1 /* 2 * fs/sysfs/symlink.c - sysfs symlink implementation 3 * 4 * Copyright (c) 2001-3 Patrick Mochel 5 * Copyright (c) 2007 SUSE Linux Products GmbH 6 * Copyright (c) 2007 Tejun Heo <teheo@suse.de> 7 * 8 * This file is released under the GPLv2. 9 * 10 * Please see Documentation/filesystems/sysfs.txt for more information. 11 */ 12 13 #include <linux/fs.h> 14 #include <linux/mount.h> 15 #include <linux/module.h> 16 #include <linux/kobject.h> 17 #include <linux/namei.h> 18 #include <linux/mutex.h> 19 20 #include "sysfs.h" 21 22 static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target, 23 const char *name, int warn) 24 { 25 struct sysfs_dirent *parent_sd = NULL; 26 struct sysfs_dirent *target_sd = NULL; 27 struct sysfs_dirent *sd = NULL; 28 struct sysfs_addrm_cxt acxt; 29 int error; 30 31 BUG_ON(!name); 32 33 if (!kobj) 34 parent_sd = &sysfs_root; 35 else 36 parent_sd = kobj->sd; 37 38 error = -EFAULT; 39 if (!parent_sd) 40 goto out_put; 41 42 /* target->sd can go away beneath us but is protected with 43 * sysfs_assoc_lock. Fetch target_sd from it. 44 */ 45 spin_lock(&sysfs_assoc_lock); 46 if (target->sd) 47 target_sd = sysfs_get(target->sd); 48 spin_unlock(&sysfs_assoc_lock); 49 50 error = -ENOENT; 51 if (!target_sd) 52 goto out_put; 53 54 error = -ENOMEM; 55 sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK); 56 if (!sd) 57 goto out_put; 58 59 sd->s_symlink.target_sd = target_sd; 60 target_sd = NULL; /* reference is now owned by the symlink */ 61 62 sysfs_addrm_start(&acxt, parent_sd); 63 if (warn) 64 error = sysfs_add_one(&acxt, sd); 65 else 66 error = __sysfs_add_one(&acxt, sd); 67 sysfs_addrm_finish(&acxt); 68 69 if (error) 70 goto out_put; 71 72 return 0; 73 74 out_put: 75 sysfs_put(target_sd); 76 sysfs_put(sd); 77 return error; 78 } 79 80 /** 81 * sysfs_create_link - create symlink between two objects. 82 * @kobj: object whose directory we're creating the link in. 83 * @target: object we're pointing to. 84 * @name: name of the symlink. 85 */ 86 int sysfs_create_link(struct kobject *kobj, struct kobject *target, 87 const char *name) 88 { 89 return sysfs_do_create_link(kobj, target, name, 1); 90 } 91 92 /** 93 * sysfs_create_link_nowarn - create symlink between two objects. 94 * @kobj: object whose directory we're creating the link in. 95 * @target: object we're pointing to. 96 * @name: name of the symlink. 97 * 98 * This function does the same as sysf_create_link(), but it 99 * doesn't warn if the link already exists. 100 */ 101 int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target, 102 const char *name) 103 { 104 return sysfs_do_create_link(kobj, target, name, 0); 105 } 106 107 /** 108 * sysfs_remove_link - remove symlink in object's directory. 109 * @kobj: object we're acting for. 110 * @name: name of the symlink to remove. 111 */ 112 113 void sysfs_remove_link(struct kobject * kobj, const char * name) 114 { 115 struct sysfs_dirent *parent_sd = NULL; 116 117 if (!kobj) 118 parent_sd = &sysfs_root; 119 else 120 parent_sd = kobj->sd; 121 122 sysfs_hash_and_remove(parent_sd, name); 123 } 124 125 static int sysfs_get_target_path(struct sysfs_dirent *parent_sd, 126 struct sysfs_dirent *target_sd, char *path) 127 { 128 struct sysfs_dirent *base, *sd; 129 char *s = path; 130 int len = 0; 131 132 /* go up to the root, stop at the base */ 133 base = parent_sd; 134 while (base->s_parent) { 135 sd = target_sd->s_parent; 136 while (sd->s_parent && base != sd) 137 sd = sd->s_parent; 138 139 if (base == sd) 140 break; 141 142 strcpy(s, "../"); 143 s += 3; 144 base = base->s_parent; 145 } 146 147 /* determine end of target string for reverse fillup */ 148 sd = target_sd; 149 while (sd->s_parent && sd != base) { 150 len += strlen(sd->s_name) + 1; 151 sd = sd->s_parent; 152 } 153 154 /* check limits */ 155 if (len < 2) 156 return -EINVAL; 157 len--; 158 if ((s - path) + len > PATH_MAX) 159 return -ENAMETOOLONG; 160 161 /* reverse fillup of target string from target to base */ 162 sd = target_sd; 163 while (sd->s_parent && sd != base) { 164 int slen = strlen(sd->s_name); 165 166 len -= slen; 167 strncpy(s + len, sd->s_name, slen); 168 if (len) 169 s[--len] = '/'; 170 171 sd = sd->s_parent; 172 } 173 174 return 0; 175 } 176 177 static int sysfs_getlink(struct dentry *dentry, char * path) 178 { 179 struct sysfs_dirent *sd = dentry->d_fsdata; 180 struct sysfs_dirent *parent_sd = sd->s_parent; 181 struct sysfs_dirent *target_sd = sd->s_symlink.target_sd; 182 int error; 183 184 mutex_lock(&sysfs_mutex); 185 error = sysfs_get_target_path(parent_sd, target_sd, path); 186 mutex_unlock(&sysfs_mutex); 187 188 return error; 189 } 190 191 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd) 192 { 193 int error = -ENOMEM; 194 unsigned long page = get_zeroed_page(GFP_KERNEL); 195 if (page) 196 error = sysfs_getlink(dentry, (char *) page); 197 nd_set_link(nd, error ? ERR_PTR(error) : (char *)page); 198 return NULL; 199 } 200 201 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie) 202 { 203 char *page = nd_get_link(nd); 204 if (!IS_ERR(page)) 205 free_page((unsigned long)page); 206 } 207 208 const struct inode_operations sysfs_symlink_inode_operations = { 209 .readlink = generic_readlink, 210 .follow_link = sysfs_follow_link, 211 .put_link = sysfs_put_link, 212 }; 213 214 215 EXPORT_SYMBOL_GPL(sysfs_create_link); 216 EXPORT_SYMBOL_GPL(sysfs_remove_link); 217