内核中的 mmap 多个缓冲区正在崩溃请帮助（使用 dma_mmap_coherent）

Question

我正在开发一个 Linux 内核模块，它为每个字符设备分配多个缓冲区，然后 user-space 应用程序将这些缓冲区映射到 user-space。我的字符设备 class 有大约 10 个或更多缓冲区，在打开时我分配这些缓冲区，每个缓冲区大小为 0x8000。我遇到的问题是将这些缓冲区 mmap 到 user-space 指针时。我只能映射一个缓冲区，但是当我尝试分配第二个缓冲区时，它就崩溃了。我不太熟悉 dma_mmap_coherent 有人可以帮我解决这个问题吗？

下面是一些代码信息：

//我的内存类型struct

typedef struct
{
    unsigned int *  uaddr;
    unsigned int *  kaddr;
    unsigned long   paddr;
    unsigned int    size;
    unsigned int    index;
    dma_addr_t      handle;
}memory_handle_t

// 内核中的缓冲区分配（IOCTL 调用）

static int allocate__memory_ioctl(struct file *pfile, void __user *uaddr)
{
    struct myClass *my_class = (struct my_class *)pfile->private_data;
    memory_handle_t  minfo;
    int idx = -1;

    if ((idx = find_handle(my_class , NULL)) == -1) {
        printk(KERN_INFO "cannot find a free slot.\n");
        return -EACCES;
    }

    if (copy_from_user(&minfo, uaddr, sizeof(memory_handle_t))) {
        printk(KERN_INFO "CANNOT COPY FROM USER POINTER. \n");
        return -EACCES;
    }

    my_class->_memory[idx].size   = minfo.size;
    my_class->_memory[idx].kaddr  = minfo.kaddr = dma_alloc_coherent(my_class->dma_device_p,
                                                                    my_class->_memory[idx].size,
                                                                    &my_class->_memory[idx].handle,
                                                                    GFP_KERNEL);

    if (my_class->_memory[idx].kaddr == NULL) {
        printk(KERN_INFO "Dma memory allocation failed!\n");
        my_class->_memory[idx].size = 0;
        my_class->_memory[idx].kaddr = NULL;
        return -1;
    } else {
        my_class->_memory[idx].paddr = minfo.paddr = virt_to_phys(my_class->_memory[idx].kaddr);
    }

    minfo.index = idx; /* Pass the index to user so he can use it to map */

    if (copy_to_user(uaddr, &minfo, sizeof(memory_handle_t))) {
        printk(KERN_INFO "CANNOT COPY TO THE USER POINTER. \n");
        return -EFAULT;
    }

    return 0;
}

// MMAP

    #define DMA_MAPPING (1 << 7)
    static int c_mmap(struct file *pfile, struct vm_area_struct *vma)
        {
            struct myClass *my_class= (struct myClass *)pfile->private_data;
        
            unsigned int idx = (vma->vm_pgoff & ~DMA_MAPPING) & 0xff; /* We are using the offset for index! */
        
            if ((vma->vm_end - vma->vm_start) > my_class->_memory[idx].size) {
                printk(KERN_ALERT "MMAP FAILED, SIZE MISMATCH. \n");
                return -EINVAL;
            }
        
            vma->vm_flags    |= VM_IO;
            vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
        
            return dma_mmap_coherent(my_class->dma_device_p, vma, my_class->_memory[idx].kaddr,
 my_class->_memory[idx].handle, my_class->_memory[idx].size);
        
        }

// USER-SPACE 应用程序

    _fd = open(dev_name.c_str(), O_RDWR);
    if (_fd < 1) {
            printf("Unable to open device file");
            exit(EXIT_FAILURE);
        }

// start allocation and mmap

    size_t     _page_sz = sysconf(_SC_PAGESIZE);
        unsigned int size = TEST_SIZE;
    
        for(int idx=0;idx<11;idx++){
            dma_memory_handle_t dh;
            _mems[idx].size = dh.size = size;
    
            int ret = ioctl(_fd, IOCTL_ALLOC_DMA_MEMORY, &dh);
    
            if  (ret < 0)
            {
                std::cerr << "memory allocation failed!";
                perror("memory allocation failed! ");
                throw(std::exception());
            }
    
            int index =  dh.index;
    // fails after the first iteration
            **unsigned int *addr = (unsigned int *) mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, _fd, index*_page_sz);**
    
            if (addr == MAP_FAILED)
            {
                std::cerr << "memory map failed!";
                perror("memory map failed! ");
                throw(std::exception());
            }
    
            _mems[idx].uaddr   = addr;
            _mems[idx].index   = dh.index;
            _mems[idx].paddr   = dh.paddr;
            _mems[idx].kaddr   = dh.kaddr;
        }

Answer 1

谢谢，在指示缓冲区的索引后，我能够通过清除 vma->vm_pgoff 来解决问题。

内核中的 mmap 多个缓冲区正在崩溃请帮助（使用 dma_mmap_coherent）

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