[ION] Sharing a buffer between kernel-space and user-space

Sharing a buffer between kernel-space and user-space

ION memory allocator 관련 글은 LWN 를 번역한 The Android ION memory allocator 참조.

이번에는 user-space 에서 할당한 메모리를 kernel driver 에서 공유하여 write 를 하고 user에서 write 한 데이터가 잘 들어가 있는지 확인하는 수준(?)으로 진행한다.

% 모바일이나 특정 브라우저에서는 syntex highlight 가 지원이 안되어 textbox 에 소스가 나올 수도 있음.

Scenario

1. User 에서 ion("/dev/ion")을 open ==> alloc ==>  share 순으로 진행하여 공유할 ion buffer 를 생성 및 공유 준비

2. User application 에서 공유하려는 kernel driver("/dev/vion_dev")를 open : 여기서 vion_dev 는 내가 만든 device driver 이다. 

3. User 에서 만들어진 shared_fd 를 vion_dev driver 로 전달.

4. Kernel driver 에서 받은 shared_fd 를 이용해 import 하여 메모리를 공유할 준비.

5. User 영역에서 특정 string("ion buffer test magic string") 을 vion_dev driver 에 write 를 요청

6. Kernel driver 에서 shared buffer 에 magic string을 write

7. User 에서 mmap 으로 shared buffer 의 내용 확인.

먼저 User application을 살펴 보면,

아래의 ion_XXX interface 들은 https://android.googlesource.com/platform/system/core/+/android-4.1.2_r1/libion/ion.c 를 살펴 보면 내용을 볼 수 있다. 

  - User-space application

#include <stdio.h> #include <linux/ioctl.h> #include <fcntl.h> #include <errno.h> #include <stdlib.h> #include <sys/mman.h> #include <string.h> #include <linux/ion.h> #include <ion/ion.h> #include <cutils/log.h> #include "ion_test_module.h" #define TEST_MODULE_NAME "/dev/vion_dev" #define DEFAULT_BUF_SIZE 128 int share_with_testdrv(int shared_fd) { int test_fd; char buff[DEFAULT_BUF_SIZE] = "ion buffer test magic string"; int size = 0; // TEST_MODULE_NAME : vion_dev 를 open test_fd = open(TEST_MODULE_NAME, O_RDWR); if (test_fd < 0) { printf("Failed to open test driver(vion)\n"); return 0; } // register ion client in driver with shared file descriptor ioctl(test_fd, VION_REGISTER_ION, &shared_fd); // write a string for confirm. size = write(test_fd, (char*)buff, DEFAULT_BUF_SIZE - 1); if (size > 0) { printf("write \"%s\" string to ion test driver complete\n", buff); } // for sync?? printf("sleep 1sec...\n"); sleep(1); close(test_fd); return size; } int main(int argc, char ** argv) { struct ion_handle *ion_hnd; size_t size = DEFAULT_BUF_SIZE; int ion_fd, shared_fd, test_fd; int ret = 0; int write_size = 0; unsigned char *confirm_vaddr = NULL; // open ion device driver ion_fd = ion_open(); if (ion_fd < 0) { printf("Failed to open ion device driver\n"); ret = ion_fd; goto out; } // allocation ion buffer with ION_HEAP_SYSTEM_CONTIG type. // ion driver 의 physical address 를 얻어오는 interface(ion_phys()) 는 // ION_HEAP_SYSTEM 의 memory type은 지원하지 않음. ret = ion_alloc(ion_fd, size, 0, ION_HEAP_SYSTEM_CONTIG_MASK, ION_FLAG_CACHED | ION_FLAG_CACHED_NEEDS_SYNC, &ion_hnd ); if (ret) { printf("ion_alloc failed\n"); goto close_fd; } // get shared file descriptor ret = ion_share(ion_fd, ion_hnd, &shared_fd); if (ret) { printf("ion_share failed %d\n", ret); goto close_ion; } // open test driver(vion_dev) and write test string. write_size = share_with_testdrv(shared_fd); if (write_size <= 0) { printf("Failed to share with test drv\n"); goto close_ion; } // mmap memory with shared file descriptor. confirm_vaddr = (unsigned char*)mmap( NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, shared_fd, 0 ); if (confirm_vaddr != NULL) // check a string which is written in ion test kernel driver. printf("confirm_vaddr is not NULL, confirm data string \"%s\"\n", confirm_vaddr); else printf("mmap failed\n"); if (confirm_vaddr) munmap((void*)confirm_vaddr, size); printf("\nion test application terminated.\n"); close_ion: ion_free(ion_fd, ion_hnd); close_fd: close(ion_fd); out: return ret; }

주석을 참조하고 Android ION 에 대한 내용의 글을 보면 이해가 쉬울 듯 한데..

