/*
 *      linux/mm/mmap.c
 *
 * Written by obz.
 */
#include <linux/slab.h>
#include <linux/shm.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/swapctl.h>
#include <linux/smp_lock.h>
#include <linux/init.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/personality.h>
#include <linux/mount.h>

#include <asm/uaccess.h>
#include <asm/pgalloc.h>

/*
 * WARNING: the debugging will use recursive algorithms so never enable this
 * unless you know what you are doing.
 */
#undef DEBUG_MM_RB

/* description of effects of mapping type and prot in current implementation.
 * this is due to the limited x86 page protection hardware.  The expected
 * behavior is in parens:
 *
 * map_type     prot
 *              PROT_NONE       PROT_READ       PROT_WRITE      PROT_EXEC
 * MAP_SHARED   r: (no) no      r: (yes) yes    r: (no) yes     r: (no) yes
 *              w: (no) no      w: (no) no      w: (yes) yes    w: (no) no
 *              x: (no) no      x: (no) yes     x: (no) yes     x: (yes) yes
 *              
 * MAP_PRIVATE  r: (no) no      r: (yes) yes    r: (no) yes     r: (no) yes
 *              w: (no) no      w: (no) no      w: (copy) copy  w: (no) no
 *              x: (no) no      x: (no) yes     x: (no) yes     x: (yes) yes
 *
 */
pgprot_t protection_map[16] = {
        __P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,
        __S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
};

int sysctl_overcommit_memory;
int max_map_count = DEFAULT_MAX_MAP_COUNT;

/* Check that a process has enough memory to allocate a
 * new virtual mapping.
 */
int vm_enough_memory(long pages)
{
        /* Stupid algorithm to decide if we have enough memory: while
         * simple, it hopefully works in most obvious cases.. Easy to
         * fool it, but this should catch most mistakes.
         */
        /* 23/11/98 NJC: Somewhat less stupid version of algorithm,
         * which tries to do "TheRightThing".  Instead of using half of
         * (buffers+cache), use the minimum values.  Allow an extra 2%
         * of num_physpages for safety margin.
         */

        unsigned long free;
        
        /* Sometimes we want to use more memory than we have. */
        if (sysctl_overcommit_memory)
            return 1;

        /* The page cache contains buffer pages these days.. */
        free = page_cache_size;
        free += nr_free_pages();
        free += nr_swap_pages;

        /*
         * This double-counts: the nrpages are both in the page-cache
         * and in the swapper space. At the same time, this compensates
         * for the swap-space over-allocation (ie "nr_swap_pages" being
         * too small.
         */
        free += swapper_space.nrpages;

        /*
         * The code below doesn't account for free space in the inode
         * and dentry slab cache, slab cache fragmentation, inodes and
         * dentries which will become freeable under VM load, etc.
         * Lets just hope all these (complex) factors balance out...
         */
        free += (dentry_stat.nr_unused * sizeof(struct dentry)) >> PAGE_SHIFT;
        free += (inodes_stat.nr_unused * sizeof(struct inode)) >> PAGE_SHIFT;

        return free > pages;
}

/* Remove one vm structure from the inode's i_mapping address space. */
static inline void __remove_shared_vm_struct(struct vm_area_struct *vma)
{
        struct file * file = vma->vm_file;

        if (file) {
                struct inode *inode = file->f_dentry->d_inode;
                if (vma->vm_flags & VM_DENYWRITE)
                        atomic_inc(&inode->i_writecount);
                if(vma->vm_next_share)
                        vma->vm_next_share->vm_pprev_share = vma->vm_pprev_share;
                *vma->vm_pprev_share = vma->vm_next_share;
        }
}

static inline void remove_shared_vm_struct(struct vm_area_struct *vma)
{
        lock_vma_mappings(vma);
        __remove_shared_vm_struct(vma);
        unlock_vma_mappings(vma);
}

void lock_vma_mappings(struct vm_area_struct *vma)
{
        struct address_space *mapping;

        mapping = NULL;
        if (vma->vm_file)
                mapping = vma->vm_file->f_dentry->d_inode->i_mapping;
        if (mapping)
                spin_lock(&mapping->i_shared_lock);
}

void unlock_vma_mappings(struct vm_area_struct *vma)
{
        struct address_space *mapping;

        mapping = NULL;
        if (vma->vm_file)
                mapping = vma->vm_file->f_dentry->d_inode->i_mapping;
        if (mapping)
                spin_unlock(&mapping->i_shared_lock);
}

/*
 *  sys_brk() for the most part doesn't need the global kernel
 *  lock, except when an application is doing something nasty
 *  like trying to un-brk an area that has already been mapped
 *  to a regular file.  in this case, the unmapping will need
 *  to invoke file system routines that need the global lock.
 */
asmlinkage unsigned long sys_brk(unsigned long brk)
{
        unsigned long rlim, retval;
        unsigned long newbrk, oldbrk;
        struct mm_struct *mm = current->mm;

        down_write(&mm->mmap_sem);

        if (brk < mm->end_code)
                goto out;
        newbrk = PAGE_ALIGN(brk);
        oldbrk = PAGE_ALIGN(mm->brk);
        if (oldbrk == newbrk)
                goto set_brk;

