linux/fs/ramfs/file-nommu.c
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   1/* file-nommu.c: no-MMU version of ramfs
   2 *
   3 * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
   4 * Written by David Howells (dhowells@redhat.com)
   5 *
   6 * This program is free software; you can redistribute it and/or
   7 * modify it under the terms of the GNU General Public License
   8 * as published by the Free Software Foundation; either version
   9 * 2 of the License, or (at your option) any later version.
  10 */
  11
  12#include <linux/module.h>
  13#include <linux/fs.h>
  14#include <linux/mm.h>
  15#include <linux/pagemap.h>
  16#include <linux/highmem.h>
  17#include <linux/init.h>
  18#include <linux/string.h>
  19#include <linux/backing-dev.h>
  20#include <linux/ramfs.h>
  21#include <linux/pagevec.h>
  22#include <linux/mman.h>
  23#include <linux/sched.h>
  24#include <linux/slab.h>
  25
  26#include <linux/uaccess.h>
  27#include "internal.h"
  28
  29static int ramfs_nommu_setattr(struct dentry *, struct iattr *);
  30static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
  31                                                   unsigned long addr,
  32                                                   unsigned long len,
  33                                                   unsigned long pgoff,
  34                                                   unsigned long flags);
  35static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma);
  36
  37static unsigned ramfs_mmap_capabilities(struct file *file)
  38{
  39        return NOMMU_MAP_DIRECT | NOMMU_MAP_COPY | NOMMU_MAP_READ |
  40                NOMMU_MAP_WRITE | NOMMU_MAP_EXEC;
  41}
  42
  43const struct file_operations ramfs_file_operations = {
  44        .mmap_capabilities      = ramfs_mmap_capabilities,
  45        .mmap                   = ramfs_nommu_mmap,
  46        .get_unmapped_area      = ramfs_nommu_get_unmapped_area,
  47        .read_iter              = generic_file_read_iter,
  48        .write_iter             = generic_file_write_iter,
  49        .fsync                  = noop_fsync,
  50        .splice_read            = generic_file_splice_read,
  51        .splice_write           = iter_file_splice_write,
  52        .llseek                 = generic_file_llseek,
  53};
  54
  55const struct inode_operations ramfs_file_inode_operations = {
  56        .setattr                = ramfs_nommu_setattr,
  57        .getattr                = simple_getattr,
  58};
  59
  60/*****************************************************************************/
  61/*
  62 * add a contiguous set of pages into a ramfs inode when it's truncated from
  63 * size 0 on the assumption that it's going to be used for an mmap of shared
  64 * memory
  65 */
  66int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
  67{
  68        unsigned long npages, xpages, loop;
  69        struct page *pages;
  70        unsigned order;
  71        void *data;
  72        int ret;
  73        gfp_t gfp = mapping_gfp_mask(inode->i_mapping);
  74
  75        /* make various checks */
  76        order = get_order(newsize);
  77        if (unlikely(order >= MAX_ORDER))
  78                return -EFBIG;
  79
  80        ret = inode_newsize_ok(inode, newsize);
  81        if (ret)
  82                return ret;
  83
  84        i_size_write(inode, newsize);
  85
  86        /* allocate enough contiguous pages to be able to satisfy the
  87         * request */
  88        pages = alloc_pages(gfp, order);
  89        if (!pages)
  90                return -ENOMEM;
  91
  92        /* split the high-order page into an array of single pages */
  93        xpages = 1UL << order;
  94        npages = (newsize + PAGE_SIZE - 1) >> PAGE_SHIFT;
  95
  96        split_page(pages, order);
  97
  98        /* trim off any pages we don't actually require */
  99        for (loop = npages; loop < xpages; loop++)
 100                __free_page(pages + loop);
 101
 102        /* clear the memory we allocated */
 103        newsize = PAGE_SIZE * npages;
 104        data = page_address(pages);
 105        memset(data, 0, newsize);
 106
 107        /* attach all the pages to the inode's address space */
 108        for (loop = 0; loop < npages; loop++) {
 109                struct page *page = pages + loop;
 110
 111                ret = add_to_page_cache_lru(page, inode->i_mapping, loop,
 112                                        gfp);
 113                if (ret < 0)
 114                        goto add_error;
 115
 116                /* prevent the page from being discarded on memory pressure */
 117                SetPageDirty(page);
 118                SetPageUptodate(page);
 119
 120                unlock_page(page);
 121                put_page(page);
 122        }
 123
 124        return 0;
 125
 126add_error:
 127        while (loop < npages)
