patch-2.3.99-pre4 linux/fs/ramfs/inode.c

• Lines: 394
• Date: Tue Apr 11 11:02:10 2000
• Orig file: v2.3.99-pre3/linux/fs/ramfs/inode.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.3.99-pre3/linux/fs/ramfs/inode.c linux/fs/ramfs/inode.c
@@ -0,0 +1,393 @@
+/*
+ * Resizable simple ram filesystem for Linux.
+ *
+ * Copyright (C) 2000 Linus Torvalds.
+ *               2000 Transmeta Corp.
+ *
+ * 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 dentry *dentry, struct page * page)
+{
+	if (!Page_Uptodate(page)) {
+		memset((void *) page_address(page), 0, PAGE_CACHE_SIZE);
+		SetPageUptodate(page);
+	}
+	UnlockPage(page);
+	return 0;
+}
+
+/*
+ * Writing: just make sure the page gets marked dirty, so that
+ * the page stealer won't grab it.
+ */
+static int ramfs_writepage(struct dentry * dentry, struct page *page)
+{
+	SetPageDirty(page);
+	return 0;
+}
+
+static int ramfs_prepare_write(struct file *file, struct page *page, unsigned offset, unsigned to)
+{
+	void *addr;
+
+	addr = (void *) kmap(page);
+	if (!Page_Uptodate(page)) {
+		memset(addr, 0, PAGE_CACHE_SIZE);
+		SetPageUptodate(page);
+	}
+	SetPageDirty(page);
+	return 0;
+}
+
+static int ramfs_commit_write(struct file *file, struct page *page, unsigned offset, unsigned to)
+{
+	struct inode *inode = (struct 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 = get_empty_inode();
+
+	if (inode) {
+		inode->i_sb = sb;
+		inode->i_dev = sb->s_dev;
+		inode->i_mode = mode;
+		inode->i_uid = current->fsuid;
+		inode->i_gid = current->fsgid;
+		inode->i_size = 0;
+		inode->i_blksize = PAGE_CACHE_SIZE;
+		inode->i_blocks = 0;
+		inode->i_rdev = dev;
+		inode->i_nlink = 1;
+		inode->i_op = NULL;
+		inode->i_fop = NULL;
+		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++;
+	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 = dentry->d_subdirs.next;
+
+	while (list != &dentry->d_subdirs) {
+		struct dentry *de = list_entry(list, struct dentry, d_child);
+
+		if (ramfs_positive(de))
+			return 0;
+		list = list->next;
+	}
+	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 */
+		d_delete(dentry);
+		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;
+}
+
+/*
+ * This really should be the same as the proc filldir,
+ * once proc does the "one dentry tree" thing..
+ */
+static int ramfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
+{
+	int i;
+	struct dentry *dentry = filp->f_dentry;
+
+	i = filp->f_pos;
+	switch (i) {
+		case 0:
+			if (filldir(dirent, ".", 1, i, dentry->d_inode->i_ino) < 0)
+				break;
+			i++;
+			filp->f_pos++;
+			/* fallthrough */
+		case 1:
+			if (filldir(dirent, "..", 2, i, dentry->d_parent->d_inode->i_ino) < 0)
+				break;
+			i++;
+			filp->f_pos++;
+			/* fallthrough */
+		default: {
+			struct list_head *list = dentry->d_subdirs.next;
+
+			int j = i-2;
+			for (;;) {
+				if (list == &dentry->d_subdirs)
+					return 0;
+				if (!j)
+					break;
+				j--;
+				list = list->next;
+			}
+
+			do {
+				struct dentry *de = list_entry(list, struct dentry, d_child);
+
+				if (ramfs_positive(de)) {
+					if (filldir(dirent, de->d_name.name, de->d_name.len, filp->f_pos, de->d_inode->i_ino) < 0)
+						break;
+				}
+				filp->f_pos++;
+				list = list->next;
+			} while (list != &dentry->d_subdirs);
+		}
+	}
+	return 0;
+}
+
+static struct address_space_operations ramfs_aops = {
+	readpage:	ramfs_readpage,
+	writepage:	ramfs_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
+};
+
+static struct file_operations ramfs_dir_operations = {
+	read:		generic_read_dir,
+	readdir:	ramfs_readdir,
+};
+
+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,
+};
+
+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, 0);
+
+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)