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/devfs_fs_kernel.h>
  16 #include <linux/vfs.h>
  17 #include <linux/mount.h>
  18 #include <linux/file.h>
  19 #include <linux/mm.h>
  20 #include <linux/module.h>
  21 #include <linux/swap.h>
  22 #include <linux/ramfs.h>
  23
  24 static struct file_system_type tmpfs_fs_type = {
  25         .name           = "tmpfs",
  26         .get_sb         = ramfs_get_sb,
  27         .kill_sb        = kill_litter_super,
  28 };
  29
  30 static struct vfsmount *shm_mnt;
  31
  32 static int __init init_tmpfs(void)
  33 {
  34         BUG_ON(register_filesystem(&tmpfs_fs_type) != 0);
  35
  36 #ifdef CONFIG_TMPFS
  37         devfs_mk_dir("shm");
  38 #endif
  39         shm_mnt = kern_mount(&tmpfs_fs_type);
  40         BUG_ON(IS_ERR(shm_mnt));
  41
  42         return 0;
  43 }
  44 module_init(init_tmpfs)
  45
  46 /*
  47  * shmem_file_setup - get an unlinked file living in tmpfs
  48  *
  49  * @name: name for dentry (to be seen in /proc/<pid>/maps
  50  * @size: size to be set for the file
  51  *
  52  */
  53 struct file *shmem_file_setup(char *name, loff_t size, unsigned long flags)
  54 {
  55         int error;
  56         struct file *file;
  57         struct inode *inode;
  58         struct dentry *dentry, *root;
  59         struct qstr this;
  60
  61         if (IS_ERR(shm_mnt))
  62                 return (void *)shm_mnt;
  63
  64         error = -ENOMEM;
  65         this.name = name;
  66         this.len = strlen(name);
  67         this.hash = 0; /* will go */
  68         root = shm_mnt->mnt_root;
  69         dentry = d_alloc(root, &this);
  70         if (!dentry)
  71                 goto put_memory;
  72
  73         error = -ENFILE;
  74         file = get_empty_filp();
  75         if (!file)
  76                 goto put_dentry;
  77
  78         error = -ENOSPC;
  79         inode = ramfs_get_inode(root->d_sb, S_IFREG | S_IRWXUGO, 0);
  80         if (!inode)
  81                 goto close_file;
  82
  83         d_instantiate(dentry, inode);
  84         inode->i_size = size;
  85         inode->i_nlink = 0;     /* It is unlinked */
  86         file->f_vfsmnt = mntget(shm_mnt);
  87         file->f_dentry = dentry;
  88         file->f_mapping = inode->i_mapping;
  89         file->f_op = &ramfs_file_operations;
  90         file->f_mode = FMODE_WRITE | FMODE_READ;
  91         return file;
  92
  93 close_file:
  94         put_filp(file);
  95 put_dentry:
  96         dput(dentry);
  97 put_memory:
  98         return ERR_PTR(error);
  99 }
 100
 101 /*
 102  * shmem_zero_setup - setup a shared anonymous mapping
 103  *
 104  * @vma: the vma to be mmapped is prepared by do_mmap_pgoff
 105  */
 106 int shmem_zero_setup(struct vm_area_struct *vma)
 107 {
 108         struct file *file;
 109         loff_t size = vma->vm_end - vma->vm_start;
 110
 111         file = shmem_file_setup("dev/zero", size, vma->vm_flags);
 112         if (IS_ERR(file))
 113                 return PTR_ERR(file);
 114
 115         if (vma->vm_file)
 116                 fput(vma->vm_file);
 117         vma->vm_file = file;
 118         vma->vm_ops = &generic_file_vm_ops;
 119         return 0;
 120 }
 121
 122 int shmem_unuse(swp_entry_t entry, struct page *page)
 123 {
 124         return 0;
 125 }