[PATCH v2 1/2] dma-buf: add reference counting for exporter module

Tomasz Stanislawski
2012-08-09T09:36:47Z

This patch adds reference counting on a module that exported dma-buf and
implements its operations. This prevents the module from being unloaded while
DMABUF file is in use.

Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com>
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
CC: linux-doc@vger.kernel.org
---
Documentation/dma-buf-sharing.txt | 3 ++-
drivers/base/dma-buf.c | 9 ++++++++-
include/linux/dma-buf.h | 2 ++
3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
index ad86fb8..2613057 100644
--- a/Documentation/dma-buf-sharing.txt
+++ b/Documentation/dma-buf-sharing.txt
@@ -49,7 +49,8 @@ The dma_buf buffer sharing API usage contains the following steps:
The buffer exporter announces its wish to export a buffer. In this, it
connects its own private buffer data, provides implementation for operations
that can be performed on the exported dma_buf, and flags for the file
- associated with this buffer.
+ associated with this buffer. The operations structure has owner field.
+ You should initialize this to THIS_MODULE in most cases.

Interface:
struct dma_buf *dma_buf_export(void *priv, struct dma_buf_ops *ops,
diff --git a/drivers/base/dma-buf.c b/drivers/base/dma-buf.c
index c30f3e1..a1d9cab 100644
--- a/drivers/base/dma-buf.c
+++ b/drivers/base/dma-buf.c
@@ -27,6 +27,7 @@
#include <linux/dma-buf.h>
#include <linux/anon_inodes.h>
#include <linux/export.h>
+#include <linux/module.h>

static inline int is_dma_buf_file(struct file *);

@@ -40,6 +41,7 @@ static int dma_buf_release(struct inode *inode, struct file *file)
dmabuf = file->private_data;

dmabuf->ops->release(dmabuf);
+ module_put(dmabuf->ops->owner);
kfree(dmabuf);
return 0;
}
@@ -105,9 +107,14 @@ struct dma_buf *dma_buf_export(void *priv, const struct dma_buf_ops *ops,
return ERR_PTR(-EINVAL);
}

+ if (!try_module_get(ops->owner))
+ return ERR_PTR(-ENOENT);
+
dmabuf = kzalloc(sizeof(struct dma_buf), GFP_KERNEL);
- if (dmabuf == NULL)
+ if (dmabuf == NULL) {
+ module_put(ops->owner);
return ERR_PTR(-ENOMEM);
+ }

dmabuf->priv = priv;
dmabuf->ops = ops;
diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
index eb48f38..22953de 100644
--- a/include/linux/dma-buf.h
+++ b/include/linux/dma-buf.h
@@ -37,6 +37,7 @@ struct dma_buf_attachment;

/**
* struct dma_buf_ops - operations possible on struct dma_buf
+ * @owner: the module that implements dma_buf operations
* @attach: [optional] allows different devices to 'attach' themselves to the
* given buffer. It might return -EBUSY to signal that backing storage
* is already allocated and incompatible with the requirements
@@ -70,6 +71,7 @@ struct dma_buf_attachment;
* @vunmap: [optional] unmaps a vmap from the buffer
*/
struct dma_buf_ops {
+ struct module *owner;
int (*attach)(struct dma_buf *, struct device *,
struct dma_buf_attachment *);

--
1.7.9.5