“DevMem note”的版本间的差异
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free6d1823（讨论 | 贡献） |
free6d1823（讨论 | 贡献） |
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| − | 4. /dev/mem mmap operator: | + | 4. mmap to /dev/mem |
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| + | 5./dev/mem mmap operator: | ||
<source lang="c"> | <source lang="c"> | ||
static int mmap_mem(struct file *file, struct vm_area_struct *vma) | static int mmap_mem(struct file *file, struct vm_area_struct *vma) | ||
2019年11月5日 (二) 16:29的版本
1.devmem ADDRESS [WIDTH [VALUE]]
Read/write from physical address ADDRESS Address to act upon WIDTH Width (8/16/...) VALUE Data to be written
2. devmem -> mmap
int devmem_main(int argc UNUSED_PARAM, char **argv) { fd = xopen("/dev/mem", argv[3] ? (O_RDWR | O_SYNC) : (O_RDONLY | O_SYNC)); //根据第三个参数确定是以只读形式打开，还是以读写形式打开。 mapped_size = page_size = getpagesize(); //4K bytes //if cross page, mapped_size *=2 map_base = mmap(NULL, mapped_size, // argv[3] ? (PROT_READ | PROT_WRITE) : PROT_READ, MAP_SHARED, fd, target & ~(off_t)(page_size - 1)//offset from 0x0000, page start address ); virt_addr = (char*)map_base + offset_in_page; }
3. mmap
#include <sys/mman.h> void *mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset); int munmap(void *addr, size_t length);
详细参数如下:
| 参数 | 详细说明 |
|---|---|
| addr | 需要映射的虚拟内存地址；如果为NULL，系统会自动选定。映射成功后返回该地址 |
| length | 需要映射多大的数据量. Mus be multiple of PAGE SIZE |
| prot | 描述映射区域内存保护方式，包括：PROT_EXEC、PROT_READ、PROT_WRITE、PROT_NONE. |
| flags | 描述映射区域的特性，比如是否对其他进程共享，是否建立匿名映射，是否创建私有的cow. |
| fd | 要映射到内存中的文件描述符 |
| offset | 文件映射的偏移量 |
4. mmap to /dev/mem
5./dev/mem mmap operator:
static int mmap_mem(struct file *file, struct vm_area_struct *vma) { size_t size = vma->vm_end - vma->vm_start; phys_addr_t offset = (phys_addr_t)vma->vm_pgoff << PAGE_SHIFT; /* It's illegal to wrap around the end of the physical address space. */ if (offset + (phys_addr_t)size - 1 < offset) return -EINVAL; if (!valid_mmap_phys_addr_range(vma->vm_pgoff, size))return -EINVAL; if (!private_mapping_ok(vma)) return -ENOSYS; if (!range_is_allowed(vma->vm_pgoff, size)) return -EPERM; if (!phys_mem_access_prot_allowed(file, vma->vm_pgoff, size, &vma->vm_page_prot)) return -EINVAL; vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_pgoff, size, vma->vm_page_prot); vma->vm_ops = &mmap_mem_ops; /* Remap-pfn-range will mark the range VM_IO */ if (remap_pfn_range(vma,---------------------------------------------将内核中vma->vm_pgoff对应的size个页面，映射到vma区域，返回的虚拟空间起始地址是vma->vm_start。 vma->vm_start, vma->vm_pgoff, size, vma->vm_page_prot)) { return -EAGAIN; } return 0; }
vm_area_struct结构体
