hugetlb: multiple hstates for multiple page sizes

[linux-2.6] / mm / nommu.c

/*
 *  linux/mm/nommu.c
 *
 *  Replacement code for mm functions to support CPU's that don't
 *  have any form of memory management unit (thus no virtual memory).
 *
 *  See Documentation/nommu-mmap.txt
 *
 *  Copyright (c) 2004-2005 David Howells <dhowells@redhat.com>
 *  Copyright (c) 2000-2003 David McCullough <davidm@snapgear.com>
 *  Copyright (c) 2000-2001 D Jeff Dionne <jeff@uClinux.org>
 *  Copyright (c) 2002      Greg Ungerer <gerg@snapgear.com>
 *  Copyright (c) 2007      Paul Mundt <lethal@linux-sh.org>
 */

#include <linux/module.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/swap.h>
#include <linux/file.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/ptrace.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/mount.h>
#include <linux/personality.h>
#include <linux/security.h>
#include <linux/syscalls.h>

#include <asm/uaccess.h>
#include <asm/tlb.h>
#include <asm/tlbflush.h>

void *high_memory;
struct page *mem_map;
unsigned long max_mapnr;
unsigned long num_physpages;
unsigned long askedalloc, realalloc;
atomic_long_t vm_committed_space = ATOMIC_LONG_INIT(0);
int sysctl_overcommit_memory = OVERCOMMIT_GUESS; /* heuristic overcommit */
int sysctl_overcommit_ratio = 50; /* default is 50% */
int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;
int heap_stack_gap = 0;

EXPORT_SYMBOL(mem_map);
EXPORT_SYMBOL(num_physpages);

/* list of shareable VMAs */
struct rb_root nommu_vma_tree = RB_ROOT;
DECLARE_RWSEM(nommu_vma_sem);

struct vm_operations_struct generic_file_vm_ops = {
};

/*
 * Handle all mappings that got truncated by a "truncate()"
 * system call.
 *
 * NOTE! We have to be ready to update the memory sharing
 * between the file and the memory map for a potential last
 * incomplete page.  Ugly, but necessary.
 */
int vmtruncate(struct inode *inode, loff_t offset)
{
        struct address_space *mapping = inode->i_mapping;
        unsigned long limit;

        if (inode->i_size < offset)
                goto do_expand;
        i_size_write(inode, offset);

        truncate_inode_pages(mapping, offset);
        goto out_truncate;

do_expand:
        limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
        if (limit != RLIM_INFINITY && offset > limit)
                goto out_sig;
        if (offset > inode->i_sb->s_maxbytes)
                goto out;
        i_size_write(inode, offset);

out_truncate:
        if (inode->i_op && inode->i_op->truncate)
                inode->i_op->truncate(inode);
        return 0;
out_sig:
        send_sig(SIGXFSZ, current, 0);
out:
        return -EFBIG;
}

EXPORT_SYMBOL(vmtruncate);

/*
 * Return the total memory allocated for this pointer, not
 * just what the caller asked for.
 *
 * Doesn't have to be accurate, i.e. may have races.
 */
unsigned int kobjsize(const void *objp)
{
        struct page *page;

        /*
         * If the object we have should not have ksize performed on it,
         * return size of 0
         */
        if (!objp || !virt_addr_valid(objp))
                return 0;

        page = virt_to_head_page(objp);

        /*
         * If the allocator sets PageSlab, we know the pointer came from
         * kmalloc().
         */
        if (PageSlab(page))
                return ksize(objp);

        /*
         * The ksize() function is only guaranteed to work for pointers
         * returned by kmalloc(). So handle arbitrary pointers here.
         */
        return PAGE_SIZE << compound_order(page);
}

/*
 * get a list of pages in an address range belonging to the specified process
 * and indicate the VMA that covers each page
 * - this is potentially dodgy as we may end incrementing the page count of a
 *   slab page or a secondary page from a compound page
 * - don't permit access to VMAs that don't support it, such as I/O mappings
 */
int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
        unsigned long start, int len, int write, int force,
        struct page **pages, struct vm_area_struct **vmas)
{
        struct vm_area_struct *vma;
        unsigned long vm_flags;
        int i;

        /* calculate required read or write permissions.
         * - if 'force' is set, we only require the "MAY" flags.
         */
        vm_flags  = write ? (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
        vm_flags &= force ? (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);

        for (i = 0; i < len; i++) {
                vma = find_vma(mm, start);
                if (!vma)
                        goto finish_or_fault;

                /* protect what we can, including chardevs */
                if (vma->vm_flags & (VM_IO | VM_PFNMAP) ||
                    !(vm_flags & vma->vm_flags))
                        goto finish_or_fault;

                if (pages) {
                        pages[i] = virt_to_page(start);
                        if (pages[i])
                                page_cache_get(pages[i]);
                }
                if (vmas)
                        vmas[i] = vma;
                start += PAGE_SIZE;
        }

        return i;

finish_or_fault:
        return i ? : -EFAULT;
}
EXPORT_SYMBOL(get_user_pages);

