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bibo713

我是名在校大学生，老师给了我们一段原代码让我们分析，可我没接触过liuix代码，不知在哪可以有这方面的入门知识．先谢谢了．
代码如下：
#include <linux/module.h>
#include <linux/spinlock.h>
#include <linux/slab.h>
#include <linux/pm.h>
#include <linux/interrupt.h>

int pm_active;

/*
*        Locking notes:
*                pm_devs_lock can be a semaphore providing pm ops are not called
*        from an interrupt handler (already a bad idea so no change here). Each
*        change must be protected so that an unlink of an entry doesnt clash
*        with a pm send - which is permitted to sleep in the current architecture
*
*        Module unloads clashing with pm events now work out safely, the module
*        unload path will block until the event has been sent. It may well block
*        until a resume but that will be fine.
*/

static DECLARE_MUTEX(pm_devs_lock);
static LIST_HEAD(pm_devs);

/**
*        pm_register - register a device with power management
*        @type: device type
*        @id: device ID
*        @callback: callback function
*
*        Add a device to the list of devices that wish to be notified about
*        power management events. A &pm_dev structure is returned on success,
*        on failure the return is %NULL.
*
*      The callback function will be called in process context and
*      it may sleep.
*/

struct pm_dev *pm_register(pm_dev_t type,
                           unsigned long id,
                           pm_callback callback)
{
        struct pm_dev *dev = kmalloc(sizeof(struct pm_dev), GFP_KERNEL);
        if (dev) {
                memset(dev, 0, sizeof(*dev));
                dev->type = type;
                dev->id = id;
                dev->callback = callback;

                down(&pm_devs_lock);
                list_add(&dev->entry, &pm_devs);
                up(&pm_devs_lock);
        }
        return dev;
}

/**
*        pm_unregister -  unregister a device with power management
*        @dev: device to unregister
*
*        Remove a device from the power management notification lists. The
*        dev passed must be a handle previously returned by pm_register.
*/

void pm_unregister(struct pm_dev *dev)
{
        if (dev) {
                down(&pm_devs_lock);
                list_del(&dev->entry);
                up(&pm_devs_lock);

                kfree(dev);
        }
}

static void __pm_unregister(struct pm_dev *dev)
{
        if (dev) {
                list_del(&dev->entry);
                kfree(dev);
        }
}

/**
*        pm_unregister_all - unregister all devices with matching callback
*        @callback: callback function pointer
*
*        Unregister every device that would call the callback passed. This
*        is primarily meant as a helper function for loadable modules. It
*        enables a module to give up all its managed devices without keeping
*        its own private list.
*/

void pm_unregister_all(pm_callback callback)
{
        struct list_head *entry;

        if (!callback)
                return;

        down(&pm_devs_lock);
        entry = pm_devs.next;
        while (entry != &pm_devs) {
                struct pm_dev *dev = list_entry(entry, struct pm_dev, entry);
                entry = entry->next;
                if (dev->callback == callback)
                        __pm_unregister(dev);
        }
        up(&pm_devs_lock);
}

/**
*        pm_send - send request to a single device
*        @dev: device to send to
*        @rqst: power management request
*        @data: data for the callback
*
*        Issue a power management request to a given device. The
*        %PM_SUSPEND and %PM_RESUME events are handled specially. The
*        data field must hold the intended next state. No call is made
*        if the state matches.
*
*        BUGS: what stops two power management requests occuring in parallel
*        and conflicting.
*
*        WARNING: Calling pm_send directly is not generally recommended, in
*        paticular there is no locking against the pm_dev going away. The
*        caller must maintain all needed locking or have 'inside knowledge'
*        on the safety. Also remember that this function is not locked against
*        pm_unregister. This means that you must handle SMP races on callback
*        execution and unload yourself.
*/

int pm_send(struct pm_dev *dev, pm_request_t rqst, void *data)
{
        int status = 0;
        int prev_state, next_state;

        if (in_interrupt())
                BUG();

        switch (rqst) {
        case PM_SUSPEND:
        case PM_RESUME:
                prev_state = dev->state;
                next_state = (int) data;
                if (prev_state != next_state) {
                        if (dev->callback)
                                status = (*dev->callback)(dev, rqst, data);
                        if (!status) {
                                dev->state = next_state;
                                dev->prev_state = prev_state;
                        }
                }
                else {
                        dev->prev_state = prev_state;
                }
                break;
        default:
                if (dev->callback)
                        status = (*dev->callback)(dev, rqst, data);
                break;
        }
        return status;
}

