* better

[mascara-docs.git] / i386 / linux-2.3.21 / mm / mmap.c

/*
 *      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 <asm/uaccess.h>
#include <asm/pgtable.h>

/* 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
};

/* SLAB cache for vm_area_struct's. */
kmem_cache_t *vm_area_cachep;

int sysctl_overcommit_memory;

/* 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.
         */

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

        free = atomic_read(&buffermem) >> PAGE_SHIFT;
        free += atomic_read(&page_cache_size);
        free += nr_free_pages;
        free += nr_swap_pages;
        free -= (page_cache.min_percent + buffer_mem.min_percent + 2)*num_physpages/100; 
        return free > pages;
}

/* Remove one vm structure from the inode's i_mmap ring. */
static inline void remove_shared_vm_struct(struct vm_area_struct *vma)
{
        struct file * file = vma->vm_file;

        if (file) {
                if (vma->vm_flags & VM_DENYWRITE)
                        atomic_inc(&file->f_dentry->d_inode->i_writecount);
                spin_lock(&file->f_dentry->d_inode->i_shared_lock);
                if(vma->vm_next_share)
                        vma->vm_next_share->vm_pprev_share = vma->vm_pprev_share;
                *vma->vm_pprev_share = vma->vm_next_share;
                spin_unlock(&file->f_dentry->d_inode->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(&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(newbrk, oldbrk-newbrk))
                        goto set_brk;
                goto out;
        }

        /* Check against rlimit and stack.. */
        rlim = current->rlim[RLIMIT_DATA].rlim_cur;
        if (rlim < RLIM_INFINITY && brk - mm->end_code > 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(&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 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
}

unsigned long do_mmap(struct file * file, unsigned long addr, unsigned long len,
        unsigned long prot, unsigned long flags, unsigned long off)
{
        struct mm_struct * mm = current->mm;
        struct vm_area_struct * vma;
        int error;

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

        if ((len = PAGE_ALIGN(len)) == 0)
                return addr;

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

        if (off & ~PAGE_MASK)
                return -EINVAL;

        /* offset overflow? */
        if (off + len < off)
                return -EINVAL;

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

        /* 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;
        }

        /* 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.
         */
        if (file != NULL) {
                switch (flags & MAP_TYPE) {
                case MAP_SHARED:
                        if ((prot & PROT_WRITE) && !(file->f_mode & 2))
                                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 & 2))
                                return -EACCES;

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

                        /* fall through */
                case MAP_PRIVATE:
                        if (!(file->f_mode & 1))
                                return -EACCES;
                        break;

                default:
                        return -EINVAL;
                }
        } else if ((flags & MAP_TYPE) != MAP_PRIVATE)
                return -EINVAL;

        /* Obtain the address to map to. we verify (or select) it and ensure
         * that it represents a valid section of the address space.
         */
        if (flags & MAP_FIXED) {
                if (addr & ~PAGE_MASK)
                        return -EINVAL;
        } else {
                addr = get_unmapped_area(addr, len);
                if (!addr)
                        return -ENOMEM;
        }

        /* 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(prot,flags) | mm->def_flags;

        if (file) {
                if (file->f_mode & 1)
                        vma->vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
                if (flags & MAP_SHARED) {
                        vma->vm_flags |= VM_SHARED | VM_MAYSHARE;

                        /* This looks strange, but when we don't have the file open
                         * for writing, we can demote the shared mapping to a simpler
                         * private mapping. That also takes care of a security hole
                         * with ptrace() writing to a shared mapping without write
                         * permissions.
                         *
                         * We leave the VM_MAYSHARE bit on, just to get correct output
                         * from /proc/xxx/maps..
                         */
                        if (!(file->f_mode & 2))
                                vma->vm_flags &= ~(VM_MAYWRITE | VM_SHARED);
                }
        } else
                vma->vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
        vma->vm_page_prot = protection_map[vma->vm_flags & 0x0f];
        vma->vm_ops = NULL;
        vma->vm_offset = off;
        vma->vm_file = NULL;
        vma->vm_private_data = NULL;

        /* Clear old maps */
        error = -ENOMEM;
        if (do_munmap(addr, len))
                goto free_vma;

