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kernfs: Add API to generate relative kernfs path

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The new function kernfs_path_from_node() generates and returns kernfs
path of a given kernfs_node relative to a given parent kernfs_node.

Signed-off-by: Aditya Kali <adityakali@google.com>
Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
tirimbino
Aditya Kali 9 years ago committed by Tejun Heo
parent 223ffb29f9
commit 9f6df573a4
2 changed files with 165 additions and 35 deletions
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
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  1. 191
      fs/kernfs/dir.c
  2. 9
      include/linux/kernfs.h

191
fs/kernfs/dir.c
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@ -44,28 +44,122 @@ static int kernfs_name_locked(struct kernfs_node *kn, char *buf, size_t buflen)
return strlcpy(buf, kn->parent ? kn->name : "/", buflen);
}
static char * __must_check kernfs_path_locked(struct kernfs_node *kn, char *buf,
size_t buflen)
/* kernfs_node_depth - compute depth from @from to @to */
static size_t kernfs_depth(struct kernfs_node *from, struct kernfs_node *to)
{
char *p = buf + buflen;
int len;
size_t depth = 0;
*--p = '\0';
while (to->parent && to != from) {
depth++;
to = to->parent;
}
return depth;
}
do {
len = strlen(kn->name);
if (p - buf < len + 1) {
buf[0] = '\0';
p = NULL;
break;
}
p -= len;
memcpy(p, kn->name, len);
*--p = '/';
kn = kn->parent;
} while (kn && kn->parent);
static struct kernfs_node *kernfs_common_ancestor(struct kernfs_node *a,
struct kernfs_node *b)
{
size_t da, db;
struct kernfs_root *ra = kernfs_root(a), *rb = kernfs_root(b);
return p;
if (ra != rb)
return NULL;
da = kernfs_depth(ra->kn, a);
db = kernfs_depth(rb->kn, b);
while (da > db) {
a = a->parent;
da--;
}
while (db > da) {
b = b->parent;
db--;
}
/* worst case b and a will be the same at root */
while (b != a) {
b = b->parent;
a = a->parent;
}
return a;
}
/**
* kernfs_path_from_node_locked - find a pseudo-absolute path to @kn_to,
* where kn_from is treated as root of the path.
* @kn_from: kernfs node which should be treated as root for the path
* @kn_to: kernfs node to which path is needed
* @buf: buffer to copy the path into
* @buflen: size of @buf
*
* We need to handle couple of scenarios here:
* [1] when @kn_from is an ancestor of @kn_to at some level
* kn_from: /n1/n2/n3
* kn_to: /n1/n2/n3/n4/n5
* result: /n4/n5
*
* [2] when @kn_from is on a different hierarchy and we need to find common
* ancestor between @kn_from and @kn_to.
* kn_from: /n1/n2/n3/n4
* kn_to: /n1/n2/n5
* result: /../../n5
* OR
* kn_from: /n1/n2/n3/n4/n5 [depth=5]
* kn_to: /n1/n2/n3 [depth=3]
* result: /../..
*
* return value: length of the string. If greater than buflen,
* then contents of buf are undefined. On error, -1 is returned.
*/
static int kernfs_path_from_node_locked(struct kernfs_node *kn_to,
struct kernfs_node *kn_from,
char *buf, size_t buflen)
{
struct kernfs_node *kn, *common;
const char parent_str[] = "/..";
size_t depth_from, depth_to, len = 0, nlen = 0;
char *p;
int i;
if (!kn_from)
kn_from = kernfs_root(kn_to)->kn;
if (kn_from == kn_to)
return strlcpy(buf, "/", buflen);
common = kernfs_common_ancestor(kn_from, kn_to);
if (WARN_ON(!common))
return -1;
depth_to = kernfs_depth(common, kn_to);
depth_from = kernfs_depth(common, kn_from);
if (buf)
buf[0] = '\0';
for (i = 0; i < depth_from; i++)
len += strlcpy(buf + len, parent_str,
len < buflen ? buflen - len : 0);
/* Calculate how many bytes we need for the rest */