DEFINE_RWLOCK(vmlist_lock);
struct vm_struct *vmlist;

void vfree(const void *addr)
{
        kfree(addr);
}
EXPORT_SYMBOL(vfree);

void *__vmalloc(unsigned long size, gfp_t gfp_mask, pgprot_t prot)
{
        /*
         *  You can't specify __GFP_HIGHMEM with kmalloc() since kmalloc()
         * returns only a logical address.
         */
        return kmalloc(size, (gfp_mask | __GFP_COMP) & ~__GFP_HIGHMEM);
}
EXPORT_SYMBOL(__vmalloc);

void *vmalloc_user(unsigned long size)
{
        void *ret;

        ret = __vmalloc(size, GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO,
                        PAGE_KERNEL);
        if (ret) {
                struct vm_area_struct *vma;

                down_write(&current->mm->mmap_sem);
                vma = find_vma(current->mm, (unsigned long)ret);
                if (vma)
                        vma->vm_flags |= VM_USERMAP;
                up_write(&current->mm->mmap_sem);
        }

        return ret;
}
EXPORT_SYMBOL(vmalloc_user);

struct page *vmalloc_to_page(const void *addr)
{
        return virt_to_page(addr);
}
EXPORT_SYMBOL(vmalloc_to_page);

unsigned long vmalloc_to_pfn(const void *addr)
{
        return page_to_pfn(virt_to_page(addr));
}
EXPORT_SYMBOL(vmalloc_to_pfn);

long vread(char *buf, char *addr, unsigned long count)
{
        memcpy(buf, addr, count);
        return count;
}

long vwrite(char *buf, char *addr, unsigned long count)
{
        /* Don't allow overflow */
        if ((unsigned long) addr + count < count)
                count = -(unsigned long) addr;

        memcpy(addr, buf, count);
        return(count);
}

/*
 *      vmalloc  -  allocate virtually continguos memory
 *
 *      @size:          allocation size
 *
 *      Allocate enough pages to cover @size from the page level
 *      allocator and map them into continguos kernel virtual space.
 *
 *      For tight control over page level allocator and protection flags
 *      use __vmalloc() instead.
 */
void *vmalloc(unsigned long size)
{
       return __vmalloc(size, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL);
}
EXPORT_SYMBOL(vmalloc);

void *vmalloc_node(unsigned long size, int node)
{
        return vmalloc(size);
}
EXPORT_SYMBOL(vmalloc_node);

/**
 * vmalloc_32  -  allocate virtually contiguous memory (32bit addressable)
 *      @size:          allocation size
 *
 *      Allocate enough 32bit PA addressable pages to cover @size from the
 *      page level allocator and map them into continguos kernel virtual space.
 */
void *vmalloc_32(unsigned long size)
{
        return __vmalloc(size, GFP_KERNEL, PAGE_KERNEL);
}
EXPORT_SYMBOL(vmalloc_32);

/**
 * vmalloc_32_user - allocate zeroed virtually contiguous 32bit memory
 *      @size:          allocation size
 *
 * The resulting memory area is 32bit addressable and zeroed so it can be
 * mapped to userspace without leaking data.
 *
 * VM_USERMAP is set on the corresponding VMA so that subsequent calls to
 * remap_vmalloc_range() are permissible.
 */
void *vmalloc_32_user(unsigned long size)
{
        /*
         * We'll have to sort out the ZONE_DMA bits for 64-bit,
         * but for now this can simply use vmalloc_user() directly.
         */
        return vmalloc_user(size);
}
EXPORT_SYMBOL(vmalloc_32_user);

void *vmap(struct page **pages, unsigned int count, unsigned long flags, pgprot_t prot)
{
        BUG();
        return NULL;
}
EXPORT_SYMBOL(vmap);

void vunmap(const void *addr)
{
        BUG();
}
EXPORT_SYMBOL(vunmap);

/*
 * Implement a stub for vmalloc_sync_all() if the architecture chose not to
 * have one.
 */
void  __attribute__((weak)) vmalloc_sync_all(void)
{
}

int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
                   struct page *page)
{
        return -EINVAL;
}
EXPORT_SYMBOL(vm_insert_page);

/*
 *  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)
{
        struct mm_struct *mm = current->mm;

        if (brk < mm->start_brk || brk > mm->context.end_brk)
                return mm->brk;

        if (mm->brk == brk)
                return mm->brk;

        /*
         * Always allow shrinking brk
         */
        if (brk <= mm->brk) {
                mm->brk = brk;
                return brk;
        }

        /*
         * Ok, looks good - let it rip.
         */
        return mm->brk = brk;
}

#ifdef DEBUG
static void show_process_blocks(void)
{
        struct vm_list_struct *vml;

        printk("Process blocks %d:", current->pid);

        for (vml = &current->mm->context.vmlist; vml; vml = vml->next) {
                printk(" %p: %p", vml, vml->vma);
                if (vml->vma)
                        printk(" (%d @%lx #%d)",
                               kobjsize((void *) vml->vma->vm_start),
                               vml->vma->vm_start,
                               atomic_read(&vml->vma->vm_usage));
                printk(vml->next ? " ->" : ".\n");
        }
}
#endif /* DEBUG */

