![David Howells](/assets/img/avatar_default.png)
Extend the get_sb() filesystem operation to take an extra argument that permits the VFS to pass in the target vfsmount that defines the mountpoint. The filesystem is then required to manually set the superblock and root dentry pointers. For most filesystems, this should be done with simple_set_mnt() which will set the superblock pointer and then set the root dentry to the superblock's s_root (as per the old default behaviour). The get_sb() op now returns an integer as there's now no need to return the superblock pointer. This patch permits a superblock to be implicitly shared amongst several mount points, such as can be done with NFS to avoid potential inode aliasing. In such a case, simple_set_mnt() would not be called, and instead the mnt_root and mnt_sb would be set directly. The patch also makes the following changes: (*) the get_sb_*() convenience functions in the core kernel now take a vfsmount pointer argument and return an integer, so most filesystems have to change very little. (*) If one of the convenience function is not used, then get_sb() should normally call simple_set_mnt() to instantiate the vfsmount. This will always return 0, and so can be tail-called from get_sb(). (*) generic_shutdown_super() now calls shrink_dcache_sb() to clean up the dcache upon superblock destruction rather than shrink_dcache_anon(). This is required because the superblock may now have multiple trees that aren't actually bound to s_root, but that still need to be cleaned up. The currently called functions assume that the whole tree is rooted at s_root, and that anonymous dentries are not the roots of trees which results in dentries being left unculled. However, with the way NFS superblock sharing are currently set to be implemented, these assumptions are violated: the root of the filesystem is simply a dummy dentry and inode (the real inode for '/' may well be inaccessible), and all the vfsmounts are rooted on anonymous[*] dentries with child trees. [*] Anonymous until discovered from another tree. (*) The documentation has been adjusted, including the additional bit of changing ext2_* into foo_* in the documentation. [akpm@osdl.org: convert ipath_fs, do other stuff] Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Cc: Nathan Scott <nathans@sgi.com> Cc: Roland Dreier <rolandd@cisco.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
231 lines
5.6 KiB
C
231 lines
5.6 KiB
C
/*
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* Resizable simple ram filesystem for Linux.
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*
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* Copyright (C) 2000 Linus Torvalds.
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* 2000 Transmeta Corp.
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*
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* Usage limits added by David Gibson, Linuxcare Australia.
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* This file is released under the GPL.
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*/
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/*
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* NOTE! This filesystem is probably most useful
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* not as a real filesystem, but as an example of
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* how virtual filesystems can be written.
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*
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* It doesn't get much simpler than this. Consider
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* that this file implements the full semantics of
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* a POSIX-compliant read-write filesystem.
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*
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* Note in particular how the filesystem does not
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* need to implement any data structures of its own
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* to keep track of the virtual data: using the VFS
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* caches is sufficient.
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*/
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#include <linux/module.h>
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#include <linux/fs.h>
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#include <linux/pagemap.h>
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#include <linux/highmem.h>
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#include <linux/time.h>
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#include <linux/init.h>
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#include <linux/string.h>
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#include <linux/smp_lock.h>
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#include <linux/backing-dev.h>
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#include <linux/ramfs.h>
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#include <asm/uaccess.h>
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#include "internal.h"
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/* some random number */
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#define RAMFS_MAGIC 0x858458f6
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static struct super_operations ramfs_ops;
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static struct inode_operations ramfs_dir_inode_operations;
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static struct backing_dev_info ramfs_backing_dev_info = {
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.ra_pages = 0, /* No readahead */
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.capabilities = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK |
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BDI_CAP_MAP_DIRECT | BDI_CAP_MAP_COPY |
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BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP,
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};
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struct inode *ramfs_get_inode(struct super_block *sb, int mode, dev_t dev)
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{
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struct inode * inode = new_inode(sb);
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if (inode) {
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inode->i_mode = mode;
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inode->i_uid = current->fsuid;
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inode->i_gid = current->fsgid;
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inode->i_blksize = PAGE_CACHE_SIZE;
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inode->i_blocks = 0;
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inode->i_mapping->a_ops = &ramfs_aops;
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inode->i_mapping->backing_dev_info = &ramfs_backing_dev_info;
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inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
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switch (mode & S_IFMT) {
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default:
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init_special_inode(inode, mode, dev);
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break;
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case S_IFREG:
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inode->i_op = &ramfs_file_inode_operations;
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inode->i_fop = &ramfs_file_operations;
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break;
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case S_IFDIR:
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inode->i_op = &ramfs_dir_inode_operations;
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inode->i_fop = &simple_dir_operations;
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/* directory inodes start off with i_nlink == 2 (for "." entry) */
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inode->i_nlink++;
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break;
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case S_IFLNK:
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inode->i_op = &page_symlink_inode_operations;
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break;
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}
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}
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return inode;
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}
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/*
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* File creation. Allocate an inode, and we're done..
