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