LXR linux/fs/ramfs/file-nommu.c

   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/* file-nommu.c: no-MMU version of ramfs
   3 *
   4 * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
   5 * Written by David Howells (dhowells@redhat.com)
   6 */
   7
   8#include <linux/module.h>
   9#include <linux/fs.h>
  10#include <linux/mm.h>
  11#include <linux/pagemap.h>
  12#include <linux/highmem.h>
  13#include <linux/init.h>
  14#include <linux/string.h>
  15#include <linux/backing-dev.h>
  16#include <linux/ramfs.h>
  17#include <linux/pagevec.h>
  18#include <linux/mman.h>
  19#include <linux/sched.h>
  20#include <linux/slab.h>
  21
  22#include <linux/uaccess.h>
  23#include "internal.h"
  24
  25static int ramfs_nommu_setattr(struct user_namespace *, struct dentry *, struct iattr *);
  26static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
  27                                                   unsigned long addr,
  28                                                   unsigned long len,
  29                                                   unsigned long pgoff,
  30                                                   unsigned long flags);
  31static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma);
  32
  33static unsigned ramfs_mmap_capabilities(struct file *file)
  34{
  35        return NOMMU_MAP_DIRECT | NOMMU_MAP_COPY | NOMMU_MAP_READ |
  36                NOMMU_MAP_WRITE | NOMMU_MAP_EXEC;
  37}
  38
  39const struct file_operations ramfs_file_operations = {
  40        .mmap_capabilities      = ramfs_mmap_capabilities,
  41        .mmap                   = ramfs_nommu_mmap,
  42        .get_unmapped_area      = ramfs_nommu_get_unmapped_area,
  43        .read_iter              = generic_file_read_iter,
  44        .write_iter             = generic_file_write_iter,
  45        .fsync                  = noop_fsync,
  46        .splice_read            = generic_file_splice_read,
  47        .splice_write           = iter_file_splice_write,
  48        .llseek                 = generic_file_llseek,
  49};
  50
  51const struct inode_operations ramfs_file_inode_operations = {
  52        .setattr                = ramfs_nommu_setattr,
  53        .getattr                = simple_getattr,
  54};
  55
  56/*****************************************************************************/
  57/*
  58 * add a contiguous set of pages into a ramfs inode when it's truncated from
  59 * size 0 on the assumption that it's going to be used for an mmap of shared
  60 * memory
  61 */
  62int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
  63{
  64        unsigned long npages, xpages, loop;
  65        struct page *pages;
  66        unsigned order;
  67        void *data;
  68        int ret;
  69        gfp_t gfp = mapping_gfp_mask(inode->i_mapping);
  70
  71        /* make various checks */
  72        order = get_order(newsize);
  73        if (unlikely(order >= MAX_ORDER))
  74                return -EFBIG;
  75
  76        ret = inode_newsize_ok(inode, newsize);
  77        if (ret)
  78                return ret;
  79
  80        i_size_write(inode, newsize);
  81
  82        /* allocate enough contiguous pages to be able to satisfy the
  83         * request */
  84        pages = alloc_pages(gfp, order);
  85        if (!pages)
  86                return -ENOMEM;
  87
  88        /* split the high-order page into an array of single pages */
  89        xpages = 1UL << order;
  90        npages = (newsize + PAGE_SIZE - 1) >> PAGE_SHIFT;
  91
  92        split_page(pages, order);
  93
  94        /* trim off any pages we don't actually require */
  95        for (loop = npages; loop < xpages; loop++)
  96                __free_page(pages + loop);
  97
  98        /* clear the memory we allocated */
  99        newsize = PAGE_SIZE * npages;
 100        data = page_address(pages);
 101        memset(data, 0, newsize);
 102
 103        /* attach all the pages to the inode's address space */
 104        for (loop = 0; loop < npages; loop++) {
 105                struct page *page = pages + loop;
 106
 107                ret = add_to_page_cache_lru(page, inode->i_mapping, loop,
 108                                        gfp);
 109                if (ret < 0)
 110                        goto add_error;
 111
 112                /* prevent the page from being discarded on memory pressure */
 113                SetPageDirty(page);
 114                SetPageUptodate(page);
 115
 116                unlock_page(page);
 117                put_page(page);
 118        }
 119
 120        return 0;
 121
 122add_error:
 123        while (loop < npages)
 124                __free_page(pages + loop++);
 125        return ret;
 126}
 127
 128/*****************************************************************************/
 129/*
 130 *
 131 */