/*
 * add a VMA into a process's mm_struct in the appropriate place in the list
 * - should be called with mm->mmap_sem held writelocked
 */
static void add_vma_to_mm(struct mm_struct *mm, struct vm_list_struct *vml)
{
        struct vm_list_struct **ppv;

        for (ppv = &current->mm->context.vmlist; *ppv; ppv = &(*ppv)->next)
                if ((*ppv)->vma->vm_start > vml->vma->vm_start)
                        break;

        vml->next = *ppv;
        *ppv = vml;
}

/*
 * look up the first VMA in which addr resides, NULL if none
 * - should be called with mm->mmap_sem at least held readlocked
 */
struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
{
        struct vm_list_struct *loop, *vml;

        /* search the vm_start ordered list */
        vml = NULL;
        for (loop = mm->context.vmlist; loop; loop = loop->next) {
                if (loop->vma->vm_start > addr)
                        break;
                vml = loop;
        }

        if (vml && vml->vma->vm_end > addr)
                return vml->vma;

        return NULL;
}
EXPORT_SYMBOL(find_vma);

/*
 * find a VMA
 * - we don't extend stack VMAs under NOMMU conditions
 */
struct vm_area_struct *find_extend_vma(struct mm_struct *mm, unsigned long addr)
{
        return find_vma(mm, addr);
}

int expand_stack(struct vm_area_struct *vma, unsigned long address)
{
        return -ENOMEM;
}

/*
 * look up the first VMA exactly that exactly matches addr
 * - should be called with mm->mmap_sem at least held readlocked
 */
static inline struct vm_area_struct *find_vma_exact(struct mm_struct *mm,
                                                    unsigned long addr)
{
        struct vm_list_struct *vml;

        /* search the vm_start ordered list */
        for (vml = mm->context.vmlist; vml; vml = vml->next) {
                if (vml->vma->vm_start == addr)
                        return vml->vma;
                if (vml->vma->vm_start > addr)
                        break;
        }

        return NULL;
}

/*
 * find a VMA in the global tree
 */
static inline struct vm_area_struct *find_nommu_vma(unsigned long start)
{
        struct vm_area_struct *vma;
        struct rb_node *n = nommu_vma_tree.rb_node;

        while (n) {
                vma = rb_entry(n, struct vm_area_struct, vm_rb);

                if (start < vma->vm_start)
                        n = n->rb_left;
                else if (start > vma->vm_start)
                        n = n->rb_right;
                else
                        return vma;
        }

        return NULL;
}

/*
 * add a VMA in the global tree
 */
static void add_nommu_vma(struct vm_area_struct *vma)
{
        struct vm_area_struct *pvma;
        struct address_space *mapping;
        struct rb_node **p = &nommu_vma_tree.rb_node;
        struct rb_node *parent = NULL;

        /* add the VMA to the mapping */
        if (vma->vm_file) {
                mapping = vma->vm_file->f_mapping;

                flush_dcache_mmap_lock(mapping);
                vma_prio_tree_insert(vma, &mapping->i_mmap);
                flush_dcache_mmap_unlock(mapping);
        }

        /* add the VMA to the master list */
        while (*p) {
                parent = *p;
                pvma = rb_entry(parent, struct vm_area_struct, vm_rb);

                if (vma->vm_start < pvma->vm_start) {
                        p = &(*p)->rb_left;
                }
                else if (vma->vm_start > pvma->vm_start) {
                        p = &(*p)->rb_right;
                }
                else {
                        /* mappings are at the same address - this can only
                         * happen for shared-mem chardevs and shared file
                         * mappings backed by ramfs/tmpfs */
                        BUG_ON(!(pvma->vm_flags & VM_SHARED));

                        if (vma < pvma)
                                p = &(*p)->rb_left;
                        else if (vma > pvma)
                                p = &(*p)->rb_right;
                        else
                                BUG();
                }
        }

        rb_link_node(&vma->vm_rb, parent, p);
        rb_insert_color(&vma->vm_rb, &nommu_vma_tree);
}

/*
 * delete a VMA from the global list
 */
static void delete_nommu_vma(struct vm_area_struct *vma)
{
        struct address_space *mapping;

        /* remove the VMA from the mapping */
        if (vma->vm_file) {
                mapping = vma->vm_file->f_mapping;

                flush_dcache_mmap_lock(mapping);
                vma_prio_tree_remove(vma, &mapping->i_mmap);
                flush_dcache_mmap_unlock(mapping);
        }

        /* remove from the master list */
        rb_erase(&vma->vm_rb, &nommu_vma_tree);
}

/*
 * determine whether a mapping should be permitted and, if so, what sort of
 * mapping we're capable of supporting
 */
static int validate_mmap_request(struct file *file,
                                 unsigned long addr,
                                 unsigned long len,
                                 unsigned long prot,
                                 unsigned long flags,
                                 unsigned long pgoff,
                                 unsigned long *_capabilities)
{
        unsigned long capabilities;
        unsigned long reqprot = prot;
        int ret;

        /* do the simple checks first */
        if (flags & MAP_FIXED || addr) {
                printk(KERN_DEBUG
                       "%d: Can't do fixed-address/overlay mmap of RAM\n",
                       current->pid);
                return -EINVAL;
        }

        if ((flags & MAP_TYPE) != MAP_PRIVATE &&
            (flags & MAP_TYPE) != MAP_SHARED)
                return -EINVAL;

        if (!len)
                return -EINVAL;

        /* Careful about overflows.. */
        len = PAGE_ALIGN(len);
        if (!len || len > TASK_SIZE)
                return -ENOMEM;

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

        if (file) {
                /* validate file mapping requests */
                struct address_space *mapping;