        /* Always allow shrinking brk. */
        if (brk <= mm->brk) {
                if (!do_munmap(mm, newbrk, oldbrk-newbrk))
                        goto set_brk;
                goto out;
        }

        /* Check against rlimit.. */
        rlim = current->rlim[RLIMIT_DATA].rlim_cur;
        if (rlim < RLIM_INFINITY && brk - mm->start_data > rlim)
                goto out;

        /* Check against existing mmap mappings. */
        if (find_vma_intersection(mm, oldbrk, newbrk+PAGE_SIZE))
                goto out;

        /* Check if we have enough memory.. */
        if (!vm_enough_memory((newbrk-oldbrk) >> PAGE_SHIFT))
                goto out;

        /* Ok, looks good - let it rip. */
        if (do_brk(oldbrk, newbrk-oldbrk) != oldbrk)
                goto out;
set_brk:
        mm->brk = brk;
out:
        retval = mm->brk;
        up_write(&mm->mmap_sem);
        return retval;
}

/* Combine the mmap "prot" and "flags" argument into one "vm_flags" used
 * internally. Essentially, translate the "PROT_xxx" and "MAP_xxx" bits
 * into "VM_xxx".
 */
static inline unsigned long calc_vm_flags(unsigned long prot, unsigned long flags)
{
#define _trans(x,bit1,bit2) \
((bit1==bit2)?(x&bit1):(x&bit1)?bit2:0)

        unsigned long prot_bits, flag_bits;
        prot_bits =
                _trans(prot, PROT_READ, VM_READ) |
                _trans(prot, PROT_WRITE, VM_WRITE) |
                _trans(prot, PROT_EXEC, VM_EXEC);
        flag_bits =
                _trans(flags, MAP_GROWSDOWN, VM_GROWSDOWN) |
                _trans(flags, MAP_DENYWRITE, VM_DENYWRITE) |
                _trans(flags, MAP_EXECUTABLE, VM_EXECUTABLE);
        return prot_bits | flag_bits;
#undef _trans
}

#ifdef DEBUG_MM_RB
static int browse_rb(rb_node_t * rb_node) {
        int i = 0;
        if (rb_node) {
                i++;
                i += browse_rb(rb_node->rb_left);
                i += browse_rb(rb_node->rb_right);
        }
        return i;
}

static void validate_mm(struct mm_struct * mm) {
        int bug = 0;
        int i = 0;
        struct vm_area_struct * tmp = mm->mmap;
        while (tmp) {
                tmp = tmp->vm_next;
                i++;
        }
        if (i != mm->map_count)
                printk("map_count %d vm_next %d\n", mm->map_count, i), bug = 1;
        i = browse_rb(mm->mm_rb.rb_node);
        if (i != mm->map_count)
                printk("map_count %d rb %d\n", mm->map_count, i), bug = 1;
        if (bug)
                BUG();
}
#else
#define validate_mm(mm) do { } while (0)
#endif

static struct vm_area_struct * find_vma_prepare(struct mm_struct * mm, unsigned long addr,
                                                struct vm_area_struct ** pprev,
                                                rb_node_t *** rb_link, rb_node_t ** rb_parent)
{
        struct vm_area_struct * vma;
        rb_node_t ** __rb_link, * __rb_parent, * rb_prev;

        __rb_link = &mm->mm_rb.rb_node;
        rb_prev = __rb_parent = NULL;
        vma = NULL;

        while (*__rb_link) {
                struct vm_area_struct *vma_tmp;

                __rb_parent = *__rb_link;
                vma_tmp = rb_entry(__rb_parent, struct vm_area_struct, vm_rb);

                if (vma_tmp->vm_end > addr) {
                        vma = vma_tmp;
                        if (vma_tmp->vm_start <= addr)
                                return vma;
                        __rb_link = &__rb_parent->rb_left;
                } else {
                        rb_prev = __rb_parent;
                        __rb_link = &__rb_parent->rb_right;
                }
        }

        *pprev = NULL;
        if (rb_prev)
                *pprev = rb_entry(rb_prev, struct vm_area_struct, vm_rb);
        *rb_link = __rb_link;
        *rb_parent = __rb_parent;
        return vma;
}

static inline void __vma_link_list(struct mm_struct * mm, struct vm_area_struct * vma, struct vm_area_struct * prev,
                                   rb_node_t * rb_parent)
{
        if (prev) {
                vma->vm_next = prev->vm_next;
                prev->vm_next = vma;
        } else {
                mm->mmap = vma;
                if (rb_parent)
                        vma->vm_next = rb_entry(rb_parent, struct vm_area_struct, vm_rb);
                else
                        vma->vm_next = NULL;
        }
}

static inline void __vma_link_rb(struct mm_struct * mm, struct vm_area_struct * vma,
                                 rb_node_t ** rb_link, rb_node_t * rb_parent)
{
        rb_link_node(&vma->vm_rb, rb_parent, rb_link);
        rb_insert_color(&vma->vm_rb, &mm->mm_rb);
}

static inline void __vma_link_file(struct vm_area_struct * vma)
{
        struct file * file;

        file = vma->vm_file;
        if (file) {
                struct inode * inode = file->f_dentry->d_inode;
                struct address_space *mapping = inode->i_mapping;
                struct vm_area_struct **head;

                if (vma->vm_flags & VM_DENYWRITE)
                        atomic_dec(&inode->i_writecount);

                head = &mapping->i_mmap;
                if (vma->vm_flags & VM_SHARED)
                        head = &mapping->i_mmap_shared;
      
