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TOMOYO Linux Cross Reference
Linux/fs/anon_inodes.c

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  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 <asm/uaccess.h>
 24 
 25 static struct vfsmount *anon_inode_mnt __read_mostly;
 26 static struct inode *anon_inode_inode;
 27 static const struct file_operations anon_inode_fops;
 28 
 29 /*
 30  * anon_inodefs_dname() is called from d_path().
 31  */
 32 static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
 33 {
 34         return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
 35                                 dentry->d_name.name);
 36 }
 37 
 38 static const struct dentry_operations anon_inodefs_dentry_operations = {
 39         .d_dname        = anon_inodefs_dname,
 40 };
 41 
 42 /*
 43  * nop .set_page_dirty method so that people can use .page_mkwrite on
 44  * anon inodes.
 45  */
 46 static int anon_set_page_dirty(struct page *page)
 47 {
 48         return 0;
 49 };
 50 
 51 static const struct address_space_operations anon_aops = {
 52         .set_page_dirty = anon_set_page_dirty,
 53 };
 54 
 55 /*
 56  * A single inode exists for all anon_inode files. Contrary to pipes,
 57  * anon_inode inodes have no associated per-instance data, so we need
 58  * only allocate one of them.
 59  */
 60 static struct inode *anon_inode_mkinode(struct super_block *s)
 61 {
 62         struct inode *inode = new_inode_pseudo(s);
 63 
 64         if (!inode)
 65                 return ERR_PTR(-ENOMEM);
 66 
 67         inode->i_ino = get_next_ino();
 68         inode->i_fop = &anon_inode_fops;
 69 
 70         inode->i_mapping->a_ops = &anon_aops;
 71 
 72         /*
 73          * Mark the inode dirty from the very beginning,
 74          * that way it will never be moved to the dirty
 75          * list because mark_inode_dirty() will think
 76          * that it already _is_ on the dirty list.
 77          */
 78         inode->i_state = I_DIRTY;
 79         inode->i_mode = S_IRUSR | S_IWUSR;
 80         inode->i_uid = current_fsuid();
 81         inode->i_gid = current_fsgid();
 82         inode->i_flags |= S_PRIVATE;
 83         inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 84         return inode;
 85 }
 86 
 87 static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type,
 88                                 int flags, const char *dev_name, void *data)
 89 {
 90         struct dentry *root;
 91         root = mount_pseudo(fs_type, "anon_inode:", NULL,
 92                         &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC);
 93         if (!IS_ERR(root)) {
 94                 struct super_block *s = root->d_sb;
 95                 anon_inode_inode = anon_inode_mkinode(s);
 96                 if (IS_ERR(anon_inode_inode)) {
 97                         dput(root);
 98                         deactivate_locked_super(s);
 99                         root = ERR_CAST(anon_inode_inode);
100                 }
101         }
102         return root;
103 }
104 
105 static struct file_system_type anon_inode_fs_type = {
106         .name           = "anon_inodefs",
107         .mount          = anon_inodefs_mount,
108         .kill_sb        = kill_anon_super,
109 };
110 
111 /**
112  * anon_inode_getfile - creates a new file instance by hooking it up to an
113  *                      anonymous inode, and a dentry that describe the "class"
114  *                      of the file
115  *
116  * @name:    [in]    name of the "class" of the new file
117  * @fops:    [in]    file operations for the new file
118  * @priv:    [in]    private data for the new file (will be file's private_data)
119  * @flags:   [in]    flags
120  *
121  * Creates a new file by hooking it on a single inode. This is useful for files
122  * that do not need to have a full-fledged inode in order to operate correctly.
123  * All the files created with anon_inode_getfile() will share a single inode,
124  * hence saving memory and avoiding code duplication for the file/inode/dentry
125  * setup.  Returns the newly created file* or an error pointer.
126  */
127 struct file *anon_inode_getfile(const char *name,
128                                 const struct file_operations *fops,
129                                 void *priv, int flags)
130 {
131         struct qstr this;
132         struct path path;
133         struct file *file;
134         int error;
135 
136         if (IS_ERR(anon_inode_inode))
137                 return ERR_PTR(-ENODEV);
138 
139         if (fops->owner && !try_module_get(fops->owner))
140                 return ERR_PTR(-ENOENT);
141 
142         /*
143          * Link the inode to a directory entry by creating a unique name
144          * using the inode sequence number.
145          */
146         error = -ENOMEM;
147         this.name = name;
148         this.len = strlen(name);
149         this.hash = 0;
150         path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this);
151         if (!path.dentry)
152                 goto err_module;
153 
154         path.mnt = mntget(anon_inode_mnt);
155         /*
156          * We know the anon_inode inode count is always greater than zero,
157          * so ihold() is safe.
158          */
159         ihold(anon_inode_inode);
160 
161         d_instantiate(path.dentry, anon_inode_inode);
162 
163         error = -ENFILE;
164         file = alloc_file(&path, OPEN_FMODE(flags), fops);
165         if (!file)
166                 goto err_dput;
167         file->f_mapping = anon_inode_inode->i_mapping;
168 
169         file->f_pos = 0;
170         file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
171         file->f_version = 0;
172         file->private_data = priv;
173 
174         return file;
175 
176 err_dput:
177         path_put(&path);
178 err_module:
179         module_put(fops->owner);
180         return ERR_PTR(error);
181 }
182 EXPORT_SYMBOL_GPL(anon_inode_getfile);
183 
184 /**
185  * anon_inode_getfd - creates a new file instance by hooking it up to an
186  *                    anonymous inode, and a dentry that describe the "class"
187  *                    of the file
188  *
189  * @name:    [in]    name of the "class" of the new file
190  * @fops:    [in]    file operations for the new file
191  * @priv:    [in]    private data for the new file (will be file's private_data)
192  * @flags:   [in]    flags
193  *
194  * Creates a new file by hooking it on a single inode. This is useful for files
195  * that do not need to have a full-fledged inode in order to operate correctly.
196  * All the files created with anon_inode_getfd() will share a single inode,
197  * hence saving memory and avoiding code duplication for the file/inode/dentry
198  * setup.  Returns new descriptor or an error code.
199  */
200 int anon_inode_getfd(const char *name, const struct file_operations *fops,
201                      void *priv, int flags)
202 {
203         int error, fd;
204         struct file *file;
205 
206         error = get_unused_fd_flags(flags);
207         if (error < 0)
208                 return error;
209         fd = error;
210 
211         file = anon_inode_getfile(name, fops, priv, flags);
212         if (IS_ERR(file)) {
213                 error = PTR_ERR(file);
214                 goto err_put_unused_fd;
215         }
216         fd_install(fd, file);
217 
218         return fd;
219 
220 err_put_unused_fd:
221         put_unused_fd(fd);
222         return error;
223 }
224 EXPORT_SYMBOL_GPL(anon_inode_getfd);
225 
226 static int __init anon_inode_init(void)
227 {
228         int error;
229 
230         error = register_filesystem(&anon_inode_fs_type);
231         if (error)
232                 goto err_exit;
233         anon_inode_mnt = kern_mount(&anon_inode_fs_type);
234         if (IS_ERR(anon_inode_mnt)) {
235                 error = PTR_ERR(anon_inode_mnt);
236                 goto err_unregister_filesystem;
237         }
238         return 0;
239 
240 err_unregister_filesystem:
241         unregister_filesystem(&anon_inode_fs_type);
242 err_exit:
243         panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
244 }
245 
246 fs_initcall(anon_inode_init);
247 
248 

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