Linux Device Drivers 3 examples

1 files changed, 396 insertions, 0 deletions

diff --git a/scull/pipe.c b/scull/pipe.c
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+/*
+ * pipe.c -- fifo driver for scull
+ *
+ * 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/module.h>
+#include <linux/moduleparam.h>
+
+#include <linux/kernel.h>	/* printk(), min() */
+#include <linux/slab.h>		/* kmalloc() */
+#include <linux/fs.h>		/* everything... */
+#include <linux/proc_fs.h>
+#include <linux/errno.h>	/* error codes */
+#include <linux/types.h>	/* size_t */
+#include <linux/fcntl.h>
+#include <linux/poll.h>
+#include <linux/cdev.h>
+#include <asm/uaccess.h>
+
+#include "scull.h"		/* local definitions */
+
+struct scull_pipe {
+        wait_queue_head_t inq, outq;       /* read and write queues */
+        char *buffer, *end;                /* begin of buf, end of buf */
+        int buffersize;                    /* used in pointer arithmetic */
+        char *rp, *wp;                     /* where to read, where to write */
+        int nreaders, nwriters;            /* number of openings for r/w */
+        struct fasync_struct *async_queue; /* asynchronous readers */
+        struct semaphore sem;              /* mutual exclusion semaphore */
+        struct cdev cdev;                  /* Char device structure */
+};
+
+/* parameters */
+static int scull_p_nr_devs = SCULL_P_NR_DEVS;	/* number of pipe devices */
+int scull_p_buffer =  SCULL_P_BUFFER;	/* buffer size */
+dev_t scull_p_devno;			/* Our first device number */
+
+module_param(scull_p_nr_devs, int, 0);	/* FIXME check perms */
+module_param(scull_p_buffer, int, 0);
+
+static struct scull_pipe *scull_p_devices;
+
+static int scull_p_fasync(int fd, struct file *filp, int mode);
+static int spacefree(struct scull_pipe *dev);
+/*
+ * Open and close
+ */
+
+
+static int scull_p_open(struct inode *inode, struct file *filp)
+{
+	struct scull_pipe *dev;
+
+	dev = container_of(inode->i_cdev, struct scull_pipe, cdev);
+	filp->private_data = dev;
+
+	if (down_interruptible(&dev->sem))
+		return -ERESTARTSYS;
+	if (!dev->buffer) {
+		/* allocate the buffer */
+		dev->buffer = kmalloc(scull_p_buffer, GFP_KERNEL);
+		if (!dev->buffer) {
+			up(&dev->sem);
+			return -ENOMEM;
+		}
+	}
+	dev->buffersize = scull_p_buffer;
+	dev->end = dev->buffer + dev->buffersize;
+	dev->rp = dev->wp = dev->buffer; /* rd and wr from the beginning */
+
+	/* use f_mode,not  f_flags: it's cleaner (fs/open.c tells why) */
+	if (filp->f_mode & FMODE_READ)
+		dev->nreaders++;
+	if (filp->f_mode & FMODE_WRITE)
+		dev->nwriters++;
+	up(&dev->sem);
+
+	return nonseekable_open(inode, filp);
+}
+
+
+
+static int scull_p_release(struct inode *inode, struct file *filp)
+{
+	struct scull_pipe *dev = filp->private_data;
+
+	/* remove this filp from the asynchronously notified filp's */
+	scull_p_fasync(-1, filp, 0);
+	down(&dev->sem);
+	if (filp->f_mode & FMODE_READ)
+		dev->nreaders--;
+	if (filp->f_mode & FMODE_WRITE)
+		dev->nwriters--;
+	if (dev->nreaders + dev->nwriters == 0) {
+		kfree(dev->buffer);
+		dev->buffer = NULL; /* the other fields are not checked on open */
+	}
+	up(&dev->sem);
+	return 0;
+}
+
+
+/*
+ * Data management: read and write
+ */
+
+static ssize_t scull_p_read (struct file *filp, char __user *buf, size_t count,
+                loff_t *f_pos)
+{
+	struct scull_pipe *dev = filp->private_data;
+
+	if (down_interruptible(&dev->sem))
+		return -ERESTARTSYS;
+
+	while (dev->rp == dev->wp) { /* nothing to read */
+		up(&dev->sem); /* release the lock */