                /* insert vma into inode's share list */
                if((vma->vm_next_share = *head) != NULL)
                        (*head)->vm_pprev_share = &vma->vm_next_share;
                *head = vma;
                vma->vm_pprev_share = head;
        }
}

static void __vma_link(struct mm_struct * mm, struct vm_area_struct * vma,  struct vm_area_struct * prev,
                       rb_node_t ** rb_link, rb_node_t * rb_parent)
{
        __vma_link_list(mm, vma, prev, rb_parent);
        __vma_link_rb(mm, vma, rb_link, rb_parent);
        __vma_link_file(vma);
}

static inline void vma_link(struct mm_struct * mm, struct vm_area_struct * vma, struct vm_area_struct * prev,
                            rb_node_t ** rb_link, rb_node_t * rb_parent)
{
        lock_vma_mappings(vma);
        spin_lock(&mm->page_table_lock);
        __vma_link(mm, vma, prev, rb_link, rb_parent);
        spin_unlock(&mm->page_table_lock);
        unlock_vma_mappings(vma);

        mm->map_count++;
        validate_mm(mm);
}

static int vma_merge(struct mm_struct * mm, struct vm_area_struct * prev,
                     rb_node_t * rb_parent, unsigned long addr, unsigned long end, unsigned long vm_flags)
{
        spinlock_t * lock = &mm->page_table_lock;
        if (!prev) {
                prev = rb_entry(rb_parent, struct vm_area_struct, vm_rb);
                goto merge_next;
        }
        if (prev->vm_end == addr && can_vma_merge(prev, vm_flags)) {
                struct vm_area_struct * next;

                spin_lock(lock);
                prev->vm_end = end;
                next = prev->vm_next;
                if (next && prev->vm_end == next->vm_start && can_vma_merge(next, vm_flags)) {
                        prev->vm_end = next->vm_end;
                        __vma_unlink(mm, next, prev);
                        spin_unlock(lock);

                        mm->map_count--;
                        kmem_cache_free(vm_area_cachep, next);
                        return 1;
                }
                spin_unlock(lock);
                return 1;
        }

        prev = prev->vm_next;
        if (prev) {
 merge_next:
                if (!can_vma_merge(prev, vm_flags))
                        return 0;
                if (end == prev->vm_start) {
                        spin_lock(lock);
                        prev->vm_start = addr;
                        spin_unlock(lock);
                        return 1;
                }
        }

        return 0;
}

unsigned long do_mmap_pgoff(struct file * file, unsigned long addr, unsigned long len,
        unsigned long prot, unsigned long flags, unsigned long pgoff)
{
        struct mm_struct * mm = current->mm;
        struct vm_area_struct * vma, * prev;
        unsigned int vm_flags;
        int correct_wcount = 0;
        int error;
        rb_node_t ** rb_link, * rb_parent;

        if (file) {
                if (!file->f_op || !file->f_op->mmap)
                        return -ENODEV;

                if ((prot & PROT_EXEC) && (file->f_vfsmnt->mnt_flags & MNT_NOEXEC))
                        return -EPERM;
        }

        if (!len)
                return addr;

        len = PAGE_ALIGN(len);

        if (len > TASK_SIZE || len == 0)
                return -EINVAL;

        /* offset overflow? */
        if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
                return -EINVAL;

        /* Too many mappings? */
        if (mm->map_count > max_map_count)
                return -ENOMEM;

        /* Obtain the address to map to. we verify (or select) it and ensure
         * that it represents a valid section of the address space.
         */
        addr = get_unmapped_area(file, addr, len, pgoff, flags);
        if (addr & ~PAGE_MASK)
                return addr;

        /* Do simple checking here so the lower-level routines won't have
         * to. we assume access permissions have been handled by the open
         * of the memory object, so we don't do any here.
         */
        vm_flags = calc_vm_flags(prot,flags) | mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;

        /* mlock MCL_FUTURE? */
        if (vm_flags & VM_LOCKED) {
                unsigned long locked = mm->locked_vm << PAGE_SHIFT;
                locked += len;
                if (locked > current->rlim[RLIMIT_MEMLOCK].rlim_cur)
                        return -EAGAIN;
        }

        if (file) {
                switch (flags & MAP_TYPE) {
                case MAP_SHARED:
                        if ((prot & PROT_WRITE) && !(file->f_mode & FMODE_WRITE))
                                return -EACCES;

                        /* Make sure we don't allow writing to an append-only file.. */
                        if (IS_APPEND(file->f_dentry->d_inode) && (file->f_mode & FMODE_WRITE))
                                return -EACCES;

