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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/slab.h>
 16 #include <linux/init.h>
 17 #include <linux/fs.h>
 18 #include <linux/mount.h>
 19 #include <linux/module.h>
 20 #include <linux/kernel.h>
 21 #include <linux/magic.h>
 22 #include <linux/anon_inodes.h>
 23 
 24 #include <asm/uaccess.h>
 25 
 26 static struct vfsmount *anon_inode_mnt __read_mostly;
 27 static struct inode *anon_inode_inode;
 28 static const struct file_operations anon_inode_fops;
 29 
 30 static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags,
 31                                const char *dev_name, void *data,
 32                                struct vfsmount *mnt)
 33 {
 34         return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC,
 35                              mnt);
 36 }
 37 
 38 static int anon_inodefs_delete_dentry(struct dentry *dentry)
 39 {
 40         /*
 41          * We faked vfs to believe the dentry was hashed when we created it.
 42          * Now we restore the flag so that dput() will work correctly.
 43          */
 44         dentry->d_flags |= DCACHE_UNHASHED;
 45         return 1;
 46 }
 47 
 48 static struct file_system_type anon_inode_fs_type = {
 49         .name           = "anon_inodefs",
 50         .get_sb         = anon_inodefs_get_sb,
 51         .kill_sb        = kill_anon_super,
 52 };
 53 static const struct dentry_operations anon_inodefs_dentry_operations = {
 54         .d_delete       = anon_inodefs_delete_dentry,
 55 };
 56 
 57 /*
 58  * nop .set_page_dirty method so that people can use .page_mkwrite on
 59  * anon inodes.
 60  */
 61 static int anon_set_page_dirty(struct page *page)
 62 {
 63         return 0;
 64 };
 65 
 66 static const struct address_space_operations anon_aops = {
 67         .set_page_dirty = anon_set_page_dirty,
 68 };
 69 
 70 /**
 71  * anon_inode_getfd - creates a new file instance by hooking it up to an
 72  *                    anonymous inode, and a dentry that describe the "class"
 73  *                    of the file
 74  *
 75  * @name:    [in]    name of the "class" of the new file
 76  * @fops:    [in]    file operations for the new file
 77  * @priv:    [in]    private data for the new file (will be file's private_data)
 78  * @flags:   [in]    flags
 79  *
 80  * Creates a new file by hooking it on a single inode. This is useful for files
 81  * that do not need to have a full-fledged inode in order to operate correctly.
 82  * All the files created with anon_inode_getfile() will share a single inode,
 83  * hence saving memory and avoiding code duplication for the file/inode/dentry
 84  * setup.  Returns the newly created file* or an error pointer.
 85  */
 86 struct file *anon_inode_getfile(const char *name,
 87                                 const struct file_operations *fops,
 88                                 void *priv, int flags)
 89 {
 90         struct qstr this;
 91         struct dentry *dentry;
 92         struct file *file;
 93         int error;
 94 
 95         if (IS_ERR(anon_inode_inode))
 96                 return ERR_PTR(-ENODEV);
 97 
 98         if (fops->owner && !try_module_get(fops->owner))
 99                 return ERR_PTR(-ENOENT);
100 
101         /*
102          * Link the inode to a directory entry by creating a unique name
103          * using the inode sequence number.
104          */
105         error = -ENOMEM;
106         this.name = name;
107         this.len = strlen(name);
108         this.hash = 0;
109         dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
110         if (!dentry)
111                 goto err_module;
112 
113         /*
114          * We know the anon_inode inode count is always greater than zero,
115          * so we can avoid doing an igrab() and we can use an open-coded
116          * atomic_inc().
