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Linux/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 <asm/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 
180 

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