                        /* make sure there are no mandatory locks on the file. */
                        if (locks_verify_locked(file->f_dentry->d_inode))
                                return -EAGAIN;

                        vm_flags |= VM_SHARED | VM_MAYSHARE;
                        if (!(file->f_mode & FMODE_WRITE))
                                vm_flags &= ~(VM_MAYWRITE | VM_SHARED);

                        /* fall through */
                case MAP_PRIVATE:
                        if (!(file->f_mode & FMODE_READ))
                                return -EACCES;
                        break;

                default:
                        return -EINVAL;
                }
        } else {
                vm_flags |= VM_SHARED | VM_MAYSHARE;
                switch (flags & MAP_TYPE) {
                default:
                        return -EINVAL;
                case MAP_PRIVATE:
                        vm_flags &= ~(VM_SHARED | VM_MAYSHARE);
                        /* fall through */
                case MAP_SHARED:
                        break;
                }
        }

        /* Clear old maps */
munmap_back:
        vma = find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
        if (vma && vma->vm_start < addr + len) {
                if (do_munmap(mm, addr, len))
                        return -ENOMEM;
                goto munmap_back;
        }

        /* Check against address space limit. */
        if ((mm->total_vm << PAGE_SHIFT) + len
            > current->rlim[RLIMIT_AS].rlim_cur)
                return -ENOMEM;

        /* Private writable mapping? Check memory availability.. */
        if ((vm_flags & (VM_SHARED | VM_WRITE)) == VM_WRITE &&
            !(flags & MAP_NORESERVE)                             &&
            !vm_enough_memory(len >> PAGE_SHIFT))
                return -ENOMEM;

        /* Can we just expand an old anonymous mapping? */
        if (!file && !(vm_flags & VM_SHARED) && rb_parent)
                if (vma_merge(mm, prev, rb_parent, addr, addr + len, vm_flags))
                        goto out;

        /* Determine the object being mapped and call the appropriate
         * specific mapper. the address has already been validated, but
         * not unmapped, but the maps are removed from the list.
         */
        vma = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
        if (!vma)
                return -ENOMEM;

        vma->vm_mm = mm;
        vma->vm_start = addr;
        vma->vm_end = addr + len;
        vma->vm_flags = vm_flags;
        vma->vm_page_prot = protection_map[vm_flags & 0x0f];
        vma->vm_ops = NULL;
        vma->vm_pgoff = pgoff;
        vma->vm_file = NULL;
        vma->vm_private_data = NULL;
        vma->vm_raend = 0;

        if (file) {
                error = -EINVAL;
                if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
                        goto free_vma;
                if (vm_flags & VM_DENYWRITE) {
                        error = deny_write_access(file);
                        if (error)
                                goto free_vma;
                        correct_wcount = 1;
                }
                vma->vm_file = file;
                get_file(file);
                error = file->f_op->mmap(file, vma);
                if (error)
                        goto unmap_and_free_vma;
        } else if (flags & MAP_SHARED) {
                error = shmem_zero_setup(vma);
                if (error)
                        goto free_vma;
        }

        /* Can addr have changed??
         *
         * Answer: Yes, several device drivers can do it in their
         *         f_op->mmap method. -DaveM
         */
        if (addr != vma->vm_start) {
                /*
                 * It is a bit too late to pretend changing the virtual
                 * area of the mapping, we just corrupted userspace
                 * in the do_munmap, so FIXME (not in 2.4 to avoid breaking
                 * the driver API).
                 */
                struct vm_area_struct * stale_vma;
                /* Since addr changed, we rely on the mmap op to prevent 
                 * collisions with existing vmas and just use find_vma_prepare 
                 * to update the tree pointers.
                 */
                addr = vma->vm_start;
                stale_vma = find_vma_prepare(mm, addr, &prev,
                                                &rb_link, &rb_parent);
                /*
                 * Make sure the lowlevel driver did its job right.
                 */
                if (unlikely(stale_vma && stale_vma->vm_start < vma->vm_end)) {
                        printk(KERN_ERR "buggy mmap operation: [<%p>]\n",
                                file ? file->f_op->mmap : NULL);
                        BUG();
                }
        }

        vma_link(mm, vma, prev, rb_link, rb_parent);
        if (correct_wcount)
                atomic_inc(&file->f_dentry->d_inode->i_writecount);

out:    
        mm->total_vm += len >> PAGE_SHIFT;
        if (vm_flags & VM_LOCKED) {
                mm->locked_vm += len >> PAGE_SHIFT;
                make_pages_present(addr, addr + len);
        }
        return addr;

unmap_and_free_vma:
        if (correct_wcount)
                atomic_inc(&file->f_dentry->d_inode->i_writecount);
        vma->vm_file = NULL;
        fput(file);

        /* Undo any partial mapping done by a device driver. */
        zap_page_range(mm, vma->vm_start, vma->vm_end - vma->vm_start);
free_vma:
        kmem_cache_free(vm_area_cachep, vma);
        return error;
}

