mm/tiny-shmem.c

   1 /*
   2  * tiny-shmem.c: simple shmemfs and tmpfs using ramfs code
   3  *
   4  * Matt Mackall <mpm@selenic.com> January, 2004
   5  * derived from mm/shmem.c and fs/ramfs/inode.c
   6  *
   7  * This is intended for small system where the benefits of the full
   8  * shmem code (swap-backed and resource-limited) are outweighed by
   9  * their complexity. On systems without swap this code should be
  10  * effectively equivalent, but much lighter weight.
  11  */
  12
  13 #include <linux/fs.h>
  14 #include <linux/init.h>
  15 #include <linux/vfs.h>
  16 #include <linux/mount.h>
  17 #include <linux/file.h>
  18 #include <linux/mm.h>
  19 #include <linux/module.h>
  20 #include <linux/swap.h>
  21 #include <linux/ramfs.h>
  22
  23 static struct file_system_type tmpfs_fs_type = {
  24         .name           = "tmpfs",
  25         .get_sb         = ramfs_get_sb,
  26         .kill_sb        = kill_litter_super,
  27 };
  28
  29 static struct vfsmount *shm_mnt;
  30
  31 static int __init init_tmpfs(void)
  32 {
  33         BUG_ON(register_filesystem(&tmpfs_fs_type) != 0);
  34
  35         shm_mnt = kern_mount(&tmpfs_fs_type);
  36         BUG_ON(IS_ERR(shm_mnt));
  37
  38         return 0;
  39 }
  40 module_init(init_tmpfs)
  41
  42 /*
  43  * shmem_file_setup - get an unlinked file living in tmpfs
  44  *
  45  * @name: name for dentry (to be seen in /proc/<pid>/maps
  46  * @size: size to be set for the file
  47  *
  48  */
  49 struct file *shmem_file_setup(char *name, loff_t size, unsigned long flags)
  50 {
  51         int error;
  52         struct file *file;
  53         struct inode *inode;
  54         struct dentry *dentry, *root;
  55         struct qstr this;
  56
  57         if (IS_ERR(shm_mnt))
  58                 return (void *)shm_mnt;
  59
  60         error = -ENOMEM;
  61         this.name = name;
  62         this.len = strlen(name);
  63         this.hash = 0; /* will go */
  64         root = shm_mnt->mnt_root;
  65         dentry = d_alloc(root, &this);
  66         if (!dentry)
  67                 goto put_memory;
  68
  69         error = -ENFILE;
  70         file = get_empty_filp();
  71         if (!file)
  72                 goto put_dentry;
  73
  74         error = -ENOSPC;
  75         inode = ramfs_get_inode(root->d_sb, S_IFREG | S_IRWXUGO, 0);
  76         if (!inode)
  77                 goto close_file;
  78
  79         d_instantiate(dentry, inode);
  80         inode->i_nlink = 0;     /* It is unlinked */
  81
  82         file->f_path.mnt = mntget(shm_mnt);
  83         file->f_path.dentry = dentry;
  84         file->f_mapping = inode->i_mapping;
  85         file->f_op = &ramfs_file_operations;
  86         file->f_mode = FMODE_WRITE | FMODE_READ;
  87
  88         /* notify everyone as to the change of file size */
  89         error = do_truncate(dentry, size, 0, file);
  90         if (error < 0)
  91                 goto close_file;
  92
  93         return file;
  94
  95 close_file:
  96         put_filp(file);
  97 put_dentry:
  98         dput(dentry);
  99 put_memory:
 100         return ERR_PTR(error);
 101 }
 102
 103 /*
 104  * shmem_zero_setup - setup a shared anonymous mapping
 105  *
 106  * @vma: the vma to be mmapped is prepared by do_mmap_pgoff
 107  */
 108 int shmem_zero_setup(struct vm_area_struct *vma)
 109 {
 110         struct file *file;
 111         loff_t size = vma->vm_end - vma->vm_start;
 112
 113         file = shmem_file_setup("dev/zero", size, vma->vm_flags);
 114         if (IS_ERR(file))
 115                 return PTR_ERR(file);
 116
 117         if (vma->vm_file)
 118                 fput(vma->vm_file);
 119         vma->vm_file = file;
 120         vma->vm_ops = &generic_file_vm_ops;
 121         return 0;
 122 }
 123
 124 int shmem_unuse(swp_entry_t entry, struct page *page)
 125 {
 126         return 0;
 127 }
 128
 129 int shmem_mmap(struct file *file, struct vm_area_struct *vma)
 130 {
 131         file_accessed(file);
 132 #ifndef CONFIG_MMU
 133         return ramfs_nommu_mmap(file, vma);
 134 #else
 135         return 0;
 136 #endif
 137 }
 138
 139 #ifndef CONFIG_MMU
 140 unsigned long shmem_get_unmapped_area(struct file *file,
 141                                       unsigned long addr,
 142                                       unsigned long len,
 143                                       unsigned long pgoff,
 144                                       unsigned long flags)
 145 {
 146         return ramfs_nommu_get_unmapped_area(file, addr, len, pgoff, flags);
 147 }
 148 #endif