 128                __free_page(pages + loop++);
 129        return ret;
 130}
 131
 132/*****************************************************************************/
 133/*
 134 *
 135 */
 136static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size)
 137{
 138        int ret;
 139
 140        /* assume a truncate from zero size is going to be for the purposes of
 141         * shared mmap */
 142        if (size == 0) {
 143                if (unlikely(newsize >> 32))
 144                        return -EFBIG;
 145
 146                return ramfs_nommu_expand_for_mapping(inode, newsize);
 147        }
 148
 149        /* check that a decrease in size doesn't cut off any shared mappings */
 150        if (newsize < size) {
 151                ret = nommu_shrink_inode_mappings(inode, size, newsize);
 152                if (ret < 0)
 153                        return ret;
 154        }
 155
 156        truncate_setsize(inode, newsize);
 157        return 0;
 158}
 159
 160/*****************************************************************************/
 161/*
 162 * handle a change of attributes
 163 * - we're specifically interested in a change of size
 164 */
 165static int ramfs_nommu_setattr(struct dentry *dentry, struct iattr *ia)
 166{
 167        struct inode *inode = d_inode(dentry);
 168        unsigned int old_ia_valid = ia->ia_valid;
 169        int ret = 0;
 170
 171        /* POSIX UID/GID verification for setting inode attributes */
 172        ret = setattr_prepare(dentry, ia);
 173        if (ret)
 174                return ret;
 175
 176        /* pick out size-changing events */
 177        if (ia->ia_valid & ATTR_SIZE) {
 178                loff_t size = inode->i_size;
 179
 180                if (ia->ia_size != size) {
 181                        ret = ramfs_nommu_resize(inode, ia->ia_size, size);
 182                        if (ret < 0 || ia->ia_valid == ATTR_SIZE)
 183                                goto out;
 184                } else {
 185                        /* we skipped the truncate but must still update
 186                         * timestamps
 187                         */
 188                        ia->ia_valid |= ATTR_MTIME|ATTR_CTIME;
 189                }
 190        }
 191
 192        setattr_copy(inode, ia);
 193 out:
 194        ia->ia_valid = old_ia_valid;
 195        return ret;
 196}
 197
 198/*****************************************************************************/
 199/*
 200 * try to determine where a shared mapping can be made
 201 * - we require that:
 202 *   - the pages to be mapped must exist
 203 *   - the pages be physically contiguous in sequence
 204 */
 205static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
 206                                            unsigned long addr, unsigned long len,
 207                                            unsigned long pgoff, unsigned long flags)
 208{
 209        unsigned long maxpages, lpages, nr, loop, ret;
 210        struct inode *inode = file_inode(file);
 211        struct page **pages = NULL, **ptr, *page;
 212        loff_t isize;
 213
 214        /* the mapping mustn't extend beyond the EOF */
 215        lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
 216        isize = i_size_read(inode);
 217
 218        ret = -ENOSYS;
 219        maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
 220        if (pgoff >= maxpages)
 221                goto out;
 222
 223        if (maxpages - pgoff < lpages)
 224                goto out;
 225
 226        /* gang-find the pages */
 227        pages = kcalloc(lpages, sizeof(struct page *), GFP_KERNEL);
 228        if (!pages)
 229                goto out_free;
 230
 231        nr = find_get_pages(inode->i_mapping, pgoff, lpages, pages);
 232        if (nr != lpages)
 233                goto out_free_pages; /* leave if some pages were missing */
 234
 235        /* check the pages for physical adjacency */
 236        ptr = pages;
 237        page = *ptr++;
 238        page++;
 239        for (loop = lpages; loop > 1; loop--)
 240                if (*ptr++ != page++)
 241                        goto out_free_pages;
 242
 243        /* okay - all conditions fulfilled */
 244        ret = (unsigned long) page_address(pages[0]);
 245
 246out_free_pages:
 247        ptr = pages;
 248        for (loop = nr; loop > 0; loop--)
 249                put_page(*ptr++);
 250out_free:
 251        kfree(pages);
 252out:
 253        return ret;
 254}
 255
 256/*****************************************************************************/
 257/*
 258 * set up a mapping for shared memory segments
 259 */
 260static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)
 261{
 262        if (!(vma->vm_flags & (VM_SHARED | VM_MAYSHARE)))
 263                return -ENOSYS;
 264
 265        file_accessed(file);
 266        vma->vm_ops = &generic_file_vm_ops;
 267        return 0;
 268}
 269