/* Get an address range which is currently unmapped.
 * For shmat() with addr=0.
 *
 * Ugly calling convention alert:
 * Return value with the low bits set means error value,
 * ie
 *      if (ret & ~PAGE_MASK)
 *              error = ret;
 *
 * This function "knows" that -ENOMEM has the bits set.
 */
#ifndef HAVE_ARCH_UNMAPPED_AREA
static inline unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr, unsigned long len, unsigned long pgoff, unsigned long flags)
{
        struct vm_area_struct *vma;

        if (len > TASK_SIZE)
                return -ENOMEM;

        if (addr) {
                addr = PAGE_ALIGN(addr);
                vma = find_vma(current->mm, addr);
                if (TASK_SIZE - len >= addr &&
                    (!vma || addr + len <= vma->vm_start))
                        return addr;
        }
        addr = PAGE_ALIGN(TASK_UNMAPPED_BASE);

        for (vma = find_vma(current->mm, addr); ; vma = vma->vm_next) {
                /* At this point:  (!vma || addr < vma->vm_end). */
                if (TASK_SIZE - len < addr)
                        return -ENOMEM;
                if (!vma || addr + len <= vma->vm_start)
                        return addr;
                addr = vma->vm_end;
        }
}
#else
extern unsigned long arch_get_unmapped_area(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
#endif  

unsigned long get_unmapped_area(struct file *file, unsigned long addr, unsigned long len, unsigned long pgoff, unsigned long flags)
{
        if (flags & MAP_FIXED) {
                if (addr > TASK_SIZE - len || addr >= TASK_SIZE)
                        return -ENOMEM;
                if (addr & ~PAGE_MASK)
                        return -EINVAL;
                return addr;
        }

        if (file && file->f_op && file->f_op->get_unmapped_area)
                return file->f_op->get_unmapped_area(file, addr, len, pgoff, flags);

        return arch_get_unmapped_area(file, addr, len, pgoff, flags);
}

/* Look up the first VMA which satisfies  addr < vm_end,  NULL if none. */
struct vm_area_struct * find_vma(struct mm_struct * mm, unsigned long addr)
{
        struct vm_area_struct *vma = NULL;

        if (mm) {
                /* Check the cache first. */
                /* (Cache hit rate is typically around 35%.) */
                vma = mm->mmap_cache;
                if (!(vma && vma->vm_end > addr && vma->vm_start <= addr)) {
                        rb_node_t * rb_node;

                        rb_node = mm->mm_rb.rb_node;
                        vma = NULL;

                        while (rb_node) {
                                struct vm_area_struct * vma_tmp;

                                vma_tmp = rb_entry(rb_node, struct vm_area_struct, vm_rb);

                                if (vma_tmp->vm_end > addr) {
                                        vma = vma_tmp;
                                        if (vma_tmp->vm_start <= addr)
                                                break;
                                        rb_node = rb_node->rb_left;
                                } else
                                        rb_node = rb_node->rb_right;
                        }
                        if (vma)
                                mm->mmap_cache = vma;
                }
        }
        return vma;
}

/* Same as find_vma, but also return a pointer to the previous VMA in *pprev. */
struct vm_area_struct * find_vma_prev(struct mm_struct * mm, unsigned long addr,
                                      struct vm_area_struct **pprev)
{
        if (mm) {
                /* Go through the RB tree quickly. */
                struct vm_area_struct * vma;
                rb_node_t * rb_node, * rb_last_right, * rb_prev;
                
                rb_node = mm->mm_rb.rb_node;
                rb_last_right = rb_prev = NULL;
                vma = NULL;

                while (rb_node) {
                        struct vm_area_struct * vma_tmp;

                        vma_tmp = rb_entry(rb_node, struct vm_area_struct, vm_rb);

                        if (vma_tmp->vm_end > addr) {
                                vma = vma_tmp;
                                rb_prev = rb_last_right;
                                if (vma_tmp->vm_start <= addr)
                                        break;
                                rb_node = rb_node->rb_left;
                        } else {
                                rb_last_right = rb_node;
                                rb_node = rb_node->rb_right;
                        }
                }
                if (vma) {
                        if (vma->vm_rb.rb_left) {
                                rb_prev = vma->vm_rb.rb_left;
                                while (rb_prev->rb_right)
                                        rb_prev = rb_prev->rb_right;
                        }
                        *pprev = NULL;
                        if (rb_prev)
                                *pprev = rb_entry(rb_prev, struct vm_area_struct, vm_rb);
                        if ((rb_prev ? (*pprev)->vm_next : mm->mmap) != vma)
                                BUG();
                        return vma;
                }
        }
        *pprev = NULL;
        return NULL;
}

struct vm_area_struct * find_extend_vma(struct mm_struct * mm, unsigned long addr)
{
        struct vm_area_struct * vma;
        unsigned long start;

        addr &= PAGE_MASK;
        vma = find_vma(mm,addr);
        if (!vma)
                return NULL;
        if (vma->vm_start <= addr)
                return vma;
        if (!(vma->vm_flags & VM_GROWSDOWN))
                return NULL;
        start = vma->vm_start;
        if (expand_stack(vma, addr))
                return NULL;
        if (vma->vm_flags & VM_LOCKED) {
                make_pages_present(addr, start);
        }
        return vma;
}

