anon_inodes.c

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/*
 *  fs/anon_inodes.c
 *
 *  Copyright (C) 2007  Davide Libenzi <[email protected]>
 *
 *  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/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;

/*
 * anon_inodefs_dname() is called from d_path().
 */
static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
{
    return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
                dentry->d_name.name);
}

static const struct dentry_operations anon_inodefs_dentry_operations = {
    .d_dname    = anon_inodefs_dname,
};

/*
 * 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,
};

/*
 * 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(struct super_block *s)
{
    struct inode *inode = new_inode_pseudo(s);

    if (!inode)
        return ERR_PTR(-ENOMEM);

    inode->i_ino = get_next_ino();
    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_flags |= S_PRIVATE;
    inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
    return inode;
}

static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type,
                int flags, const char *dev_name, void *data)
{
    struct dentry *root;
    root = mount_pseudo(fs_type, "anon_inode:", NULL,
            &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC);
    if (!IS_ERR(root)) {
        struct super_block *s = root->d_sb;
        anon_inode_inode = anon_inode_mkinode(s);
        if (IS_ERR(anon_inode_inode)) {
            dput(root);
            deactivate_locked_super(s);
            root = ERR_CAST(anon_inode_inode);
        }
    }
    return root;
}

static struct file_system_type anon_inode_fs_type = {
    .name       = "anon_inodefs",
    .mount      = anon_inodefs_mount,
    .kill_sb    = kill_anon_super,
};

struct file *anon_inode_getfile(const char *name,
                const struct file_operations *fops,
                void *priv, int flags)
{
    struct qstr this;
    struct path path;
    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;
    path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this);
    if (!path.dentry)
        goto err_module;

    path.mnt = mntget(anon_inode_mnt);
    /*
     * We know the anon_inode inode count is always greater than zero,
     * so ihold() is safe.
     */
    ihold(anon_inode_inode);

    d_instantiate(path.dentry, anon_inode_inode);

    error = -ENFILE;
    file = alloc_file(&path, OPEN_FMODE(flags), fops);
    if (!file)
        goto err_dput;
    file->f_mapping = anon_inode_inode->i_mapping;

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

    return file;

err_dput:
    path_put(&path);
err_module:
    module_put(fops->owner);
    return ERR_PTR(error);
}
EXPORT_SYMBOL_GPL(anon_inode_getfile);

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);

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;
    }
    return 0;

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);