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

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

        if (file) {
                int correct_wcount = 0;
                if (vma->vm_flags & VM_DENYWRITE) {
                        if (atomic_read(&file->f_dentry->d_inode->i_writecount) > 0) {
                                error = -ETXTBSY;
                                goto free_vma;
                        }
                        /* f_op->mmap might possibly sleep
                         * (generic_file_mmap doesn't, but other code
                         * might). In any case, this takes care of any
                         * race that this might cause.
                         */
                        atomic_dec(&file->f_dentry->d_inode->i_writecount);
                        correct_wcount = 1;
                }
                error = file->f_op->mmap(file, vma);
                /* Fix up the count if necessary, then check for an error */
                if (correct_wcount)
                        atomic_inc(&file->f_dentry->d_inode->i_writecount);
                if (error)
                        goto unmap_and_free_vma;
                vma->vm_file = file;
                get_file(file);
        }

        /*
         * merge_segments may merge our vma, so we can't refer to it
         * after the call.  Save the values we need now ...
         */
        flags = vma->vm_flags;
        addr = vma->vm_start; /* can addr have changed?? */
        insert_vm_struct(mm, vma);
        merge_segments(mm, vma->vm_start, vma->vm_end);
        
        mm->total_vm += len >> PAGE_SHIFT;
        if (flags & VM_LOCKED) {
                mm->locked_vm += len >> PAGE_SHIFT;
                make_pages_present(addr, addr + len);
        }
        return addr;

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

/* Get an address range which is currently unmapped.
 * For mmap() without MAP_FIXED and shmat() with addr=0.
 * Return value 0 means ENOMEM.
 */
unsigned long get_unmapped_area(unsigned long addr, unsigned long len)
{
        struct vm_area_struct * vmm;

        if (len > TASK_SIZE)
                return 0;
        if (!addr)
                addr = TASK_UNMAPPED_BASE;
        addr = PAGE_ALIGN(addr);

        for (vmm = find_vma(current->mm, addr); ; vmm = vmm->vm_next) {
                /* At this point:  (!vmm || addr < vmm->vm_end). */
                if (TASK_SIZE - len < addr)
                        return 0;
                if (!vmm || addr + len <= vmm->vm_start)
                        return addr;
                addr = vmm->vm_end;
        }
}

#define vm_avl_empty    (struct vm_area_struct *) NULL

#include "mmap_avl.c"

/* 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)) {
                        if (!mm->mmap_avl) {
                                /* Go through the linear list. */
                                vma = mm->mmap;
                                while (vma && vma->vm_end <= addr)
                                        vma = vma->vm_next;
                        } else {
                                /* Then go through the AVL tree quickly. */
                                struct vm_area_struct * tree = mm->mmap_avl;
                                vma = NULL;
                                for (;;) {
                                        if (tree == vm_avl_empty)
                                                break;
                                        if (tree->vm_end > addr) {
                                                vma = tree;
                                                if (tree->vm_start <= addr)
                                                        break;
                                                tree = tree->vm_avl_left;
                                        } else
                                                tree = tree->vm_avl_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) {
                if (!mm->mmap_avl) {
                        /* Go through the linear list. */
                        struct vm_area_struct * prev = NULL;
                        struct vm_area_struct * vma = mm->mmap;
                        while (vma && vma->vm_end <= addr) {
                                prev = vma;
                                vma = vma->vm_next;
                        }
                        *pprev = prev;
                        return vma;
                } else {
                        /* Go through the AVL tree quickly. */
                        struct vm_area_struct * vma = NULL;
                        struct vm_area_struct * last_turn_right = NULL;
                        struct vm_area_struct * prev = NULL;
                        struct vm_area_struct * tree = mm->mmap_avl;
                        for (;;) {
                                if (tree == vm_avl_empty)
                                        break;
                                if (tree->vm_end > addr) {
                                        vma = tree;
                                        prev = last_turn_right;
                                        if (tree->vm_start <= addr)
                                                break;
                                        tree = tree->vm_avl_left;
                                } else {
                                        last_turn_right = tree;
                                        tree = tree->vm_avl_right;
                                }
                        }
                        if (vma) {
                                if (vma->vm_avl_left != vm_avl_empty) {
                                        prev = vma->vm_avl_left;
                                        while (prev->vm_avl_right != vm_avl_empty)
                                                prev = prev->vm_avl_right;
                                }
                                if ((prev ? prev->vm_next : mm->mmap) != vma)
                                        printk("find_vma_prev: tree inconsistent with list\n");
                                *pprev = prev;
                                return vma;
                        }
                }
        }
        *pprev = NULL;
        return NULL;
}

struct vm_area_struct * find_extend_vma(struct task_struct * tsk, unsigned long addr)
{
        struct vm_area_struct * vma;
        unsigned long start;

        addr &= PAGE_MASK;
        vma = find_vma(tsk->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 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)
                area->vm_end = addr;
        else if (addr == area->vm_start) {
                area->vm_offset += (end - area->vm_start);
                area->vm_start = end;
        } 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_ops = area->vm_ops;
                mpnt->vm_offset = area->vm_offset + (end - area->vm_start);
                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 */
                insert_vm_struct(current->mm, mpnt);
        }

        insert_vm_struct(current->mm, 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) & PGDIR_MASK;