117          */
118         atomic_inc(&anon_inode_inode->i_count);
119 
120         dentry->d_op = &anon_inodefs_dentry_operations;
121         /* Do not publish this dentry inside the global dentry hash table */
122         dentry->d_flags &= ~DCACHE_UNHASHED;
123         d_instantiate(dentry, anon_inode_inode);
124 
125         error = -ENFILE;
126         file = alloc_file(anon_inode_mnt, dentry,
127                           FMODE_READ | FMODE_WRITE, fops);
128         if (!file)
129                 goto err_dput;
130         file->f_mapping = anon_inode_inode->i_mapping;
131 
132         file->f_pos = 0;
133         file->f_flags = O_RDWR | (flags & O_NONBLOCK);
134         file->f_version = 0;
135         file->private_data = priv;
136 
137         return file;
138 
139 err_dput:
140         dput(dentry);
141 err_module:
142         module_put(fops->owner);
143         return ERR_PTR(error);
144 }
145 EXPORT_SYMBOL_GPL(anon_inode_getfile);
146 
147 /**
148  * anon_inode_getfd - creates a new file instance by hooking it up to an
149  *                    anonymous inode, and a dentry that describe the "class"
150  *                    of the file
151  *
152  * @name:    [in]    name of the "class" of the new file
153  * @fops:    [in]    file operations for the new file
154  * @priv:    [in]    private data for the new file (will be file's private_data)
155  * @flags:   [in]    flags
156  *
157  * Creates a new file by hooking it on a single inode. This is useful for files
158  * that do not need to have a full-fledged inode in order to operate correctly.
159  * All the files created with anon_inode_getfd() will share a single inode,
160  * hence saving memory and avoiding code duplication for the file/inode/dentry
161  * setup.  Returns new descriptor or an error code.
162  */
163 int anon_inode_getfd(const char *name, const struct file_operations *fops,
164                      void *priv, int flags)
165 {
166         int error, fd;
167         struct file *file;
168 
169         error = get_unused_fd_flags(flags);
170         if (error < 0)
171                 return error;
172         fd = error;
173 
174         file = anon_inode_getfile(name, fops, priv, flags);
175         if (IS_ERR(file)) {
176                 error = PTR_ERR(file);
177                 goto err_put_unused_fd;
178         }
179         fd_install(fd, file);
180 
181         return fd;
182 
183 err_put_unused_fd:
184         put_unused_fd(fd);
185         return error;
186 }
187 EXPORT_SYMBOL_GPL(anon_inode_getfd);
188 
189 /*
190  * A single inode exists for all anon_inode files. Contrary to pipes,
191  * anon_inode inodes have no associated per-instance data, so we need
192  * only allocate one of them.
193  */
194 static struct inode *anon_inode_mkinode(void)
195 {
196         struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
197 
198         if (!inode)
199                 return ERR_PTR(-ENOMEM);
200 
201         inode->i_fop = &anon_inode_fops;
202 
203         inode->i_mapping->a_ops = &anon_aops;
204 
205         /*
206          * Mark the inode dirty from the very beginning,
207          * that way it will never be moved to the dirty
208          * list because mark_inode_dirty() will think
209          * that it already _is_ on the dirty list.
210          */
211         inode->i_state = I_DIRTY;
212         inode->i_mode = S_IRUSR | S_IWUSR;
213         inode->i_uid = current_fsuid();
214         inode->i_gid = current_fsgid();
215         inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
216         return inode;
217 }
218 
219 static int __init anon_inode_init(void)
220 {
221         int error;
222 
223         error = register_filesystem(&anon_inode_fs_type);
224         if (error)
225                 goto err_exit;
226         anon_inode_mnt = kern_mount(&anon_inode_fs_type);
227         if (IS_ERR(anon_inode_mnt)) {
228                 error = PTR_ERR(anon_inode_mnt);
229                 goto err_unregister_filesystem;
230         }
231         anon_inode_inode = anon_inode_mkinode();
232         if (IS_ERR(anon_inode_inode)) {
233                 error = PTR_ERR(anon_inode_inode);
234                 goto err_mntput;
235         }
236 
237         return 0;
238 
239 err_mntput:
240         mntput(anon_inode_mnt);
241 err_unregister_filesystem:
242         unregister_filesystem(&anon_inode_fs_type);
243 err_exit:
244         panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
245 }
246 
247 fs_initcall(anon_inode_init);
248 
249 

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