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/*
* Resizable simple ram filesystem for Linux.
*
* Copyright (C) 2000 Linus Torvalds.
* 2000 Transmeta Corp.
*
* Usage limits added by David Gibson, Linuxcare Australia.
* This file is released under the GPL.
*/
/*
* NOTE! This filesystem is probably most useful
* not as a real filesystem, but as an example of
* how virtual filesystems can be written.
*
* It doesn't get much simpler than this. Consider
* that this file implements the full semantics of
* a POSIX-compliant read-write filesystem.
*
* Note in particular how the filesystem does not
* need to implement any data structures of its own
* to keep track of the virtual data: using the VFS
* caches is sufficient.
*/
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/locks.h>
#include <asm/uaccess.h>
/* some random number */
#define RAMFS_MAGIC 0x858458f6
static struct super_operations ramfs_ops;
static struct address_space_operations ramfs_aops;
static struct file_operations ramfs_dir_operations;
static struct file_operations ramfs_file_operations;
static struct inode_operations ramfs_dir_inode_operations;
static int ramfs_statfs(struct super_block *sb, struct statfs *buf)
{
buf->f_type = RAMFS_MAGIC;
buf->f_bsize = PAGE_CACHE_SIZE;
buf->f_namelen = 255;
return 0;
}
/*
* Lookup the data. This is trivial - if the dentry didn't already
* exist, we know it is negative.
*/
static struct dentry * ramfs_lookup(struct inode *dir, struct dentry *dentry)
{
d_add(dentry, NULL);
return NULL;
}
/*
* Read a page. Again trivial. If it didn't already exist
* in the page cache, it is zero-filled.
*/
static int ramfs_readpage(struct file *file, struct page * page)
{
if (!Page_Uptodate(page)) {
memset(kmap(page), 0, PAGE_CACHE_SIZE);
kunmap(page);
flush_dcache_page(page);
SetPageUptodate(page);
}
UnlockPage(page);
return 0;
}
static int ramfs_prepare_write(struct file *file, struct page *page, unsigned offset, unsigned to)
{
void *addr = kmap(page);
if (!Page_Uptodate(page)) {
memset(addr, 0, PAGE_CACHE_SIZE);
flush_dcache_page(page);
SetPageUptodate(page);
}
SetPageDirty(page);
return 0;
}
static int ramfs_commit_write(struct file *file, struct page *page, unsigned offset, unsigned to)
{
struct inode *inode = page->mapping->host;
loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
kunmap(page);
if (pos > inode->i_size)
inode->i_size = pos;
return 0;
}
struct inode *ramfs_get_inode(struct super_block *sb, int mode, int dev)
{
struct inode * inode = new_inode(sb);
if (inode) {
inode->i_mode = mode;
inode->i_uid = current->fsuid;
inode->i_gid = current->fsgid;
inode->i_blksize = PAGE_CACHE_SIZE;
inode->i_blocks = 0;
inode->i_rdev = NODEV;
inode->i_mapping->a_ops = &ramfs_aops;
inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
switch (mode & S_IFMT) {
default:
init_special_inode(inode, mode, dev);
break;
case S_IFREG:
inode->i_fop = &ramfs_file_operations;
break;
case S_IFDIR:
inode->i_op = &ramfs_dir_inode_operations;
inode->i_fop = &ramfs_dir_operations;
break;
case S_IFLNK:
inode->i_op = &page_symlink_inode_operations;
break;
}
}
return inode;
}
/*
* File creation. Allocate an inode, and we're done..
*/
static int ramfs_mknod(struct inode *dir, struct dentry *dentry, int mode, int dev)
{
struct inode * inode = ramfs_get_inode(dir->i_sb, mode, dev);
int error = -ENOSPC;
if (inode) {
d_instantiate(dentry, inode);
dget(dentry); /* Extra count - pin the dentry in core */
error = 0;
}
return error;
}
static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, int mode)
{
return ramfs_mknod(dir, dentry, mode | S_IFDIR, 0);
}
static int ramfs_create(struct inode *dir, struct dentry *dentry, int mode)
{
return ramfs_mknod(dir, dentry, mode | S_IFREG, 0);
}
/*
* Link a file..