/*
* Undo incomplete request
*/
static void pm_undo_all(struct pm_dev *last)
{
        struct list_head *entry = last->entry.prev;
        while (entry != &pm_devs) {
                struct pm_dev *dev = list_entry(entry, struct pm_dev, entry);
                if (dev->state != dev->prev_state) {
                        /* previous state was zero (running) resume or
                         * previous state was non-zero (suspended) suspend
                         */
                        pm_request_t undo = (dev->prev_state
                                             ? PM_SUSPENDM_RESUME);
                        pm_send(dev, undo, (void*) dev->prev_state);
                }
                entry = entry->prev;
        }
}

/**
*        pm_send_all - send request to all managed devices
*        @rqst: power management request
*        @data: data for the callback
*
*        Issue a power management request to a all devices. The
*        %PM_SUSPEND events are handled specially. Any device is
*        permitted to fail a suspend by returning a non zero (error)
*        value from its callback function. If any device vetoes a
*        suspend request then all other devices that have suspended
*        during the processing of this request are restored to their
*        previous state.
*
*        WARNING:  This function takes the pm_devs_lock. The lock is not dropped until
*        the callbacks have completed. This prevents races against pm locking
*        functions, races against module unload pm_unregister code. It does
*        mean however that you must not issue pm_ functions within the callback
*        or you will deadlock and users will hate you.
*
*        Zero is returned on success. If a suspend fails then the status
*        from the device that vetoes the suspend is returned.
*
*        BUGS: what stops two power management requests occuring in parallel
*        and conflicting.
*/

int pm_send_all(pm_request_t rqst, void *data)
{
        struct list_head *entry;
       
        down(&pm_devs_lock);
        entry = pm_devs.next;
        while (entry != &pm_devs) {
                struct pm_dev *dev = list_entry(entry, struct pm_dev, entry);
                if (dev->callback) {
                        int status = pm_send(dev, rqst, data);
                        if (status) {
                                /* return devices to previous state on
                                 * failed suspend request
                                 */
                                if (rqst == PM_SUSPEND)
                                        pm_undo_all(dev);
                                up(&pm_devs_lock);
                                return status;
                        }
                }
                entry = entry->next;
        }
        up(&pm_devs_lock);
        return 0;
}

/**
*        pm_find  - find a device
*        @type: type of device
*        @from: where to start looking
*
*        Scan the power management list for devices of a specific type. The
*        return value for a matching device may be passed to further calls
*        to this function to find further matches. A %NULL indicates the end
*        of the list.
*
*        To search from the beginning pass %NULL as the @from value.
*
*        The caller MUST hold the pm_devs_lock lock when calling this
*        function. The instant that the lock is dropped all pointers returned
*        may become invalid.
*/

struct pm_dev *pm_find(pm_dev_t type, struct pm_dev *from)
{
        struct list_head *entry = from ? from->entry.next:pm_devs.next;
        while (entry != &pm_devs) {
                struct pm_dev *dev = list_entry(entry, struct pm_dev, entry);
                if (type == PM_UNKNOWN_DEV || dev->type == type)
                        return dev;
                entry = entry->next;
        }
        return 0;
}

EXPORT_SYMBOL(pm_register);
EXPORT_SYMBOL(pm_unregister);
EXPORT_SYMBOL(pm_unregister_all);
EXPORT_SYMBOL(pm_send);
EXPORT_SYMBOL(pm_send_all);
EXPORT_SYMBOL(pm_find);
EXPORT_SYMBOL(pm_active);

strugglest

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