diff options
Diffstat (limited to 'fs/anon_inodes.c')
| -rw-r--r-- | fs/anon_inodes.c | 200 |
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); + |