关于ioctl,unlocked_ioctl和compat_ioctl执行的顺序

关于ioctl,unlocked_ioctl和compat_ioctl执行的顺序

对于ioctl操作,优先执行f_op->unlocked_ioctl,如果没有unlocked_ioctl,那么执行f_op->ioctl

sys_ioctl
==> vfs_ioctl
==> file_ioctl
==> do_ioctl
static long do_ioctl(struct file *filp, unsigned int cmd,
        unsigned long arg)
{
    int error = -ENOTTY;

    if (!filp->f_op)
        goto out;

    if (filp->f_op->unlocked_ioctl) { // 优先执行f_op->unlocked_ioctl
        error = filp->f_op->unlocked_ioctl(filp, cmd, arg);
        if (error == -ENOIOCTLCMD)
            error = -EINVAL;
        goto out;
    } else if (filp->f_op->ioctl) { // 如果没有unlocked_ioctl,那么执行f_op->ioctl
        lock_kernel();
        error = filp->f_op->ioctl(filp->f_path.dentry->d_inode,
                      filp, cmd, arg);
        unlock_kernel();
    }

 out:
    return error;
}

对于compat_sys_ioctl系统调用的使用比较麻烦一些,因为默认kernel是不将它built-in进内核的,
可以通过fs/Makefile看到如下定义obj-$(CONFIG_COMPAT) += compat.o compat_ioctl.o
对于CONFIG_COMPAT的定义于cpu体系结构有关,比如下面几个默认cpu配置了CONFIG_COMPAT=y
arch/x86_64/defconfig
arch/sparc64/defconfig
arch/powerpc/configs/ppc64_defconfig
arch/s390/defconfig
arch/parisc/configs/a500_defconfig
arch/mips/configs/ip32_defconfig

compat_sys_ioctl
filp->f_op->compat_ioctl(filp, cmd, arg);
如果该cmd在compat_ioctl中没有找到对应的处理,同时没有filp->f_op方法集[luther.gliethttp]
或者filp->f_op->ioct且filp->f_op->unlocked_ioctl均没有,那么将尝试调用vfs_ioctl,看看是不是一些经典的ioctl命令.

对于sound/core/control.c文件[luther.gliethttp]
#ifdef CONFIG_COMPAT
#include "control_compat.c"
#else
#define snd_ctl_ioctl_compat    NULL
#endif
下面的"controlC%i"声卡对应的控制节点fops的compat_ioctl,当没有定义CONFIG_COMPAT时,将被置为NULL
static const struct file_operations snd_ctl_f_ops =
{
    .owner =    THIS_MODULE,
    .read =        snd_ctl_read,
    .open =        snd_ctl_open,
    .release =    snd_ctl_release,
    .poll =        snd_ctl_poll,
    .unlocked_ioctl =    snd_ctl_ioctl,
    .compat_ioctl =    snd_ctl_ioctl_compat,
    .fasync =    snd_ctl_fasync,
};