/*
 *  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/cred.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/sched.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 const struct dentry_operations anon_inodefs_dentry_operations = {
        .d_delete       = anon_inodefs_delete_dentry,
};

/*
 * nop .set_page_dirty method so that people can use .page_mkwrite on
 * anon inodes.
 */
static int anon_set_page_dirty(struct page *page)
{
        return 0;
};

static const struct address_space_operations anon_aops = {
        .set_page_dirty = anon_set_page_dirty,
};

/**
 * 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
 *
 * @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)
 * @flags:   [in]    flags
 *
 * 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_getfile() will share a single inode,
 * hence saving memory and avoiding code duplication for the file/inode/dentry
 * setup.  Returns the newly created file* or an error pointer.
 */
struct file *anon_inode_getfile(const char *name,
                                const struct file_operations *fops,
                                void *priv, int flags)
{
        struct qstr this;
        struct dentry *dentry;
        struct file *file;
        int error;

        if (IS_ERR(anon_inode_inode))
                return ERR_PTR(-ENODEV);

        if (fops->owner && !try_module_get(fops->owner))
                return ERR_PTR(-ENOENT);

        /*
         * 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_module;

        /*
         * 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);

        error = -ENFILE;
        file = alloc_file(anon_inode_mnt, dentry,
                          FMODE_READ | FMODE_WRITE, fops);
        if (!file)
                goto err_dput;
        file->f_mapping = anon_inode_inode->i_mapping;

        file->f_pos = 0;
        file->f_flags = O_RDWR | (flags & O_NONBLOCK);
        file->f_version = 0;
        file->private_data = priv;

        return file;

err_dput:
        dput(dentry);
err_module:
        module_put(fops->owner);
        return ERR_PTR(error);
}
EXPORT_SYMBOL_GPL(anon_inode_getfile);

/**
 * 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
 *
 * @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)
 * @flags:   [in]    flags
 *
 * 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.  Returns new descriptor or an error code.
 */
int anon_inode_getfd(const char *name, const struct file_operations *fops,
                     void *priv, int flags)
{
        int error, fd;
        struct file *file;

        error = get_unused_fd_flags(flags);
        if (error < 0)
                return error;
        fd = error;

        file = anon_inode_getfile(name, fops, priv, flags);
        if (IS_ERR(file)) {
                error = PTR_ERR(file);
                goto err_put_unused_fd;
        }
        fd_install(fd, file);

        return fd;

err_put_unused_fd:
        put_unused_fd(fd);
        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;

        inode->i_mapping->a_ops = &anon_aops;

        /*
         * 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);