+		if (filp->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+		PDEBUG("\"%s\" reading: going to sleep\n", current->comm);
+		if (wait_event_interruptible(dev->inq, (dev->rp != dev->wp)))
+			return -ERESTARTSYS; /* signal: tell the fs layer to handle it */
+		/* otherwise loop, but first reacquire the lock */
+		if (down_interruptible(&dev->sem))
+			return -ERESTARTSYS;
+	}
+	/* ok, data is there, return something */
+	if (dev->wp > dev->rp)
+		count = min(count, (size_t)(dev->wp - dev->rp));
+	else /* the write pointer has wrapped, return data up to dev->end */
+		count = min(count, (size_t)(dev->end - dev->rp));
+	if (copy_to_user(buf, dev->rp, count)) {
+		up (&dev->sem);
+		return -EFAULT;
+	}
+	dev->rp += count;
+	if (dev->rp == dev->end)
+		dev->rp = dev->buffer; /* wrapped */
+	up (&dev->sem);
+
+	/* finally, awake any writers and return */
+	wake_up_interruptible(&dev->outq);
+	PDEBUG("\"%s\" did read %li bytes\n",current->comm, (long)count);
+	return count;
+}
+
+/* Wait for space for writing; caller must hold device semaphore.  On
+ * error the semaphore will be released before returning. */
+static int scull_getwritespace(struct scull_pipe *dev, struct file *filp)
+{
+	while (spacefree(dev) == 0) { /* full */
+		DEFINE_WAIT(wait);
+		
+		up(&dev->sem);
+		if (filp->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+		PDEBUG("\"%s\" writing: going to sleep\n",current->comm);
+		prepare_to_wait(&dev->outq, &wait, TASK_INTERRUPTIBLE);
+		if (spacefree(dev) == 0)
+			schedule();
+		finish_wait(&dev->outq, &wait);
+		if (signal_pending(current))
+			return -ERESTARTSYS; /* signal: tell the fs layer to handle it */
+		if (down_interruptible(&dev->sem))
+			return -ERESTARTSYS;
+	}
+	return 0;
+}	
+
+/* How much space is free? */
+static int spacefree(struct scull_pipe *dev)
+{
+	if (dev->rp == dev->wp)
+		return dev->buffersize - 1;
+	return ((dev->rp + dev->buffersize - dev->wp) % dev->buffersize) - 1;
+}
+
+static ssize_t scull_p_write(struct file *filp, const char __user *buf, size_t count,
+                loff_t *f_pos)
+{
+	struct scull_pipe *dev = filp->private_data;
+	int result;
+
+	if (down_interruptible(&dev->sem))
+		return -ERESTARTSYS;
+
+	/* Make sure there's space to write */
+	result = scull_getwritespace(dev, filp);
+	if (result)
+		return result; /* scull_getwritespace called up(&dev->sem) */
+
+	/* ok, space is there, accept something */
+	count = min(count, (size_t)spacefree(dev));
+	if (dev->wp >= dev->rp)
+		count = min(count, (size_t)(dev->end - dev->wp)); /* to end-of-buf */
+	else /* the write pointer has wrapped, fill up to rp-1 */
+		count = min(count, (size_t)(dev->rp - dev->wp - 1));
+	PDEBUG("Going to accept %li bytes to %p from %p\n", (long)count, dev->wp, buf);
+	if (copy_from_user(dev->wp, buf, count)) {
+		up (&dev->sem);
+		return -EFAULT;
+	}
+	dev->wp += count;
+	if (dev->wp == dev->end)
+		dev->wp = dev->buffer; /* wrapped */
+	up(&dev->sem);
+
+	/* finally, awake any reader */
+	wake_up_interruptible(&dev->inq);  /* blocked in read() and select() */
+
+	/* and signal asynchronous readers, explained late in chapter 5 */
+	if (dev->async_queue)
+		kill_fasync(&dev->async_queue, SIGIO, POLL_IN);
+	PDEBUG("\"%s\" did write %li bytes\n",current->comm, (long)count);
+	return count;
+}
+
+static unsigned int scull_p_poll(struct file *filp, poll_table *wait)
+{
+	struct scull_pipe *dev = filp->private_data;
+	unsigned int mask = 0;
+
+	/*
+	 * The buffer is circular; it is considered full
+	 * if "wp" is right behind "rp" and empty if the
+	 * two are equal.
