Re: [RESEND PATCH v3 2/3] dma-buf: add DMA_BUF_{GET,SET}_NAME ioctls

[Suren Baghdasaryan]

On Wed, Jun 12, 2019 at 2:49 PM 'Chenbo Feng' via kernel-team
<kernel-team@xxxxxxxxxxx> wrote:
>
> On Wed, Jun 12, 2019 at 7:43 AM Sumit Semwal <sumit.semwal@xxxxxxxxxx> 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@xxxxxxxxxx> wrote:
> > >
> > > From: Greg Hackmann <ghackmann@xxxxxxxxxx>
> > >
> > > 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@xxxxxxxxxx>
> > > Signed-off-by: Chenbo Feng <fengc@xxxxxxxxxx>
> > > ---
> > >  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;

Sorry, I commented on an older version... I think you need kfree(name); here.

> > > +               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
>
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