fs/anon_inodes.c

   1 /*
   2  *  fs/anon_inodes.c
   3  *
   4  *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
   5  *
   6  *  Thanks to Arnd Bergmann for code review and suggestions.
   7  *  More changes for Thomas Gleixner suggestions.
   8  *
   9  */
  10
  11 #include <linux/cred.h>
  12 #include <linux/file.h>
  13 #include <linux/poll.h>
  14 #include <linux/sched.h>
  15 #include <linux/init.h>
  16 #include <linux/fs.h>
  17 #include <linux/mount.h>
  18 #include <linux/module.h>
  19 #include <linux/kernel.h>
  20 #include <linux/magic.h>
  21 #include <linux/anon_inodes.h>
  22
  23 #include <linux/uaccess.h>
  24
  25 static struct vfsmount *anon_inode_mnt __read_mostly;
  26 static struct inode *anon_inode_inode;
  27
  28 /*
  29  * anon_inodefs_dname() is called from d_path().
  30  */
  31 static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
  32 {
  33         return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
  34                                 dentry->d_name.name);
  35 }
  36
  37 static const struct dentry_operations anon_inodefs_dentry_operations = {
  38         .d_dname        = anon_inodefs_dname,
  39 };
  40
  41 static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type,
  42                                 int flags, const char *dev_name, void *data)
  43 {
  44         return mount_pseudo(fs_type, "anon_inode:", NULL,
  45                         &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC);
  46 }
  47
  48 static struct file_system_type anon_inode_fs_type = {
  49         .name           = "anon_inodefs",
  50         .mount          = anon_inodefs_mount,
  51         .kill_sb        = kill_anon_super,
  52 };
  53
  54 /**
  55  * anon_inode_getfile - creates a new file instance by hooking it up to an
  56  *                      anonymous inode, and a dentry that describe the "class"
  57  *                      of the file
  58  *
  59  * @name:    [in]    name of the "class" of the new file
  60  * @fops:    [in]    file operations for the new file
  61  * @priv:    [in]    private data for the new file (will be file's private_data)
  62  * @flags:   [in]    flags
  63  *
  64  * Creates a new file by hooking it on a single inode. This is useful for files
  65  * that do not need to have a full-fledged inode in order to operate correctly.
  66  * All the files created with anon_inode_getfile() will share a single inode,
  67  * hence saving memory and avoiding code duplication for the file/inode/dentry
  68  * setup.  Returns the newly created file* or an error pointer.
  69  */
  70 struct file *anon_inode_getfile(const char *name,
  71                                 const struct file_operations *fops,
  72                                 void *priv, int flags)
  73 {
  74         struct qstr this;
  75         struct path path;
  76         struct file *file;
  77
  78         if (IS_ERR(anon_inode_inode))
  79                 return ERR_PTR(-ENODEV);
  80
  81         if (fops->owner && !try_module_get(fops->owner))
  82                 return ERR_PTR(-ENOENT);
  83
  84         /*
  85          * Link the inode to a directory entry by creating a unique name
  86          * using the inode sequence number.
  87          */
  88         file = ERR_PTR(-ENOMEM);
  89         this.name = name;
  90         this.len = strlen(name);
  91         this.hash = 0;
  92         path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this);
  93         if (!path.dentry)
  94                 goto err_module;
  95
  96         path.mnt = mntget(anon_inode_mnt);
  97         /*
  98          * We know the anon_inode inode count is always greater than zero,
  99          * so ihold() is safe.
 100          */
 101         ihold(anon_inode_inode);
 102
 103         d_instantiate(path.dentry, anon_inode_inode);
 104
 105         file = alloc_file(&path, OPEN_FMODE(flags), fops);
 106         if (IS_ERR(file))
 107                 goto err_dput;
 108         file->f_mapping = anon_inode_inode->i_mapping;
 109
 110         file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
 111         file->private_data = priv;
 112
 113         return file;
 114
 115 err_dput:
 116         path_put(&path);
 117 err_module:
 118         module_put(fops->owner);
 119         return file;
 120 }
 121 EXPORT_SYMBOL_GPL(anon_inode_getfile);
 122
 123 /**
 124  * anon_inode_getfd - creates a new file instance by hooking it up to an
 125  *                    anonymous inode, and a dentry that describe the "class"
 126  *                    of the file
 127  *
 128  * @name:    [in]    name of the "class" of the new file
 129  * @fops:    [in]    file operations for the new file
 130  * @priv:    [in]    private data for the new file (will be file's private_data)
 131  * @flags:   [in]    flags
 132  *
 133  * Creates a new file by hooking it on a single inode. This is useful for files
 134  * that do not need to have a full-fledged inode in order to operate correctly.
 135  * All the files created with anon_inode_getfd() will share a single inode,
 136  * hence saving memory and avoiding code duplication for the file/inode/dentry
 137  * setup.  Returns new descriptor or an error code.
 138  */
 139 int anon_inode_getfd(const char *name, const struct file_operations *fops,
 140                      void *priv, int flags)
 141 {
 142         int error, fd;
 143         struct file *file;
 144
 145         error = get_unused_fd_flags(flags);
 146         if (error < 0)
 147                 return error;
 148         fd = error;
 149
 150         file = anon_inode_getfile(name, fops, priv, flags);
 151         if (IS_ERR(file)) {
 152                 error = PTR_ERR(file);
 153                 goto err_put_unused_fd;
 154         }
 155         fd_install(fd, file);
 156
 157         return fd;
 158
 159 err_put_unused_fd:
 160         put_unused_fd(fd);
 161         return error;
 162 }
 163 EXPORT_SYMBOL_GPL(anon_inode_getfd);
 164
 165 static int __init anon_inode_init(void)
 166 {
 167         anon_inode_mnt = kern_mount(&anon_inode_fs_type);
 168         if (IS_ERR(anon_inode_mnt))
 169                 panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt));
 170
 171         anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
 172         if (IS_ERR(anon_inode_inode))
 173                 panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode));
 174
 175         return 0;
 176 }
 177
 178 fs_initcall(anon_inode_init);
 179