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/*

 *  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 an

 *                    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,

 * 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 file *file;

        int error, fd;

        if (IS_ERR(anon_inode_inode))

                return -ENODEV;

        file = get_empty_filp();

        if (!file)

                return -ENFILE;

        error = get_unused_fd();

        if (error < 0)

                goto err_put_filp;

        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;

        /*

         * We know the anon_inode inode count is always greater than zero,

         * so we can avoid doing an igrab() and we can use an open-coded

         * atomic_inc().

         */

        atomic_inc(&anon_inode_inode->i_count);

        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, anon_inode_inode);

        file->f_path.mnt = mntget(anon_inode_mnt);

        file->f_path.dentry = dentry;

        file->f_mapping = anon_inode_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 = anon_inode_inode;

        *pfile = file;

        return 0;

err_put_unused_fd:

        put_unused_fd(fd);

err_put_filp:

        put_filp(file);

        return error;

}

EXPORT_SYMBOL_GPL(anon_inode_getfd);

/*

 * A single inode exists for all anon_inode files. Contrary to pipes,

 * anon_inode inodes have no associated per-instance data, so we need

 * only allocate one 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);