1 /* 2 * symlink.c - operations for sysfs symlinks. 3 */ 4 5 #include <linux/fs.h> 6 #include <linux/mount.h> 7 #include <linux/module.h> 8 #include <linux/kobject.h> 9 #include <linux/namei.h> 10 #include <asm/semaphore.h> 11 12 #include "sysfs.h" 13 14 static int object_depth(struct sysfs_dirent *sd) 15 { 16 int depth = 0; 17 18 for (; sd->s_parent; sd = sd->s_parent) 19 depth++; 20 21 return depth; 22 } 23 24 static int object_path_length(struct sysfs_dirent * sd) 25 { 26 int length = 1; 27 28 for (; sd->s_parent; sd = sd->s_parent) 29 length += strlen(sd->s_name) + 1; 30 31 return length; 32 } 33 34 static void fill_object_path(struct sysfs_dirent *sd, char *buffer, int length) 35 { 36 --length; 37 for (; sd->s_parent; sd = sd->s_parent) { 38 int cur = strlen(sd->s_name); 39 40 /* back up enough to print this bus id with '/' */ 41 length -= cur; 42 strncpy(buffer + length, sd->s_name, cur); 43 *(buffer + --length) = '/'; 44 } 45 } 46 47 /** 48 * sysfs_create_link - create symlink between two objects. 49 * @kobj: object whose directory we're creating the link in. 50 * @target: object we're pointing to. 51 * @name: name of the symlink. 52 */ 53 int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name) 54 { 55 struct sysfs_dirent *parent_sd = NULL; 56 struct sysfs_dirent *target_sd = NULL; 57 struct sysfs_dirent *sd = NULL; 58 struct sysfs_addrm_cxt acxt; 59 int error; 60 61 BUG_ON(!name); 62 63 if (!kobj) { 64 if (sysfs_mount && sysfs_mount->mnt_sb) 65 parent_sd = sysfs_mount->mnt_sb->s_root->d_fsdata; 66 } else 67 parent_sd = kobj->sd; 68 69 error = -EFAULT; 70 if (!parent_sd) 71 goto out_put; 72 73 /* target->sd can go away beneath us but is protected with 74 * sysfs_assoc_lock. Fetch target_sd from it. 75 */ 76 spin_lock(&sysfs_assoc_lock); 77 if (target->sd) 78 target_sd = sysfs_get(target->sd); 79 spin_unlock(&sysfs_assoc_lock); 80 81 error = -ENOENT; 82 if (!target_sd) 83 goto out_put; 84 85 error = -ENOMEM; 86 sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK); 87 if (!sd) 88 goto out_put; 89 90 sd->s_elem.symlink.target_sd = target_sd; 91 target_sd = NULL; /* reference is now owned by the symlink */ 92 93 sysfs_addrm_start(&acxt, parent_sd); 94 95 if (!sysfs_find_dirent(parent_sd, name)) { 96 sysfs_add_one(&acxt, sd); 97 sysfs_link_sibling(sd); 98 } 99 100 if (!sysfs_addrm_finish(&acxt)) { 101 error = -EEXIST; 102 goto out_put; 103 } 104 105 return 0; 106 107 out_put: 108 sysfs_put(target_sd); 109 sysfs_put(sd); 110 return error; 111 } 112 113 114 /** 115 * sysfs_remove_link - remove symlink in object's directory. 116 * @kobj: object we're acting for. 117 * @name: name of the symlink to remove. 118 */ 119 120 void sysfs_remove_link(struct kobject * kobj, const char * name) 121 { 122 sysfs_hash_and_remove(kobj->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 char * s; 129 int depth, size; 130 131 depth = object_depth(parent_sd); 132 size = object_path_length(target_sd) + depth * 3 - 1; 133 if (size > PATH_MAX) 134 return -ENAMETOOLONG; 135 136 pr_debug("%s: depth = %d, size = %d\n", __FUNCTION__, depth, size); 137 138 for (s = path; depth--; s += 3) 139 strcpy(s,"../"); 140 141 fill_object_path(target_sd, path, size); 142 pr_debug("%s: path = '%s'\n", __FUNCTION__, path); 143 144 return 0; 145 } 146 147 static int sysfs_getlink(struct dentry *dentry, char * path) 148 { 149 struct sysfs_dirent *sd = dentry->d_fsdata; 150 struct sysfs_dirent *parent_sd = sd->s_parent; 151 struct sysfs_dirent *target_sd = sd->s_elem.symlink.target_sd; 152 int error; 153 154 mutex_lock(&sysfs_mutex); 155 error = sysfs_get_target_path(parent_sd, target_sd, path); 156 mutex_unlock(&sysfs_mutex); 157 158 return error; 159 } 160 161 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd) 162 { 163 int error = -ENOMEM; 164 unsigned long page = get_zeroed_page(GFP_KERNEL); 165 if (page) 166 error = sysfs_getlink(dentry, (char *) page); 167 nd_set_link(nd, error ? ERR_PTR(error) : (char *)page); 168 return NULL; 169 } 170 171 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie) 172 { 173 char *page = nd_get_link(nd); 174 if (!IS_ERR(page)) 175 free_page((unsigned long)page); 176 } 177 178 const struct inode_operations sysfs_symlink_inode_operations = { 179 .readlink = generic_readlink, 180 .follow_link = sysfs_follow_link, 181 .put_link = sysfs_put_link, 182 }; 183 184 185 EXPORT_SYMBOL_GPL(sysfs_create_link); 186 EXPORT_SYMBOL_GPL(sysfs_remove_link); 187