linux-kernel - [PATCH 44/79] link_path

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Date:	Tue,  5 May 2015 06:22:18 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Neil Brown <neilb@...e.de>, Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: [PATCH 44/79] link_path_walk: kill the recursion

From: Al Viro <viro@...iv.linux.org.uk>

absolutely straightforward now - the only variables we need to preserve
across the recursive call are name, link and cookie, and recursion depth
is limited (and can is equal to nd->depth).  So arrange an array of
triples to hold instances of those and be done with that.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 fs/namei.c | 40 +++++++++++++++++++++++++++++-----------
 1 file changed, 29 insertions(+), 11 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index ac73d9e..3c622ad 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1703,8 +1703,14 @@ static inline u64 hash_name(const char *name)
  */
 static int link_path_walk(const char *name, struct nameidata *nd)
 {
+	struct saved {
+		struct path link;
+		void *cookie;
+		const char *name;
+	} stack[MAX_NESTED_LINKS], *last = stack + nd->depth - 1;
 	int err;
-	
+
+start:
 	while (*name=='/')
 		name++;
 	if (!*name)
@@ -1768,8 +1774,6 @@ Walked:
 			goto Err;
 
 		if (err) {
-			struct path link;
-			void *cookie;
 			const char *s;
 
 			if (unlikely(current->link_count >= MAX_NESTED_LINKS)) {
@@ -1782,22 +1786,25 @@ Walked:
 
 			nd->depth++;
 			current->link_count++;
+			last++;
 
-			link = nd->link;
-			s = get_link(&link, nd, &cookie);
+			last->link = nd->link;
+			s = get_link(&last->link, nd, &last->cookie);
 
 			if (unlikely(IS_ERR(s))) {
 				err = PTR_ERR(s);
 				current->link_count--;
 				nd->depth--;
+				last--;
 				goto Err;
 			}
 			err = 0;
 			if (unlikely(!s)) {
 				/* jumped */
-				put_link(nd, &link, cookie);
+				put_link(nd, &last->link, last->cookie);
 				current->link_count--;
 				nd->depth--;
+				last--;
 			} else {
 				if (*s == '/') {
 					if (!nd->root.mnt)
@@ -1808,17 +1815,24 @@ Walked:
 					nd->flags |= LOOKUP_JUMPED;
 				}
 				nd->inode = nd->path.dentry->d_inode;
-				err = link_path_walk(s, nd);
+				last->name = name;
+				name = s;
+				goto start;
+
+back:
+				name = last->name;
 				if (unlikely(err)) {
-					put_link(nd, &link, cookie);
+					put_link(nd, &last->link, last->cookie);
 					current->link_count--;
 					nd->depth--;
+					last--;
 					goto Err;
 				} else {
 					err = walk_component(nd, LOOKUP_FOLLOW);
-					put_link(nd, &link, cookie);
+					put_link(nd, &last->link, last->cookie);
 					current->link_count--;
 					nd->depth--;
+					last--;
 					goto Walked;
 				}
 			}
@@ -1830,9 +1844,13 @@ Walked:
 	}
 	terminate_walk(nd);
 Err:
-	return err;
+	if (likely(!nd->depth))
+		return err;
+	goto back;
 OK:
-	return 0;
+	if (likely(!nd->depth))
+		return 0;
+	goto back;
 }
 
 static int path_init(int dfd, const struct filename *name, unsigned int flags,
-- 
2.1.4

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