                /* files must support mmap */
                if (!file->f_op || !file->f_op->mmap)
                        return -ENODEV;

                /* work out if what we've got could possibly be shared
                 * - we support chardevs that provide their own "memory"
                 * - we support files/blockdevs that are memory backed
                 */
                mapping = file->f_mapping;
                if (!mapping)
                        mapping = file->f_path.dentry->d_inode->i_mapping;

                capabilities = 0;
                if (mapping && mapping->backing_dev_info)
                        capabilities = mapping->backing_dev_info->capabilities;

                if (!capabilities) {
                        /* no explicit capabilities set, so assume some
                         * defaults */
                        switch (file->f_path.dentry->d_inode->i_mode & S_IFMT) {
                        case S_IFREG:
                        case S_IFBLK:
                                capabilities = BDI_CAP_MAP_COPY;
                                break;

                        case S_IFCHR:
                                capabilities =
                                        BDI_CAP_MAP_DIRECT |
                                        BDI_CAP_READ_MAP |
                                        BDI_CAP_WRITE_MAP;
                                break;

                        default:
                                return -EINVAL;
                        }
                }

                /* eliminate any capabilities that we can't support on this
                 * device */
                if (!file->f_op->get_unmapped_area)
                        capabilities &= ~BDI_CAP_MAP_DIRECT;
                if (!file->f_op->read)
                        capabilities &= ~BDI_CAP_MAP_COPY;

                if (flags & MAP_SHARED) {
                        /* do checks for writing, appending and locking */
                        if ((prot & PROT_WRITE) &&
                            !(file->f_mode & FMODE_WRITE))
                                return -EACCES;

                        if (IS_APPEND(file->f_path.dentry->d_inode) &&
                            (file->f_mode & FMODE_WRITE))
                                return -EACCES;

                        if (locks_verify_locked(file->f_path.dentry->d_inode))
                                return -EAGAIN;

                        if (!(capabilities & BDI_CAP_MAP_DIRECT))
                                return -ENODEV;

                        if (((prot & PROT_READ)  && !(capabilities & BDI_CAP_READ_MAP))  ||
                            ((prot & PROT_WRITE) && !(capabilities & BDI_CAP_WRITE_MAP)) ||
                            ((prot & PROT_EXEC)  && !(capabilities & BDI_CAP_EXEC_MAP))
                            ) {
                                printk("MAP_SHARED not completely supported on !MMU\n");
                                return -EINVAL;
                        }

                        /* we mustn't privatise shared mappings */
                        capabilities &= ~BDI_CAP_MAP_COPY;
                }
                else {
                        /* we're going to read the file into private memory we
                         * allocate */
                        if (!(capabilities & BDI_CAP_MAP_COPY))
                                return -ENODEV;

                        /* we don't permit a private writable mapping to be
                         * shared with the backing device */
                        if (prot & PROT_WRITE)
                                capabilities &= ~BDI_CAP_MAP_DIRECT;
                }

                /* handle executable mappings and implied executable
                 * mappings */
                if (file->f_path.mnt->mnt_flags & MNT_NOEXEC) {
                        if (prot & PROT_EXEC)
                                return -EPERM;
                }
                else if ((prot & PROT_READ) && !(prot & PROT_EXEC)) {
                        /* handle implication of PROT_EXEC by PROT_READ */
                        if (current->personality & READ_IMPLIES_EXEC) {
                                if (capabilities & BDI_CAP_EXEC_MAP)
                                        prot |= PROT_EXEC;
                        }
                }
                else if ((prot & PROT_READ) &&
                         (prot & PROT_EXEC) &&
                         !(capabilities & BDI_CAP_EXEC_MAP)
                         ) {
                        /* backing file is not executable, try to copy */
                        capabilities &= ~BDI_CAP_MAP_DIRECT;
                }
        }
        else {
                /* anonymous mappings are always memory backed and can be
                 * privately mapped
                 */
                capabilities = BDI_CAP_MAP_COPY;

                /* handle PROT_EXEC implication by PROT_READ */
                if ((prot & PROT_READ) &&
                    (current->personality & READ_IMPLIES_EXEC))
                        prot |= PROT_EXEC;
        }

        /* allow the security API to have its say */
        ret = security_file_mmap(file, reqprot, prot, flags, addr, 0);
        if (ret < 0)
                return ret;

        /* looks okay */
        *_capabilities = capabilities;
        return 0;
}

/*
 * we've determined that we can make the mapping, now translate what we
 * now know into VMA flags
 */
static unsigned long determine_vm_flags(struct file *file,
                                        unsigned long prot,
                                        unsigned long flags,
                                        unsigned long capabilities)
{
        unsigned long vm_flags;

        vm_flags = calc_vm_prot_bits(prot) | calc_vm_flag_bits(flags);
        vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
        /* vm_flags |= mm->def_flags; */

        if (!(capabilities & BDI_CAP_MAP_DIRECT)) {
                /* attempt to share read-only copies of mapped file chunks */
                if (file && !(prot & PROT_WRITE))
                        vm_flags |= VM_MAYSHARE;
        }
        else {
                /* overlay a shareable mapping on the backing device or inode
                 * if possible - used for chardevs, ramfs/tmpfs/shmfs and
                 * romfs/cramfs */
                if (flags & MAP_SHARED)
                        vm_flags |= VM_MAYSHARE | VM_SHARED;
                else if ((((vm_flags & capabilities) ^ vm_flags) & BDI_CAP_VMFLAGS) == 0)
                        vm_flags |= VM_MAYSHARE;
        }

