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From:   Chenbo Feng <fengc@google.com>
Date:   Wed, 12 Jun 2019 14:49:03 -0700
Message-ID: <CAMOXUJkpDi4YuVDi_z2cDZSdipXaj-=Y2Q=FooUeynAsB-kJuw@mail.gmail.com>
Subject: Re: [RESEND PATCH v3 2/3] dma-buf: add DMA_BUF_{GET,SET}_NAME ioctls
To:     Sumit Semwal <sumit.semwal@linaro.org>
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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On Wed, Jun 12, 2019 at 7:43 AM Sumit Semwal <sumit.semwal@linaro.org> wrote:
>
> 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.

Thanks for the feedback, I updated the commit message and resent the patch.

Chenbo