*/
static int ramfs_link(struct dentry *old_dentry, struct inode * dir, struct dentry * dentry)
{
struct inode *inode = old_dentry->d_inode;
if (S_ISDIR(inode->i_mode))
return -EPERM;
inode->i_nlink++;
atomic_inc(&inode->i_count); /* New dentry reference */
dget(dentry); /* Extra pinning count for the created dentry */
d_instantiate(dentry, inode);
return 0;
}
static inline int ramfs_positive(struct dentry *dentry)
{
return dentry->d_inode && !d_unhashed(dentry);
}
/*
* Check that a directory is empty (this works
* for regular files too, they'll just always be
* considered empty..).
*
* Note that an empty directory can still have
* children, they just all have to be negative..
*/
static int ramfs_empty(struct dentry *dentry)
{
struct list_head *list;
spin_lock(&dcache_lock);
list = dentry->d_subdirs.next;
while (list != &dentry->d_subdirs) {
struct dentry *de = list_entry(list, struct dentry, d_child);
if (ramfs_positive(de)) {
spin_unlock(&dcache_lock);
return 0;
}
list = list->next;
}
spin_unlock(&dcache_lock);
return 1;
}
/*
* This works for both directories and regular files.
* (non-directories will always have empty subdirs)
*/
static int ramfs_unlink(struct inode * dir, struct dentry *dentry)
{
int retval = -ENOTEMPTY;
if (ramfs_empty(dentry)) {
struct inode *inode = dentry->d_inode;
inode->i_nlink--;
dput(dentry); /* Undo the count from "create" - this does all the work */
retval = 0;
}
return retval;
}
#define ramfs_rmdir ramfs_unlink
/*
* The VFS layer already does all the dentry stuff for rename,
* we just have to decrement the usage count for the target if
* it exists so that the VFS layer correctly free's it when it
* gets overwritten.
*/
static int ramfs_rename(struct inode * old_dir, struct dentry *old_dentry, struct inode * new_dir,struct dentry *new_dentry)
{
int error = -ENOTEMPTY;
if (ramfs_empty(new_dentry)) {
struct inode *inode = new_dentry->d_inode;
if (inode) {
inode->i_nlink--;
dput(new_dentry);
}
error = 0;
}
return error;
}
static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname)
{
int error;
error = ramfs_mknod(dir, dentry, S_IFLNK | S_IRWXUGO, 0);
if (!error) {
int l = strlen(symname)+1;
struct inode *inode = dentry->d_inode;
error = block_symlink(inode, symname, l);
}
return error;
}
static int ramfs_sync_file(struct file * file, struct dentry *dentry, int datasync)
{
return 0;
}
static struct address_space_operations ramfs_aops = {
readpage: ramfs_readpage,
writepage: fail_writepage,
prepare_write: ramfs_prepare_write,
commit_write: ramfs_commit_write
};
static struct file_operations ramfs_file_operations = {
read: generic_file_read,
write: generic_file_write,
mmap: generic_file_mmap,
fsync: ramfs_sync_file,
};
static struct file_operations ramfs_dir_operations = {
read: generic_read_dir,
readdir: dcache_readdir,
fsync: ramfs_sync_file,
};
static struct inode_operations ramfs_dir_inode_operations = {
create: ramfs_create,
lookup: ramfs_lookup,
link: ramfs_link,
unlink: ramfs_unlink,
symlink: ramfs_symlink,
mkdir: ramfs_mkdir,
rmdir: ramfs_rmdir,
mknod: ramfs_mknod,
rename: ramfs_rename,
};
static struct super_operations ramfs_ops = {
statfs: ramfs_statfs,
put_inode: force_delete,
};
static struct super_block *ramfs_read_super(struct super_block * sb, void * data, int silent)
{
struct inode * inode;
struct dentry * root;
sb->s_blocksize = PAGE_CACHE_SIZE;
sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
sb->s_magic = RAMFS_MAGIC;
sb->s_op = &ramfs_ops;
inode = ramfs_get_inode(sb, S_IFDIR | 0755, 0);
if (!inode)
return NULL;
root = d_alloc_root(inode);
if (!root) {
iput(inode);
return NULL;
}
sb->s_root = root;
return sb;
}
static DECLARE_FSTYPE(ramfs_fs_type, "ramfs", ramfs_read_super, FS_LITTER);
static int __init init_ramfs_fs(void)
{
return register_filesystem(&ramfs_fs_type);
}
static void __exit exit_ramfs_fs(void)
{
unregister_filesystem(&ramfs_fs_type);
}
module_init(init_ramfs_fs)
module_exit(exit_ramfs_fs)
MODULE_LICENSE("GPL");
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