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Subject[PATCH 1/5] kernfs: Add API to get generate relative kernfs path
Date
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>
---
fs/kernfs/dir.c | 51 ++++++++++++++++++++++++++++++++++++++++----------
include/linux/kernfs.h | 3 +++
2 files changed, 44 insertions(+), 10 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index a693f5b..2224f08 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -44,14 +44,22 @@ 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)
+static char * __must_check kernfs_path_from_node_locked(
+ struct kernfs_node *kn_root,
+ struct kernfs_node *kn,
+ char *buf,
+ size_t buflen)
{
char *p = buf + buflen;
int len;

*--p = '\0';

+ if (kn == kn_root) {
+ *--p = '/';
+ return p;
+ }
+
do {
len = strlen(kn->name);
if (p - buf < len + 1) {
@@ -63,6 +71,8 @@ static char * __must_check kernfs_path_locked(struct kernfs_node *kn, char *buf,
memcpy(p, kn->name, len);
*--p = '/';
kn = kn->parent;
+ if (kn == kn_root)
+ break;
} while (kn && kn->parent);

return p;
@@ -92,26 +102,47 @@ int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
}

/**
- * kernfs_path - build full path of a given node
+ * kernfs_path_from_node - build path of node @kn relative to @kn_root.
+ * @kn_root: parent kernfs_node relative to which we need to build the path
* @kn: kernfs_node of interest
- * @buf: buffer to copy @kn's name into
+ * @buf: buffer to copy @kn's path into
* @buflen: size of @buf
*
- * Builds and returns the full path of @kn in @buf of @buflen bytes. The
- * path is built from the end of @buf so the returned pointer usually
+ * Builds and returns @kn's path relative to @kn_root. @kn_root is expected to
+ * be parent of @kn at some level. If this is not true or if @kn_root is NULL,
+ * then full path of @kn is returned.
+ * The path is built from the end of @buf so the returned pointer usually
* doesn't match @buf. If @buf isn't long enough, @buf is nul terminated
* and %NULL is returned.
*/
-char *kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen)
+char *kernfs_path_from_node(struct kernfs_node *kn_root, struct kernfs_node *kn,
+ char *buf, size_t buflen)
{
unsigned long flags;
char *p;

spin_lock_irqsave(&kernfs_rename_lock, flags);
- p = kernfs_path_locked(kn, buf, buflen);
+ p = kernfs_path_from_node_locked(kn_root, kn, buf, buflen);
spin_unlock_irqrestore(&kernfs_rename_lock, flags);
return p;
}
+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
+ * @buflen: size of @buf
+ *
+ * Builds and returns the full path of @kn in @buf of @buflen bytes. The
+ * path is built from the end of @buf so the returned pointer usually
+ * doesn't match @buf. If @buf isn't long enough, @buf is nul terminated
+ * and %NULL is returned.
+ */
+char *kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen)
+{
+ return kernfs_path_from_node(NULL, kn, buf, buflen);
+}
EXPORT_SYMBOL_GPL(kernfs_path);

/**
@@ -145,8 +176,8 @@ void pr_cont_kernfs_path(struct kernfs_node *kn)

spin_lock_irqsave(&kernfs_rename_lock, flags);

- p = kernfs_path_locked(kn, kernfs_pr_cont_buf,
- sizeof(kernfs_pr_cont_buf));
+ p = kernfs_path_from_node_locked(NULL, kn, kernfs_pr_cont_buf,
+ sizeof(kernfs_pr_cont_buf));
if (p)
pr_cont("%s", p);
else
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 20f4935..1627341 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -257,6 +257,9 @@ static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
}

int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen);
+char * __must_check kernfs_path_from_node(struct kernfs_node *root_kn,
+ struct kernfs_node *kn, char *buf,
+ size_t buflen);
char * __must_check kernfs_path(struct kernfs_node *kn, char *buf,
size_t buflen);
void pr_cont_kernfs_name(struct kernfs_node *kn);
--
2.0.0.526.g5318336


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