/*  -*- C -*- * mmap.c -- memory mapping for the scullv 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. * * $Id: _mmap.c.in,v 1.21 2001/07/18 22:28:18 rubini Exp $ */#ifndef __KERNEL__#  define __KERNEL__#endif#ifndef MODULE#  define MODULE#endif#include <linux/config.h>#define __NO_VERSION__#include <linux/module.h>#include <linux/mm.h>     /* everything */#include <linux/errno.h>  /* error codes */#include <asm/pgtable.h>#include "scullv.h"        /* local definitions */#ifdef LINUX_20static struct mm_struct *init_mm_ptr;#define init_mm (*init_mm_ptr) /* to avoid ifdefs later */static void retrieve_init_mm_ptr(void){    struct task_struct *p;    for (p = current ; (p = p->next_task) != current ; )        if (p->pid == 0)            break;    init_mm_ptr = p->mm;}#endif/* * Given a VMA, get our device pointer from it. */static inline ScullV_Dev *scullv_vma_to_dev (struct vm_area_struct *vma){#if defined(LINUX_24)    return (ScullV_Dev *) vma->vm_private_data;#elif defined(LINUX_22)    struct inode *inode = INODE_FROM_F(vma->vm_file);     return scullv_devices + MINOR(inode->i_rdev);#else /* LINUX_20 */    return scullv_devices + MINOR(vma->vm_inode->i_rdev);#endif}/* * open and close: just keep track of how many times the device is * mapped, to avoid releasing it. */void scullv_vma_open(struct vm_area_struct *vma){    ScullV_Dev *dev = scullv_vma_to_dev(vma);    dev->vmas++;    MOD_INC_USE_COUNT;}void scullv_vma_close(struct vm_area_struct *vma){    ScullV_Dev *dev = scullv_vma_to_dev(vma);    dev->vmas--;    MOD_DEC_USE_COUNT;}/* * The nopage method: the core of the file. It retrieves the * page required from the scullv device and returns it to the * user. The count for the page must be incremented, because * it is automatically decremented at page unmap. * * For this reason, "order" must be zero. Otherwise, only the first * page has its count incremented, and the allocating module must * release it as a whole block. Therefore, it isn't possible to map * pages from a multipage block: when they are unmapped, their count * is individually decreased, and would drop to 0. */struct page *scullv_vma_nopage(struct vm_area_struct *vma,                                unsigned long address, int write){    unsigned long offset;    ScullV_Dev *ptr, *dev = scullv_vma_to_dev(vma);    struct page *page = NOPAGE_SIGBUS;    void *pageptr = NULL; /* default to "missing" */    pgd_t *pgd; pmd_t *pmd; pte_t *pte;    unsigned long lpage;    down(&dev->sem);    offset = (address - vma->vm_start) + VMA_OFFSET(vma);    if (offset >= dev->size) goto out; /* out of range */    /*     * Now retrieve the scullv device from the list,then the page.     * If the device has holes, the process receives a SIGBUS when     * accessing the hole.     */    offset >>= PAGE_SHIFT; /* offset is a number of pages */    for (ptr = dev; ptr && offset >= dev->qset;) {        ptr = ptr->next;        offset -= dev->qset;    }    if (ptr && ptr->data) pageptr = ptr->data[offset];    if (!pageptr) goto out; /* hole or end-of-file */    /*     * After scullv lookup, "page" is now the address of the page     * needed by the current process. Since it's a vmalloc address,     * first retrieve the unsigned long value to be looked up     * in page tables.     */    lpage = VMALLOC_VMADDR(pageptr);#ifdef LINUX_24						    spin_lock(&init_mm.page_table_lock);#endif  						    pgd = pgd_offset(&init_mm, lpage);    pmd = pmd_offset(pgd, lpage);    pte = pte_offset(pmd, lpage);#ifdef LINUX_24  					    page = pte_page(*pte);    spin_unlock(&init_mm.page_table_lock);#else  							    page = mem_map + MAP_NR(pte_page(*pte));  		#endif  						        /* got it, now increment the count */    get_page(page);out:    up(&dev->sem);    return page;}#ifndef LINUX_24unsigned long scullv_vma_nopage_old(struct vm_area_struct *vma,                unsigned long address, int write){    struct page *page = scullv_vma_nopage(vma, address, write);    if (page)#ifdef LINUX_20        return (page->map_nr << PAGE_SHIFT);#else  /* 2.2 */        return (unsigned long) __va ((page - mem_map) << PAGE_SHIFT);#endif    return 0;}#define scullv_vma_nopage scullv_vma_nopage_old /* for the ops table */#endif /* not 2.4 */struct vm_operations_struct scullv_vm_ops = {    open:     scullv_vma_open,    close:  scullv_vma_close,    nopage:   scullv_vma_nopage,};#ifndef LINUX_20int scullv_mmap(struct file *filp, struct vm_area_struct *vma){    struct inode *inode = INODE_FROM_F(filp);    if (VMA_OFFSET(vma) & (PAGE_SIZE-1))                        return -ENXIO; /* need aligned offsets */	    /* don't do anything here: "nopage" will fill the holes */    vma->vm_ops = &scullv_vm_ops;    vma->vm_flags |= VM_RESERVED;#ifdef LINUX_24					    vma->vm_private_data = scullv_devices + MINOR(inode->i_rdev);#else						    vma->vm_file = filp;			#endif						    scullv_vma_open(vma);    return 0;}#else /* LINUX_20 */int scullv_mmap(struct inode *inode, struct file *filp,                struct vm_area_struct *vma){    if (VMA_OFFSET(vma) & (PAGE_SIZE-1))        return -ENXIO; /* need aligned offsets */    /*     * A pointer to init_mm is needed to access page tables     */    if (!init_mm_ptr)        retrieve_init_mm_ptr();    /* don't do anything here: "nopage" will fill the holes */    vma->vm_ops = &scullv_vm_ops;    vma->vm_inode = inode;    inode->i_count++;    scullv_vma_open(vma);    return 0;}#endif /* LINUX_20 */