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  * @name: name for dentry (to be seen in /proc/<pid>/maps
  45  * @size: size to be set for the file
  46  * @flags: vm_flags
  47  */
  48 struct file *shmem_file_setup(char *name, loff_t size, unsigned long flags)
  49 {
  50         int error;
  51         struct file *file;
  52         struct inode *inode;
  53         struct dentry *dentry, *root;
  54         struct qstr this;
  55
  56         if (IS_ERR(shm_mnt))
  57                 return (void *)shm_mnt;
  58
  59         error = -ENOMEM;
  60         this.name = name;
  61         this.len = strlen(name);
  62         this.hash = 0; /* will go */
  63         root = shm_mnt->mnt_root;
  64         dentry = d_alloc(root, &this);
  65         if (!dentry)
  66                 goto put_memory;
  67
  68         error = -ENFILE;
  69         file = get_empty_filp();
  70         if (!file)
  71                 goto put_dentry;
  72
  73         error = -ENOSPC;
  74         inode = ramfs_get_inode(root->d_sb, S_IFREG | S_IRWXUGO, 0);
  75         if (!inode)
  76                 goto close_file;
  77
  78         d_instantiate(dentry, inode);
  79         inode->i_size = size;
  80         inode->i_nlink = 0;     /* It is unlinked */
  81         init_file(file, shm_mnt, dentry, FMODE_WRITE | FMODE_READ,
  82                         &ramfs_file_operations);
  83         return file;
  84
  85 close_file:
  86         put_filp(file);
  87 put_dentry:
  88         dput(dentry);
  89 put_memory:
  90         return ERR_PTR(error);
  91 }
  92
  93 /**
  94  * shmem_zero_setup - setup a shared anonymous mapping
  95  * @vma: the vma to be mmapped is prepared by do_mmap_pgoff
  96  */
  97 int shmem_zero_setup(struct vm_area_struct *vma)
  98 {
  99         struct file *file;
 100         loff_t size = vma->vm_end - vma->vm_start;
 101
 102         file = shmem_file_setup("dev/zero", size, vma->vm_flags);
 103         if (IS_ERR(file))
 104                 return PTR_ERR(file);
 105
 106         if (vma->vm_file)
 107                 fput(vma->vm_file);
 108         vma->vm_file = file;
 109         vma->vm_ops = &generic_file_vm_ops;
 110         return 0;
 111 }
 112
 113 int shmem_unuse(swp_entry_t entry, struct page *page)
 114 {
 115         return 0;
 116 }
 117
 118 #ifndef CONFIG_MMU
 119 unsigned long shmem_get_unmapped_area(struct file *file,
 120                                       unsigned long addr,
 121                                       unsigned long len,
 122                                       unsigned long pgoff,
 123                                       unsigned long flags)
 124 {
 125         return ramfs_nommu_get_unmapped_area(file, addr, len, pgoff, flags);
 126 }
 127 #endif