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Message-Id: <1417744550-6461-2-git-send-email-adityakali@google.com>
Date: Thu, 4 Dec 2014 17:55:43 -0800
From: Aditya Kali <adityakali@...gle.com>
To: tj@...nel.org, lizefan@...wei.com, serge.hallyn@...ntu.com,
luto@...capital.net, ebiederm@...ssion.com,
cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-api@...r.kernel.org, mingo@...hat.com
Cc: containers@...ts.linux-foundation.org, jnagal@...gle.com,
vgoyal@...hat.com, richard.weinberger@...il.com,
Aditya Kali <adityakali@...gle.com>
Subject: [PATCHv3 1/8] kernfs: Add API to generate relative kernfs path
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@...gle.com>
---
fs/kernfs/dir.c | 195 +++++++++++++++++++++++++++++++++++++++++++------
include/linux/kernfs.h | 3 +
2 files changed, 177 insertions(+), 21 deletions(-)
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 1c77193..cb225a7 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -44,28 +44,159 @@ 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 of the kernfs node from root.
+ * The root node itself is considered to be at depth 0.
+ */
+static size_t kernfs_node_depth(struct kernfs_node *kn)
{
- char *p = buf + buflen;
+ size_t depth = 0;
+
+ BUG_ON(!kn);
+ while (kn->parent) {
+ depth++;
+ kn = kn->parent;
+ }
+ return depth;
+}
+
+/**
+ * kernfs_path_from_node_locked - find a relative path from @kn_from to @kn_to
+ * @kn_from: reference node of 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: /../..
+ */
+static char * __must_check kernfs_path_from_node_locked(
+ struct kernfs_node *kn_from,
+ struct kernfs_node *kn_to,
+ char *buf,
+ size_t buflen)
+{
+ char *p = buf;
+ struct kernfs_node *kn;
+ size_t depth_from = 0, depth_to, d;
int len;
- *--p = '\0';
+ /* We atleast need 2 bytes to write "/\0". */
+ BUG_ON(buflen < 2);
- do {
- len = strlen(kn->name);
- if (p - buf < len + 1) {
- buf[0] = '\0';
- p = NULL;
- break;
+ /* Short-circuit the easy case - kn_to is the root node. */
+ if ((kn_from == kn_to) || (!kn_from && !kn_to->parent)) {
+ *p = '/';
+ *(p + 1) = '\0';
+ return p;
+ }
+
+ /* We can find the relative path only if both the nodes belong to the
+ * same kernfs root.
+ */
+ if (kn_from) {
+ BUG_ON(kernfs_root(kn_from) != kernfs_root(kn_to));
+ depth_from = kernfs_node_depth(kn_from);
+ }
+
+ depth_to = kernfs_node_depth(kn_to);
+
+ /* We compose path from left to right. So first write out all possible
+ * "/.." strings needed to reach from 'kn_from' to the common ancestor.
+ */
+ if (kn_from) {
+ while (depth_from > depth_to) {
+ len = strlen("/..");
+ if ((buflen - (p - buf)) < len + 1) {
+ /* buffer not big enough. */
+ buf[0] = '\0';
+ return NULL;
+ }
+ memcpy(p, "/..", len);
+ p += len;
+ *p = '\0';
+ --depth_from;
+ kn_from = kn_from->parent;
}
+
+ d = depth_to;
+ kn = kn_to;
+ while (depth_from < d) {
+ kn = kn->parent;
+ d--;
+ }
+
+ /* Now we have 'depth_from == depth_to' at this point. Add more
+ * "/.."s until we reach common ancestor. In the worst case,
+ * root node will be the common ancestor.
+ */
+ while (depth_from > 0) {
+ /* If we reached common ancestor, stop. */
+ if (kn_from == kn)
+ break;
+ len = strlen("/..");
+ if ((buflen - (p - buf)) < len + 1) {
+ /* buffer not big enough. */
+ buf[0] = '\0';
+ return NULL;
+ }
+ memcpy(p, "/..", len);
+ p += len;
+ *p = '\0';
+ --depth_from;
+ kn_from = kn_from->parent;
+ kn = kn->parent;
+ }
+ }
+
+ /* Figure out how many bytes we need to write the path.
+ */
+ d = depth_to;
+ kn = kn_to;
+ len = 0;
+ while (depth_from < d) {
+ /* Account for "/<name>". */
+ len += strlen(kn->name) + 1;
+ kn = kn->parent;
+ --d;
+ }
+
+ if ((buflen - (p - buf)) < len + 1) {
+ /* buffer not big enough. */
+ buf[0] = '\0';
+ return NULL;
+ }
+
+ /* We have enough space. Move 'p' ahead by computed length and start
+ * writing node names into buffer.
+ */
+ p += len;
+ *p = '\0';
+ d = depth_to;
+ kn = kn_to;
+ while (d > depth_from) {
+ len = strlen(kn->name);
p -= len;
memcpy(p, kn->name, len);
*--p = '/';
kn = kn->parent;
- } while (kn && kn->parent);
+ --d;
+ }
- return p;
+ return buf;
}
/**
@@ -92,26 +223,48 @@ 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
- * doesn't match @buf. If @buf isn't long enough, @buf is nul terminated
+ * Builds and returns @kn's path relative to @kn_root. @kn_root and @kn must
+ * be on the same kernfs-root. If @kn_root is not parent of @kn, then a relative
+ * path (which includes '..'s) as needed to reach from @kn_root to @kn is
+ * returned.
+ * The path may be built from the end of @buf so the returned pointer may not
+ * 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 +298,8 @@ 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 30faf79..3c2be75 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -258,6 +258,9 @@ 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);
--
2.2.0.rc0.207.ga3a616c
--
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