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authorTejun Heo <htejun@gmail.com>2007-06-13 14:45:15 -0400
committerGreg Kroah-Hartman <gregkh@suse.de>2007-07-11 19:09:04 -0400
commit2b29ac252afff87b8465b064ca2d9740cf1f6e52 (patch)
tree9f4930db68ace50adc7c11feba12aafe34e2cdbe /fs/sysfs/symlink.c
parentaecdcedaab49ca40620dc7dd70f67ee7269a66c9 (diff)
sysfs: reimplement symlink using sysfs_dirent tree
sysfs symlink is implemented by referencing dentry and kobject from sysfs_dirent - symlink entry references kobject, dentry is used to walk the tree. This complicates object lifetimes rules and is dangerous - for example, there is no way to tell to which module the target of a symlink belongs and referencing that kobject can make it linger after the module is gone. This patch reimplements symlink using only sysfs_dirent tree. sd for a symlink points and holds reference to the target sysfs_dirent and all walking is done using sysfs_dirent tree. Simpler and safer. Please read the following message for more info. http://article.gmane.org/gmane.linux.kernel/510293 Signed-off-by: Tejun Heo <htejun@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'fs/sysfs/symlink.c')
-rw-r--r--fs/sysfs/symlink.c88
1 files changed, 47 insertions, 41 deletions
diff --git a/fs/sysfs/symlink.c b/fs/sysfs/symlink.c
index 27df635b786a..ff605d3f4d33 100644
--- a/fs/sysfs/symlink.c
+++ b/fs/sysfs/symlink.c
@@ -11,50 +11,49 @@
11 11
12#include "sysfs.h" 12#include "sysfs.h"
13 13
14static int object_depth(struct kobject * kobj) 14static int object_depth(struct sysfs_dirent *sd)
15{ 15{
16 struct kobject * p = kobj;
17 int depth = 0; 16 int depth = 0;
18 do { depth++; } while ((p = p->parent)); 17
18 for (; sd->s_parent; sd = sd->s_parent)
19 depth++;
20
19 return depth; 21 return depth;
20} 22}
21 23
22static int object_path_length(struct kobject * kobj) 24static int object_path_length(struct sysfs_dirent * sd)
23{ 25{
24 struct kobject * p = kobj;
25 int length = 1; 26 int length = 1;
26 do { 27
27 length += strlen(kobject_name(p)) + 1; 28 for (; sd->s_parent; sd = sd->s_parent)
28 p = p->parent; 29 length += strlen(sd->s_name) + 1;
29 } while (p); 30
30 return length; 31 return length;
31} 32}
32 33
33static void fill_object_path(struct kobject * kobj, char * buffer, int length) 34static void fill_object_path(struct sysfs_dirent *sd, char *buffer, int length)
34{ 35{
35 struct kobject * p;
36
37 --length; 36 --length;
38 for (p = kobj; p; p = p->parent) { 37 for (; sd->s_parent; sd = sd->s_parent) {
39 int cur = strlen(kobject_name(p)); 38 int cur = strlen(sd->s_name);
40 39
41 /* back up enough to print this bus id with '/' */ 40 /* back up enough to print this bus id with '/' */
42 length -= cur; 41 length -= cur;
43 strncpy(buffer + length,kobject_name(p),cur); 42 strncpy(buffer + length, sd->s_name, cur);
44 *(buffer + --length) = '/'; 43 *(buffer + --length) = '/';
45 } 44 }
46} 45}
47 46
48static int sysfs_add_link(struct dentry * parent, const char * name, struct kobject * target) 47static int sysfs_add_link(struct sysfs_dirent * parent_sd, const char * name,
48 struct sysfs_dirent * target_sd)
49{ 49{
50 struct sysfs_dirent * parent_sd = parent->d_fsdata;
51 struct sysfs_dirent * sd; 50 struct sysfs_dirent * sd;
52 51
53 sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK); 52 sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
54 if (!sd) 53 if (!sd)
55 return -ENOMEM; 54 return -ENOMEM;
56 55
57 sd->s_elem.symlink.target_kobj = kobject_get(target); 56 sd->s_elem.symlink.target_sd = target_sd;
58 sysfs_attach_dirent(sd, parent_sd, NULL); 57 sysfs_attach_dirent(sd, parent_sd, NULL);
59 return 0; 58 return 0;
60} 59}
@@ -68,6 +67,8 @@ static int sysfs_add_link(struct dentry * parent, const char * name, struct kobj
68int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name) 67int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name)
69{ 68{
70 struct dentry *dentry = NULL; 69 struct dentry *dentry = NULL;
70 struct sysfs_dirent *parent_sd = NULL;
71 struct sysfs_dirent *target_sd = NULL;
71 int error = -EEXIST; 72 int error = -EEXIST;
72 73
73 BUG_ON(!name); 74 BUG_ON(!name);
@@ -80,11 +81,27 @@ int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char
80 81
81 if (!dentry) 82 if (!dentry)
82 return -EFAULT; 83 return -EFAULT;
84 parent_sd = dentry->d_fsdata;
85
86 /* target->dentry can go away beneath us but is protected with
87 * kobj_sysfs_assoc_lock. Fetch target_sd from it.