 132static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size)
 133{
 134        int ret;
 135
 136        /* assume a truncate from zero size is going to be for the purposes of
 137         * shared mmap */
 138        if (size == 0) {
 139                if (unlikely(newsize >> 32))
 140                        return -EFBIG;
 141
 142                return ramfs_nommu_expand_for_mapping(inode, newsize);
 143        }
 144
 145        /* check that a decrease in size doesn't cut off any shared mappings */
 146        if (newsize < size) {
 147                ret = nommu_shrink_inode_mappings(inode, size, newsize);
 148                if (ret < 0)
 149                        return ret;
 150        }
 151
 152        truncate_setsize(inode, newsize);
 153        return 0;
 154}
 155
 156/*****************************************************************************/
 157/*
 158 * handle a change of attributes
 159 * - we're specifically interested in a change of size
 160 */
 161static int ramfs_nommu_setattr(struct user_namespace *mnt_userns,
 162                               struct dentry *dentry, struct iattr *ia)
 163{
 164        struct inode *inode = d_inode(dentry);
 165        unsigned int old_ia_valid = ia->ia_valid;
 166        int ret = 0;
 167
 168        /* POSIX UID/GID verification for setting inode attributes */
 169        ret = setattr_prepare(&init_user_ns, dentry, ia);
 170        if (ret)
 171                return ret;
 172
 173        /* pick out size-changing events */
 174        if (ia->ia_valid & ATTR_SIZE) {
 175                loff_t size = inode->i_size;
 176
 177                if (ia->ia_size != size) {
 178                        ret = ramfs_nommu_resize(inode, ia->ia_size, size);
 179                        if (ret < 0 || ia->ia_valid == ATTR_SIZE)
 180                                goto out;
 181                } else {
 182                        /* we skipped the truncate but must still update
 183                         * timestamps
 184                         */
 185                        ia->ia_valid |= ATTR_MTIME|ATTR_CTIME;
 186                }
 187        }
 188
 189        setattr_copy(&init_user_ns, inode, ia);
 190 out:
 191        ia->ia_valid = old_ia_valid;
 192        return ret;
 193}
 194
 195/*****************************************************************************/
 196/*
 197 * try to determine where a shared mapping can be made
 198 * - we require that:
 199 *   - the pages to be mapped must exist
 200 *   - the pages be physically contiguous in sequence
 201 */
 202static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
 203                                            unsigned long addr, unsigned long len,
 204                                            unsigned long pgoff, unsigned long flags)
 205{
 206        unsigned long maxpages, lpages, nr, loop, ret;
 207        struct inode *inode = file_inode(file);
 208        struct page **pages = NULL, **ptr, *page;
 209        loff_t isize;
 210
 211        /* the mapping mustn't extend beyond the EOF */
 212        lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
 213        isize = i_size_read(inode);
 214
 215        ret = -ENOSYS;
 216        maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
 217        if (pgoff >= maxpages)
 218                goto out;
 219
 220        if (maxpages - pgoff < lpages)
 221                goto out;
 222
 223        /* gang-find the pages */
 224        pages = kcalloc(lpages, sizeof(struct page *), GFP_KERNEL);
 225        if (!pages)
 226                goto out_free;
 227
 228        nr = find_get_pages_contig(inode->i_mapping, pgoff, lpages, pages);
 229        if (nr != lpages)
 230                goto out_free_pages; /* leave if some pages were missing */
 231
 232        /* check the pages for physical adjacency */
 233        ptr = pages;
 234        page = *ptr++;
 235        page++;
 236        for (loop = lpages; loop > 1; loop--)
 237                if (*ptr++ != page++)
 238                        goto out_free_pages;
 239
 240        /* okay - all conditions fulfilled */
 241        ret = (unsigned long) page_address(pages[0]);
 242
 243out_free_pages:
 244        ptr = pages;
 245        for (loop = nr; loop > 0; loop--)
 246                put_page(*ptr++);
 247out_free:
 248        kfree(pages);
 249out:
 250        return ret;
 251}
 252
 253/*****************************************************************************/
 254/*
 255 * set up a mapping for shared memory segments
 256 */
 257static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)
 258{
 259        if (!(vma->vm_flags & (VM_SHARED | VM_MAYSHARE)))
 260                return -ENOSYS;
 261
 262        file_accessed(file);
 263        vma->vm_ops = &generic_file_vm_ops;
 264        return 0;
 265}
 266