[RFC v2 2/3] dma-buf: add DMA_BUF_{GET,SET}_NAME ioctls

[Chenbo Feng]

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 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    | 48 ++++++++++++++++++++++++++++++++++--
 include/linux/dma-buf.h      |  5 +++-
 include/uapi/linux/dma-buf.h |  4 +++
 3 files changed, 54 insertions(+), 3 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index ffd5a2ad7d6f..f5e8d4fab950 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -297,6 +297,42 @@ 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;
+	}
+	kfree(dmabuf->name);
+	dmabuf->name = name;
+
+out_unlock:
+	mutex_unlock(&dmabuf->lock);
+	return ret;
+}
+
+static long dma_buf_get_name(struct dma_buf *dmabuf, char __user *buf)
+{
+	const char *name = "";
+	long ret = 0;
+
+	mutex_lock(&dmabuf->lock);
+	if (dmabuf->name)
+		name = dmabuf->name;
+	if (copy_to_user(buf, name, strlen(name) + 1))
+		ret = -EFAULT;
+	mutex_unlock(&dmabuf->lock);
+
+	return ret;
+}
+
 static long dma_buf_ioctl(struct file *file,
 			  unsigned int cmd, unsigned long arg)
 {
@@ -335,6 +371,13 @@ 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);
+
+	case DMA_BUF_GET_NAME:
+		return dma_buf_get_name(dmabuf, (char __user *)arg);
+
 	default:
 		return -ENOTTY;
 	}
@@ -1082,12 +1125,13 @@ 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..4e9c5fe7aecd 100644
--- a/include/uapi/linux/dma-buf.h
+++ b/include/uapi/linux/dma-buf.h
@@ -35,7 +35,11 @@ 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 *)
+#define DMA_BUF_GET_NAME	_IOR(DMA_BUF_BASE, 2, char *)
 
 #endif
-- 
2.21.0.225.g810b269d1ac-goog