Linux设备驱动学习(2) 全局内存“设备” scull

Myth丶恋晨 2022-06-13 06:53 211阅读 0赞

这次分析的是LDD3中的第一个程序scull

scull设备也是一个内存”设备“

结构图如下，来自LDD3

![1332829939_8636.png][]

/*
     * Representation of scull quantum sets.
     */
    struct scull_qset {
            void **data;//指针的指针,(*data)是一个指针变量，指示一片内存空间，这片内存中间内存储的也是地址
            struct scull_qset *next;
    };
    
    struct scull_dev {
            struct scull_qset *data;  /* Pointer to first quantum set *///第一个scull_qset的地址
            int quantum;              /* the current quantum size *///每一个数据块的大小
            int qset;                 /* the current array size *///每个scull_qset包含多少个指针
            unsigned long size;       /* amount of data stored here *///设备中有多少可用的数据内存，也就是Quantum中的内存数据。
            unsigned int access_key;  /* used by sculluid and scullpriv */
            struct semaphore sem;     /* mutual exclusion semaphore     *///信号量
            struct cdev cdev;         /* Char device structure              *///字符设备结构
    };
    
    
    
    //主程序
    /*
     * main.c -- the bare scull char module
     *
     * Copyright (C) 2001 Alessandro Rubini and Jonathan Corbet
     * Copyright (C) 2001 O'Reilly & Associates
     *
     * The source code in this file can be freely used, adapted,
     * and redistributed in source or binary form, so long as an
     * acknowledgment appears in derived source files.  The citation
     * should list that the code comes from the book "Linux Device
     * Drivers" by Alessandro Rubini and Jonathan Corbet, published
     * by O'Reilly & Associates.   No warranty is attached;
     * we cannot take responsibility for errors or fitness for use.
     *
     */
    
    #include <linux/config.h>
    #include <linux/module.h>
    #include <linux/moduleparam.h>
    #include <linux/init.h>
    
    #include <linux/kernel.h>	/* printk() */
    #include <linux/slab.h>		/* kmalloc() */
    #include <linux/fs.h>		/* everything... */
    #include <linux/errno.h>	/* error codes */
    #include <linux/types.h>	/* size_t */
    #include <linux/proc_fs.h>
    #include <linux/fcntl.h>	/* O_ACCMODE */
    #include <linux/seq_file.h>
    #include <linux/cdev.h>
    
    #include <asm/system.h>		/* cli(), *_flags */
    #include <asm/uaccess.h>	/* copy_*_user */
    
    #include "scull.h"		/* local definitions */
    
    /*
     * Our parameters which can be set at load time.
     */
    
    int scull_major =   SCULL_MAJOR;
    int scull_minor =   0;
    int scull_nr_devs = SCULL_NR_DEVS;	/* number of bare scull devices */
    int scull_quantum = SCULL_QUANTUM;		//4000
    int scull_qset =    SCULL_QSET;			//1000
    
    module_param(scull_major, int, S_IRUGO);
    module_param(scull_minor, int, S_IRUGO);
    module_param(scull_nr_devs, int, S_IRUGO);
    module_param(scull_quantum, int, S_IRUGO);
    module_param(scull_qset, int, S_IRUGO);
    
    MODULE_AUTHOR("Alessandro Rubini, Jonathan Corbet");
    MODULE_LICENSE("Dual BSD/GPL");
    
    struct scull_dev *scull_devices;	/* allocated in scull_init_module */
    
    
    /*
     * Empty out the scull device; must be called with the device
     * semaphore held.
     *///释放数据结构，最后剩下scull_dev结构
    int scull_trim(struct scull_dev *dev)
    {
    	struct scull_qset *next, *dptr;
    	int qset = dev->qset;   /* "dev" is not-null */
    	int i;
    
