[Linaro-mm-sig] Re: [PATCH v7 3/9] dma-buf: Provide dma_buf_set_name()

On 9/24/26 17:21, Matt Evans wrote:

Allow exporters to set the name of buffers, during export or for subsequent updates. This is useful to express buffer-specific debug information, indicate state particular to the exporter's usage, etc. Only exporters and userspace are expected to set names; it isn't sensible for importers to do it.

Originally, the static dma_buf_set_name() was used for DMA_BUF_SET_NAME ioctls, taking a __user string parameter. Export this function as a generic set-name helper, taking a kernel-allocated string. The SET_NAME ioctls now locally duplicate the __user string, and use the new function to set the name.

Signed-off-by: Matt Evans matt@ozlabs.org

drivers/dma-buf/dma-buf.c | 78 ++++++++++++++++++++++++--------------- include/linux/dma-buf.h | 2 + 2 files changed, 50 insertions(+), 30 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 4c9add51f9ef..e4ec504e9288 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -404,34 +404,6 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll) return events; } -/**

• • dma_buf_set_name - Set a name to a specific dma_buf to track the usage.
• • It could support changing the name of the dma-buf if the same
• • piece of memory is used for multiple purpose between different devices.
• • @dmabuf: [in] dmabuf buffer that will be renamed.
• • @buf: [in] A piece of userspace memory that contains the name of

• •               the dma-buf.
    

• • Returns 0 on success. If the dma-buf buffer is already attached to
• • devices, return -EBUSY.
• */

-static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf) -{

• char *name = strndup_user(buf, DMA_BUF_NAME_LEN);
• if (IS_ERR(name))

• return PTR_ERR(name);
  

• spin_lock(&dmabuf->name_lock);
• kfree(dmabuf->name);
• dmabuf->name = name;
• spin_unlock(&dmabuf->name_lock);
• return 0;

-}

#if IS_ENABLED(CONFIG_SYNC_FILE) static long dma_buf_export_sync_file(struct dma_buf *dmabuf, void __user *user_data) @@ -577,8 +549,19 @@ static long dma_buf_ioctl(struct file *file, return ret; case DMA_BUF_SET_NAME_A:

• case DMA_BUF_SET_NAME_B:

• return dma_buf_set_name(dmabuf, (const char __user *)arg);
  

• case DMA_BUF_SET_NAME_B: {

• char *name = strndup_user((const char __user *)arg,
  

• 			  DMA_BUF_NAME_LEN);
  

• if (IS_ERR(name))
  

• 	return PTR_ERR(name);
  

• ret = dma_buf_set_name(dmabuf, name);
  

• if (ret)
  

• 	kfree(name);
  

• return ret;
  

• }

#if IS_ENABLED(CONFIG_SYNC_FILE) case DMA_BUF_IOCTL_EXPORT_SYNC_FILE: @@ -874,6 +857,41 @@ void dma_buf_put(struct dma_buf *dmabuf) } EXPORT_SYMBOL_NS_GPL(dma_buf_put, "DMA_BUF"); +/**

• • dma_buf_set_name - Set a dmabuf's name
• • Intended to be used by the exporter to set a name for debug
• • purposes. This can also change an existing name if the same piece
• • of memory is used for multiple purposes over time.

Add something like "Importers should *NOT* use this function to overwrite the name." here and add some note under "DOC: locking convention" how this function is supposed to be called.

Apart from that looks good to me, Christian.

• • @dmabuf: [in] dmabuf buffer that will be renamed.
• • @name: [in] The name of the dma-buf, allocated with kmalloc() or

• •               similar.  This takes ownership of the allocation
    

• •               on success, which will be kfree()d when the
    

• •               dmabuf is released or a new name assigned.
    

• • Returns 0 on success, -EINVAL if the name is NULL, or -E2BIG if the
• • name (including terminator) exceeds DMA_BUF_NAME_LEN.
• */

+int dma_buf_set_name(struct dma_buf *dmabuf, char *name) +{

• if (!name)

• return -EINVAL;
  

• /* dmabuffs_dname() won't use the string if the length

• * (including terminator) exceeds DMA_BUF_NAME_LEN:
  

• */
  

• if (strlen(name) >= DMA_BUF_NAME_LEN)

• return -E2BIG;
  

• spin_lock(&dmabuf->name_lock);
• kfree(dmabuf->name);
• dmabuf->name = name;
• spin_unlock(&dmabuf->name_lock);
• return 0;

+} +EXPORT_SYMBOL_NS_GPL(dma_buf_set_name, "DMA_BUF");

static int dma_buf_wrap_sg_table(struct sg_table **sg_table) { struct scatterlist *to_sg, *from_sg; diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index d15b2b31d3c9..952a2c196ad4 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -571,6 +571,8 @@ void dma_buf_fd_install(struct dma_buf *dmabuf, int fd); struct dma_buf *dma_buf_get(int fd); void dma_buf_put(struct dma_buf *dmabuf); +int dma_buf_set_name(struct dma_buf *dmabuf, char *name);

struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *, enum dma_data_direction); void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,