/* Normal function to fix up a mapping
 * This function is the default for when an area has no specific
 * function.  This may be used as part of a more specific routine.
 * This function works out what part of an area is affected and
 * adjusts the mapping information.  Since the actual page
 * manipulation is done in do_mmap(), none need be done here,
 * though it would probably be more appropriate.
 *
 * By the time this function is called, the area struct has been
 * removed from the process mapping list, so it needs to be
 * reinserted if necessary.
 *
 * The 4 main cases are:
 *    Unmapping the whole area
 *    Unmapping from the start of the segment to a point in it
 *    Unmapping from an intermediate point to the end
 *    Unmapping between to intermediate points, making a hole.
 *
 * Case 4 involves the creation of 2 new areas, for each side of
 * the hole.  If possible, we reuse the existing area rather than
 * allocate a new one, and the return indicates whether the old
 * area was reused.
 */
static struct vm_area_struct * unmap_fixup(struct mm_struct *mm, 
        struct vm_area_struct *area, unsigned long addr, size_t len, 
        struct vm_area_struct *extra)
{
        struct vm_area_struct *mpnt;
        unsigned long end = addr + len;

        area->vm_mm->total_vm -= len >> PAGE_SHIFT;
        if (area->vm_flags & VM_LOCKED)
                area->vm_mm->locked_vm -= len >> PAGE_SHIFT;

        /* Unmapping the whole area. */
        if (addr == area->vm_start && end == area->vm_end) {
                if (area->vm_ops && area->vm_ops->close)
                        area->vm_ops->close(area);
                if (area->vm_file)
                        fput(area->vm_file);
                kmem_cache_free(vm_area_cachep, area);
                return extra;
        }

        /* Work out to one of the ends. */
        if (end == area->vm_end) {
                /*
                 * here area isn't visible to the semaphore-less readers
                 * so we don't need to update it under the spinlock.
                 */
                area->vm_end = addr;
                lock_vma_mappings(area);
                spin_lock(&mm->page_table_lock);
        } else if (addr == area->vm_start) {
                area->vm_pgoff += (end - area->vm_start) >> PAGE_SHIFT;
                /* same locking considerations of the above case */
                area->vm_start = end;
                lock_vma_mappings(area);
                spin_lock(&mm->page_table_lock);
        } else {
        /* Unmapping a hole: area->vm_start < addr <= end < area->vm_end */
                /* Add end mapping -- leave beginning for below */
                mpnt = extra;
                extra = NULL;

                mpnt->vm_mm = area->vm_mm;
                mpnt->vm_start = end;
                mpnt->vm_end = area->vm_end;
                mpnt->vm_page_prot = area->vm_page_prot;
                mpnt->vm_flags = area->vm_flags;
                mpnt->vm_raend = 0;
                mpnt->vm_ops = area->vm_ops;
                mpnt->vm_pgoff = area->vm_pgoff + ((end - area->vm_start) >> PAGE_SHIFT);
                mpnt->vm_file = area->vm_file;
                mpnt->vm_private_data = area->vm_private_data;
                if (mpnt->vm_file)
                        get_file(mpnt->vm_file);
                if (mpnt->vm_ops && mpnt->vm_ops->open)
                        mpnt->vm_ops->open(mpnt);
                area->vm_end = addr;    /* Truncate area */

                /* Because mpnt->vm_file == area->vm_file this locks
                 * things correctly.
                 */
                lock_vma_mappings(area);
                spin_lock(&mm->page_table_lock);
                __insert_vm_struct(mm, mpnt);
        }

        __insert_vm_struct(mm, area);
        spin_unlock(&mm->page_table_lock);
        unlock_vma_mappings(area);
        return extra;
}

/*
 * Try to free as many page directory entries as we can,
 * without having to work very hard at actually scanning
 * the page tables themselves.
 *
 * Right now we try to free page tables if we have a nice
 * PGDIR-aligned area that got free'd up. We could be more
 * granular if we want to, but this is fast and simple,
 * and covers the bad cases.
 *
 * "prev", if it exists, points to a vma before the one
 * we just free'd - but there's no telling how much before.
 */
static void free_pgtables(struct mm_struct * mm, struct vm_area_struct *prev,
        unsigned long start, unsigned long end)
{
        unsigned long first = start & PGDIR_MASK;
        unsigned long last = end + PGDIR_SIZE - 1;
        unsigned long start_index, end_index;

        if (!prev) {
                prev = mm->mmap;
                if (!prev)
                        goto no_mmaps;
                if (prev->vm_end > start) {
                        if (last > prev->vm_start)
                                last = prev->vm_start;
                        goto no_mmaps;
                }
        }
        for (;;) {
                struct vm_area_struct *next = prev->vm_next;

                if (next) {
                        if (next->vm_start < start) {
                                prev = next;
                                continue;
                        }
                        if (last > next->vm_start)
                                last = next->vm_start;
                }
                if (prev->vm_end > first)
                        first = prev->vm_end + PGDIR_SIZE - 1;
                break;
        }
no_mmaps:
        if (last < first)
                return;
        /*
         * If the PGD bits are not consecutive in the virtual address, the
         * old method of shifting the VA >> by PGDIR_SHIFT doesn't work.
         */
        start_index = pgd_index(first);
        end_index = pgd_index(last);
        if (end_index > start_index) {
                clear_page_tables(mm, start_index, end_index - start_index);
                flush_tlb_pgtables(mm, first & PGDIR_MASK, last & PGDIR_MASK);
        }
}

