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   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
  84 #ifndef CONFIG_MMU
  85         error = ramfs_nommu_expand_for_mapping(inode, size);
  86         if (error)
  87                 goto close_file;
  88 #endif
  89         return file;
  90
  91 close_file:
  92         put_filp(file);
  93 put_dentry:
  94         dput(dentry);
  95 put_memory:
  96         return ERR_PTR(error);
  97 }
  98 EXPORT_SYMBOL_GPL(shmem_file_setup);
  99
 100 /**
 101  * shmem_zero_setup - setup a shared anonymous mapping
 102  * @vma: the vma to be mmapped is prepared by do_mmap_pgoff
 103  */
 104 int shmem_zero_setup(struct vm_area_struct *vma)
 105 {
 106         struct file *file;
 107         loff_t size = vma->vm_end - vma->vm_start;
 108
 109         file = shmem_file_setup("dev/zero", size, vma->vm_flags);
 110         if (IS_ERR(file))
 111                 return PTR_ERR(file);
 112
 113         if (vma->vm_file)
 114                 fput(vma->vm_file);
 115         vma->vm_file = file;
 116         vma->vm_ops = &generic_file_vm_ops;
 117         return 0;
 118 }
 119
 120 int shmem_unuse(swp_entry_t entry, struct page *page)
 121 {
 122         return 0;
 123 }
 124
 125 #ifndef CONFIG_MMU
 126 unsigned long shmem_get_unmapped_area(struct file *file,
 127                                       unsigned long addr,
 128                                       unsigned long len,
 129                                       unsigned long pgoff,
 130                                       unsigned long flags)
 131 {
 132         return ramfs_nommu_get_unmapped_area(file, addr, len, pgoff, flags);
 133 }
 134 #endif