内核中的mmap多个缓冲区正在崩溃，请提供帮助(使用dma_mmap_coherent)

Question

我正在开发一个Linux内核模块，该模块为每个char设备分配多个缓冲区，然后用户空间应用程序将这些缓冲区映射到用户空间。我的角色设备类有大约十个或更多的缓冲区，在打开时，我会分配这些缓冲区，每个缓冲区的大小为0x8000。我遇到的问题是当将这些缓冲区映射到用户空间指针时。我只能映射一个缓冲区，但当我试图分配第二个缓冲区时，它就会崩溃。我不太熟悉dma_mmap_coherent，有人能帮我解决这个问题吗。

以下是一些代码信息：

//我的内存类型结构

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，我通过清除vma->vm_pgoff指示缓冲区的索引之后。