/* Munmap is split into 2 main parts -- this part which finds
 * what needs doing, and the areas themselves, which do the
 * work.  This now handles partial unmappings.
 * Jeremy Fitzhardine <jeremy@sw.oz.au>
 */
int do_munmap(struct mm_struct *mm, unsigned long addr, size_t len)
{
        struct vm_area_struct *mpnt, *prev, **npp, *free, *extra;

        if ((addr & ~PAGE_MASK) || addr >= TASK_SIZE || len > TASK_SIZE-addr)
                return -EINVAL;

        if ((len = PAGE_ALIGN(len)) == 0)
                return -EINVAL;

        /* Check if this memory area is ok - put it on the temporary
         * list if so..  The checks here are pretty simple --
         * every area affected in some way (by any overlap) is put
         * on the list.  If nothing is put on, nothing is affected.
         */
        mpnt = find_vma_prev(mm, addr, &prev);
        if (!mpnt)
                return 0;
        /* we have  addr < mpnt->vm_end  */

        if (mpnt->vm_start >= addr+len)
                return 0;

        /* If we'll make "hole", check the vm areas limit */
        if ((mpnt->vm_start < addr && mpnt->vm_end > addr+len)
            && mm->map_count >= max_map_count)
                return -ENOMEM;

        /*
         * We may need one additional vma to fix up the mappings ... 
         * and this is the last chance for an easy error exit.
         */
        extra = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
        if (!extra)
                return -ENOMEM;

        npp = (prev ? &prev->vm_next : &mm->mmap);
        free = NULL;
        spin_lock(&mm->page_table_lock);
        for ( ; mpnt && mpnt->vm_start < addr+len; mpnt = *npp) {
                *npp = mpnt->vm_next;
                mpnt->vm_next = free;
                free = mpnt;
                rb_erase(&mpnt->vm_rb, &mm->mm_rb);
        }
        mm->mmap_cache = NULL;  /* Kill the cache. */
        spin_unlock(&mm->page_table_lock);

        /* Ok - we have the memory areas we should free on the 'free' list,
         * so release them, and unmap the page range..
         * If the one of the segments is only being partially unmapped,
         * it will put new vm_area_struct(s) into the address space.
         * In that case we have to be careful with VM_DENYWRITE.
         */
        while ((mpnt = free) != NULL) {
                unsigned long st, end, size;
                struct file *file = NULL;

                free = free->vm_next;

                st = addr < mpnt->vm_start ? mpnt->vm_start : addr;
                end = addr+len;
                end = end > mpnt->vm_end ? mpnt->vm_end : end;
                size = end - st;

                if (mpnt->vm_flags & VM_DENYWRITE &&
                    (st != mpnt->vm_start || end != mpnt->vm_end) &&
                    (file = mpnt->vm_file) != NULL) {
                        atomic_dec(&file->f_dentry->d_inode->i_writecount);
                }
                remove_shared_vm_struct(mpnt);

                mm->map_count--;

                zap_page_range(mm, st, size);

                /*
                 * Fix the mapping, and free the old area if it wasn't reused.
                 */
                extra = unmap_fixup(mm, mpnt, st, size, extra);
                if (file)
                        atomic_inc(&file->f_dentry->d_inode->i_writecount);
        }
        validate_mm(mm);

        /* Release the extra vma struct if it wasn't used */
        if (extra)
                kmem_cache_free(vm_area_cachep, extra);

        free_pgtables(mm, prev, addr, addr+len);

        return 0;
}

asmlinkage long sys_munmap(unsigned long addr, size_t len)
{
        int ret;
        struct mm_struct *mm = current->mm;

        down_write(&mm->mmap_sem);
        ret = do_munmap(mm, addr, len);
        up_write(&mm->mmap_sem);
        return ret;
}


static inline void verify_mmap_write_lock_held(struct mm_struct *mm)
{
        if (down_read_trylock(&mm->mmap_sem)) {
                WARN_ON(1);
                up_read(&mm->mmap_sem);
        }
}

/*
 *  this is really a simplified "do_mmap".  it only handles
 *  anonymous maps.  eventually we may be able to do some
 *  brk-specific accounting here.
 */
unsigned long do_brk(unsigned long addr, unsigned long len)
{
        struct mm_struct * mm = current->mm;
        struct vm_area_struct * vma, * prev;
        unsigned long flags;
        rb_node_t ** rb_link, * rb_parent;

        len = PAGE_ALIGN(len);
        if (!len)
                return addr;

        if ((addr + len) > TASK_SIZE || (addr + len) < addr)
                return -EINVAL;

        /*
         * mlock MCL_FUTURE?
         */
        if (mm->def_flags & VM_LOCKED) {
                unsigned long locked = mm->locked_vm << PAGE_SHIFT;
                locked += len;
                if (locked > current->rlim[RLIMIT_MEMLOCK].rlim_cur)
                        return -EAGAIN;
        }

