Using semaphore in scull - from ldd3

最新推荐文章于 2018-11-12 11:25:41 发布

原创最新推荐文章于 2018-11-12 11:25:41 发布 · 368 阅读

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#semaphore #struct #structure #access #each #up

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本文详细解析了scull虚拟字符设备的结构与初始化过程。重点介绍了scull_dev结构体成员的作用，包括量子集指针、量子大小等。此外，还阐述了互斥信号量在scull设备中的使用方式及初始化顺序。

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struct scull_dev {
     struct scull_qset *data; /* Pointer to first quantum set */
     int quantum; /* the current quantum size */
     int qset; /* the current array size */
     unsigned long size; /* amount of data stored here */
     unsigned int access_key; /* used by sculluid and scullpriv */
     struct semaphore sem; /* mutual exclusion semaphore */
     struct cdev cdev; /* Char device structure */
};

each virtual scull device uses a semaphore seperately.

semaphore has to be intialized before the other section of scull device initialization.

for (i = 0; i < scull_nr_devs; i++) {
scull_devices[i].quantum = scull_quantum;
scull_devices[i].qset = scull_qset;
init_MUTEX(&scull_devices[i].sem);
scull_setup_cdev(&scull_devices[i], i);
}

scull_write starts from the following:

if (down_interruptible(&dev->sem))
return -ERESTARTSYS;

and release semaphore as follow(whether it can successfully carry out its other task):

out:
up(&dev->sem);
return retval;

if some mistake ocurrs during scull_write operating, use : "goto out" to release semaphore correctly.