        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:
        first = first >> PGDIR_SHIFT;
        last = last >> PGDIR_SHIFT;
        if (last > first)
                clear_page_tables(mm, first, last-first);
}

/* 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(unsigned long addr, size_t len)
{
        struct mm_struct * mm;
        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.
         */
        mm = current->mm;
        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;
        for ( ; mpnt && mpnt->vm_start < addr+len; mpnt = *npp) {
                *npp = mpnt->vm_next;
                mpnt->vm_next = free;
                free = mpnt;
                if (mm->mmap_avl)
                        avl_remove(mpnt, &mm->mmap_avl);
        }

        /* 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.
         */
        while ((mpnt = free) != NULL) {
                unsigned long st, end, size;

                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;

                lock_kernel();
                if (mpnt->vm_ops && mpnt->vm_ops->unmap)
                        mpnt->vm_ops->unmap(mpnt, st, size);
                unlock_kernel();

                remove_shared_vm_struct(mpnt);
                mm->map_count--;

                flush_cache_range(mm, st, end);
                zap_page_range(mm, st, size);
                flush_tlb_range(mm, st, end);

                /*
                 * Fix the mapping, and free the old area if it wasn't reused.
                 */
                extra = unmap_fixup(mpnt, st, size, extra);
        }

        /* 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);

        mm->mmap_cache = NULL;  /* Kill the cache. */
        return 0;
}

asmlinkage long sys_munmap(unsigned long addr, size_t len)
{
        int ret;

        down(&current->mm->mmap_sem);
        ret = do_munmap(addr, len);
        up(&current->mm->mmap_sem);
        return ret;
}

/*
 *  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;
        unsigned long flags, retval;

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

        /*
         * 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;
        }

        /*
         * Clear old maps.  this also does some error checking for us
         */
        retval = do_munmap(addr, len);
        if (retval != 0)
                return retval;

        /* 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;

        /*
         * 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 = vm_flags(PROT_READ|PROT_WRITE|PROT_EXEC,
                                MAP_FIXED|MAP_PRIVATE) | mm->def_flags;

        vma->vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
        vma->vm_page_prot = protection_map[vma->vm_flags & 0x0f];
        vma->vm_ops = NULL;
        vma->vm_offset = 0;
        vma->vm_file = NULL;
        vma->vm_private_data = NULL;

        /*
         * merge_segments may merge our vma, so we can't refer to it
         * after the call.  Save the values we need now ...
         */
        flags = vma->vm_flags;
        addr = vma->vm_start;

        insert_vm_struct(mm, vma);
        merge_segments(mm, vma->vm_start, vma->vm_end);
        
        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 AVL tree corresponding to the VMA list. */
void build_mmap_avl(struct mm_struct * mm)
{
        struct vm_area_struct * vma;

        mm->mmap_avl = NULL;
        for (vma = mm->mmap; vma; vma = vma->vm_next)
                avl_insert(vma, &mm->mmap_avl);
}

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

        release_segments(mm);
        mpnt = mm->mmap;
        mm->mmap = mm->mmap_avl = mm->mmap_cache = NULL;
        mm->rss = 0;
        mm->total_vm = 0;
        mm->locked_vm = 0;
        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->unmap)
                                mpnt->vm_ops->unmap(mpnt, start, size);
                        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)
                printk("exit_mmap: map count is %d\n", mm->map_count);

        clear_page_tables(mm, 0, USER_PTRS_PER_PGD);
}

/* Insert vm structure into process list sorted by address
 * and into the inode's i_mmap ring.
 */
void insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vmp)
{
        struct vm_area_struct **pprev;
        struct file * file;