    	for (dptr = dev->data; dptr; dptr = next) { /* all the list items */
    		if (dptr->data) {
    			for (i = 0; i < qset; i++)//遍历指针数组中的每个元素，释放其所指的空间
    				kfree(dptr->data[i]);
    			kfree(dptr->data);	//最后释放这个指针数组。
    			dptr->data = NULL;	//置空
    		}
    		next = dptr->next;
    		kfree(dptr);			//释放scull_qset结构
    	}
    	dev->size = 0;				//表示设备拥有的可读写的数据内存
    	dev->quantum = scull_quantum;		//重置各个参数
    	dev->qset = scull_qset;
    	dev->data = NULL;
    	return 0;
    }
    #ifdef SCULL_DEBUG /* use proc only if debugging */
    /*
     * The proc filesystem: function to read and entry
     */
    
    int scull_read_procmem(char *buf, char **start, off_t offset,
                       int count, int *eof, void *data)
    {
    	int i, j, len = 0;
    	int limit = count - 80; /* Don't print more than this */
    
    	for (i = 0; i < scull_nr_devs && len <= limit; i++) {
    		struct scull_dev *d = &scull_devices[i];
    		struct scull_qset *qs = d->data;
    		if (down_interruptible(&d->sem))
    			return -ERESTARTSYS;
    		len += sprintf(buf+len,"\nDevice %i: qset %i, q %i, sz %li\n",
    				i, d->qset, d->quantum, d->size);
    		for (; qs && len <= limit; qs = qs->next) { /* scan the list */
    			len += sprintf(buf + len, "  item at %p, qset at %p\n",
    					qs, qs->data);
    			if (qs->data && !qs->next) /* dump only the last item */
    				for (j = 0; j < d->qset; j++) {
    					if (qs->data[j])
    						len += sprintf(buf + len,
    								"    % 4i: %8p\n",
    								j, qs->data[j]);
    				}
    		}
    		up(&scull_devices[i].sem);
    	}
    	*eof = 1;
    	return len;
    }
    
    
    /*
     * For now, the seq_file implementation will exist in parallel.  The
     * older read_procmem function should maybe go away, though.
     */
    
    /*
     * Here are our sequence iteration methods.  Our "position" is
     * simply the device number.
     */
    static void *scull_seq_start(struct seq_file *s, loff_t *pos)
    {
    	if (*pos >= scull_nr_devs)
    		return NULL;   /* No more to read */
    	return scull_devices + *pos;
    }
    
    static void *scull_seq_next(struct seq_file *s, void *v, loff_t *pos)
    {
    	(*pos)++;
    	if (*pos >= scull_nr_devs)
    		return NULL;
    	return scull_devices + *pos;
    }
    
    static void scull_seq_stop(struct seq_file *s, void *v)
    {
    	/* Actually, there's nothing to do here */
    }
    
    static int scull_seq_show(struct seq_file *s, void *v)
    {
    	struct scull_dev *dev = (struct scull_dev *) v;
    	struct scull_qset *d;
    	int i;
    
    	if (down_interruptible(&dev->sem))
    		return -ERESTARTSYS;
    	seq_printf(s, "\nDevice %i: qset %i, q %i, sz %li\n",
    			(int) (dev - scull_devices), dev->qset,
    			dev->quantum, dev->size);
    	for (d = dev->data; d; d = d->next) { /* scan the list */
    		seq_printf(s, "  item at %p, qset at %p\n", d, d->data);
    		if (d->data && !d->next) /* dump only the last item */
    			for (i = 0; i < dev->qset; i++) {
    				if (d->data[i])
    					seq_printf(s, "    % 4i: %8p\n",
    							i, d->data[i]);
    			}
    	}
    	up(&dev->sem);
    	return 0;
    }
    	
    /*
     * Tie the sequence operators up.
     */
    static struct seq_operations scull_seq_ops = {
    	.start = scull_seq_start,
    	.next  = scull_seq_next,
    	.stop  = scull_seq_stop,
    	.show  = scull_seq_show
    };
    
    /*
     * Now to implement the /proc file we need only make an open
     * method which sets up the sequence operators.
     */
    static int scull_proc_open(struct inode *inode, struct file *file)
    {
    	return seq_open(file, &scull_seq_ops);
    }
    
    /*
     * Create a set of file operations for our proc file.
     */
    static struct file_operations scull_proc_ops = {
    	.owner   = THIS_MODULE,
    	.open    = scull_proc_open,
    	.read    = seq_read,
    	.llseek  = seq_lseek,
    	.release = seq_release
    };
    	