        /*
         * mm->mmap_sem is required to protect against another thread
         * changing the mappings while we sleep (on kmalloc for one).
         */
        verify_mmap_write_lock_held(mm);

        /*
         * Clear old maps.  this also does some error checking for us
         */
 munmap_back:
        vma = find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
        if (vma && vma->vm_start < addr + len) {
                if (do_munmap(mm, addr, len))
                        return -ENOMEM;
                goto munmap_back;
        }

        /* Check against address space limits *after* clearing old maps... */
        if ((mm->total_vm << PAGE_SHIFT) + len
            > current->rlim[RLIMIT_AS].rlim_cur)
                return -ENOMEM;

        if (mm->map_count > max_map_count)
                return -ENOMEM;

        if (!vm_enough_memory(len >> PAGE_SHIFT))
                return -ENOMEM;

        flags = VM_DATA_DEFAULT_FLAGS | mm->def_flags;

        /* Can we just expand an old anonymous mapping? */
        if (rb_parent && vma_merge(mm, prev, rb_parent, addr, addr + len, flags))
                goto out;

        /*
         * create a vma struct for an anonymous mapping
         */
        vma = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
        if (!vma)
                return -ENOMEM;

        vma->vm_mm = mm;
        vma->vm_start = addr;
        vma->vm_end = addr + len;
        vma->vm_flags = flags;
        vma->vm_page_prot = protection_map[flags & 0x0f];
        vma->vm_ops = NULL;
        vma->vm_pgoff = 0;
        vma->vm_file = NULL;
        vma->vm_private_data = NULL;

        vma_link(mm, vma, prev, rb_link, rb_parent);

out:
        mm->total_vm += len >> PAGE_SHIFT;
        if (flags & VM_LOCKED) {
                mm->locked_vm += len >> PAGE_SHIFT;
                make_pages_present(addr, addr + len);
        }
        return addr;
}

/* Build the RB tree corresponding to the VMA list. */
void build_mmap_rb(struct mm_struct * mm)
{
        struct vm_area_struct * vma;
        rb_node_t ** rb_link, * rb_parent;

        mm->mm_rb = RB_ROOT;
        rb_link = &mm->mm_rb.rb_node;
        rb_parent = NULL;
        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                __vma_link_rb(mm, vma, rb_link, rb_parent);
                rb_parent = &vma->vm_rb;
                rb_link = &rb_parent->rb_right;
        }
}

/* Release all mmaps. */
void exit_mmap(struct mm_struct * mm)
{
        struct vm_area_struct * mpnt;

        release_segments(mm);
        spin_lock(&mm->page_table_lock);
        mpnt = mm->mmap;
        mm->mmap = mm->mmap_cache = NULL;
        mm->mm_rb = RB_ROOT;
        mm->rss = 0;
        spin_unlock(&mm->page_table_lock);
        mm->total_vm = 0;
        mm->locked_vm = 0;

        flush_cache_mm(mm);
        while (mpnt) {
                struct vm_area_struct * next = mpnt->vm_next;
                unsigned long start = mpnt->vm_start;
                unsigned long end = mpnt->vm_end;
                unsigned long size = end - start;

                if (mpnt->vm_ops) {
                        if (mpnt->vm_ops->close)
                                mpnt->vm_ops->close(mpnt);
                }
                mm->map_count--;
                remove_shared_vm_struct(mpnt);
                zap_page_range(mm, start, size);
                if (mpnt->vm_file)
                        fput(mpnt->vm_file);
                kmem_cache_free(vm_area_cachep, mpnt);
                mpnt = next;
        }

        /* This is just debugging */
        if (mm->map_count)
                BUG();

        clear_page_tables(mm, FIRST_USER_PGD_NR, USER_PTRS_PER_PGD);

        flush_tlb_mm(mm);
}

/* Insert vm structure into process list sorted by address
 * and into the inode's i_mmap ring.  If vm_file is non-NULL
 * then the i_shared_lock must be held here.
 */
void __insert_vm_struct(struct mm_struct * mm, struct vm_area_struct * vma)
{
        struct vm_area_struct * __vma, * prev;
        rb_node_t ** rb_link, * rb_parent;

        __vma = find_vma_prepare(mm, vma->vm_start, &prev, &rb_link, &rb_parent);
        if (__vma && __vma->vm_start < vma->vm_end)
                BUG();
        __vma_link(mm, vma, prev, rb_link, rb_parent);
        mm->map_count++;
        validate_mm(mm);
}

int insert_vm_struct(struct mm_struct * mm, struct vm_area_struct * vma)
{
        struct vm_area_struct * __vma, * prev;
        rb_node_t ** rb_link, * rb_parent;

        __vma = find_vma_prepare(mm, vma->vm_start, &prev, &rb_link, &rb_parent);
        if (__vma && __vma->vm_start < vma->vm_end)
                return -ENOMEM;
        vma_link(mm, vma, prev, rb_link, rb_parent);
        validate_mm(mm);
        return 0;
}