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 <[email protected]>
> ---
> 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 *,