    
    /*
     * Actually create (and remove) the /proc file(s).
     */
    
    static void scull_create_proc(void)
    {
    	struct proc_dir_entry *entry;
    	create_proc_read_entry("scullmem", 0 /* default mode */,
    			NULL /* parent dir */, scull_read_procmem,
    			NULL /* client data */);
    	entry = create_proc_entry("scullseq", 0, NULL);//create a read-only file in /proc
    	if (entry)
    		entry->proc_fops = &scull_proc_ops;//关联文件和对应的文件操作函数集
    }
    
    static void scull_remove_proc(void)
    {
    	/* no problem if it was not registered */
    	remove_proc_entry("scullmem", NULL /* parent dir */);
    	remove_proc_entry("scullseq", NULL);
    }
    
    
    #endif /* SCULL_DEBUG */
    
    
    
    
    
    /*
     * Open and close
     */
    
    int scull_open(struct inode *inode, struct file *filp)
    {
    	struct scull_dev *dev; /* device information */
    
    	dev = container_of(inode->i_cdev, struct scull_dev, cdev);//经典的一个宏，cdev是scull_dev中的一个成员，现在有cdev的指针inode->i_cdev得到scull_dev的指针
    	filp->private_data = dev; /* for other methods */
    
    	/* now trim to 0 the length of the device if open was write-only */
    	if ( (filp->f_flags & O_ACCMODE) == O_WRONLY) {
    		if (down_interruptible(&dev->sem))		//清空前先得到信号量
    			return -ERESTARTSYS;
    		scull_trim(dev); /* ignore errors */
    		up(&dev->sem);					//清空后释放信号量
    	}
    	return 0;          /* success */
    }
    
    int scull_release(struct inode *inode, struct file *filp)
    {
    	return 0;
    }
    /*
     * Follow the list
     */					//得到第n个scull_qset的结构体指针（从0开始）
    struct scull_qset *scull_follow(struct scull_dev *dev, int n)
    {
    	struct scull_qset *qs = dev->data;
    
            /* Allocate first qset explicitly if need be */
    	if (! qs) {//为第一个scull_qset分配空间
    		qs = dev->data = kmalloc(sizeof(struct scull_qset), GFP_KERNEL);
    		if (qs == NULL)
    			return NULL;  /* Never mind */
    		memset(qs, 0, sizeof(struct scull_qset));
    	}
    
    	/* Then follow the list */
    	while (n--) {
    		if (!qs->next) {
    			qs->next = kmalloc(sizeof(struct scull_qset), GFP_KERNEL);
    			if (qs->next == NULL)
    				return NULL;  /* Never mind */
    			memset(qs->next, 0, sizeof(struct scull_qset));
    		}
    		qs = qs->next;
    		continue;
    	}
    	return qs;
    }
    
    /*
     * Data management: read and write
     */
    
    ssize_t scull_read(struct file *filp, char __user *buf, size_t count,
                    loff_t *f_pos)
    {
    	struct scull_dev *dev = filp->private_data; //先得到设备的指针
    	struct scull_qset *dptr;	/* the first listitem */
    	int quantum = dev->quantum, qset = dev->qset;
    	int itemsize = quantum * qset; /* how many bytes in the listitem *///在一个scull_qset中总共有itemsize个字节可使用。
    	int item, s_pos, q_pos, rest;
    	ssize_t retval = 0;
    
    	if (down_interruptible(&dev->sem))
    		return -ERESTARTSYS;
    	if (*f_pos >= dev->size)	//*f_pos表示已读的字节数
    		goto out;
    	if (*f_pos + count > dev->size)
    		count = dev->size - *f_pos;
    
