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From:   Sumit Semwal <sumit.semwal@linaro.org>
Date:   Wed, 12 Jun 2019 20:13:26 +0530
Message-ID: <CAO_48GHkU5aZby7835mx+od6g2BbgvWLKo=dFOxnmEtscArDkg@mail.gmail.com>
Subject: Re: [RESEND PATCH v3 2/3] dma-buf: add DMA_BUF_{GET,SET}_NAME ioctls
To:     Chenbo Feng <fengc@google.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        DRI mailing list <dri-devel@lists.freedesktop.org>,
        Android Kernel Team <kernel-team@android.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Hello Chenbo,

Thanks very much for your patches. Other than a couple tiny nits
below, I think these look good, and I will merge them before the end
of this week.
On Tue, 11 Jun 2019 at 05:32, Chenbo Feng <fengc@google.com> wrote:
>
> From: Greg Hackmann <ghackmann@google.com>
>
> This patch adds complimentary DMA_BUF_SET_NAME and DMA_BUF_GET_NAME
> ioctls, which lets userspace processes attach a free-form name to each
> buffer.
This should remove the _GET_NAME bit since it's not there anymore.
>
> This information can be extremely helpful for tracking and accounting
> shared buffers.  For example, on Android, we know what each buffer will
> be used for at allocation time: GL, multimedia, camera, etc.  The
> userspace allocator can use DMA_BUF_SET_NAME to associate that
> information with the buffer, so we can later give developers a
> breakdown of how much memory they're allocating for graphics, camera,
> etc.
>
> Signed-off-by: Greg Hackmann <ghackmann@google.com>
> Signed-off-by: Chenbo Feng <fengc@google.com>
> ---
>  drivers/dma-buf/dma-buf.c    | 49 +++++++++++++++++++++++++++++++++---
>  include/linux/dma-buf.h      |  5 +++-
>  include/uapi/linux/dma-buf.h |  3 +++
>  3 files changed, 53 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index ffd5a2ad7d6f..c1da5f9ce44d 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -48,8 +48,24 @@ struct dma_buf_list {
>
>  static struct dma_buf_list db_list;
>
> +static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen)
> +{
> +       struct dma_buf *dmabuf;
> +       char name[DMA_BUF_NAME_LEN];
> +       size_t ret = 0;
> +
> +       dmabuf = dentry->d_fsdata;
> +       mutex_lock(&dmabuf->lock);
> +       if (dmabuf->name)
> +               ret = strlcpy(name, dmabuf->name, DMA_BUF_NAME_LEN);
> +       mutex_unlock(&dmabuf->lock);
> +
> +       return dynamic_dname(dentry, buffer, buflen, "/%s:%s",
> +                            dentry->d_name.name, ret > 0 ? name : "");
> +}
> +
>  static const struct dentry_operations dma_buf_dentry_ops = {
> -       .d_dname = simple_dname,
> +       .d_dname = dmabuffs_dname,
>  };
>
>  static struct vfsmount *dma_buf_mnt;
> @@ -297,6 +313,27 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
>         return events;
>  }
>
> +static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
> +{
> +       char *name = strndup_user(buf, DMA_BUF_NAME_LEN);
> +       long ret = 0;
> +
> +       if (IS_ERR(name))
> +               return PTR_ERR(name);
> +
> +       mutex_lock(&dmabuf->lock);
> +       if (!list_empty(&dmabuf->attachments)) {
> +               ret = -EBUSY;
> +               goto out_unlock;
> +       }
We might also want to document this better - that name change for a
buffer is still allowed if it doesn't have any attached devices after
its usage is done but before it is destroyed? (theoritically it could
be reused with a different name?)

> +       kfree(dmabuf->name);
> +       dmabuf->name = name;
> +
> +out_unlock:
> +       mutex_unlock(&dmabuf->lock);
> +       return ret;
> +}
> +
>  static long dma_buf_ioctl(struct file *file,
>                           unsigned int cmd, unsigned long arg)
>  {
> @@ -335,6 +372,10 @@ static long dma_buf_ioctl(struct file *file,
>                         ret = dma_buf_begin_cpu_access(dmabuf, direction);
>
>                 return ret;
> +
> +       case DMA_BUF_SET_NAME:
> +               return dma_buf_set_name(dmabuf, (const char __user *)arg);
> +
>         default:
>                 return -ENOTTY;
>         }
> @@ -376,6 +417,7 @@ static struct file *dma_buf_getfile(struct dma_buf *dmabuf, int flags)
>                 goto err_alloc_file;
>         file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
>         file->private_data = dmabuf;
> +       file->f_path.dentry->d_fsdata = dmabuf;
>
>         return file;
>
> @@ -1082,12 +1124,13 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
>                         continue;
>                 }
>
> -               seq_printf(s, "%08zu\t%08x\t%08x\t%08ld\t%s\t%08lu\n",
> +               seq_printf(s, "%08zu\t%08x\t%08x\t%08ld\t%s\t%08lu\t%s\n",
>                                 buf_obj->size,
>                                 buf_obj->file->f_flags, buf_obj->file->f_mode,
>                                 file_count(buf_obj->file),
>                                 buf_obj->exp_name,
> -                               file_inode(buf_obj->file)->i_ino);
> +                               file_inode(buf_obj->file)->i_ino,
> +                               buf_obj->name ?: "");
>
>                 robj = buf_obj->resv;
>                 while (true) {
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index 58725f890b5b..582998e19df6 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -255,10 +255,12 @@ struct dma_buf_ops {
>   * @file: file pointer used for sharing buffers across, and for refcounting.
>   * @attachments: list of dma_buf_attachment that denotes all devices attached.
>   * @ops: dma_buf_ops associated with this buffer object.
> - * @lock: used internally to serialize list manipulation, attach/detach and vmap/unmap
> + * @lock: used internally to serialize list manipulation, attach/detach and
> + *        vmap/unmap, and accesses to name
>   * @vmapping_counter: used internally to refcnt the vmaps
>   * @vmap_ptr: the current vmap ptr if vmapping_counter > 0
>   * @exp_name: name of the exporter; useful for debugging.
> + * @name: userspace-provided name; useful for accounting and debugging.
>   * @owner: pointer to exporter module; used for refcounting when exporter is a
>   *         kernel module.
>   * @list_node: node for dma_buf accounting and debugging.
> @@ -286,6 +288,7 @@ struct dma_buf {
>         unsigned vmapping_counter;
>         void *vmap_ptr;
>         const char *exp_name;
> +       const char *name;
>         struct module *owner;
>         struct list_head list_node;
>         void *priv;
> diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h
> index d75df5210a4a..dbc7092e04b5 100644
> --- a/include/uapi/linux/dma-buf.h
> +++ b/include/uapi/linux/dma-buf.h
> @@ -35,7 +35,10 @@ struct dma_buf_sync {
>  #define DMA_BUF_SYNC_VALID_FLAGS_MASK \
>         (DMA_BUF_SYNC_RW | DMA_BUF_SYNC_END)
>
> +#define DMA_BUF_NAME_LEN       32
> +
>  #define DMA_BUF_BASE           'b'
>  #define DMA_BUF_IOCTL_SYNC     _IOW(DMA_BUF_BASE, 0, struct dma_buf_sync)
> +#define DMA_BUF_SET_NAME       _IOW(DMA_BUF_BASE, 1, const char *)
>
>  #endif
> --
> 2.22.0.rc2.383.gf4fbbf30c2-goog
>

Best,
Sumit.