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linux-next/fs/internal.h
Miklos Szeredi 4ed5e82fe7 vfs: protect remounting superblock read-only
Currently remouting superblock read-only is racy in a major way.

With the per mount read-only infrastructure it is now possible to
prevent most races, which this patch attempts.

Before starting the remount read-only, iterate through all mounts
belonging to the superblock and if none of them have any pending
writes, set sb->s_readonly_remount.  This indicates that remount is in
progress and no further write requests are allowed.  If the remount
succeeds set MS_RDONLY and reset s_readonly_remount.

If the remounting is unsuccessful just reset s_readonly_remount.
This can result in transient EROFS errors, despite the fact the
remount failed.  Unfortunately hodling off writes is difficult as
remount itself may touch the filesystem (e.g. through load_nls())
which would deadlock.

A later patch deals with delayed writes due to nlink going to zero.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Tested-by: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-01-06 23:20:12 -05:00

122 lines
2.9 KiB
C

/* fs/ internal definitions
*
* Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include <linux/lglock.h>
struct super_block;
struct file_system_type;
struct linux_binprm;
struct path;
struct mount;
/*
* block_dev.c
*/
#ifdef CONFIG_BLOCK
extern void __init bdev_cache_init(void);
extern int __sync_blockdev(struct block_device *bdev, int wait);
#else
static inline void bdev_cache_init(void)
{
}
static inline int __sync_blockdev(struct block_device *bdev, int wait)
{
return 0;
}
#endif
/*
* char_dev.c
*/
extern void __init chrdev_init(void);
/*
* namespace.c
*/
extern int copy_mount_options(const void __user *, unsigned long *);
extern int copy_mount_string(const void __user *, char **);
extern struct vfsmount *lookup_mnt(struct path *);
extern int finish_automount(struct vfsmount *, struct path *);
extern void mnt_make_longterm(struct vfsmount *);
extern void mnt_make_shortterm(struct vfsmount *);
extern int sb_prepare_remount_readonly(struct super_block *);
extern void __init mnt_init(void);
DECLARE_BRLOCK(vfsmount_lock);
/*
* fs_struct.c
*/
extern void chroot_fs_refs(struct path *, struct path *);
/*
* file_table.c
*/
extern void file_sb_list_add(struct file *f, struct super_block *sb);
extern void file_sb_list_del(struct file *f);
extern void mark_files_ro(struct super_block *);
extern struct file *get_empty_filp(void);
/*
* super.c
*/
extern int do_remount_sb(struct super_block *, int, void *, int);
extern bool grab_super_passive(struct super_block *sb);
extern struct dentry *mount_fs(struct file_system_type *,
int, const char *, void *);
extern struct super_block *user_get_super(dev_t);
/*
* open.c
*/
struct nameidata;
extern struct file *nameidata_to_filp(struct nameidata *);
extern void release_open_intent(struct nameidata *);
struct open_flags {
int open_flag;
umode_t mode;
int acc_mode;
int intent;
};
extern struct file *do_filp_open(int dfd, const char *pathname,
const struct open_flags *op, int lookup_flags);
extern struct file *do_file_open_root(struct dentry *, struct vfsmount *,
const char *, const struct open_flags *, int lookup_flags);
extern long do_handle_open(int mountdirfd,
struct file_handle __user *ufh, int open_flag);
/*
* inode.c
*/
extern spinlock_t inode_sb_list_lock;
/*
* fs-writeback.c
*/
extern void inode_wb_list_del(struct inode *inode);
extern int get_nr_dirty_inodes(void);
extern void evict_inodes(struct super_block *);
extern int invalidate_inodes(struct super_block *, bool);
/*
* dcache.c
*/
extern struct dentry *__d_alloc(struct super_block *, const struct qstr *);