  - Kernel-space driver#include <linux/device.h> #include <linux/module.h> #include <linux/kernel.h> #include <linux/init.h> #include <linux/cdev.h> #include <linux/fs.h> #include <asm/uaccess.h> #include <linux/export.h> #include <asm/io.h> #include <linux/ion.h> #include "ion_test_module.h" #define DEVICE_NAME "vion" static int major = 0, minor = 0; static struct cdev vion_cdev; static struct class *cl; static struct ion_client *m_client; static struct ion_handle *m_handle; static int device_opened = 0; extern struct ion_device *lg115x_dev; void *kernel_vaddr = NULL; static int vion_open(struct inode *inode, struct file *filp) { #ifdef DEBUG printk(KERN_INFO "vion device open\n"); #endif if (device_opened > 0) return -EBUSY; device_opened++; return 0; } static int vion_release(struct inode *inode, struct file *filp) { // Already open? if (device_opened <= 0) return 0; device_opened--; return 0; } static long vion_ioctl(struct file *f, unsigned int cmd, unsigned long arg) { int result = 0; switch(cmd) { case VION_REGISTER_ION: { int ion_register; if (copy_from_user(&ion_register, (int *)arg, sizeof(int))) { printk(KERN_ERR "cmd %d : Error get data from ion\n", cmd); result = -EFAULT; goto exit; } if (m_client == NULL) { // lg115x_dev is exported from driver/gpu/ion/lg115x/lg115x_ion.c m_client = ion_client_create(lg115x_dev, ION_HEAP_TYPE_SYSTEM_CONTIG, "vion"); } if (m_client == NULL) { printk(KERN_ERR "Failed to create ion client with lg115x interface\n"); result = -EFAULT; goto exit; } // get handle by ion_import_dma_buf() call. m_handle = ion_import_dma_buf(m_client, ion_register); return 0; } // 아직 필요하진 않지만(ion buffer는 user level에서 free해주니까) register와 pair로 // 작성됨. case VION_UNREGISTER_ION: { int ion_register; if (copy_from_user(&ion_register, (int *)arg, sizeof(int))) { printk(KERN_ERR "cmd %d : Error get data from ion\n", cmd); result = -EFAULT; goto exit; } if (m_client == NULL) { printk(KERN_ERR "Failed to free with ion client\n"); result = -EFAULT; goto exit; } ion_free(m_client, m_handle); return 0; } } exit: return result; } size_t get_vaddr_from_ion_buffer(void) { ion_phys_addr_t phyaddr = 0; size_t len = 0; int ret_val = 0; if (m_client == NULL || m_handle == NULL) { printk(KERN_ERR "Can't get client or handle in read operation\n"); return 0; } // get physical address and length from handle. ret_val = ion_phys(m_client, m_handle, &phyaddr, &len); if (ret_val || !phyaddr) { printk(KERN_ERR "Error get physical address from ion\n"); return 0; } else { printk(KERN_INFO "Read : physaddr 0x%x, len 0x%x\n", (unsigned long)phyaddr, (unsigned int)len); } // ION_HEAP_TYPE_SYSTEM_CONTIG 은 map 할 필요가 없을 듯. // virtual address를 바로 얻어와 copy 하도록 함. // kernel_vaddr = ion_map_kernel(m_client, m_handle); kernel_vaddr = phys_to_virt(phyaddr); printk(KERN_INFO "phys to virt 0x%x\n", kernel_vaddr); return len; } // read 도 작성되었지만 사용할 필요는 없습니다. 테스트 용도로 만들어짐. static ssize_t vion_read(struct file *f, char __user *buf, size_t len, loff_t *off) { size_t size = 0; if ((size = get_vaddr_from_ion_buffer()) < 1) { printk(KERN_ERR "Need to ready buffer for read\n"); return 0; } if (size < len) len = size; if (copy_to_user((char*)kernel_vaddr, buf, len) < 0) return 0; return len; } static ssize_t vion_write(struct file *f, const char __user *buf, size_t len, loff_t *off) { size_t size = 0; #ifdef DEBUG printk(KERN_INFO "write data %s\n", buf); #endif if ((size = get_vaddr_from_ion_buffer()) < 1) { printk(KERN_ERR "Need to ready buffer for read\n"); return 0; } if (size < len) { printk(KERN_ERR "Not enough buffer, set to MAX 0x%x\n", size); len = size; } if (kernel_vaddr != NULL) strncpy((char*)kernel_vaddr, buf, len); else printk(KERN_ERR "virtual address is NULL \n"); return len; } static struct file_operations vion_fops = { .open = vion_open, .release = vion_release, .read = vion_read, .write = vion_write, .unlocked_ioctl = vion_ioctl }; static int __init verify_iondev_init(void) { int ret_val; dev_t dev; // Get a number of device node dynamically. ret_val = alloc_chrdev_region(&dev, minor, 1, DEVICE_NAME); major = MAJOR(dev); if (ret_val < 0) { printk(KERN_ERR "Error allocating charater device region\n"); ret_val = -ENODEV; return ret_val; } // Register the character device. if ((cl = class_create(THIS_MODULE, "chardrv")) == NULL) { printk(KERN_ERR "class_create failed\n"); unregister_chrdev_region(dev, 1); return -1; } if (device_create(cl, NULL, dev, NULL, "vion_dev") == NULL) { printk(KERN_ERR "device_create failed\n"); class_destroy(cl); unregister_chrdev_region(dev, 1); return -1; } cdev_init(&vion_cdev, &vion_fops); if (cdev_add(&vion_cdev, dev, 1) == -1) { printk(KERN_ERR "cdev_failed failed\n"); class_destroy(cl); unregister_chrdev_region(dev, 1); } // Initialize ion client m_client = NULL; #ifdef DEBUG printk(KERN_INFO "vion driver : major %d, minor %d\n", MAJOR(dev), MINOR(dev)); #endif return 0; } static void __exit verify_iondev_exit(void) { dev_t dev = MKDEV(major, minor); device_destory(cl, dev); class_destory(cl); cdev_del(&vion_cdev); unregister_chrdev_region(dev, 1); return; } module_init(verify_iondev_init); module_exit(verify_iondev_exit);

참고 할 정도의 code는 되지 않을까? ^^