[PATCH 1/2] dmabuf: add DMA_BUF_IOCTL_RW_FILE

[Christian König]

On 5/13/25 17:55, T.J. Mercier wrote:
> On Tue, May 13, 2025 at 4:31 AM Christian König
> <christian.koenig at amd.com> wrote:
>>
>> On 5/13/25 11:27, wangtao wrote:
>>> Add DMA_BUF_IOCTL_RW_FILE to save/restore data from/to a dma-buf.
>>
>> Similar approach where rejected before in favor of using udmabuf.
>>
>> Is there any reason you can't use that approach as well?
> 
> I also recently verified that udmabuf + O_DIRECT works with
> sendfile(), and you can even MADV_COLLAPSE the underlying shmem if you
> want.

Oh, nice :)

Going to keep that in mind if somebody ask for that feature again.

Regards,
Christian.

> 
>> Regards,
>> Christian.
>>
>>>
>>> Signed-off-by: wangtao <tao.wangtao at honor.com>
>>> ---
>>>  drivers/dma-buf/dma-buf.c    |  8 ++++++++
>>>  include/linux/dma-buf.h      |  3 +++
>>>  include/uapi/linux/dma-buf.h | 29 +++++++++++++++++++++++++++++
>>>  3 files changed, 40 insertions(+)
>>>
>>> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
>>> index 5baa83b85515..95d8b0158ffd 100644
>>> --- a/drivers/dma-buf/dma-buf.c
>>> +++ b/drivers/dma-buf/dma-buf.c
>>> @@ -460,6 +460,7 @@ static long dma_buf_ioctl(struct file *file,
>>>       struct dma_buf *dmabuf;
>>>       struct dma_buf_sync sync;
>>>       enum dma_data_direction direction;
>>> +     struct dma_buf_rw_file kfile;
>>>       int ret;
>>>
>>>       dmabuf = file->private_data;
>>> @@ -504,6 +505,13 @@ static long dma_buf_ioctl(struct file *file,
>>>               return dma_buf_import_sync_file(dmabuf, (const void __user *)arg);
>>>  #endif
>>>
>>> +     case DMA_BUF_IOCTL_RW_FILE:
>>> +             if (copy_from_user(&kfile, (void __user *) arg, sizeof(kfile)))
>>> +                     return -EFAULT;
>>> +             if (!dmabuf->ops->rw_file)
>>> +                     return -EINVAL;
>>> +             return dmabuf->ops->rw_file(dmabuf, &kfile);
>>> +
>>>       default:
>>>               return -ENOTTY;
>>>       }
>>> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
>>> index 36216d28d8bd..de236ba2094b 100644
>>> --- a/include/linux/dma-buf.h
>>> +++ b/include/linux/dma-buf.h
>>> @@ -22,6 +22,7 @@
>>>  #include <linux/fs.h>
>>>  #include <linux/dma-fence.h>
>>>  #include <linux/wait.h>
>>> +#include <uapi/linux/dma-buf.h>
>>>
>>>  struct device;
>>>  struct dma_buf;
>>> @@ -285,6 +286,8 @@ struct dma_buf_ops {
>>>
>>>       int (*vmap)(struct dma_buf *dmabuf, struct iosys_map *map);
>>>       void (*vunmap)(struct dma_buf *dmabuf, struct iosys_map *map);
>>> +
>>> +     int (*rw_file)(struct dma_buf *dmabuf, struct dma_buf_rw_file *file);
>>>  };
>>>
>>>  /**
>>> diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h
>>> index 5a6fda66d9ad..ec9164b7b753 100644
>>> --- a/include/uapi/linux/dma-buf.h
>>> +++ b/include/uapi/linux/dma-buf.h
>>> @@ -167,6 +167,29 @@ struct dma_buf_import_sync_file {
>>>       __s32 fd;
>>>  };
>>>
>>> +/**
>>> + * struct dma_buf_rw_file - read/write file associated with a dma-buf
>>> + *
>>> + * Userspace can performs a DMA_BUF_IOCTL_BACK to save data from a dma-buf or
>>> + * restore data to a dma-buf.
>>> + */
>>> +struct dma_buf_rw_file {
>>> +
>>> +     /** @flags: Flags indicating read/write for this dma-buf. */
>>> +     __u32 flags;
>>> +     /** @fd: File descriptor of the file associated with this dma-buf. */
>>> +     __s32 fd;
>>> +     /** @file_offset: Offset within the file where this dma-buf starts.
>>> +      *
>>> +      *  Offset and Length must be page-aligned for direct I/O.
>>> +      */
>>> +     __u64 file_offset;
>>> +     /** @buf_offset: Offset within this dma-buf where the read/write starts. */
>>> +     __u64 buf_offset;
>>> +     /** @buf_len: Length of this dma-buf read/write. */
>>> +     __u64 buf_len;
>>> +};
>>> +
>>>  #define DMA_BUF_BASE         'b'
>>>  #define DMA_BUF_IOCTL_SYNC   _IOW(DMA_BUF_BASE, 0, struct dma_buf_sync)
>>>
>>> @@ -179,4 +202,10 @@ struct dma_buf_import_sync_file {
>>>  #define DMA_BUF_IOCTL_EXPORT_SYNC_FILE       _IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file)
>>>  #define DMA_BUF_IOCTL_IMPORT_SYNC_FILE       _IOW(DMA_BUF_BASE, 3, struct dma_buf_import_sync_file)
>>>
>>> +#define DMA_BUF_RW_FLAGS_OP_MASK (0xFF << 0)
>>> +#define DMA_BUF_RW_FLAGS_READ (1 << 0) /* Restore dma-buf data */
>>> +#define DMA_BUF_RW_FLAGS_WRITE (2 << 0) /* Save dma-buf data */
>>> +#define DMA_BUF_RW_FLAGS_DIRECT (1u << 31) /* Direct read/write file */
>>> +#define DMA_BUF_IOCTL_RW_FILE        _IOW(DMA_BUF_BASE, 4, struct dma_buf_rw_file)
>>> +
>>>  #endif
>>