1 /* 2 * fs/kernfs/symlink.c - kernfs symlink implementation 3 * 4 * Copyright (c) 2001-3 Patrick Mochel 5 * Copyright (c) 2007 SUSE Linux Products GmbH 6 * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org> 7 * 8 * This file is released under the GPLv2. 9 */ 10 11 #include <linux/fs.h> 12 #include <linux/gfp.h> 13 #include <linux/namei.h> 14 15 #include "kernfs-internal.h" 16 17 /** 18 * kernfs_create_link - create a symlink 19 * @parent: directory to create the symlink in 20 * @name: name of the symlink 21 * @target: target node for the symlink to point to 22 * 23 * Returns the created node on success, ERR_PTR() value on error. 24 */ 25 struct kernfs_node *kernfs_create_link(struct kernfs_node *parent, 26 const char *name, 27 struct kernfs_node *target) 28 { 29 struct kernfs_node *kn; 30 struct kernfs_addrm_cxt acxt; 31 int error; 32 33 kn = kernfs_new_node(parent, name, S_IFLNK|S_IRWXUGO, KERNFS_LINK); 34 if (!kn) 35 return ERR_PTR(-ENOMEM); 36 37 if (kernfs_ns_enabled(parent)) 38 kn->ns = target->ns; 39 kn->symlink.target_kn = target; 40 kernfs_get(target); /* ref owned by symlink */ 41 42 kernfs_addrm_start(&acxt); 43 error = kernfs_add_one(&acxt, kn); 44 kernfs_addrm_finish(&acxt); 45 46 if (!error) 47 return kn; 48 49 kernfs_put(kn); 50 return ERR_PTR(error); 51 } 52 53 static int kernfs_get_target_path(struct kernfs_node *parent, 54 struct kernfs_node *target, char *path) 55 { 56 struct kernfs_node *base, *kn; 57 char *s = path; 58 int len = 0; 59 60 /* go up to the root, stop at the base */ 61 base = parent; 62 while (base->parent) { 63 kn = target->parent; 64 while (kn->parent && base != kn) 65 kn = kn->parent; 66 67 if (base == kn) 68 break; 69 70 strcpy(s, "../"); 71 s += 3; 72 base = base->parent; 73 } 74 75 /* determine end of target string for reverse fillup */ 76 kn = target; 77 while (kn->parent && kn != base) { 78 len += strlen(kn->name) + 1; 79 kn = kn->parent; 80 } 81 82 /* check limits */ 83 if (len < 2) 84 return -EINVAL; 85 len--; 86 if ((s - path) + len > PATH_MAX) 87 return -ENAMETOOLONG; 88 89 /* reverse fillup of target string from target to base */ 90 kn = target; 91 while (kn->parent && kn != base) { 92 int slen = strlen(kn->name); 93 94 len -= slen; 95 strncpy(s + len, kn->name, slen); 96 if (len) 97 s[--len] = '/'; 98 99 kn = kn->parent; 100 } 101 102 return 0; 103 } 104 105 static int kernfs_getlink(struct dentry *dentry, char *path) 106 { 107 struct kernfs_node *kn = dentry->d_fsdata; 108 struct kernfs_node *parent = kn->parent; 109 struct kernfs_node *target = kn->symlink.target_kn; 110 int error; 111 112 mutex_lock(&kernfs_mutex); 113 error = kernfs_get_target_path(parent, target, path); 114 mutex_unlock(&kernfs_mutex); 115 116 return error; 117 } 118 119 static void *kernfs_iop_follow_link(struct dentry *dentry, struct nameidata *nd) 120 { 121 int error = -ENOMEM; 122 unsigned long page = get_zeroed_page(GFP_KERNEL); 123 if (page) { 124 error = kernfs_getlink(dentry, (char *) page); 125 if (error < 0) 126 free_page((unsigned long)page); 127 } 128 nd_set_link(nd, error ? ERR_PTR(error) : (char *)page); 129 return NULL; 130 } 131 132 static void kernfs_iop_put_link(struct dentry *dentry, struct nameidata *nd, 133 void *cookie) 134 { 135 char *page = nd_get_link(nd); 136 if (!IS_ERR(page)) 137 free_page((unsigned long)page); 138 } 139 140 const struct inode_operations kernfs_symlink_iops = { 141 .setxattr = kernfs_iop_setxattr, 142 .removexattr = kernfs_iop_removexattr, 143 .getxattr = kernfs_iop_getxattr, 144 .listxattr = kernfs_iop_listxattr, 145 .readlink = generic_readlink, 146 .follow_link = kernfs_iop_follow_link, 147 .put_link = kernfs_iop_put_link, 148 .setattr = kernfs_iop_setattr, 149 .getattr = kernfs_iop_getattr, 150 .permission = kernfs_iop_permission, 151 }; 152