    	/* find listitem, qset index, and offset in the quantum *///这里举个例子比较好，比如*f_pos为4000*1000+4000*500+100
    	item = (long)*f_pos / itemsize;	//找到是第几个scull_qset结构（从第0个开始），例子里就是1了
    	rest = (long)*f_pos % itemsize; //找到在1000个指针数组中指向的数据块中的偏移（从第0个开始），例子里就是4000*500+100
    	s_pos = rest / quantum; q_pos = rest % quantum;//q_pos找到在这块4000B的空间里的偏移（0～3999）
    	//s_pos找到是在第几个指针指向的数据块中，（从0开始）
    	/* follow the list up to the right position (defined elsewhere) */
    	dptr = scull_follow(dev, item);//找到第item个scull_qset结构，（从第0个开始）
    
    	if (dptr == NULL || !dptr->data || ! dptr->data[s_pos])
    		goto out; /* don't fill holes */
    
    	/* read only up to the end of this quantum */
    	if (count > quantum - q_pos)	//最多只读完这个数据块4000B
    		count = quantum - q_pos;
    
    	if (copy_to_user(buf, dptr->data[s_pos] + q_pos, count)) {
    		retval = -EFAULT;
    		goto out;
    	}
    	*f_pos += count;
    	retval = count;
    
      out:
    	up(&dev->sem);		//释放信号量
    	return retval;
    }
    
    ssize_t scull_write(struct file *filp, const char __user *buf, size_t count,
                    loff_t *f_pos)
    {
    	struct scull_dev *dev = filp->private_data;
    	struct scull_qset *dptr;
    	int quantum = dev->quantum, qset = dev->qset;
    	int itemsize = quantum * qset;
    	int item, s_pos, q_pos, rest;
    	ssize_t retval = -ENOMEM; /* value used in "goto out" statements */
    
    	if (down_interruptible(&dev->sem))
    		return -ERESTARTSYS;
    
    	/* find listitem, qset index and offset in the quantum *///写和读类似
    	item = (long)*f_pos / itemsize;
    	rest = (long)*f_pos % itemsize;
    	s_pos = rest / quantum; q_pos = rest % quantum;
    
    	/* follow the list up to the right position */
    	dptr = scull_follow(dev, item);
    	if (dptr == NULL)
    		goto out;
    	if (!dptr->data) {
    		dptr->data = kmalloc(qset * sizeof(char *), GFP_KERNEL);
    		if (!dptr->data)
    			goto out;
    		memset(dptr->data, 0, qset * sizeof(char *));
    	}
    	if (!dptr->data[s_pos]) {
    		dptr->data[s_pos] = kmalloc(quantum, GFP_KERNEL);
    		if (!dptr->data[s_pos])
    			goto out;
    	}
    	/* write only up to the end of this quantum */
    	if (count > quantum - q_pos)
    		count = quantum - q_pos;
    
    	if (copy_from_user(dptr->data[s_pos]+q_pos, buf, count)) {
    		retval = -EFAULT;
    		goto out;
    	}
    	*f_pos += count;
    	retval = count;
    
            /* update the size */
    	if (dev->size < *f_pos)//更新设备拥有的数据内存
    		dev->size = *f_pos;
    
      out:
    	up(&dev->sem);
    	return retval;
    }
    
    /*
     * The ioctl() implementation
     */
    
    int scull_ioctl(struct inode *inode, struct file *filp,
                     unsigned int cmd, unsigned long arg)
    {
    
    	int err = 0, tmp;
    	int retval = 0;
        
    	/*
    	 * extract the type and number bitfields, and don't decode
    	 * wrong cmds: return ENOTTY (inappropriate ioctl) before access_ok()
    	 */
    	if (_IOC_TYPE(cmd) != SCULL_IOC_MAGIC) return -ENOTTY;
    	if (_IOC_NR(cmd) > SCULL_IOC_MAXNR) return -ENOTTY;
    
