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

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Date:   Fri, 5 Feb 2021 08:56:36 +0100
From:   Christian König <christian.koenig@....com>
To:     Kalesh Singh <kaleshsingh@...gle.com>
Cc:     jannh@...gle.com, jeffv@...gle.com, keescook@...omium.org,
        surenb@...gle.com, minchan@...nel.org, hridya@...gle.com,
        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>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v3 2/2] dmabuf: Add dmabuf inode number to /proc/*/fdinfo

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?

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);