        /* refuse to let anyone share private mappings with this process if
         * it's being traced - otherwise breakpoints set in it may interfere
         * with another untraced process
         */
        if ((flags & MAP_PRIVATE) && (current->ptrace & PT_PTRACED))
                vm_flags &= ~VM_MAYSHARE;

        return vm_flags;
}

/*
 * set up a shared mapping on a file
 */
static int do_mmap_shared_file(struct vm_area_struct *vma, unsigned long len)
{
        int ret;

        ret = vma->vm_file->f_op->mmap(vma->vm_file, vma);
        if (ret != -ENOSYS)
                return ret;

        /* getting an ENOSYS error indicates that direct mmap isn't
         * possible (as opposed to tried but failed) so we'll fall
         * through to making a private copy of the data and mapping
         * that if we can */
        return -ENODEV;
}

/*
 * set up a private mapping or an anonymous shared mapping
 */
static int do_mmap_private(struct vm_area_struct *vma, unsigned long len)
{
        void *base;
        int ret;

        /* invoke the file's mapping function so that it can keep track of
         * shared mappings on devices or memory
         * - VM_MAYSHARE will be set if it may attempt to share
         */
        if (vma->vm_file) {
                ret = vma->vm_file->f_op->mmap(vma->vm_file, vma);
                if (ret != -ENOSYS) {
                        /* shouldn't return success if we're not sharing */
                        BUG_ON(ret == 0 && !(vma->vm_flags & VM_MAYSHARE));
                        return ret; /* success or a real error */
                }

                /* getting an ENOSYS error indicates that direct mmap isn't
                 * possible (as opposed to tried but failed) so we'll try to
                 * make a private copy of the data and map that instead */
        }

        /* allocate some memory to hold the mapping
         * - note that this may not return a page-aligned address if the object
         *   we're allocating is smaller than a page
         */
        base = kmalloc(len, GFP_KERNEL|__GFP_COMP);
        if (!base)
                goto enomem;

        vma->vm_start = (unsigned long) base;
        vma->vm_end = vma->vm_start + len;
        vma->vm_flags |= VM_MAPPED_COPY;

#ifdef WARN_ON_SLACK
        if (len + WARN_ON_SLACK <= kobjsize(result))
                printk("Allocation of %lu bytes from process %d has %lu bytes of slack\n",
                       len, current->pid, kobjsize(result) - len);
#endif

        if (vma->vm_file) {
                /* read the contents of a file into the copy */
                mm_segment_t old_fs;
                loff_t fpos;

                fpos = vma->vm_pgoff;
                fpos <<= PAGE_SHIFT;

                old_fs = get_fs();
                set_fs(KERNEL_DS);
                ret = vma->vm_file->f_op->read(vma->vm_file, base, len, &fpos);
                set_fs(old_fs);

                if (ret < 0)
                        goto error_free;

                /* clear the last little bit */
                if (ret < len)
                        memset(base + ret, 0, len - ret);

        } else {
                /* if it's an anonymous mapping, then just clear it */
                memset(base, 0, len);
        }

        return 0;

error_free:
        kfree(base);
        vma->vm_start = 0;
        return ret;

enomem:
        printk("Allocation of length %lu from process %d failed\n",
               len, current->pid);
        show_free_areas();
        return -ENOMEM;
}

/*
 * handle mapping creation for uClinux
 */
unsigned long do_mmap_pgoff(struct file *file,
                            unsigned long addr,
                            unsigned long len,
                            unsigned long prot,
                            unsigned long flags,
                            unsigned long pgoff)
{
        struct vm_list_struct *vml = NULL;
        struct vm_area_struct *vma = NULL;
        struct rb_node *rb;
        unsigned long capabilities, vm_flags;
        void *result;
        int ret;

        if (!(flags & MAP_FIXED))
                addr = round_hint_to_min(addr);

        /* decide whether we should attempt the mapping, and if so what sort of
         * mapping */
        ret = validate_mmap_request(file, addr, len, prot, flags, pgoff,
                                    &capabilities);
        if (ret < 0)
                return ret;

        /* we've determined that we can make the mapping, now translate what we
         * now know into VMA flags */
        vm_flags = determine_vm_flags(file, prot, flags, capabilities);

        /* we're going to need to record the mapping if it works */
        vml = kzalloc(sizeof(struct vm_list_struct), GFP_KERNEL);
        if (!vml)
                goto error_getting_vml;

        down_write(&nommu_vma_sem);

        /* if we want to share, we need to check for VMAs created by other
         * mmap() calls that overlap with our proposed mapping
         * - we can only share with an exact match on most regular files
         * - shared mappings on character devices and memory backed files are
         *   permitted to overlap inexactly as far as we are concerned for in
         *   these cases, sharing is handled in the driver or filesystem rather
         *   than here
         */
        if (vm_flags & VM_MAYSHARE) {
                unsigned long pglen = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
                unsigned long vmpglen;

