六、binder_write 方法
在 binder_write 方法中 , 调用了内核中的 ioctl(bs->fd, BINDER_WRITE_READ, &bwr) 方法 ; 具体方法参考 【Binder 机制】分析 Android 内核源码中的 Binder 驱动源码 binder.c ( googlesource 中的 Android 内核源码 | 内核源码下载 ) 博客进行分析 ;
int binder_write(struct binder_state *bs, void *data, size_t len) { struct binder_write_read bwr; int res; bwr.write_size = len; bwr.write_consumed = 0; bwr.write_buffer = (uintptr_t) data; bwr.read_size = 0; bwr.read_consumed = 0; bwr.read_buffer = 0; // 此处调用了内核方法 res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr); if (res < 0) { fprintf(stderr,"binder_write: ioctl failed (%s)\n", strerror(errno)); } return res; }
完整代码参考 /frameworks/native/cmds/servicemanager/binder.c ;
七、binder_ioctl 内核方法
分析调用内核方法 ioctl(bs->fd, BINDER_WRITE_READ, &bwr) , 传入 BINDER_WRITE_READ 常量 , 走如下分支代码 ; 主要调用了 binder_ioctl_write_read 方法 ;
case BINDER_WRITE_READ: ret = binder_ioctl_write_read(filp, cmd, arg, thread); if (ret) goto err; break;
android-mainline/drivers/android/binder.c 部分内核 Binder 驱动代码 :
static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) { int ret; struct binder_proc *proc = filp->private_data; struct binder_thread *thread; unsigned int size = _IOC_SIZE(cmd); void __user *ubuf = (void __user *)arg; /*pr_info("binder_ioctl: %d:%d %x %lx\n", proc->pid, current->pid, cmd, arg);*/ binder_selftest_alloc(&proc->alloc); trace_binder_ioctl(cmd, arg); ret = wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2); if (ret) goto err_unlocked; thread = binder_get_thread(proc); if (thread == NULL) { ret = -ENOMEM; goto err; } switch (cmd) { case BINDER_WRITE_READ: ret = binder_ioctl_write_read(filp, cmd, arg, thread); if (ret) goto err; break; default: ret = -EINVAL; goto err; } ret = 0; err: if (thread) thread->looper_need_return = false; wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2); if (ret && ret != -EINTR) pr_info("%d:%d ioctl %x %lx returned %d\n", proc->pid, current->pid, cmd, arg, ret); err_unlocked: trace_binder_ioctl_done(ret); return ret; }
八、binder_ioctl_write_read 内核方法
在 方法中 , 调用了 2 22 个重要的方法 , copy_from_user(&bwr, ubuf, sizeof(bwr)) 从用户空间的进程缓冲区中读取到内核空间缓冲区 , copy_to_user(ubuf, &bwr, sizeof(bwr)) 从内核空间写出到用户空间进程中 ;
如果写出的数据大于 0 , 则调用 binder_thread_write 方法 ;
如果读取的数据大于 0 , 则调用 binder_thread_read 方法 ;
static int binder_ioctl_write_read(struct file *filp, unsigned int cmd, unsigned long arg, struct binder_thread *thread) { int ret = 0; struct binder_proc *proc = filp->private_data; unsigned int size = _IOC_SIZE(cmd); void __user *ubuf = (void __user *)arg; struct binder_write_read bwr; if (size != sizeof(struct binder_write_read)) { ret = -EINVAL; goto out; } // 从用户空间的进程缓冲区中读取到内核空间缓冲区 if (copy_from_user(&bwr, ubuf, sizeof(bwr))) { ret = -EFAULT; goto out; } binder_debug(BINDER_DEBUG_READ_WRITE, "%d:%d write %lld at %016llx, read %lld at %016llx\n", proc->pid, thread->pid, (u64)bwr.write_size, (u64)bwr.write_buffer, (u64)bwr.read_size, (u64)bwr.read_buffer); // 如果写出的数据大于 0 if (bwr.write_size > 0) { ret = binder_thread_write(proc, thread, bwr.write_buffer, bwr.write_size, &bwr.write_consumed); trace_binder_write_done(ret); if (ret < 0) { bwr.read_consumed = 0; if (copy_to_user(ubuf, &bwr, sizeof(bwr))) ret = -EFAULT; goto out; } } // 如果读取的数据大于 0 if (bwr.read_size > 0) { ret = binder_thread_read(proc, thread, bwr.read_buffer, bwr.read_size, &bwr.read_consumed, filp->f_flags & O_NONBLOCK); trace_binder_read_done(ret); binder_inner_proc_lock(proc); if (!binder_worklist_empty_ilocked(&proc->todo)) binder_wakeup_proc_ilocked(proc); binder_inner_proc_unlock(proc); if (ret < 0) { if (copy_to_user(ubuf, &bwr, sizeof(bwr))) ret = -EFAULT; goto out; } } binder_debug(BINDER_DEBUG_READ_WRITE, "%d:%d wrote %lld of %lld, read return %lld of %lld\n", proc->pid, thread->pid, (u64)bwr.write_consumed, (u64)bwr.write_size, (u64)bwr.read_consumed, (u64)bwr.read_size); // 从内核空间写出到用户空间进程中 if (copy_to_user(ubuf, &bwr, sizeof(bwr))) { ret = -EFAULT; goto out; } out: return ret; }
