[media] videobuf2: Add support for file access mode flags for DMABUF exporting

Currently it is not possible for userspace to map a DMABUF exported buffer
with write permissions. This patch allows to also pass O_RDONLY/O_RDWR when
exporting the buffer, so that userspace may map it with write permissions.

Signed-off-by: Philipp Zabel <[e-mail]>
Signed-off-by: Sylwester Nawrocki <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

Documentation/DocBook/media/v4l/vidioc-expbuf.xml

···
 format. For the single-planar API, applications must set <structfield> plane
 </structfield> to zero.  Additional flags may be posted in the <structfield>
 flags </structfield> field.  Refer to a manual for open() for details.
-Currently only O_CLOEXEC is supported.  All other fields must be set to zero.
+Currently only O_CLOEXEC, O_RDONLY, O_WRONLY, and O_RDWR are supported.  All
+other fields must be set to zero.
 In the case of multi-planar API, every plane is exported separately using
 multiple <constant> VIDIOC_EXPBUF </constant> calls. </para>
 
···
 	    <entry>__u32</entry>
 	    <entry><structfield>flags</structfield></entry>
 	    <entry>Flags for the newly created file, currently only <constant>
-O_CLOEXEC </constant> is supported, refer to the manual of open() for more
-details.</entry>
+O_CLOEXEC </constant>, <constant>O_RDONLY</constant>, <constant>O_WRONLY
+</constant>, and <constant>O_RDWR</constant> are supported, refer to the manual
+of open() for more details.</entry>
 	  </row>
 	  <row>
 	    <entry>__s32</entry>

drivers/media/v4l2-core/videobuf2-core.c

···
 		return -EINVAL;
 	}
 
-	if (eb->flags & ~O_CLOEXEC) {
-		dprintk(1, "Queue does support only O_CLOEXEC flag\n");
+	if (eb->flags & ~(O_CLOEXEC | O_ACCMODE)) {
+		dprintk(1, "Queue does support only O_CLOEXEC and access mode flags\n");
 		return -EINVAL;
 	}
 
···
 
 	vb_plane = &vb->planes[eb->plane];
 
-	dbuf = call_memop(q, get_dmabuf, vb_plane->mem_priv);
+	dbuf = call_memop(q, get_dmabuf, vb_plane->mem_priv, eb->flags & O_ACCMODE);
 	if (IS_ERR_OR_NULL(dbuf)) {
 		dprintk(1, "Failed to export buffer %d, plane %d\n",
 			eb->index, eb->plane);
 		return -EINVAL;
 	}
 
-	ret = dma_buf_fd(dbuf, eb->flags);
+	ret = dma_buf_fd(dbuf, eb->flags & ~O_ACCMODE);
 	if (ret < 0) {
 		dprintk(3, "buffer %d, plane %d failed to export (%d)\n",
 			eb->index, eb->plane, ret);

drivers/media/v4l2-core/videobuf2-dma-contig.c

···
 	return sgt;
 }
 
-static struct dma_buf *vb2_dc_get_dmabuf(void *buf_priv)
+static struct dma_buf *vb2_dc_get_dmabuf(void *buf_priv, unsigned long flags)
 {
 	struct vb2_dc_buf *buf = buf_priv;
 	struct dma_buf *dbuf;
···
 	if (WARN_ON(!buf->sgt_base))
 		return NULL;
 
-	dbuf = dma_buf_export(buf, &vb2_dc_dmabuf_ops, buf->size, 0);
+	dbuf = dma_buf_export(buf, &vb2_dc_dmabuf_ops, buf->size, flags);
 	if (IS_ERR(dbuf))
 		return NULL;
 

include/media/videobuf2-core.h

···
 struct vb2_mem_ops {
 	void		*(*alloc)(void *alloc_ctx, unsigned long size, gfp_t gfp_flags);
 	void		(*put)(void *buf_priv);
-	struct dma_buf *(*get_dmabuf)(void *buf_priv);
+	struct dma_buf *(*get_dmabuf)(void *buf_priv, unsigned long flags);
 
 	void		*(*get_userptr)(void *alloc_ctx, unsigned long vaddr,
 					unsigned long size, int write);