/* * linux/fs/filesystems.c * * Copyright (C) 1991, 1992 Linus Torvalds * * table of configured filesystems */ #include <linux/syscalls.h> #include <linux/fs.h> #include <linux/slab.h> #include <linux/kmod.h> #include <linux/init.h> #include <linux/module.h> #include <linux/sched.h> /* for 'current' */ #include <asm/uaccess.h> /* * Handling of filesystem drivers list. * Rules: * Inclusion to/removals from/scanning of list are protected by spinlock. * During the unload module must call unregister_filesystem(). * We can access the fields of list element if: * 1) spinlock is held or * 2) we hold the reference to the module. * The latter can be guaranteed by call of try_module_get(); if it * returned 0 we must skip the element, otherwise we got the reference. * Once the reference is obtained we can drop the spinlock. */ static struct file_system_type *file_systems; static DEFINE_RWLOCK(file_systems_lock); /* WARNING: This can be used only if we _already_ own a reference */ void get_filesystem(struct file_system_type *fs) { __module_get(fs->owner); } void put_filesystem(struct file_system_type *fs) { module_put(fs->owner); } static struct file_system_type **find_filesystem(const char *name) { struct file_system_type **p; for (p=&file_systems; *p; p=&(*p)->next) if (strcmp((*p)->name,name) == 0) break; return p; } /** * register_filesystem - register a new filesystem * @fs: the file system structure * * Adds the file system passed to the list of file systems the kernel * is aware of for mount and other syscalls. Returns 0 on success, * or a negative errno code on an error. * * The &struct file_system_type that is passed is linked into the kernel * structures and must not be freed until the file system has been * unregistered. */ int register_filesystem(struct file_system_type * fs) { int res = 0; struct file_system_type ** p; if (!fs) return -EINVAL; if (fs->next) return -EBUSY; INIT_LIST_HEAD(&fs->fs_supers); write_lock(&file_systems_lock); p = find_filesystem(fs->name); if (*p) res = -EBUSY; else *p = fs; write_unlock(&file_systems_lock); return res; } EXPORT_SYMBOL(register_filesystem); /** * unregister_filesystem - unregister a file system * @fs: filesystem to unregister * * Remove a file system that was previously successfully registered * with the kernel. An error is returned if the file system is not found. * Zero is returned on a success. * * Once this function has returned the &struct file_system_type structure * may be freed or reused. */ int unregister_filesystem(struct file_system_type * fs) { struct file_system_type ** tmp; write_lock(&file_systems_lock); tmp = &file_systems; while (*tmp) { if (fs == *tmp) { *tmp = fs->next; fs->next = NULL; write_unlock(&file_systems_lock); return 0; } tmp = &(*tmp)->next; } write_unlock(&file_systems_lock); return -EINVAL; } EXPORT_SYMBOL(unregister_filesystem); static int fs_index(const char __user * __name) { struct file_system_type * tmp; char * name; int err, index; name = getname(__name); err = PTR_ERR(name); if (IS_ERR(name)) return err; err = -EINVAL; read_lock(&file_systems_lock); for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) { if (strcmp(tmp->name,name) == 0) { err = index; break; } } read_unlock(&file_systems_lock); putname(name); return err; } static int fs_name(unsigned int index, char __user * buf) { struct file_system_type * tmp; int len, res; read_lock(&file_systems_lock); for (tmp = file_systems; tmp; tmp = tmp->next, index--) if (index <= 0 && try_module_get(tmp->owner)) break; read_unlock(&file_systems_lock); if (!tmp) return -EINVAL; /* OK, we got the reference, so we can safely block */ len = strlen(tmp->name) + 1; res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0; put_filesystem(tmp); return res; } static int fs_maxindex(void) { struct file_system_type * tmp; int index; read_lock(&file_systems_lock); for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++) ; read_unlock(&file_systems_lock); return index; } /* * Whee.. Weird sysv syscall. */ asmlinkage long sys_sysfs(int option, unsigned long arg1, unsigned long arg2) { int retval = -EINVAL; switch (option) { case 1: retval = fs_index((const char __user *) arg1); break; case 2: retval = fs_name(arg1, (char __user *) arg2); break; case 3: retval = fs_maxindex(); break; } return retval; } int get_filesystem_list(char * buf) { int len = 0; struct file_system_type * tmp; read_lock(&file_systems_lock); tmp = file_systems; while (tmp && len < PAGE_SIZE - 80) { len += sprintf(buf+len, "%s\t%s\n", (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev", tmp->name); tmp = tmp->next; } read_unlock(&file_systems_lock); return len; } struct file_system_type *get_fs_type(const char *name) { struct file_system_type *fs; read_lock(&file_systems_lock); fs = *(find_filesystem(name)); if (fs && !try_module_get(fs->owner)) fs = NULL; read_unlock(&file_systems_lock); if (!fs && (request_module("%s", name) == 0)) { read_lock(&file_systems_lock); fs = *(find_filesystem(name)); if (fs && !try_module_get(fs->owner)) fs = NULL; read_unlock(&file_systems_lock); } return fs; } EXPORT_SYMBOL(get_fs_type);