watchdog: WatchDog Timer Driver Core - Add basic framework

The WatchDog Timer Driver Core is a framework
that contains the common code for all watchdog-driver's.
It also introduces a watchdog device structure and the
operations that go with it.

This is the introduction of this framework. This part
supports the minimal watchdog userspace API (or with
other words: the functionality to use /dev/watchdog's
open, release and write functionality as defined in
the simplest watchdog API). Extra functionality will
follow in the next set of patches.

Signed-off-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>

1 files changed, 235 insertions, 0 deletions

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
new file mode 100644
index 000000000000..366f49ce69b8
--- /dev/null
+++ b/drivers/watchdog/watchdog_dev.c
@@ -0,0 +1,235 @@
+/*
+ *      watchdog_dev.c
+ *
+ *      (c) Copyright 2008-2011 Alan Cox <alan@lxorguk.ukuu.org.uk>,
+ *                                              All Rights Reserved.
+ *
+ *      (c) Copyright 2008-2011 Wim Van Sebroeck <wim@iguana.be>.
+ *
+ *
+ *      This source code is part of the generic code that can be used
+ *      by all the watchdog timer drivers.
+ *
+ *      This part of the generic code takes care of the following
+ *      misc device: /dev/watchdog.
+ *
+ *      Based on source code of the following authors:
+ *        Matt Domsch <Matt_Domsch@dell.com>,
+ *        Rob Radez <rob@osinvestor.com>,
+ *        Rusty Lynch <rusty@linux.co.intel.com>
+ *        Satyam Sharma <satyam@infradead.org>
+ *        Randy Dunlap <randy.dunlap@oracle.com>
+ *
+ *      This program is free software; you can redistribute it and/or
+ *      modify it under the terms of the GNU General Public License
+ *      as published by the Free Software Foundation; either version
+ *      2 of the License, or (at your option) any later version.
+ *
+ *      Neither Alan Cox, CymruNet Ltd., Wim Van Sebroeck nor Iguana vzw.
+ *      admit liability nor provide warranty for any of this software.
+ *      This material is provided "AS-IS" and at no charge.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>       /* For module stuff/... */
+#include <linux/types.h>        /* For standard types (like size_t) */
+#include <linux/errno.h>        /* For the -ENODEV/... values */
+#include <linux/kernel.h>       /* For printk/panic/... */
+#include <linux/fs.h>           /* For file operations */
+#include <linux/watchdog.h>     /* For watchdog specific items */
+#include <linux/miscdevice.h>   /* For handling misc devices */
+#include <linux/init.h>         /* For __init/__exit/... */
+#include <linux/uaccess.h>      /* For copy_to_user/put_user/... */
+
+/* make sure we only register one /dev/watchdog device */
+static unsigned long watchdog_dev_busy;
+/* the watchdog device behind /dev/watchdog */
+static struct watchdog_device *wdd;
+
+/*
+ *      watchdog_ping: ping the watchdog.
+ *      @wddev: the watchdog device to ping
+ *
+ *      If the watchdog has no own ping operation then it needs to be
+ *      restarted via the start operation. This wrapper function does
+ *      exactly that.
+ */
+
+static int watchdog_ping(struct watchdog_device *wddev)
+{
+        if (wddev->ops->ping)
+                return wddev->ops->ping(wddev);  /* ping the watchdog */
+        else
+                return wddev->ops->start(wddev); /* restart the watchdog */
+}
+
+/*
+ *      watchdog_write: writes to the watchdog.
+ *      @file: file from VFS
+ *      @data: user address of data
+ *      @len: length of data
+ *      @ppos: pointer to the file offset
+ *
+ *      A write to a watchdog device is defined as a keepalive ping.
+ */
+
+static ssize_t watchdog_write(struct file *file, const char __user *data,
+                                                size_t len, loff_t *ppos)
+{
+        size_t i;
+        char c;
+
+        if (len == 0)
+                return 0;
+
+        for (i = 0; i != len; i++) {
+                if (get_user(c, data + i))
+                        return -EFAULT;
+        }
+
