1 files changed, 200 insertions, 0 deletions
diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
new file mode 100644
index 000000000000..40fe3a3222e4
--- /dev/null
+++ b/fs/anon_inodes.c
@@ -0,0 +1,200 @@
+/*
+ *  fs/anon_inodes.c
+ *
+ *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
+ *
+ *  Thanks to Arnd Bergmann for code review and suggestions.
+ *  More changes for Thomas Gleixner suggestions.
+ *
+ */
+
+#include <linux/file.h>
+#include <linux/poll.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/mount.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/magic.h>
+#include <linux/anon_inodes.h>
+
+#include <asm/uaccess.h>
+
+static struct vfsmount *anon_inode_mnt __read_mostly;
+static struct inode *anon_inode_inode;
+static const struct file_operations anon_inode_fops;
+
+static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags,
+			       const char *dev_name, void *data,
+			       struct vfsmount *mnt)
+{
+	return get_sb_pseudo(fs_type, "anon_inode:", NULL, ANON_INODE_FS_MAGIC,
+			     mnt);
+}
+
+static int anon_inodefs_delete_dentry(struct dentry *dentry)
+{
+	/*
+	 * We faked vfs to believe the dentry was hashed when we created it.
+	 * Now we restore the flag so that dput() will work correctly.
+	 */
+	dentry->d_flags |= DCACHE_UNHASHED;
+	return 1;
+}
+
+static struct file_system_type anon_inode_fs_type = {
+	.name		= "anon_inodefs",
+	.get_sb		= anon_inodefs_get_sb,
+	.kill_sb	= kill_anon_super,
+};
+static struct dentry_operations anon_inodefs_dentry_operations = {
+	.d_delete	= anon_inodefs_delete_dentry,
+};
+
+/**
+ * anon_inode_getfd - creates a new file instance by hooking it up to and
+ *                    anonymous inode, and a dentry that describe the "class"
+ *                    of the file
+ *
+ * @pfd:     [out]   pointer to the file descriptor
+ * @dpinode: [out]   pointer to the inode
+ * @pfile:   [out]   pointer to the file struct
+ * @name:    [in]    name of the "class" of the new file
+ * @fops     [in]    file operations for the new file
+ * @priv     [in]    private data for the new file (will be file's private_data)
+ *
+ * Creates a new file by hooking it on a single inode. This is useful for files
+ * that do not need to have a full-fledged inode in order to operate correctly.
+ * All the files created with anon_inode_getfd() will share a single inode, by
+ * hence saving memory and avoiding code duplication for the file/inode/dentry
+ * setup.
+ */
+int anon_inode_getfd(int *pfd, struct inode **pinode, struct file **pfile,
+		     const char *name, const struct file_operations *fops,
+		     void *priv)
+{
+	struct qstr this;
+	struct dentry *dentry;
+	struct inode *inode;
+	struct file *file;
+	int error, fd;
+
+	if (IS_ERR(anon_inode_inode))
+		return -ENODEV;
+	file = get_empty_filp();
+	if (!file)
+		return -ENFILE;
+
+	inode = igrab(anon_inode_inode);
+	if (IS_ERR(inode)) {
+		error = PTR_ERR(inode);
+		goto err_put_filp;
+	}
+
+	error = get_unused_fd();
+	if (error < 0)
+		goto err_iput;
+	fd = error;
+
+	/*
+	 * Link the inode to a directory entry by creating a unique name
+	 * using the inode sequence number.
+	 */
+	error = -ENOMEM;
+	this.name = name;
+	this.len = strlen(name);
+	this.hash = 0;
+	dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
+	if (!dentry)
+		goto err_put_unused_fd;
+	dentry->d_op = &anon_inodefs_dentry_operations;
+	/* Do not publish this dentry inside the global dentry hash table */
+	dentry->d_flags &= ~DCACHE_UNHASHED;
+	d_instantiate(dentry, inode);
+
+	file->f_path.mnt = mntget(anon_inode_mnt);
+	file->f_path.dentry = dentry;
+	file->f_mapping = inode->i_mapping;
+
+	file->f_pos = 0;
+	file->f_flags = O_RDWR;
+	file->f_op = fops;
+	file->f_mode = FMODE_READ | FMODE_WRITE;
+	file->f_version = 0;
+	file->private_data = priv;
+
+	fd_install(fd, file);
+
+	*pfd = fd;
+	*pinode = inode;
+	*pfile = file;
+	return 0;
+
+err_put_unused_fd:
+	put_unused_fd(fd);
+err_iput:
+	iput(inode);
+err_put_filp:
+	put_filp(file);
+	return error;
+}
+
+/*
+ * A single inode exist for all anon_inode files. Contrary to pipes,
+ * anon_inode inodes has no per-instance data associated, so we can avoid
+ * the allocation of multiple of them.
+ */
+static struct inode *anon_inode_mkinode(void)
+{
+	struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
+
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+
+	inode->i_fop = &anon_inode_fops;
+
+	/*
+	 * Mark the inode dirty from the very beginning,
+	 * that way it will never be moved to the dirty
+	 * list because mark_inode_dirty() will think
+	 * that it already _is_ on the dirty list.
+	 */
+	inode->i_state = I_DIRTY;
+	inode->i_mode = S_IRUSR | S_IWUSR;
+	inode->i_uid = current->fsuid;
+	inode->i_gid = current->fsgid;
+	inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
+	return inode;
+}
+
+static int __init anon_inode_init(void)
+{
+	int error;
+
+	error = register_filesystem(&anon_inode_fs_type);
+	if (error)
+		goto err_exit;
+	anon_inode_mnt = kern_mount(&anon_inode_fs_type);
+	if (IS_ERR(anon_inode_mnt)) {
+		error = PTR_ERR(anon_inode_mnt);
+		goto err_unregister_filesystem;
+	}
+	anon_inode_inode = anon_inode_mkinode();
+	if (IS_ERR(anon_inode_inode)) {
+		error = PTR_ERR(anon_inode_inode);
+		goto err_mntput;
+	}
+
+	return 0;
+
+err_mntput:
+	mntput(anon_inode_mnt);
+err_unregister_filesystem:
+	unregister_filesystem(&anon_inode_fs_type);
+err_exit:
+	panic(KERN_ERR "anon_inode_init() failed (%d)\n", error);
+}
+
+fs_initcall(anon_inode_init);
+