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-rw-r--r--scull/pipe.c396
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 */
+}
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