                /* suppress VMA sharing for shared regions */
                if (vm_flags & VM_SHARED &&
                    capabilities & BDI_CAP_MAP_DIRECT)
                        goto dont_share_VMAs;

                for (rb = rb_first(&nommu_vma_tree); rb; rb = rb_next(rb)) {
                        vma = rb_entry(rb, struct vm_area_struct, vm_rb);

                        if (!(vma->vm_flags & VM_MAYSHARE))
                                continue;

                        /* search for overlapping mappings on the same file */
                        if (vma->vm_file->f_path.dentry->d_inode != file->f_path.dentry->d_inode)
                                continue;

                        if (vma->vm_pgoff >= pgoff + pglen)
                                continue;

                        vmpglen = vma->vm_end - vma->vm_start + PAGE_SIZE - 1;
                        vmpglen >>= PAGE_SHIFT;
                        if (pgoff >= vma->vm_pgoff + vmpglen)
                                continue;

                        /* handle inexactly overlapping matches between mappings */
                        if (vma->vm_pgoff != pgoff || vmpglen != pglen) {
                                if (!(capabilities & BDI_CAP_MAP_DIRECT))
                                        goto sharing_violation;
                                continue;
                        }

                        /* we've found a VMA we can share */
                        atomic_inc(&vma->vm_usage);

                        vml->vma = vma;
                        result = (void *) vma->vm_start;
                        goto shared;
                }

        dont_share_VMAs:
                vma = NULL;

                /* obtain the address at which to make a shared mapping
                 * - this is the hook for quasi-memory character devices to
                 *   tell us the location of a shared mapping
                 */
                if (file && file->f_op->get_unmapped_area) {
                        addr = file->f_op->get_unmapped_area(file, addr, len,
                                                             pgoff, flags);
                        if (IS_ERR((void *) addr)) {
                                ret = addr;
                                if (ret != (unsigned long) -ENOSYS)
                                        goto error;

                                /* the driver refused to tell us where to site
                                 * the mapping so we'll have to attempt to copy
                                 * it */
                                ret = (unsigned long) -ENODEV;
                                if (!(capabilities & BDI_CAP_MAP_COPY))
                                        goto error;

                                capabilities &= ~BDI_CAP_MAP_DIRECT;
                        }
                }
        }

        /* we're going to need a VMA struct as well */
        vma = kzalloc(sizeof(struct vm_area_struct), GFP_KERNEL);
        if (!vma)
                goto error_getting_vma;

        INIT_LIST_HEAD(&vma->anon_vma_node);
        atomic_set(&vma->vm_usage, 1);
        if (file) {
                get_file(file);
                if (vm_flags & VM_EXECUTABLE) {
                        added_exe_file_vma(current->mm);
                        vma->vm_mm = current->mm;
                }
        }
        vma->vm_file    = file;
        vma->vm_flags   = vm_flags;
        vma->vm_start   = addr;
        vma->vm_end     = addr + len;
        vma->vm_pgoff   = pgoff;

        vml->vma = vma;

        /* set up the mapping */
        if (file && vma->vm_flags & VM_SHARED)
                ret = do_mmap_shared_file(vma, len);
        else
                ret = do_mmap_private(vma, len);
        if (ret < 0)
                goto error;

        /* okay... we have a mapping; now we have to register it */
        result = (void *) vma->vm_start;

        if (vma->vm_flags & VM_MAPPED_COPY) {
                realalloc += kobjsize(result);
                askedalloc += len;
        }

        realalloc += kobjsize(vma);
        askedalloc += sizeof(*vma);

        current->mm->total_vm += len >> PAGE_SHIFT;

        add_nommu_vma(vma);

 shared:
        realalloc += kobjsize(vml);
        askedalloc += sizeof(*vml);

        add_vma_to_mm(current->mm, vml);

        up_write(&nommu_vma_sem);

        if (prot & PROT_EXEC)
                flush_icache_range((unsigned long) result,
                                   (unsigned long) result + len);

#ifdef DEBUG
        printk("do_mmap:\n");
        show_process_blocks();
#endif

        return (unsigned long) result;

 error:
        up_write(&nommu_vma_sem);
        kfree(vml);
        if (vma) {
                if (vma->vm_file) {
                        fput(vma->vm_file);
                        if (vma->vm_flags & VM_EXECUTABLE)
                                removed_exe_file_vma(vma->vm_mm);
                }
                kfree(vma);
        }
        return ret;

 sharing_violation:
        up_write(&nommu_vma_sem);
        printk("Attempt to share mismatched mappings\n");
        kfree(vml);
        return -EINVAL;

 error_getting_vma:
        up_write(&nommu_vma_sem);
        kfree(vml);
        printk("Allocation of vma for %lu byte allocation from process %d failed\n",
               len, current->pid);
        show_free_areas();
        return -ENOMEM;

 error_getting_vml:
        printk("Allocation of vml for %lu byte allocation from process %d failed\n",
               len, current->pid);
        show_free_areas();
        return -ENOMEM;
}
EXPORT_SYMBOL(do_mmap_pgoff);

/*
 * handle mapping disposal for uClinux
 */
static void put_vma(struct mm_struct *mm, struct vm_area_struct *vma)
{
        if (vma) {
                down_write(&nommu_vma_sem);

                if (atomic_dec_and_test(&vma->vm_usage)) {
                        delete_nommu_vma(vma);

