency on /proc/<pid>/fd/* when accounting per-process
> > DMA buffer sizes.
>
> BTW: Why do we make this DMA-buf specific? Couldn't we always print the
> inode number for all fds?

Good point. We can make this a common field instead of DMA buf
specific. I will update in the next version.

Thanks,
Kalesh
>
> Regards,
> Christian.
>
> >
> > Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
> > ---
> > Changes in v3:
> >    - Add documentation in proc.rst
> > Changes in v2:
> >    - Update patch description
> >
> >   Documentation/filesystems/proc.rst | 17 +++++++++++++++++
> >   drivers/dma-buf/dma-buf.c          |  1 +
> >   2 files changed, 18 insertions(+)
> >
> > diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> > index 2fa69f710e2a..fdd38676f57f 100644
> > --- a/Documentation/filesystems/proc.rst
> > +++ b/Documentation/filesystems/proc.rst
> > @@ -2031,6 +2031,23 @@ details]. 'it_value' is remaining time until the timer expiration.
> >   with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
> >   still exhibits timer's remaining time.
> >
> > +DMA Buffer files
> > +~~~~~~~~~~~~~~~~
> > +
> > +::
> > +
> > +     pos:    0
> > +     flags:  04002
> > +     mnt_id: 9
> > +     dmabuf_inode_no: 63107
> > +     size:   32768
> > +     count:  2
> > +     exp_name:  system-heap
> > +
> > +where 'dmabuf_inode_no' is the unique inode number of the DMA buffer file.
> > +'size' is the size of the DMA buffer in bytes. 'count' is the file count of
> > +the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter.
> > +
> >   3.9 /proc/<pid>/map_files - Information about memory mapped files
> >   ---------------------------------------------------------------------
> >   This directory contains symbolic links which represent memory mapped files
> > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> > index 9ad6397aaa97..d869099ede83 100644
> > --- a/drivers/dma-buf/dma-buf.c
> > +++ b/drivers/dma-buf/dma-buf.c
> > @@ -414,6 +414,7 @@ static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file)
> >   {
> >       struct dma_buf *dmabuf = file->private_data;
> >
> > +     seq_printf(m, "dmabuf_inode_no:\t%lu\n", file_inode(file)->i_ino);
> >       seq_printf(m, "size:\t%zu\n", dmabuf->size);
> >       /* Don't count the temporary reference taken inside procfs seq_show */
> >       seq_printf(m, "count:\t%ld\n", file_count(dmabuf->file) - 1);
>