/* file-nommu.c: no-MMU version of ramfs
 *
 * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/backing-dev.h>
#include <linux/ramfs.h>
#include <linux/pagevec.h>
#include <linux/mman.h>
#include <linux/sched.h>

#include <asm/uaccess.h>
#include "internal.h"

static int ramfs_nommu_setattr(struct dentry *, struct iattr *);

const struct address_space_operations ramfs_aops = {
        .readpage               = simple_readpage,
        .write_begin            = simple_write_begin,
        .write_end              = simple_write_end,
        .set_page_dirty         = __set_page_dirty_no_writeback,
};

const struct file_operations ramfs_file_operations = {
        .mmap                   = ramfs_nommu_mmap,
        .get_unmapped_area      = ramfs_nommu_get_unmapped_area,
        .read                   = do_sync_read,
        .aio_read               = generic_file_aio_read,
        .write                  = do_sync_write,
        .aio_write              = generic_file_aio_write,
        .fsync                  = simple_sync_file,
        .splice_read            = generic_file_splice_read,
        .splice_write           = generic_file_splice_write,
        .llseek                 = generic_file_llseek,
};

const struct inode_operations ramfs_file_inode_operations = {
        .setattr                = ramfs_nommu_setattr,
        .getattr                = simple_getattr,
};

/*****************************************************************************/
/*
 * add a contiguous set of pages into a ramfs inode when it's truncated from
 * size 0 on the assumption that it's going to be used for an mmap of shared
 * memory
 */
int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
{
        unsigned long npages, xpages, loop, limit;
        struct page *pages;
        unsigned order;
        void *data;
        int ret;

        /* make various checks */
        order = get_order(newsize);
        if (unlikely(order >= MAX_ORDER))
                return -EFBIG;

        ret = inode_newsize_ok(inode, newsize);
        if (ret)
                return ret;

        i_size_write(inode, newsize);

        /* allocate enough contiguous pages to be able to satisfy the
         * request */
        pages = alloc_pages(mapping_gfp_mask(inode->i_mapping), order);
        if (!pages)
                return -ENOMEM;

        /* split the high-order page into an array of single pages */
        xpages = 1UL << order;
        npages = (newsize + PAGE_SIZE - 1) >> PAGE_SHIFT;

        split_page(pages, order);

        /* trim off any pages we don't actually require */
        for (loop = npages; loop < xpages; loop++)
                __free_page(pages + loop);

        /* clear the memory we allocated */
        newsize = PAGE_SIZE * npages;
        data = page_address(pages);
        memset(data, 0, newsize);

        /* attach all the pages to the inode's address space */
        for (loop = 0; loop < npages; loop++) {
                struct page *page = pages + loop;

                ret = add_to_page_cache_lru(page, inode->i_mapping, loop,
                                        GFP_KERNEL);
                if (ret < 0)
                        goto add_error;

                /* prevent the page from being discarded on memory pressure */
                SetPageDirty(page);

                unlock_page(page);
        }

        return 0;

add_error:
        while (loop < npages)
                __free_page(pages + loop++);
        return ret;
}

/*****************************************************************************/
/*
 * check that file shrinkage doesn't leave any VMAs dangling in midair
 */
static int ramfs_nommu_check_mappings(struct inode *inode,
                                      size_t newsize, size_t size)
{
        struct vm_area_struct *vma;
        struct prio_tree_iter iter;

        /* search for VMAs that fall within the dead zone */
        vma_prio_tree_foreach(vma, &iter, &inode->i_mapping->i_mmap,
                              newsize >> PAGE_SHIFT,
                              (size + PAGE_SIZE - 1) >> PAGE_SHIFT
                              ) {
                /* found one - only interested if it's shared out of the page
                 * cache */
                if (vma->vm_flags & VM_SHARED)
                        return -ETXTBSY; /* not quite true, but near enough */
        }

        return 0;
}

/*****************************************************************************/
/*
 *
 */
static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size)
{
        int ret;

        /* assume a truncate from zero size is going to be for the purposes of
         * shared mmap */
        if (size == 0) {
                if (unlikely(newsize >> 32))
                        return -EFBIG;

                return ramfs_nommu_expand_for_mapping(inode, newsize);
        }

        /* check that a decrease in size doesn't cut off any shared mappings */
        if (newsize < size) {
                ret = ramfs_nommu_check_mappings(inode, newsize, size);
                if (ret < 0)
                        return ret;
        }

        ret = vmtruncate(inode, newsize);

        return ret;
}

/*****************************************************************************/
/*
 * handle a change of attributes
 * - we're specifically interested in a change of size
 */
static int ramfs_nommu_setattr(struct dentry *dentry, struct iattr *ia)
{
        struct inode *inode = dentry->d_inode;
        unsigned int old_ia_valid = ia->ia_valid;
        int ret = 0;

        /* POSIX UID/GID verification for setting inode attributes */
        ret = inode_change_ok(inode, ia);
        if (ret)
                return ret;

        /* pick out size-changing events */
        if (ia->ia_valid & ATTR_SIZE) {
                loff_t size = i_size_read(inode);
                if (ia->ia_size != size) {
                        ret = ramfs_nommu_resize(inode, ia->ia_size, size);
                        if (ret < 0 || ia->ia_valid == ATTR_SIZE)
                                goto out;
                } else {
                        /* we skipped the truncate but must still update
                         * timestamps
                         */
                        ia->ia_valid |= ATTR_MTIME|ATTR_CTIME;
                }
        }

        ret = inode_setattr(inode, ia);
 out:
        ia->ia_valid = old_ia_valid;
        return ret;
}

/*****************************************************************************/
/*
 * try to determine where a shared mapping can be made
 * - we require that:
 *   - the pages to be mapped must exist
 *   - the pages be physically contiguous in sequence
 */
unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
                                            unsigned long addr, unsigned long len,
                                            unsigned long pgoff, unsigned long flags)
{
        unsigned long maxpages, lpages, nr, loop, ret;
        struct inode *inode = file->f_path.dentry->d_inode;
        struct page **pages = NULL, **ptr, *page;
        loff_t isize;

        if (!(flags & MAP_SHARED))
                return addr;

        /* the mapping mustn't extend beyond the EOF */
        lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
        isize = i_size_read(inode);

        ret = -EINVAL;
        maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
        if (pgoff >= maxpages)
                goto out;

        if (maxpages - pgoff < lpages)
                goto out;

        /* gang-find the pages */
        ret = -ENOMEM;
        pages = kzalloc(lpages * sizeof(struct page *), GFP_KERNEL);
        if (!pages)
                goto out_free;

        nr = find_get_pages(inode->i_mapping, pgoff, lpages, pages);
        if (nr != lpages)
                goto out_free_pages; /* leave if some pages were missing */

        /* check the pages for physical adjacency */
        ptr = pages;
        page = *ptr++;
        page++;
        for (loop = lpages; loop > 1; loop--)
                if (*ptr++ != page++)
                        goto out_free_pages;

        /* okay - all conditions fulfilled */
        ret = (unsigned long) page_address(pages[0]);

out_free_pages:
        ptr = pages;
        for (loop = nr; loop > 0; loop--)
                put_page(*ptr++);
out_free:
        kfree(pages);
out:
        return ret;
}

/*****************************************************************************/
/*
 * set up a mapping for shared memory segments
 */
int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)
{
        if (!(vma->vm_flags & VM_SHARED))
                return -ENOSYS;

        file_accessed(file);
        vma->vm_ops = &generic_file_vm_ops;
        return 0;
}