                        if (vma->vm_ops && vma->vm_ops->close)
                                vma->vm_ops->close(vma);

                        /* IO memory and memory shared directly out of the pagecache from
                         * ramfs/tmpfs mustn't be released here */
                        if (vma->vm_flags & VM_MAPPED_COPY) {
                                realalloc -= kobjsize((void *) vma->vm_start);
                                askedalloc -= vma->vm_end - vma->vm_start;
                                kfree((void *) vma->vm_start);
                        }

                        realalloc -= kobjsize(vma);
                        askedalloc -= sizeof(*vma);

                        if (vma->vm_file) {
                                fput(vma->vm_file);
                                if (vma->vm_flags & VM_EXECUTABLE)
                                        removed_exe_file_vma(mm);
                        }
                        kfree(vma);
                }

                up_write(&nommu_vma_sem);
        }
}

/*
 * release a mapping
 * - under NOMMU conditions the parameters must match exactly to the mapping to
 *   be removed
 */
int do_munmap(struct mm_struct *mm, unsigned long addr, size_t len)
{
        struct vm_list_struct *vml, **parent;
        unsigned long end = addr + len;

#ifdef DEBUG
        printk("do_munmap:\n");
#endif

        for (parent = &mm->context.vmlist; *parent; parent = &(*parent)->next) {
                if ((*parent)->vma->vm_start > addr)
                        break;
                if ((*parent)->vma->vm_start == addr &&
                    ((len == 0) || ((*parent)->vma->vm_end == end)))
                        goto found;
        }

        printk("munmap of non-mmaped memory by process %d (%s): %p\n",
               current->pid, current->comm, (void *) addr);
        return -EINVAL;

 found:
        vml = *parent;

        put_vma(mm, vml->vma);

        *parent = vml->next;
        realalloc -= kobjsize(vml);
        askedalloc -= sizeof(*vml);
        kfree(vml);

        update_hiwater_vm(mm);
        mm->total_vm -= len >> PAGE_SHIFT;

#ifdef DEBUG
        show_process_blocks();
#endif

        return 0;
}
EXPORT_SYMBOL(do_munmap);

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;
}

/*
 * Release all mappings
 */
void exit_mmap(struct mm_struct * mm)
{
        struct vm_list_struct *tmp;

        if (mm) {
#ifdef DEBUG
                printk("Exit_mmap:\n");
#endif

                mm->total_vm = 0;

                while ((tmp = mm->context.vmlist)) {
                        mm->context.vmlist = tmp->next;
                        put_vma(mm, tmp->vma);

                        realalloc -= kobjsize(tmp);
                        askedalloc -= sizeof(*tmp);
                        kfree(tmp);
                }

#ifdef DEBUG
                show_process_blocks();
#endif
        }
}

unsigned long do_brk(unsigned long addr, unsigned long len)
{
        return -ENOMEM;
}

/*
 * expand (or shrink) an existing mapping, potentially moving it at the same
 * time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 *
 * under NOMMU conditions, we only permit changing a mapping's size, and only
 * as long as it stays within the hole allocated by the kmalloc() call in
 * do_mmap_pgoff() and the block is not shareable
 *
 * MREMAP_FIXED is not supported under NOMMU conditions
 */
unsigned long do_mremap(unsigned long addr,
                        unsigned long old_len, unsigned long new_len,
                        unsigned long flags, unsigned long new_addr)
{
        struct vm_area_struct *vma;

        /* insanity checks first */
        if (new_len == 0)
                return (unsigned long) -EINVAL;

        if (flags & MREMAP_FIXED && new_addr != addr)
                return (unsigned long) -EINVAL;

        vma = find_vma_exact(current->mm, addr);
        if (!vma)
                return (unsigned long) -EINVAL;

        if (vma->vm_end != vma->vm_start + old_len)
                return (unsigned long) -EFAULT;

        if (vma->vm_flags & VM_MAYSHARE)
                return (unsigned long) -EPERM;

        if (new_len > kobjsize((void *) addr))
                return (unsigned long) -ENOMEM;

        /* all checks complete - do it */
        vma->vm_end = vma->vm_start + new_len;

        askedalloc -= old_len;
        askedalloc += new_len;

        return vma->vm_start;
}
EXPORT_SYMBOL(do_mremap);

asmlinkage unsigned long sys_mremap(unsigned long addr,
        unsigned long old_len, unsigned long new_len,
        unsigned long flags, unsigned long new_addr)
{
        unsigned long ret;

        down_write(&current->mm->mmap_sem);
        ret = do_mremap(addr, old_len, new_len, flags, new_addr);
        up_write(&current->mm->mmap_sem);
        return ret;
}

struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
                        unsigned int foll_flags)
{
        return NULL;
}

int remap_pfn_range(struct vm_area_struct *vma, unsigned long from,
                unsigned long to, unsigned long size, pgprot_t prot)
{
        vma->vm_start = vma->vm_pgoff << PAGE_SHIFT;
        return 0;
}
EXPORT_SYMBOL(remap_pfn_range);

int remap_vmalloc_range(struct vm_area_struct *vma, void *addr,
                        unsigned long pgoff)
{
        unsigned int size = vma->vm_end - vma->vm_start;

        if (!(vma->vm_flags & VM_USERMAP))
                return -EINVAL;

        vma->vm_start = (unsigned long)(addr + (pgoff << PAGE_SHIFT));
        vma->vm_end = vma->vm_start + size;

        return 0;
}
EXPORT_SYMBOL(remap_vmalloc_range);

void swap_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
{
}

unsigned long arch_get_unmapped_area(struct file *file, unsigned long addr,
        unsigned long len, unsigned long pgoff, unsigned long flags)
{
        return -ENOMEM;
}

void arch_unmap_area(struct mm_struct *mm, unsigned long addr)
{
}

void unmap_mapping_range(struct address_space *mapping,
                         loff_t const holebegin, loff_t const holelen,
                         int even_cows)
{
}
EXPORT_SYMBOL(unmap_mapping_range);

