5 files changed, 228 insertions, 0 deletions

diff --git a/fs/Makefile b/fs/Makefile
index 9edf4112bee0..b5cd46a88cb0 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -22,6 +22,7 @@ endif
 obj-$(CONFIG_INOTIFY)           += inotify.o
 obj-$(CONFIG_INOTIFY_USER)      += inotify_user.o
 obj-$(CONFIG_EPOLL)             += eventpoll.o
+obj-$(CONFIG_ANON_INODES)       += anon_inodes.o
 obj-$(CONFIG_COMPAT)            += compat.o compat_ioctl.o
 
 nfsd-$(CONFIG_NFSD)             := nfsctl.o
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);
+
diff --git a/include/linux/anon_inodes.h b/include/linux/anon_inodes.h
new file mode 100644
index 000000000000..b2e1ba325b9a
--- /dev/null
+++ b/include/linux/anon_inodes.h
@@ -0,0 +1,16 @@
+/*
+ *  include/linux/anon_inodes.h
+ *
+ *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
+ *
+ */
+
+#ifndef _LINUX_ANON_INODES_H
+#define _LINUX_ANON_INODES_H
+
+int anon_inode_getfd(int *pfd, struct inode **pinode, struct file **pfile,
+                     const char *name, const struct file_operations *fops,
+                     void *priv);
+
+#endif /* _LINUX_ANON_INODES_H */
+
diff --git a/include/linux/magic.h b/include/linux/magic.h
index a9c6567fe70c..9d713c03e3da 100644
--- a/include/linux/magic.h
+++ b/include/linux/magic.h
@@ -14,6 +14,7 @@
 #define ISOFS_SUPER_MAGIC       0x9660
 #define JFFS2_SUPER_MAGIC       0x72b6
 #define KVMFS_SUPER_MAGIC       0x19700426
+#define ANON_INODE_FS_MAGIC     0x09041934
 
 #define MINIX_SUPER_MAGIC       0x137F          /* original minix fs */
 #define MINIX_SUPER_MAGIC2      0x138F          /* minix fs, 30 char names */
diff --git a/init/Kconfig b/init/Kconfig
index 322b1f8c21b3..a80bd8326bc6 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -475,9 +475,19 @@ config FUTEX
           support for "fast userspace mutexes".  The resulting kernel may not
           run glibc-based applications correctly.
 
+config ANON_INODES
+        bool "Enable anonymous inode source" if EMBEDDED
+        default y
+        help
+          Anonymous inode source for pseudo-files like epoll, signalfd,
+          timerfd and eventfd.
+
+          If unsure, say Y.
+
 config EPOLL
         bool "Enable eventpoll support" if EMBEDDED
         default y
+        depends on ANON_INODES
         help
           Disabling this option will cause the kernel to be built without
           support for epoll family of system calls.