The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/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 

Cache object: 09a9d3fb420663e7be1d980b32a79123


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