请教高手
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_SUSPEND:PM_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); !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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