tiny-shmem.c

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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

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sys/mm/tiny-shmem.c