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 int error; 31 32 kn = kernfs_new_node(parent, name, S_IFLNK|S_IRWXUGO, KERNFS_LINK); 33 if (!kn) 34 return ERR_PTR(-ENOMEM); 35 36 if (kernfs_ns_enabled(parent)) 37 kn->ns = target->ns; 38 kn->symlink.target_kn = target; 39 kernfs_get(target); /* ref owned by symlink */ 40 41 error = kernfs_add_one(kn); 42 if (!error) 43 return kn; 44 45 kernfs_put(kn); 46 return ERR_PTR(error); 47 } 48 49 static int kernfs_get_target_path(struct kernfs_node *parent, 50 struct kernfs_node *target, char *path) 51 { 52 struct kernfs_node *base, *kn; 53 char *s = path; 54 int len = 0; 55 56 /* go up to the root, stop at the base */ 57 base = parent; 58 while (base->parent) { 59 kn = target->parent; 60 while (kn->parent && base != kn) 61 kn = kn->parent; 62 63 if (base == kn) 64 break; 65 66 strcpy(s, "../"); 67 s += 3; 68 base = base->parent; 69 } 70 71 /* determine end of target string for reverse fillup */ 72 kn = target; 73 while (kn->parent && kn != base) { 74 len += strlen(kn->name) + 1; 75 kn = kn->parent; 76 } 77 78 /* check limits */ 79 if (len < 2) 80 return -EINVAL; 81 len--; 82 if ((s - path) + len > PATH_MAX) 83 return -ENAMETOOLONG; 84 85 /* reverse fillup of target string from target to base */ 86 kn = target; 87 while (kn->parent && kn != base) { 88 int slen = strlen(kn->name); 89 90 len -= slen; 91 strncpy(s + len, kn->name, slen); 92 if (len) 93 s[--len] = '/'; 94 95 kn = kn->parent; 96 } 97 98 return 0; 99 } 100 101 static int kernfs_getlink(struct dentry *dentry, char *path) 102 { 103 struct kernfs_node *kn = dentry->d_fsdata; 104 struct kernfs_node *parent = kn->parent; 105 struct kernfs_node *target = kn->symlink.target_kn; 106 int error; 107 108 mutex_lock(&kernfs_mutex); 109 error = kernfs_get_target_path(parent, target, path); 110 mutex_unlock(&kernfs_mutex); 111 112 return error; 113 } 114 115 static const char *kernfs_iop_follow_link(struct dentry *dentry, void **cookie) 116 { 117 int error = -ENOMEM; 118 unsigned long page = get_zeroed_page(GFP_KERNEL); 119 if (!page) 120 return ERR_PTR(-ENOMEM); 121 error = kernfs_getlink(dentry, (char *)page); 122 if (unlikely(error < 0)) { 123 free_page((unsigned long)page); 124 return ERR_PTR(error); 125 } 126 return *cookie = (char *)page; 127 } 128 129 const struct inode_operations kernfs_symlink_iops = { 130 .setxattr = kernfs_iop_setxattr, 131 .removexattr = kernfs_iop_removexattr, 132 .getxattr = kernfs_iop_getxattr, 133 .listxattr = kernfs_iop_listxattr, 134 .readlink = generic_readlink, 135 .follow_link = kernfs_iop_follow_link, 136 .put_link = free_page_put_link, 137 .setattr = kernfs_iop_setattr, 138 .getattr = kernfs_iop_getattr, 139 .permission = kernfs_iop_permission, 140 }; 141