    	/*
    	 * the direction is a bitmask, and VERIFY_WRITE catches R/W
    	 * transfers. `Type' is user-oriented, while
    	 * access_ok is kernel-oriented, so the concept of "read" and
    	 * "write" is reversed
    	 */
    	if (_IOC_DIR(cmd) & _IOC_READ)
    		err = !access_ok(VERIFY_WRITE, (void __user *)arg, _IOC_SIZE(cmd));
    	else if (_IOC_DIR(cmd) & _IOC_WRITE)
    		err =  !access_ok(VERIFY_READ, (void __user *)arg, _IOC_SIZE(cmd));
    	if (err) return -EFAULT;
    
    	switch(cmd) {
    
    	  case SCULL_IOCRESET:
    		scull_quantum = SCULL_QUANTUM;
    		scull_qset = SCULL_QSET;
    		break;
            
    	  case SCULL_IOCSQUANTUM: /* Set: arg points to the value */
    		if (! capable (CAP_SYS_ADMIN))
    			return -EPERM;
    		retval = __get_user(scull_quantum, (int __user *)arg);
    		break;
    
    	  case SCULL_IOCTQUANTUM: /* Tell: arg is the value */
    		if (! capable (CAP_SYS_ADMIN))
    			return -EPERM;
    		scull_quantum = arg;
    		break;
    
    	  case SCULL_IOCGQUANTUM: /* Get: arg is pointer to result */
    		retval = __put_user(scull_quantum, (int __user *)arg);
    		break;
    
    	  case SCULL_IOCQQUANTUM: /* Query: return it (it's positive) */
    		return scull_quantum;
    
    	  case SCULL_IOCXQUANTUM: /* eXchange: use arg as pointer */
    		if (! capable (CAP_SYS_ADMIN))
    			return -EPERM;
    		tmp = scull_quantum;
    		retval = __get_user(scull_quantum, (int __user *)arg);
    		if (retval == 0)
    			retval = __put_user(tmp, (int __user *)arg);
    		break;
    
    	  case SCULL_IOCHQUANTUM: /* sHift: like Tell + Query */
    		if (! capable (CAP_SYS_ADMIN))
    			return -EPERM;
    		tmp = scull_quantum;
    		scull_quantum = arg;
    		return tmp;
            
    	  case SCULL_IOCSQSET:
    		if (! capable (CAP_SYS_ADMIN))
    			return -EPERM;
    		retval = __get_user(scull_qset, (int __user *)arg);
    		break;
    
    	  case SCULL_IOCTQSET:
    		if (! capable (CAP_SYS_ADMIN))
    			return -EPERM;
    		scull_qset = arg;
    		break;
    
    	  case SCULL_IOCGQSET:
    		retval = __put_user(scull_qset, (int __user *)arg);
    		break;
    
    	  case SCULL_IOCQQSET:
    		return scull_qset;
    
    	  case SCULL_IOCXQSET:
    		if (! capable (CAP_SYS_ADMIN))
    			return -EPERM;
    		tmp = scull_qset;
    		retval = __get_user(scull_qset, (int __user *)arg);
    		if (retval == 0)
    			retval = put_user(tmp, (int __user *)arg);
    		break;
    
    	  case SCULL_IOCHQSET:
    		if (! capable (CAP_SYS_ADMIN))
    			return -EPERM;
    		tmp = scull_qset;
    		scull_qset = arg;
    		return tmp;
    
            /*
             * The following two change the buffer size for scullpipe.
             * The scullpipe device uses this same ioctl method, just to
             * write less code. Actually, it's the same driver, isn't it?
             */
    
    	  case SCULL_P_IOCTSIZE:
    		scull_p_buffer = arg;
    		break;
    
    	  case SCULL_P_IOCQSIZE:
    		return scull_p_buffer;
    
    
    	  default:  /* redundant, as cmd was checked against MAXNR */
    		return -ENOTTY;
    	}
    	return retval;
    
    }
    
    
    
    /*
     * The "extended" operations -- only seek
     */
    
    loff_t scull_llseek(struct file *filp, loff_t off, int whence)
    {
    	struct scull_dev *dev = filp->private_data;
    	loff_t newpos;
    
    	switch(whence) {
    	  case 0: /* SEEK_SET */
    		newpos = off;
    		break;
    
    	  case 1: /* SEEK_CUR */
    		newpos = filp->f_pos + off;
    		break;
    
    	  case 2: /* SEEK_END */
    		newpos = dev->size + off;
    		break;
    
    	  default: /* can't happen */
    		return -EINVAL;
    	}
    	if (newpos < 0) return -EINVAL;
    	filp->f_pos = newpos;
    	return newpos;
    }
    
