On Mon, Aug 19, 2019 at 03:37:01PM -0500, minyard@xxxxxxx wrote:
> From: Corey Minyard <cminyard@xxxxxxxxxx>
>
> This is for the read data pretimeout governor.
>
> Signed-off-by: Corey Minyard <cminyard@xxxxxxxxxx>
On further thought, I think it would be a bad idea to add this
functionality: It changes the userspace ABI for accessing the watchdog
device. Today, when a watchdog device is opened, it does not provide
read data, it does not hang, and returns immediately. A "cat" from it
is an easy and quick means to test if a watchdog works.
Guenter
> ---
> drivers/watchdog/watchdog_core.c | 3 +
> drivers/watchdog/watchdog_dev.c | 113 +++++++++++++++++++++++++++++++
> include/linux/watchdog.h | 5 ++
> 3 files changed, 121 insertions(+)
>
> diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
> index 21e8085b848b..80149ac229fc 100644
> --- a/drivers/watchdog/watchdog_core.c
> +++ b/drivers/watchdog/watchdog_core.c
> @@ -216,6 +216,9 @@ static int __watchdog_register_device(struct watchdog_device *wdd)
> return id;
> wdd->id = id;
>
> + spin_lock_init(&wdd->readlock);
> + init_waitqueue_head(&wdd->read_q);
> +
> ret = watchdog_dev_register(wdd);
> if (ret) {
> ida_simple_remove(&watchdog_ida, id);
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index dbd2ad4c9294..8e8304607a8c 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -44,6 +44,8 @@
> #include <linux/types.h> /* For standard types (like size_t) */
> #include <linux/watchdog.h> /* For watchdog specific items */
> #include <linux/uaccess.h> /* For copy_to_user/put_user/... */
> +#include <linux/poll.h> /* For poll_table/... */
> +#include <linux/sched/signal.h> /* For signal_pending */
>
> #include <uapi/linux/sched/types.h> /* For struct sched_param */
>
> @@ -929,12 +931,120 @@ static int watchdog_release(struct inode *inode, struct file *file)
> return 0;
> }
>
> +static ssize_t watchdog_read(struct file *file,
> + char __user *buf,
> + size_t count,
> + loff_t *ppos)
> +{
> + struct watchdog_core_data *wd_data = file->private_data;
> + struct watchdog_device *wdd;
> + int err = 0;
> + wait_queue_entry_t wait;
> + char dummy = 1;
> +
> + if (count <= 0)
> + return 0;
> +
> + mutex_lock(&wd_data->lock);
> +
> + wdd = wd_data->wdd;
> + if (!wdd)
> + goto done;
> +
> + /*
> + * Reading returns if the pretimeout has gone off, and it only does
> + * it once per pretimeout.
> + */
> + spin_lock_irq(&wdd->readlock);
> + while (!wdd->data_to_read) {
> + if (file->f_flags & O_NONBLOCK) {
> + err = -EAGAIN;
> + goto out;
> + }
> +
> + init_waitqueue_entry(&wait, current);
> + add_wait_queue(&wdd->read_q, &wait);
> + set_current_state(TASK_INTERRUPTIBLE);
> + spin_unlock_irq(&wdd->readlock);
> + schedule();
> + spin_lock_irq(&wdd->readlock);
> + remove_wait_queue(&wdd->read_q, &wait);
> +
> + if (signal_pending(current)) {
> + err = -ERESTARTSYS;
> + goto out;
> + }
> + }
> + dummy = wdd->data_to_read;
> + wdd->data_to_read = 0;
> +
> + out:
> + spin_unlock_irq(&wdd->readlock);
> +
> + if (err == 0) {
> + if (copy_to_user(buf, &dummy, 1))
> + err = -EFAULT;
> + else
> + err = 1;
> + }
> +
> + done:
> + mutex_unlock(&wd_data->lock);
> +
> + return err;
> +}
> +
> +static __poll_t watchdog_poll(struct file *file, poll_table *wait)
> +{
> + struct watchdog_core_data *wd_data = file->private_data;
> + struct watchdog_device *wdd;
> + __poll_t mask = 0;
> +
> + mutex_lock(&wd_data->lock);
> +
> + wdd = wd_data->wdd;
> + if (!wdd)
> + goto done;
> +
> + poll_wait(file, &wdd->read_q, wait);
> +
> + spin_lock_irq(&wdd->readlock);
> + if (wdd->data_to_read)
> + mask |= (EPOLLIN | EPOLLRDNORM);
> + spin_unlock_irq(&wdd->readlock);
> +
> +done:
> + mutex_unlock(&wd_data->lock);
> + return mask;
> +}
> +
> +static int watchdog_fasync(int fd, struct file *file, int on)
> +{
> + struct watchdog_core_data *wd_data = file->private_data;
> + struct watchdog_device *wdd;
> + int err = -ENODEV;
> +
> + mutex_lock(&wd_data->lock);
> +
> + wdd = wd_data->wdd;
> + if (!wdd)
> + goto done;
> +
> + err = fasync_helper(fd, file, on, &wdd->fasync_q);
> +done:
> + mutex_unlock(&wd_data->lock);
> + return err;
> +}
> +
> static const struct file_operations watchdog_fops = {
> .owner = THIS_MODULE,
> .write = watchdog_write,
> .unlocked_ioctl = watchdog_ioctl,
> .open = watchdog_open,
> .release = watchdog_release,
> + .read = watchdog_read,
> + .poll = watchdog_poll,
> + .fasync = watchdog_fasync,
> };
>
> static struct miscdevice watchdog_miscdev = {
> @@ -970,6 +1080,9 @@ static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
> if (IS_ERR_OR_NULL(watchdog_kworker))
> return -ENODEV;
>
> + spin_lock_init(&wdd->readlock);
> + init_waitqueue_head(&wdd->read_q);
> +
> kthread_init_work(&wd_data->work, watchdog_ping_work);
> hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> wd_data->timer.function = watchdog_timer_expired;
> diff --git a/include/linux/watchdog.h b/include/linux/watchdog.h
> index 417d9f37077a..e34501a822f0 100644
> --- a/include/linux/watchdog.h
> +++ b/include/linux/watchdog.h
> @@ -117,6 +117,11 @@ struct watchdog_device {
> #define WDOG_HW_RUNNING 3 /* True if HW watchdog running */
> #define WDOG_STOP_ON_UNREGISTER 4 /* Should be stopped on unregister */
> struct list_head deferred;
> +
> + spinlock_t readlock;
> + bool data_to_read;
> + struct wait_queue_head read_q;
> + struct fasync_struct *fasync_q;
> };
>
> #define WATCHDOG_NOWAYOUT IS_BUILTIN(CONFIG_WATCHDOG_NOWAYOUT)
> --
> 2.17.1
>