        if (!mm->mmap_avl) {
                pprev = &mm->mmap;
                while (*pprev && (*pprev)->vm_start <= vmp->vm_start)
                        pprev = &(*pprev)->vm_next;
        } else {
                struct vm_area_struct *prev, *next;
                avl_insert_neighbours(vmp, &mm->mmap_avl, &prev, &next);
                pprev = (prev ? &prev->vm_next : &mm->mmap);
                if (*pprev != next)
                        printk("insert_vm_struct: tree inconsistent with list\n");
        }
        vmp->vm_next = *pprev;
        *pprev = vmp;

        mm->map_count++;
        if (mm->map_count >= AVL_MIN_MAP_COUNT && !mm->mmap_avl)
                build_mmap_avl(mm);

        file = vmp->vm_file;
        if (file) {
                struct inode * inode = file->f_dentry->d_inode;
                if (vmp->vm_flags & VM_DENYWRITE)
                        atomic_dec(&inode->i_writecount);
      
                /* insert vmp into inode's share list */
                spin_lock(&inode->i_shared_lock);
                if((vmp->vm_next_share = inode->i_mmap) != NULL)
                        inode->i_mmap->vm_pprev_share = &vmp->vm_next_share;
                inode->i_mmap = vmp;
                vmp->vm_pprev_share = &inode->i_mmap;
                spin_unlock(&inode->i_shared_lock);
        }
}

/* Merge the list of memory segments if possible.
 * Redundant vm_area_structs are freed.
 * This assumes that the list is ordered by address.
 * We don't need to traverse the entire list, only those segments
 * which intersect or are adjacent to a given interval.
 *
 * We must already hold the mm semaphore when we get here..
 */
void merge_segments (struct mm_struct * mm, unsigned long start_addr, unsigned long end_addr)
{
        struct vm_area_struct *prev, *mpnt, *next, *prev1;

        mpnt = find_vma_prev(mm, start_addr, &prev1);
        if (!mpnt)
                return;

        if (prev1) {
                prev = prev1;
        } else {
                prev = mpnt;
                mpnt = mpnt->vm_next;
        }

        /* prev and mpnt cycle through the list, as long as
         * start_addr < mpnt->vm_end && prev->vm_start < end_addr
         */
        for ( ; mpnt && prev->vm_start < end_addr ; prev = mpnt, mpnt = next) {
                next = mpnt->vm_next;

                /* To share, we must have the same file, operations.. */
                if ((mpnt->vm_file != prev->vm_file)||
                    (mpnt->vm_private_data != prev->vm_private_data)    ||
                    (mpnt->vm_ops != prev->vm_ops)      ||
                    (mpnt->vm_flags != prev->vm_flags)  ||
                    (prev->vm_end != mpnt->vm_start))
                        continue;

                /*
                 * If we have a file or it's a shared memory area
                 * the offsets must be contiguous..
                 */
                if ((mpnt->vm_file != NULL) || (mpnt->vm_flags & VM_SHM)) {
                        unsigned long off = prev->vm_offset+prev->vm_end-prev->vm_start;
                        if (off != mpnt->vm_offset)
                                continue;
                }

                /* merge prev with mpnt and set up pointers so the new
                 * big segment can possibly merge with the next one.
                 * The old unused mpnt is freed.
                 */
                if (mm->mmap_avl)
                        avl_remove(mpnt, &mm->mmap_avl);
                prev->vm_end = mpnt->vm_end;
                prev->vm_next = mpnt->vm_next;
                if (mpnt->vm_ops && mpnt->vm_ops->close) {
                        mpnt->vm_offset += mpnt->vm_end - mpnt->vm_start;
                        mpnt->vm_start = mpnt->vm_end;
                        mpnt->vm_ops->close(mpnt);
                }
                mm->map_count--;
                remove_shared_vm_struct(mpnt);
                if (mpnt->vm_file)
                        fput(mpnt->vm_file);
                kmem_cache_free(vm_area_cachep, mpnt);
                mpnt = prev;
        }
        mm->mmap_cache = NULL;          /* Kill the cache. */
}

void __init vma_init(void)
{
        vm_area_cachep = kmem_cache_create("vm_area_struct",
                                           sizeof(struct vm_area_struct),
                                           0, SLAB_HWCACHE_ALIGN,
                                           NULL, NULL);
        if(!vm_area_cachep)
                panic("vma_init: Cannot alloc vm_area_struct cache.");

        mm_cachep = kmem_cache_create("mm_struct",
                                      sizeof(struct mm_struct),
                                      0, SLAB_HWCACHE_ALIGN,
                                      NULL, NULL);
        if(!mm_cachep)
                panic("vma_init: Cannot alloc mm_struct cache.");
}