    
    
    struct file_operations scull_fops = {
    	.owner =    THIS_MODULE,
    	.llseek =   scull_llseek,
    	.read =     scull_read,
    	.write =    scull_write,
    	.ioctl =    scull_ioctl,
    	.open =     scull_open,
    	.release =  scull_release,
    };
    
    /*
     * Finally, the module stuff
     */
    
    /*
     * The cleanup function is used to handle initialization failures as well.
     * Thefore, it must be careful to work correctly even if some of the items
     * have not been initialized
     */
    void scull_cleanup_module(void)
    {
    	int i;
    	dev_t devno = MKDEV(scull_major, scull_minor);
    
    	/* Get rid of our char dev entries */
    	if (scull_devices) {
    		for (i = 0; i < scull_nr_devs; i++) {
    			scull_trim(scull_devices + i);
    			cdev_del(&scull_devices[i].cdev);
    		}
    		kfree(scull_devices);
    	}
    
    #ifdef SCULL_DEBUG /* use proc only if debugging */
    	scull_remove_proc();
    #endif
    
    	/* cleanup_module is never called if registering failed */
    	unregister_chrdev_region(devno, scull_nr_devs);
    
    	/* and call the cleanup functions for friend devices */
    	scull_p_cleanup();
    	scull_access_cleanup();
    
    }
    
    
    /*
     * Set up the char_dev structure for this device.
     */
    static void scull_setup_cdev(struct scull_dev *dev, int index)
    {
    	int err, devno = MKDEV(scull_major, scull_minor + index);
        
    	cdev_init(&dev->cdev, &scull_fops);
    	dev->cdev.owner = THIS_MODULE;
    	dev->cdev.ops = &scull_fops;
    	err = cdev_add (&dev->cdev, devno, 1);
    	/* Fail gracefully if need be */
    	if (err)
    		printk(KERN_NOTICE "Error %d adding scull%d", err, index);
    }
    
    
    int scull_init_module(void)
    {
    	int result, i;
    	dev_t dev = 0;
    
    /*
     * Get a range of minor numbers to work with, asking for a dynamic
     * major unless directed otherwise at load time.
     */
    	if (scull_major) {
    		dev = MKDEV(scull_major, scull_minor);//静态分配，分配scull_nr_devs个设备号
    		result = register_chrdev_region(dev, scull_nr_devs, "scull");
    	} else {					//动态分配
    		result = alloc_chrdev_region(&dev, scull_minor, scull_nr_devs,
    				"scull");
    		scull_major = MAJOR(dev);
    	}
    	if (result < 0) {
    		printk(KERN_WARNING "scull: can't get major %d\n", scull_major);
    		return result;
    	}
    
            /* 
    	 * allocate the devices -- we can't have them static, as the number
    	 * can be specified at load time
    	 */
    	scull_devices = kmalloc(scull_nr_devs * sizeof(struct scull_dev), GFP_KERNEL);//为设备结构体分配空间
    	if (!scull_devices) {
    		result = -ENOMEM;
    		goto fail;  /* Make this more graceful */
    	}
    	memset(scull_devices, 0, scull_nr_devs * sizeof(struct scull_dev));
    
            /* Initialize each device. */
    	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);     //信号量在模块初始化时便已设置
    		scull_setup_cdev(&scull_devices[i], i);//初始化字符设备cdev，次设备号为i
    	}
    
            /* At this point call the init function for any friend device */
    	dev = MKDEV(scull_major, scull_minor + scull_nr_devs);//生成后续的总设备号
    	dev += scull_p_init(dev);//scull_p_init()返回pipe设备数目
    	dev += scull_access_init(dev);
    
    #ifdef SCULL_DEBUG /* only when debugging */
    	scull_create_proc();
    #endif
    
    	return 0; /* succeed */
    
      fail:
    	scull_cleanup_module();
    	return result;
    }
    
    module_init(scull_init_module);
    module_exit(scull_cleanup_module);

关于对proc文件系统的操作没有深入探查，我会在后面的学习中逐步研究的。

[1332829939_8636.png]: https://img-my.csdn.net/uploads/201203/27/1332829939_8636.png