/*
 * ask for an unmapped area at which to create a mapping on a file
 */
unsigned long get_unmapped_area(struct file *file, unsigned long addr,
                                unsigned long len, unsigned long pgoff,
                                unsigned long flags)
{
        unsigned long (*get_area)(struct file *, unsigned long, unsigned long,
                                  unsigned long, unsigned long);

        get_area = current->mm->get_unmapped_area;
        if (file && file->f_op && file->f_op->get_unmapped_area)
                get_area = file->f_op->get_unmapped_area;

        if (!get_area)
                return -ENOSYS;

        return get_area(file, addr, len, pgoff, flags);
}
EXPORT_SYMBOL(get_unmapped_area);

/*
 * Check that a process has enough memory to allocate a new virtual
 * mapping. 0 means there is enough memory for the allocation to
 * succeed and -ENOMEM implies there is not.
 *
 * We currently support three overcommit policies, which are set via the
 * vm.overcommit_memory sysctl.  See Documentation/vm/overcommit-accounting
 *
 * Strict overcommit modes added 2002 Feb 26 by Alan Cox.
 * Additional code 2002 Jul 20 by Robert Love.
 *
 * cap_sys_admin is 1 if the process has admin privileges, 0 otherwise.
 *
 * Note this is a helper function intended to be used by LSMs which
 * wish to use this logic.
 */
int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
{
        unsigned long free, allowed;

        vm_acct_memory(pages);

        /*
         * Sometimes we want to use more memory than we have
         */
        if (sysctl_overcommit_memory == OVERCOMMIT_ALWAYS)
                return 0;

        if (sysctl_overcommit_memory == OVERCOMMIT_GUESS) {
                unsigned long n;

                free = global_page_state(NR_FILE_PAGES);
                free += nr_swap_pages;

                /*
                 * Any slabs which are created with the
                 * SLAB_RECLAIM_ACCOUNT flag claim to have contents
                 * which are reclaimable, under pressure.  The dentry
                 * cache and most inode caches should fall into this
                 */
                free += global_page_state(NR_SLAB_RECLAIMABLE);

                /*
                 * Leave the last 3% for root
                 */
                if (!cap_sys_admin)
                        free -= free / 32;

                if (free > pages)
                        return 0;

                /*
                 * nr_free_pages() is very expensive on large systems,
                 * only call if we're about to fail.
                 */
                n = nr_free_pages();

                /*
                 * Leave reserved pages. The pages are not for anonymous pages.
                 */
                if (n <= totalreserve_pages)
                        goto error;
                else
                        n -= totalreserve_pages;

                /*
                 * Leave the last 3% for root
                 */
                if (!cap_sys_admin)
                        n -= n / 32;
                free += n;

                if (free > pages)
                        return 0;

                goto error;
        }

        allowed = totalram_pages * sysctl_overcommit_ratio / 100;
        /*
         * Leave the last 3% for root
         */
        if (!cap_sys_admin)
                allowed -= allowed / 32;
        allowed += total_swap_pages;

        /* Don't let a single process grow too big:
           leave 3% of the size of this process for other processes */
        allowed -= current->mm->total_vm / 32;

        /*
         * cast `allowed' as a signed long because vm_committed_space
         * sometimes has a negative value
         */
        if (atomic_long_read(&vm_committed_space) < (long)allowed)
                return 0;
error:
        vm_unacct_memory(pages);

        return -ENOMEM;
}

int in_gate_area_no_task(unsigned long addr)
{
        return 0;
}

int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
        BUG();
        return 0;
}
EXPORT_SYMBOL(filemap_fault);

/*
 * Access another process' address space.
 * - source/target buffer must be kernel space
 */
int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write)
{
        struct vm_area_struct *vma;
        struct mm_struct *mm;

        if (addr + len < addr)
                return 0;

        mm = get_task_mm(tsk);
        if (!mm)
                return 0;

        down_read(&mm->mmap_sem);

        /* the access must start within one of the target process's mappings */
        vma = find_vma(mm, addr);
        if (vma) {
                /* don't overrun this mapping */
                if (addr + len >= vma->vm_end)
                        len = vma->vm_end - addr;

                /* only read or write mappings where it is permitted */
                if (write && vma->vm_flags & VM_MAYWRITE)
                        len -= copy_to_user((void *) addr, buf, len);
                else if (!write && vma->vm_flags & VM_MAYREAD)
                        len -= copy_from_user(buf, (void *) addr, len);
                else
                        len = 0;
        } else {
                len = 0;
        }

        up_read(&mm->mmap_sem);
        mmput(mm);
        return len;
}