88 */
89 spin_lock(&kobj_sysfs_assoc_lock);
90 if (target->dentry)
91 target_sd = sysfs_get(target->dentry->d_fsdata);
92 spin_unlock(&kobj_sysfs_assoc_lock);
93
94 if (!target_sd)
95 return -ENOENT;
83 96
84 mutex_lock(&dentry->d_inode->i_mutex); 97 mutex_lock(&dentry->d_inode->i_mutex);
85 if (!sysfs_dirent_exist(dentry->d_fsdata, name)) 98 if (!sysfs_dirent_exist(dentry->d_fsdata, name))
86 error = sysfs_add_link(dentry, name, target); 99 error = sysfs_add_link(parent_sd, name, target_sd);
87 mutex_unlock(&dentry->d_inode->i_mutex); 100 mutex_unlock(&dentry->d_inode->i_mutex);
101
102 if (error)
103 sysfs_put(target_sd);
104
88 return error; 105 return error;
89} 106}
90 107
@@ -100,14 +117,14 @@ void sysfs_remove_link(struct kobject * kobj, const char * name)
100 sysfs_hash_and_remove(kobj->dentry,name); 117 sysfs_hash_and_remove(kobj->dentry,name);
101} 118}
102 119
103static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target, 120static int sysfs_get_target_path(struct sysfs_dirent * parent_sd,
104 char *path) 121 struct sysfs_dirent * target_sd, char *path)
105{ 122{
106 char * s; 123 char * s;
107 int depth, size; 124 int depth, size;
108 125
109 depth = object_depth(kobj); 126 depth = object_depth(parent_sd);
110 size = object_path_length(target) + depth * 3 - 1; 127 size = object_path_length(target_sd) + depth * 3 - 1;
111 if (size > PATH_MAX) 128 if (size > PATH_MAX)
112 return -ENAMETOOLONG; 129 return -ENAMETOOLONG;
113 130
@@ -116,7 +133,7 @@ static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target,
116 for (s = path; depth--; s += 3) 133 for (s = path; depth--; s += 3)
117 strcpy(s,"../"); 134 strcpy(s,"../");
118 135
119 fill_object_path(target, path, size); 136 fill_object_path(target_sd, path, size);
120 pr_debug("%s: path = '%s'\n", __FUNCTION__, path); 137 pr_debug("%s: path = '%s'\n", __FUNCTION__, path);
121 138
122 return 0; 139 return 0;
@@ -124,27 +141,16 @@ static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target,
124 141
125static int sysfs_getlink(struct dentry *dentry, char * path) 142static int sysfs_getlink(struct dentry *dentry, char * path)
126{ 143{
127 struct kobject *kobj, *target_kobj; 144 struct sysfs_dirent *sd = dentry->d_fsdata;
128 int error = 0; 145 struct sysfs_dirent *parent_sd = sd->s_parent;
129 146 struct sysfs_dirent *target_sd = sd->s_elem.symlink.target_sd;
130 kobj = sysfs_get_kobject(dentry->d_parent); 147 int error;
131 if (!kobj)
132 return -EINVAL;
133
134 target_kobj = sysfs_get_kobject(dentry);
135 if (!target_kobj) {
136 kobject_put(kobj);
137 return -EINVAL;
138 }
139 148
140 down_read(&sysfs_rename_sem); 149 down_read(&sysfs_rename_sem);
141 error = sysfs_get_target_path(kobj, target_kobj, path); 150 error = sysfs_get_target_path(parent_sd, target_sd, path);
142 up_read(&sysfs_rename_sem); 151 up_read(&sysfs_rename_sem);
143
144 kobject_put(kobj);
145 kobject_put(target_kobj);
146 return error;
147 152
153 return error;
148} 154}
149 155
150static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd) 156static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)