[PATCH 1/2] dmabuf: add DMA_BUF_IOCTL_RW_FILE

[PATCH 1/2] dmabuf: add DMA_BUF_IOCTL_RW_FILE

[wangtao]

Add DMA_BUF_IOCTL_RW_FILE to save/restore data from/to a dma-buf.

Signed-off-by: wangtao <tao.wangtao@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
-- 
2.17.1

Re: [PATCH 1/2] dmabuf: add DMA_BUF_IOCTL_RW_FILE

[Christian König]

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?

Regards,
Christian. 

> 
> Signed-off-by: wangtao <tao.wangtao@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

RE: [PATCH 1/2] dmabuf: add DMA_BUF_IOCTL_RW_FILE

[wangtao]

> -----Original Message-----
> From: Christian König <christian.koenig@amd.com>
> Sent: Tuesday, May 13, 2025 7:31 PM
> To: wangtao <tao.wangtao@honor.com>; sumit.semwal@linaro.org;
> benjamin.gaignard@collabora.com; Brian.Starkey@arm.com;
> jstultz@google.com; tjmercier@google.com
> Cc: linux-media@vger.kernel.org; dri-devel@lists.freedesktop.org; linaro-
> mm-sig@lists.linaro.org; linux-kernel@vger.kernel.org;
> wangbintian(BintianWang) <bintian.wang@honor.com>; yipengxiang
> <yipengxiang@honor.com>; liulu 00013167 <liulu.liu@honor.com>; hanfeng
> 00012985 <feng.han@honor.com>
> Subject: Re: [PATCH 1/2] dmabuf: add DMA_BUF_IOCTL_RW_FILE
> 
> 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?
[wangtao] For performance optimization, we can achieves 3776 MB/s (UFS 4.0 device @ 4GB/s).
Apologies, my three previous emails were not consolidated into the same thread.
> 
> Regards,
> Christian.
> 
> >
> > Signed-off-by: wangtao <tao.wangtao@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

Re: [PATCH 1/2] dmabuf: add DMA_BUF_IOCTL_RW_FILE

[T.J. Mercier]

[-- Attachment #1: Type: text/plain, Size: 4496 bytes --]

On Tue, May 13, 2025 at 4:31 AM Christian König
<christian.koenig@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.

> Regards,
> Christian.
>
> >
> > Signed-off-by: wangtao <tao.wangtao@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
>

[-- Attachment #2: udmabuf_odirect.cpp --]
[-- Type: text/x-c++src, Size: 1898 bytes --]

#include <cstdlib>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/sendfile.h>
#include <unistd.h>

#include <linux/udmabuf.h>

namespace {

int createMemfd(size_t bytes, unsigned int flags) {

    int fd(memfd_create("memfd_test", flags));
    if (fd == -1) {
        perror("memfd_create");
        return -1;
    }

    int rc = ftruncate(fd, bytes);
    if (rc == -1) {
        perror("ftruncate");
        return -1;
    }

    return fd;
}

int createUdmabuf(size_t bytes, int memfd) {
    int udmabuf_dev_fd(open("/dev/udmabuf", O_RDONLY));
    if (udmabuf_dev_fd == -1) {
        perror("udmabuf open");
        return -1;
    }

    struct udmabuf_create create;
    create.memfd = memfd;
    create.flags = UDMABUF_FLAGS_CLOEXEC;
    create.offset = 0;
    create.size = bytes;

    int dmabuf_fd(ioctl(udmabuf_dev_fd, UDMABUF_CREATE, &create));
    if (dmabuf_fd == -1) perror("UDMABUF_CREATE");

    return dmabuf_fd;
}

} // anonymous namespace


int main(int argc, char **argv) {
	size_t bytes = 1ull << 30;

	int memfd = createMemfd(bytes, MFD_ALLOW_SEALING);
	if (memfd < 0) return EXIT_FAILURE;

	if (fcntl(memfd, F_ADD_SEALS, F_SEAL_SHRINK) < 0) {
		perror("F_SEAL_SHRINK");
		return EXIT_FAILURE;
	}

    if (ftruncate(memfd, bytes)) {
        perror("ftruncate");
        return EXIT_FAILURE;
    }

    int bigfile = open(argv[1], O_RDONLY | O_DIRECT);
    if (bigfile < 0) {
        perror("open");
        return EXIT_FAILURE;
    }

    off_t offset = 0;
    for (ssize_t n = sendfile(memfd, bigfile, &offset, bytes - offset);
         offset < bytes && n > 0;
         n = sendfile(memfd, bigfile, &offset, bytes - offset))
    {}
    printf("Offset %ld\n", offset);

    int udmabuf = createUdmabuf(bytes, memfd);
    if (udmabuf < 0) return EXIT_FAILURE;

    return EXIT_SUCCESS;
}

Re: [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@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@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
>>