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*/
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/* SMP-safe */
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static int
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ramfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
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{
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struct inode * inode = ramfs_get_inode(dir->i_sb, mode, dev);
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int error = -ENOSPC;
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if (inode) {
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if (dir->i_mode & S_ISGID) {
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inode->i_gid = dir->i_gid;
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if (S_ISDIR(mode))
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inode->i_mode |= S_ISGID;
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}
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d_instantiate(dentry, inode);
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dget(dentry); /* Extra count - pin the dentry in core */
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error = 0;
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dir->i_mtime = dir->i_ctime = CURRENT_TIME;
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}
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return error;
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}
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static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, int mode)
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{
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int retval = ramfs_mknod(dir, dentry, mode | S_IFDIR, 0);
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if (!retval)
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dir->i_nlink++;
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return retval;
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}
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static int ramfs_create(struct inode *dir, struct dentry *dentry, int mode, struct nameidata *nd)
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{
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return ramfs_mknod(dir, dentry, mode | S_IFREG, 0);
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}
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static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname)
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{
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struct inode *inode;
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int error = -ENOSPC;
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inode = ramfs_get_inode(dir->i_sb, S_IFLNK|S_IRWXUGO, 0);
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if (inode) {
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int l = strlen(symname)+1;
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error = page_symlink(inode, symname, l);
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if (!error) {
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if (dir->i_mode & S_ISGID)
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inode->i_gid = dir->i_gid;
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d_instantiate(dentry, inode);
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dget(dentry);
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dir->i_mtime = dir->i_ctime = CURRENT_TIME;
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} else
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iput(inode);
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}
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return error;
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}
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static struct inode_operations ramfs_dir_inode_operations = {
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.create = ramfs_create,
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.lookup = simple_lookup,
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.link = simple_link,
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.unlink = simple_unlink,
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.symlink = ramfs_symlink,
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.mkdir = ramfs_mkdir,
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.rmdir = simple_rmdir,
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.mknod = ramfs_mknod,
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.rename = simple_rename,
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};
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static struct super_operations ramfs_ops = {
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.statfs = simple_statfs,
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.drop_inode = generic_delete_inode,
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};
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static int ramfs_fill_super(struct super_block * sb, void * data, int silent)
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{
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struct inode * inode;
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struct dentry * root;
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sb->s_maxbytes = MAX_LFS_FILESIZE;
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sb->s_blocksize = PAGE_CACHE_SIZE;
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sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
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sb->s_magic = RAMFS_MAGIC;
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sb->s_op = &ramfs_ops;
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sb->s_time_gran = 1;
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inode = ramfs_get_inode(sb, S_IFDIR | 0755, 0);
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if (!inode)
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return -ENOMEM;
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root = d_alloc_root(inode);
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if (!root) {
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iput(inode);
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return -ENOMEM;
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}
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sb->s_root = root;
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return 0;
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}
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int ramfs_get_sb(struct file_system_type *fs_type,
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int flags, const char *dev_name, void *data, struct vfsmount *mnt)
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{
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return get_sb_nodev(fs_type, flags, data, ramfs_fill_super, mnt);
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}
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static int rootfs_get_sb(struct file_system_type *fs_type,
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int flags, const char *dev_name, void *data, struct vfsmount *mnt)
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{
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return get_sb_nodev(fs_type, flags|MS_NOUSER, data, ramfs_fill_super,
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mnt);
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}
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static struct file_system_type ramfs_fs_type = {
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.name = "ramfs",
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.get_sb = ramfs_get_sb,
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.kill_sb = kill_litter_super,
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};
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static struct file_system_type rootfs_fs_type = {
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.name = "rootfs",
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.get_sb = rootfs_get_sb,
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.kill_sb = kill_litter_super,
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};
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static int __init init_ramfs_fs(void)
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{
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return register_filesystem(&ramfs_fs_type);
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}
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static void __exit exit_ramfs_fs(void)
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{
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unregister_filesystem(&ramfs_fs_type);
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}
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module_init(init_ramfs_fs)
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module_exit(exit_ramfs_fs)
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int __init init_rootfs(void)
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{
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return register_filesystem(&rootfs_fs_type);
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}
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MODULE_LICENSE("GPL");
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