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,

};