for (kn = kn_to; kn != common; kn = kn->parent)
nlen += strlen(kn->name) + 1;
if (len + nlen >= buflen)
return len + nlen;
p = buf + len + nlen;
*p = '\0';
for (kn = kn_to; kn != common; kn = kn->parent) {
nlen = strlen(kn->name);
p -= nlen;
memcpy(p, kn->name, nlen);
*(--p) = '/';
}
return len + nlen;
}
/**
@ -114,6 +208,34 @@ size_t kernfs_path_len(struct kernfs_node *kn)
return len;
}
/**
* kernfs_path_from_node - build path of node @to relative to @from.
* @from: parent kernfs_node relative to which we need to build the path
* @to: kernfs_node of interest
* @buf: buffer to copy @to's path into
* @buflen: size of @buf
*
* Builds @to's path relative to @from in @buf. @from and @to must
* be on the same kernfs-root. If @from is not parent of @to, then a relative
* path (which includes '..'s) as needed to reach from @from to @to is
* returned.
*
* If @buf isn't long enough, the return value will be greater than @buflen
* and @buf contents are undefined.
*/
int kernfs_path_from_node(struct kernfs_node *to, struct kernfs_node *from,
char *buf, size_t buflen)
{
unsigned long flags;
int ret;
spin_lock_irqsave(&kernfs_rename_lock, flags);
ret = kernfs_path_from_node_locked(to, from, buf, buflen);
spin_unlock_irqrestore(&kernfs_rename_lock, flags);
return ret;
}
EXPORT_SYMBOL_GPL(kernfs_path_from_node);
/**
* kernfs_path - build full path of a given node
* @kn: kernfs_node of interest
@ -127,13 +249,12 @@ size_t kernfs_path_len(struct kernfs_node *kn)
*/
char *kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen)
{
unsigned long flags;
char *p;
int ret;
spin_lock_irqsave(&kernfs_rename_lock, flags);
p = kernfs_path_locked(kn, buf, buflen);
spin_unlock_irqrestore(&kernfs_rename_lock, flags);
return p;
ret = kernfs_path_from_node(kn, NULL, buf, buflen);
if (ret < 0 || ret >= buflen)
return NULL;
return buf;
}
EXPORT_SYMBOL_GPL(kernfs_path);
@ -164,17 +285,25 @@ void pr_cont_kernfs_name(struct kernfs_node *kn)
void pr_cont_kernfs_path(struct kernfs_node *kn)
{
unsigned long flags;
char *p;
int sz;
spin_lock_irqsave(&kernfs_rename_lock, flags);
p = kernfs_path_locked(kn, kernfs_pr_cont_buf,
sizeof(kernfs_pr_cont_buf));
if (p)
pr_cont("%s", p);
else
pr_cont("<name too long>");
sz = kernfs_path_from_node_locked(kn, NULL, kernfs_pr_cont_buf,
sizeof(kernfs_pr_cont_buf));
if (sz < 0) {
pr_cont("(error)");
goto out;
}
if (sz >= sizeof(kernfs_pr_cont_buf)) {
pr_cont("(name too long)");
goto out;
}
pr_cont("%s", kernfs_pr_cont_buf);
out:
spin_unlock_irqrestore(&kernfs_rename_lock, flags);
}

9
include/linux/kernfs.h
Unescape View File

@ -267,8 +267,9 @@ static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen);
size_t kernfs_path_len(struct kernfs_node *kn);
char * __must_check kernfs_path(struct kernfs_node *kn, char *buf,
size_t buflen);
int kernfs_path_from_node(struct kernfs_node *root_kn, struct kernfs_node *kn,
char *buf, size_t buflen);
char *kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen);
void pr_cont_kernfs_name(struct kernfs_node *kn);
void pr_cont_kernfs_path(struct kernfs_node *kn);
struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn);
@ -338,8 +339,8 @@ static inline int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
static inline size_t kernfs_path_len(struct kernfs_node *kn)
{ return 0; }
static inline char * __must_check kernfs_path(struct kernfs_node *kn, char *buf,
size_t buflen)
static inline char *kernfs_path(struct kernfs_node *kn, char *buf,
size_t buflen)
{ return NULL; }
static inline void pr_cont_kernfs_name(struct kernfs_node *kn) { }

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