“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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__SYSCALL(__NR_mmap, sys_mmap) | __SYSCALL(__NR_mmap, sys_mmap) | ||
</source> | </source> | ||
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| + | Reference: https://www.cnblogs.com/sky-heaven/p/5689072.html | ||
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5. sys_mmap to dev/mem drive's mmap_mem | 5. sys_mmap to dev/mem drive's mmap_mem | ||
2019年11月6日 (三) 11:23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 sys_mmap
Questions:
offset 如何变成是物理地址? offset 跟vma->pgoff 的关系?
vma->vm_start = addr ? 若 addr=NULL 如何给址?
系统调用的入口是entry_SYSCALL_64_fastpath，然后根据系统调用号在sys_call_table中找到对应的函数。
mmap()和munmap()对应的系统调用分别是SyS_mmap()和SyS_munmap()
arch/arc/kernel/sys.c
#define __SYSCALL(nr, call) [nr] = (call), void *sys_call_table[NR_syscalls] = { [0 ... NR_syscalls-1] = sys_ni_syscall, #include <asm/unistd.h> };
include/uapiasm-generic/unistd.h
#define __NR_munmap 215 __SYSCALL(__NR_munmap, sys_munmap) #define __NR_mremap 216 __SYSCALL(__NR_mremap, sys_mremap) #define __NR_mmap 1058 __SYSCALL(__NR_mmap, sys_mmap)
Reference: https://www.cnblogs.com/sky-heaven/p/5689072.html
5. sys_mmap to dev/mem drive's mmap_mem
6./dev/mem driver in inux-kernel/drivers/char/mem.c
static int mmap_mem(struct file *file, struct vm_area_struct *vma) { size_t size = vma->vm_end - vma->vm_start; if (!valid_mmap_phys_addr_range(vma->vm_pgoff, size))//没检查 return -EINVAL; if (!private_mapping_ok(vma))//vm_flags must have VM_MAYSHARE return -ENOSYS; if (!range_is_allowed(vma->vm_pgoff, size))//check each page is allowed by calling devmem_is_allowed. ARCH_HAS_VALID_PHYS_ADDR_RANGE return -EPERM; if (!phys_mem_access_prot_allowed(file, vma->vm_pgoff, size, &vma->vm_page_prot))//没检查 return -EINVAL; vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_pgoff, size, vma->vm_page_prot);// 跟 cache 有关 先不管 vma->vm_ops = &mmap_mem_ops; /* Remap-pfn-range will mark the range VM_IO */ if (remap_pfn_range(vma, vma->vm_start, //Virt 开头位址 vma->vm_pgoff, size, vma->vm_page_prot)) { return -EAGAIN; } return 0; }
remap_pfn_range im ./mm/memory.c
remap_pfn_range(vma, //user vma to map to addr, //target user address pfn, //physic address of kernel memory. Page #? size, //size of map area prot //page protection flags for this mapping ) { vma->vm_pgoff = pfn; vma->flags |= VM_IO|VM_PFNMAP|VM_DONTEXPAD |VM_DONTDUMP; mm = vma->mm; do { //for each page, update mm next = pgd_addr_end(addr, end) remap_pud_range(mm, pgd, addr, next, pfn+page#, prot) pgd++, addr = next, }while (addr != end)
Question：
如何确认offset 合理区域? length 可以有多大?
Reference:
https://blog.csdn.net/junllee/article/details/82146351
