/*
 *   linux/mm/fremap.c
 * 
 * Explicit pagetable population and nonlinear (random) mappings support.
 *
 * started by Ingo Molnar, Copyright (C) 2002, 2003
 */

#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/file.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/swapops.h>
#include <linux/rmap.h>
#include <linux/module.h>
#include <linux/syscalls.h>

#include <asm/mmu_context.h>
#include <asm/cacheflush.h>
#include <asm/tlbflush.h>

static inline void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
                        unsigned long addr, pte_t *ptep)
{
        pte_t pte = *ptep;

        if (pte_none(pte))
                return;
        if (pte_present(pte)) {
                unsigned long pfn = pte_pfn(pte);

                flush_cache_page(vma, addr);
                pte = ptep_clear_flush(vma, addr, ptep);
                if (pfn_valid(pfn)) {
                        struct page *page = pfn_to_page(pfn);
                        if (!PageReserved(page)) {
                                if (pte_dirty(pte))
                                        set_page_dirty(page);
                                page_remove_rmap(page);
                                page_cache_release(page);
                                mm->rss--;
                        }
                }
        } else {
                if (!pte_file(pte))
                        free_swap_and_cache(pte_to_swp_entry(pte));
                pte_clear(ptep);
        }
}

/*
 * Install a file page to a given virtual memory address, release any
 * previously existing mapping.
 */
int install_page(struct mm_struct *mm, struct vm_area_struct *vma,
                unsigned long addr, struct page *page, pgprot_t prot)
{
        struct inode *inode;
        pgoff_t size;
        int err = -ENOMEM;
        pte_t *pte;
        pmd_t *pmd;
        pud_t *pud;
        pgd_t *pgd;
        pte_t pte_val;

        pgd = pgd_offset(mm, addr);
        spin_lock(&mm->page_table_lock);
        
        pud = pud_alloc(mm, pgd, addr);
        if (!pud)
                goto err_unlock;

        pmd = pmd_alloc(mm, pud, addr);
        if (!pmd)
                goto err_unlock;

        pte = pte_alloc_map(mm, pmd, addr);
        if (!pte)
                goto err_unlock;

        /*
         * This page may have been truncated. Tell the
         * caller about it.
         */
        err = -EINVAL;
        inode = vma->vm_file->f_mapping->host;
        size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
        if (!page->mapping || page->index >= size)
                goto err_unlock;

        zap_pte(mm, vma, addr, pte);

        mm->rss++;
        flush_icache_page(vma, page);
        set_pte(pte, mk_pte(page, prot));
        page_add_file_rmap(page);
        pte_val = *pte;
        pte_unmap(pte);
        update_mmu_cache(vma, addr, pte_val);

        err = 0;
err_unlock:
        spin_unlock(&mm->page_table_lock);
        return err;
}
EXPORT_SYMBOL(install_page);


/*
 * Install a file pte to a given virtual memory address, release any
 * previously existing mapping.
 */
int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
                unsigned long addr, unsigned long pgoff, pgprot_t prot)
{
        int err = -ENOMEM;
        pte_t *pte;
        pmd_t *pmd;
        pud_t *pud;
        pgd_t *pgd;
        pte_t pte_val;

        pgd = pgd_offset(mm, addr);
        spin_lock(&mm->page_table_lock);
        
        pud = pud_alloc(mm, pgd, addr);
        if (!pud)
                goto err_unlock;

        pmd = pmd_alloc(mm, pud, addr);
        if (!pmd)
                goto err_unlock;

        pte = pte_alloc_map(mm, pmd, addr);
        if (!pte)
                goto err_unlock;

        zap_pte(mm, vma, addr, pte);

        set_pte(pte, pgoff_to_pte(pgoff));
        pte_val = *pte;
        pte_unmap(pte);
        update_mmu_cache(vma, addr, pte_val);
        spin_unlock(&mm->page_table_lock);
        return 0;

err_unlock:
        spin_unlock(&mm->page_table_lock);
        return err;
}


/***
 * sys_remap_file_pages - remap arbitrary pages of a shared backing store
 *                        file within an existing vma.
 * @start: start of the remapped virtual memory range
 * @size: size of the remapped virtual memory range
 * @prot: new protection bits of the range
 * @pgoff: to be mapped page of the backing store file
 * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
 *
 * this syscall works purely via pagetables, so it's the most efficient
 * way to map the same (large) file into a given virtual window. Unlike
 * mmap()/mremap() it does not create any new vmas. The new mappings are
 * also safe across swapout.
 *
 * NOTE: the 'prot' parameter right now is ignored, and the vma's default
 * protection is used. Arbitrary protections might be implemented in the
 * future.
 */
asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
        unsigned long __prot, unsigned long pgoff, unsigned long flags)
{
        struct mm_struct *mm = current->mm;
        struct address_space *mapping;
        unsigned long end = start + size;
        struct vm_area_struct *vma;
        int err = -EINVAL;
        int has_write_lock = 0;

        if (__prot)
                return err;
        /*
         * Sanitize the syscall parameters:
         */
        start = start & PAGE_MASK;
        size = size & PAGE_MASK;

        /* Does the address range wrap, or is the span zero-sized? */
        if (start + size <= start)
                return err;

        /* Can we represent this offset inside this architecture's pte's? */
#if PTE_FILE_MAX_BITS < BITS_PER_LONG
        if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
                return err;
#endif

        /* We need down_write() to change vma->vm_flags. */
        down_read(&mm->mmap_sem);
 retry:
        vma = find_vma(mm, start);

        /*
         * Make sure the vma is shared, that it supports prefaulting,
         * and that the remapped range is valid and fully within
         * the single existing vma.  vm_private_data is used as a
         * swapout cursor in a VM_NONLINEAR vma (unless VM_RESERVED
         * or VM_LOCKED, but VM_LOCKED could be revoked later on).
         */
        if (vma && (vma->vm_flags & VM_SHARED) &&
                (!vma->vm_private_data ||
                        (vma->vm_flags & (VM_NONLINEAR|VM_RESERVED))) &&
                vma->vm_ops && vma->vm_ops->populate &&
                        end > start && start >= vma->vm_start &&
                                end <= vma->vm_end) {

                /* Must set VM_NONLINEAR before any pages are populated. */
                if (pgoff != linear_page_index(vma, start) &&
                    !(vma->vm_flags & VM_NONLINEAR)) {
                        if (!has_write_lock) {
                                up_read(&mm->mmap_sem);
                                down_write(&mm->mmap_sem);
                                has_write_lock = 1;
                                goto retry;
                        }
                        mapping = vma->vm_file->f_mapping;
                        spin_lock(&mapping->i_mmap_lock);
                        flush_dcache_mmap_lock(mapping);
                        vma->vm_flags |= VM_NONLINEAR;
                        vma_prio_tree_remove(vma, &mapping->i_mmap);
                        vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
                        flush_dcache_mmap_unlock(mapping);
                        spin_unlock(&mapping->i_mmap_lock);
                }

                err = vma->vm_ops->populate(vma, start, size,
                                            vma->vm_page_prot,
                                            pgoff, flags & MAP_NONBLOCK);

                /*
                 * We can't clear VM_NONLINEAR because we'd have to do
                 * it after ->populate completes, and that would prevent
                 * downgrading the lock.  (Locks can't be upgraded).
                 */
        }
        if (likely(!has_write_lock))
                up_read(&mm->mmap_sem);
        else
                up_write(&mm->mmap_sem);

        return err;
}