+        /* someone wrote to us, so we send the watchdog a keepalive ping */
+        watchdog_ping(wdd);
+
+        return len;
+}
+
+/*
+ *      watchdog_open: open the /dev/watchdog device.
+ *      @inode: inode of device
+ *      @file: file handle to device
+ *
+ *      When the /dev/watchdog device gets opened, we start the watchdog.
+ *      Watch out: the /dev/watchdog device is single open, so we make sure
+ *      it can only be opened once.
+ */
+
+static int watchdog_open(struct inode *inode, struct file *file)
+{
+        int err = -EBUSY;
+
+        /* the watchdog is single open! */
+        if (test_and_set_bit(WDOG_DEV_OPEN, &wdd->status))
+                return -EBUSY;
+
+        /*
+         * If the /dev/watchdog device is open, we don't want the module
+         * to be unloaded.
+         */
+        if (!try_module_get(wdd->ops->owner))
+                goto out;
+
+        err = wdd->ops->start(wdd);
+        if (err < 0)
+                goto out_mod;
+
+        /* dev/watchdog is a virtual (and thus non-seekable) filesystem */
+        return nonseekable_open(inode, file);
+
+out_mod:
+        module_put(wdd->ops->owner);
+out:
+        clear_bit(WDOG_DEV_OPEN, &wdd->status);
+        return err;
+}
+
+/*
+ *      watchdog_release: release the /dev/watchdog device.
+ *      @inode: inode of device
+ *      @file: file handle to device
+ *
+ *      This is the code for when /dev/watchdog gets closed.
+ */
+
+static int watchdog_release(struct inode *inode, struct file *file)
+{
+        int err;
+
+        err = wdd->ops->stop(wdd);
+        if (err != 0) {
+                pr_crit("%s: watchdog did not stop!\n", wdd->info->identity);
+                watchdog_ping(wdd);
+        }
+
+        /* Allow the owner module to be unloaded again */
+        module_put(wdd->ops->owner);
+
+        /* make sure that /dev/watchdog can be re-opened */
+        clear_bit(WDOG_DEV_OPEN, &wdd->status);
+
+        return 0;
+}
+
+static const struct file_operations watchdog_fops = {
+        .owner          = THIS_MODULE,
+        .write          = watchdog_write,
+        .open           = watchdog_open,
+        .release        = watchdog_release,
+};
+
+static struct miscdevice watchdog_miscdev = {
+        .minor          = WATCHDOG_MINOR,
+        .name           = "watchdog",
+        .fops           = &watchdog_fops,
+};
+
+/*
+ *      watchdog_dev_register:
+ *      @watchdog: watchdog device
+ *
+ *      Register a watchdog device as /dev/watchdog. /dev/watchdog
+ *      is actually a miscdevice and thus we set it up like that.
+ */
+
+int watchdog_dev_register(struct watchdog_device *watchdog)
+{
+        int err;
+
+        /* Only one device can register for /dev/watchdog */
+        if (test_and_set_bit(0, &watchdog_dev_busy)) {
+                pr_err("only one watchdog can use /dev/watchdog.\n");
+                return -EBUSY;
+        }
+
+        wdd = watchdog;
+
+        err = misc_register(&watchdog_miscdev);
+        if (err != 0) {
+                pr_err("%s: cannot register miscdev on minor=%d (err=%d).\n",
+                        watchdog->info->identity, WATCHDOG_MINOR, err);
+                goto out;
+        }
+
+        return 0;
+
+out:
+        wdd = NULL;
+        clear_bit(0, &watchdog_dev_busy);
+        return err;
+}
+
+/*
+ *      watchdog_dev_unregister:
+ *      @watchdog: watchdog device
+ *
+ *      Deregister the /dev/watchdog device.
+ */
+
+int watchdog_dev_unregister(struct watchdog_device *watchdog)
+{
+        /* Check that a watchdog device was registered in the past */
+        if (!test_bit(0, &watchdog_dev_busy) || !wdd)
+                return -ENODEV;
+
+        /* We can only unregister the watchdog device that was registered */
+        if (watchdog != wdd) {
+                pr_err("%s: watchdog was not registered as /dev/watchdog.\n",
+                        watchdog->info->identity);
+                return -ENODEV;
+        }
+
+        misc_deregister(&watchdog_miscdev);
+        wdd = NULL;
+        clear_bit(0, &watchdog_dev_busy);
+        return 0;
+}