+	 */
+	down(&dev->sem);
+	poll_wait(filp, &dev->inq,  wait);
+	poll_wait(filp, &dev->outq, wait);
+	if (dev->rp != dev->wp)
+		mask |= POLLIN | POLLRDNORM;	/* readable */
+	if (spacefree(dev))
+		mask |= POLLOUT | POLLWRNORM;	/* writable */
+	up(&dev->sem);
+	return mask;
+}
+
+
+
+
+
+static int scull_p_fasync(int fd, struct file *filp, int mode)
+{
+	struct scull_pipe *dev = filp->private_data;
+
+	return fasync_helper(fd, filp, mode, &dev->async_queue);
+}
+
+
+
+/* FIXME this should use seq_file */
+#ifdef SCULL_DEBUG
+static void scullp_proc_offset(char *buf, char **start, off_t *offset, int *len)
+{
+	if (*offset == 0)
+		return;
+	if (*offset >= *len) {	/* Not there yet */
+		*offset -= *len;
+		*len = 0;
+	}
+	else {			/* We're into the interesting stuff now */
+		*start = buf + *offset;
+		*offset = 0;
+	}
+}
+
+
+static int scull_read_p_mem(char *buf, char **start, off_t offset, int count,
+		int *eof, void *data)
+{
+	int i, len;
+	struct scull_pipe *p;
+
+#define LIMIT (PAGE_SIZE-200)	/* don't print any more after this size */
+	*start = buf;
+	len = sprintf(buf, "Default buffersize is %i\n", scull_p_buffer);
+	for(i = 0; i<scull_p_nr_devs && len <= LIMIT; i++) {
+		p = &scull_p_devices[i];
+		if (down_interruptible(&p->sem))
+			return -ERESTARTSYS;
+		len += sprintf(buf+len, "\nDevice %i: %p\n", i, p);
+/*		len += sprintf(buf+len, "   Queues: %p %p\n", p->inq, p->outq);*/
+		len += sprintf(buf+len, "   Buffer: %p to %p (%i bytes)\n", p->buffer, p->end, p->buffersize);
+		len += sprintf(buf+len, "   rp %p   wp %p\n", p->rp, p->wp);
+		len += sprintf(buf+len, "   readers %i   writers %i\n", p->nreaders, p->nwriters);
+		up(&p->sem);
+		scullp_proc_offset(buf, start, &offset, &len);
+	}
+	*eof = (len <= LIMIT);
+	return len;
+}
+
+
+#endif
+
+
+
+/*
+ * The file operations for the pipe device
+ * (some are overlayed with bare scull)
+ */
+struct file_operations scull_pipe_fops = {
+	.owner =	THIS_MODULE,
+	.llseek =	no_llseek,
+	.read =		scull_p_read,
+	.write =	scull_p_write,
+	.poll =		scull_p_poll,
+	.ioctl =	scull_ioctl,
+	.open =		scull_p_open,
+	.release =	scull_p_release,
+	.fasync =	scull_p_fasync,
+};
+
+
+/*
+ * Set up a cdev entry.
+ */
+static void scull_p_setup_cdev(struct scull_pipe *dev, int index)
+{
+	int err, devno = scull_p_devno + index;
+    
+	cdev_init(&dev->cdev, &scull_pipe_fops);
+	dev->cdev.owner = THIS_MODULE;
+	err = cdev_add (&dev->cdev, devno, 1);
+	/* Fail gracefully if need be */
+	if (err)
+		printk(KERN_NOTICE "Error %d adding scullpipe%d", err, index);
+}
+
+ 
+
+/*
+ * Initialize the pipe devs; return how many we did.
+ */
+int scull_p_init(dev_t firstdev)
+{
+	int i, result;
+
+	result = register_chrdev_region(firstdev, scull_p_nr_devs, "scullp");
+	if (result < 0) {
+		printk(KERN_NOTICE "Unable to get scullp region, error %d\n", result);
+		return 0;
+	}
+	scull_p_devno = firstdev;
+	scull_p_devices = kmalloc(scull_p_nr_devs * sizeof(struct scull_pipe), GFP_KERNEL);
+	if (scull_p_devices == NULL) {
+		unregister_chrdev_region(firstdev, scull_p_nr_devs);
+		return 0;
+	}
+	memset(scull_p_devices, 0, scull_p_nr_devs * sizeof(struct scull_pipe));
+	for (i = 0; i < scull_p_nr_devs; i++) {
+		init_waitqueue_head(&(scull_p_devices[i].inq));
+		init_waitqueue_head(&(scull_p_devices[i].outq));
+		init_MUTEX(&scull_p_devices[i].sem);
+		scull_p_setup_cdev(scull_p_devices + i, i);
+	}
+#ifdef SCULL_DEBUG
+	create_proc_read_entry("scullpipe", 0, NULL, scull_read_p_mem, NULL);
+#endif
+	return scull_p_nr_devs;
+}
+
+/*
+ * This is called by cleanup_module or on failure.
+ * It is required to never fail, even if nothing was initialized first
+ */
+void scull_p_cleanup(void)
+{
+	int i;
+
+#ifdef SCULL_DEBUG
+	remove_proc_entry("scullpipe", NULL);
+#endif
+
+	if (!scull_p_devices)
+		return; /* nothing else to release */
+
+	for (i = 0; i < scull_p_nr_devs; i++) {
+		cdev_del(&scull_p_devices[i].cdev);
+		kfree(scull_p_devices[i].buffer);
+	}
+	kfree(scull_p_devices);
+	unregister_chrdev_region(scull_p_devno, scull_p_nr_devs);
+	scull_p_devices = NULL; /* pedantic */
+}