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@xxxxxxxxxx>
Signed-off-by: Serge E. Hallyn <serge.hallyn@xxxxxxxxxxxxx>
Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
Changelog 20151125:
- Fully-wing multilinecomments
- Rework kernfs_path_from_node_locked() logic
- Replace BUG_ONs with returning NULL
- Use a const char* for /.. and precalculate its size
Changelog 20151130:
- Update kernfs_path_from_node_locked comment
Changelog 20151208:
- kernfs_node_distance:
* Remove BUG_ON(NULL)s
* Rename kernfs_node_distance to kernfs_depth
- kernfs_common-ancestor:
* Remove useless checks for depth == 0
* Add check to ensure nodes are from same root
- kernfs_path_from_node_locked:
* Remove needless __must_check
* Put p;len on its own decl line.
* Fix wrong WARN_ONCE usage
Changelog 20151209:
- kernfs_path_from_node: change arguments to 'to' and 'from', and
change their order.
Changelog 20151222:
- kernfs_path_from_node{,_locked}: return the string length.
kernfs_path is gpl-exported, so changing their return value seemed
ill-advised, but if noone minds I can update it too.
Changelog 20151223:
- don't allocate memory pr_cont_kernfs_path() under spinlock
---
fs/kernfs/dir.c | 192 ++++++++++++++++++++++++++++++++++++++++--------
include/linux/kernfs.h | 9 ++-
2 files changed, 166 insertions(+), 35 deletions(-)
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 742bf4a..8cf0810 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -44,28 +44,123 @@ 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);
+
+ 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';
- return p;
+ 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;
}
/**
@@ -115,6 +210,34 @@ size_t kernfs_path_len(struct kernfs_node *kn)
}
/**
+ * 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
* @buf: buffer to copy @kn's name into
@@ -127,13 +250,12 @@ 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 +286,25 @@ 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);
}
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index af51df3..716bfde 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -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) { }
--
1.7.9.5
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