292 lines
6.5 KiB
C
292 lines
6.5 KiB
C
/*
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* linux/fs/filesystems.c
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*
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* Copyright (C) 1991, 1992 Linus Torvalds
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*
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* table of configured filesystems
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*/
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#include <linux/syscalls.h>
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#include <linux/fs.h>
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#include <linux/proc_fs.h>
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#include <linux/seq_file.h>
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#include <linux/kmod.h>
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <linux/uaccess.h>
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/*
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* Handling of filesystem drivers list.
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* Rules:
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* Inclusion to/removals from/scanning of list are protected by spinlock.
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* During the unload module must call unregister_filesystem().
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* We can access the fields of list element if:
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* 1) spinlock is held or
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* 2) we hold the reference to the module.
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* The latter can be guaranteed by call of try_module_get(); if it
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* returned 0 we must skip the element, otherwise we got the reference.
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* Once the reference is obtained we can drop the spinlock.
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*/
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static struct file_system_type *file_systems;
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static DEFINE_RWLOCK(file_systems_lock);
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/* WARNING: This can be used only if we _already_ own a reference */
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struct file_system_type *get_filesystem(struct file_system_type *fs)
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{
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__module_get(fs->owner);
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return fs;
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}
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void put_filesystem(struct file_system_type *fs)
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{
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module_put(fs->owner);
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}
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static struct file_system_type **find_filesystem(const char *name, unsigned len)
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{
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struct file_system_type **p;
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for (p = &file_systems; *p; p = &(*p)->next)
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if (strncmp((*p)->name, name, len) == 0 &&
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!(*p)->name[len])
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break;
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return p;
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}
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/**
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* register_filesystem - register a new filesystem
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* @fs: the file system structure
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*
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* Adds the file system passed to the list of file systems the kernel
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* is aware of for mount and other syscalls. Returns 0 on success,
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* or a negative errno code on an error.
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*
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* The &struct file_system_type that is passed is linked into the kernel
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* structures and must not be freed until the file system has been
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* unregistered.
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*/
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int register_filesystem(struct file_system_type * fs)
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{
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int res = 0;
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struct file_system_type ** p;
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BUG_ON(strchr(fs->name, '.'));
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if (fs->next)
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return -EBUSY;
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write_lock(&file_systems_lock);
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p = find_filesystem(fs->name, strlen(fs->name));
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if (*p)
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res = -EBUSY;
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else
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*p = fs;
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write_unlock(&file_systems_lock);
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return res;
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}
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EXPORT_SYMBOL(register_filesystem);
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/**
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* unregister_filesystem - unregister a file system
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* @fs: filesystem to unregister
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*
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* Remove a file system that was previously successfully registered
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* with the kernel. An error is returned if the file system is not found.
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* Zero is returned on a success.
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*
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* Once this function has returned the &struct file_system_type structure
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* may be freed or reused.
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*/
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int unregister_filesystem(struct file_system_type * fs)
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{
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struct file_system_type ** tmp;
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write_lock(&file_systems_lock);
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tmp = &file_systems;
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while (*tmp) {
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if (fs == *tmp) {
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*tmp = fs->next;
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fs->next = NULL;
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write_unlock(&file_systems_lock);
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synchronize_rcu();
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return 0;
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}
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tmp = &(*tmp)->next;
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}
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write_unlock(&file_systems_lock);
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return -EINVAL;
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}
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EXPORT_SYMBOL(unregister_filesystem);
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#ifdef CONFIG_SYSFS_SYSCALL
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static int fs_index(const char __user * __name)
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{
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struct file_system_type * tmp;
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struct filename *name;
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int err, index;
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name = getname(__name);
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err = PTR_ERR(name);
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if (IS_ERR(name))
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return err;
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err = -EINVAL;
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read_lock(&file_systems_lock);
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for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
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if (strcmp(tmp->name, name->name) == 0) {
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err = index;
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break;
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}
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}
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read_unlock(&file_systems_lock);
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putname(name);
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return err;
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}
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static int fs_name(unsigned int index, char __user * buf)
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{
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struct file_system_type * tmp;
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int len, res;
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read_lock(&file_systems_lock);
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for (tmp = file_systems; tmp; tmp = tmp->next, index--)
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if (index <= 0 && try_module_get(tmp->owner))
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break;
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read_unlock(&file_systems_lock);
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if (!tmp)
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return -EINVAL;
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/* OK, we got the reference, so we can safely block */
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len = strlen(tmp->name) + 1;
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res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
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put_filesystem(tmp);
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return res;
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}
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static int fs_maxindex(void)
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{
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struct file_system_type * tmp;
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int index;
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read_lock(&file_systems_lock);
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for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
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;
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read_unlock(&file_systems_lock);
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return index;
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}
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/*
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* Whee.. Weird sysv syscall.
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*/
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SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
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{
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int retval = -EINVAL;
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switch (option) {
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case 1:
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retval = fs_index((const char __user *) arg1);
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break;
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case 2:
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retval = fs_name(arg1, (char __user *) arg2);
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break;
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case 3:
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retval = fs_maxindex();
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break;
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}
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return retval;
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}
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#endif
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int __init get_filesystem_list(char *buf)
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{
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int len = 0;
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struct file_system_type * tmp;
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read_lock(&file_systems_lock);
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tmp = file_systems;
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while (tmp && len < PAGE_SIZE - 80) {
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len += sprintf(buf+len, "%s\t%s\n",
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(tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
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tmp->name);
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tmp = tmp->next;
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}
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read_unlock(&file_systems_lock);
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return len;
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}
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#ifdef CONFIG_PROC_FS
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static int filesystems_proc_show(struct seq_file *m, void *v)
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{
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struct file_system_type * tmp;
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read_lock(&file_systems_lock);
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tmp = file_systems;
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while (tmp) {
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seq_printf(m, "%s\t%s\n",
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(tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
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tmp->name);
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tmp = tmp->next;
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}
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read_unlock(&file_systems_lock);
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return 0;
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}
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static int filesystems_proc_open(struct inode *inode, struct file *file)
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{
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return single_open(file, filesystems_proc_show, NULL);
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}
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static const struct file_operations filesystems_proc_fops = {
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.open = filesystems_proc_open,
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.read = seq_read,
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.llseek = seq_lseek,
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.release = single_release,
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};
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static int __init proc_filesystems_init(void)
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{
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proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
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return 0;
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}
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module_init(proc_filesystems_init);
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#endif
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static struct file_system_type *__get_fs_type(const char *name, int len)
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{
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struct file_system_type *fs;
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read_lock(&file_systems_lock);
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fs = *(find_filesystem(name, len));
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if (fs && !try_module_get(fs->owner))
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fs = NULL;
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read_unlock(&file_systems_lock);
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return fs;
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}
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struct file_system_type *get_fs_type(const char *name)
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{
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struct file_system_type *fs;
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const char *dot = strchr(name, '.');
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int len = dot ? dot - name : strlen(name);
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fs = __get_fs_type(name, len);
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if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
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fs = __get_fs_type(name, len);
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WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no fs?\n", len, name);
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}
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if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
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put_filesystem(fs);
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fs = NULL;
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}
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return fs;
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}
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EXPORT_SYMBOL(get_fs_type);
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