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linux
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filesystems.c
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/* * linux/fs/filesystems.c * * Copyright (C) 1991, 1992 Linus Torvalds * * table of configured filesystems */ #include <linux/syscalls.h> #include <linux/fs.h> #include <linux/proc_fs.h> #include <linux/seq_file.h> #include <linux/kmod.h> #include <linux/init.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/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, unsigned len) { struct file_system_type **p; for (p = &file_systems; *p; p = &(*p)->next) if (strncmp((*p)->name, name, len) == 0 && !(*p)->name[len]) 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; BUG_ON(strchr(fs->name, '.')); if (fs->next) return -EBUSY; write_lock(&file_systems_lock); p = find_filesystem(fs->name, strlen(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); synchronize_rcu(); return 0; } tmp = &(*tmp)->next; } write_unlock(&file_systems_lock); return -EINVAL; } EXPORT_SYMBOL(unregister_filesystem); #ifdef CONFIG_SYSFS_SYSCALL static int fs_index(const char __user * __name) { struct file_system_type * tmp; struct filename *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->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. */ SYSCALL_DEFINE3(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; } #endif int __init 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; } #ifdef CONFIG_PROC_FS static int filesystems_proc_show(struct seq_file *m, void *v) { struct file_system_type * tmp; read_lock(&file_systems_lock); tmp = file_systems; while (tmp) { seq_printf(m, "%s\t%s\n", (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev", tmp->name); tmp = tmp->next; } read_unlock(&file_systems_lock); return 0; } static int filesystems_proc_open(struct inode *inode, struct file *file) { return single_open(file, filesystems_proc_show, NULL); } static const struct file_operations filesystems_proc_fops = { .open = filesystems_proc_open, .read = seq_read, .llseek = seq_lseek, .release = single_release, }; static int __init proc_filesystems_init(void) { proc_create("filesystems", 0, NULL, &filesystems_proc_fops); return 0; } module_init(proc_filesystems_init); #endif static struct file_system_type *__get_fs_type(const char *name, int len) { struct file_system_type *fs; read_lock(&file_systems_lock); fs = *(find_filesystem(name, len)); if (fs && !try_module_get(fs->owner)) fs = NULL; read_unlock(&file_systems_lock); return fs; } struct file_system_type *get_fs_type(const char *name) { struct file_system_type *fs; const char *dot = strchr(name, '.'); int len = dot ? dot - name : strlen(name); fs = __get_fs_type(name, len); if (!fs && (request_module("fs-%.*s", len, name) == 0)) { fs = __get_fs_type(name, len); WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no fs?\n", len, name); } if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) { put_filesystem(fs); fs = NULL; } return fs; } EXPORT_SYMBOL(get_fs_type);
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