1 files changed, 75 insertions, 67 deletions

diff --git a/fs/d_path.c b/fs/d_path.c
index 83db83446afd..06e93dd031bf 100644
--- a/fs/d_path.c
+++ b/fs/d_path.c
@@ -8,12 +8,26 @@
 #include <linux/prefetch.h>
 #include "mount.h"
 
-static void prepend(char **buffer, int *buflen, const char *str, int namelen)
+struct prepend_buffer {
+	char *buf;
+	int len;
+};
+#define DECLARE_BUFFER(__name, __buf, __len) \
+	struct prepend_buffer __name = {.buf = __buf + __len, .len = __len}
+
+static char *extract_string(struct prepend_buffer *p)
 {
-	*buflen -= namelen;
-	if (likely(*buflen >= 0)) {
-		*buffer -= namelen;
-		memcpy(*buffer, str, namelen);
+	if (likely(p->len >= 0))
+		return p->buf;
+	return ERR_PTR(-ENAMETOOLONG);
+}
+
+static void prepend(struct prepend_buffer *p, const char *str, int namelen)
+{
+	p->len -= namelen;
+	if (likely(p->len >= 0)) {
+		p->buf -= namelen;
+		memcpy(p->buf, str, namelen);
 	}
 }
 
@@ -34,22 +48,22 @@ static void prepend(char **buffer, int *buflen, const char *str, int namelen)
  *
  * Load acquire is needed to make sure that we see that terminating NUL.
  */
-static bool prepend_name(char **buffer, int *buflen, const struct qstr *name)
+static bool prepend_name(struct prepend_buffer *p, const struct qstr *name)
 {
 	const char *dname = smp_load_acquire(&name->name); /* ^^^ */
 	u32 dlen = READ_ONCE(name->len);
-	char *p;
+	char *s;
 
-	*buflen -= dlen + 1;
-	if (unlikely(*buflen < 0))
+	p->len -= dlen + 1;
+	if (unlikely(p->len < 0))
 		return false;
-	p = *buffer -= dlen + 1;
-	*p++ = '/';
+	s = p->buf -= dlen + 1;
+	*s++ = '/';
 	while (dlen--) {
 		char c = *dname++;
 		if (!c)
 			break;
-		*p++ = c;
+		*s++ = c;
 	}
 	return true;
 }
@@ -73,15 +87,14 @@ static bool prepend_name(char **buffer, int *buflen, const struct qstr *name)
  */
 static int prepend_path(const struct path *path,
 			const struct path *root,
-			char **buffer, int *buflen)
+			struct prepend_buffer *p)
 {
 	struct dentry *dentry;
 	struct vfsmount *vfsmnt;
 	struct mount *mnt;
 	int error = 0;
 	unsigned seq, m_seq = 0;
-	char *bptr;
-	int blen;
+	struct prepend_buffer b;
 
 	rcu_read_lock();
 restart_mnt:
@@ -89,8 +102,7 @@ restart_mnt:
 	seq = 0;
 	rcu_read_lock();
 restart:
-	bptr = *buffer;
-	blen = *buflen;
+	b = *p;
 	error = 0;
 	dentry = path->dentry;
 	vfsmnt = path->mnt;
@@ -105,8 +117,7 @@ restart:
 
 			/* Escaped? */
 			if (dentry != vfsmnt->mnt_root) {
-				bptr = *buffer;
-				blen = *buflen;
+				b = *p;
 				error = 3;
 				break;
 			}
@@ -127,7 +138,7 @@ restart:
 		}
 		parent = dentry->d_parent;
 		prefetch(parent);
-		if (!prepend_name(&bptr, &blen, &dentry->d_name))
+		if (!prepend_name(&b, &dentry->d_name))
 			break;
 
 		dentry = parent;
@@ -148,11 +159,10 @@ restart:
 	}
 	done_seqretry(&mount_lock, m_seq);
 
-	if (blen == *buflen)
-		prepend(&bptr, &blen, "/", 1);
+	if (b.len == p->len)
+		prepend(&b, "/", 1);
 
-	*buffer = bptr;
-	*buflen = blen;
+	*p = b;
 	return error;
 }
 
@@ -176,24 +186,24 @@ char *__d_path(const struct path *path,
 	       const struct path *root,
 	       char *buf, int buflen)
 {
-	char *res = buf + buflen;
+	DECLARE_BUFFER(b, buf, buflen);
 
-	prepend(&res, &buflen, "", 1);
-	if (prepend_path(path, root, &res, &buflen) > 0)
+	prepend(&b, "", 1);
+	if (prepend_path(path, root, &b) > 0)
 		return NULL;
-	return buflen >= 0 ? res : ERR_PTR(-ENAMETOOLONG);
+	return extract_string(&b);
 }
 
 char *d_absolute_path(const struct path *path,
 	       char *buf, int buflen)
 {
 	struct path root = {};
-	char *res = buf + buflen;
+	DECLARE_BUFFER(b, buf, buflen);
 
-	prepend(&res, &buflen, "", 1);
-	if (prepend_path(path, &root, &res, &buflen) > 1)
+	prepend(&b, "", 1);
+	if (prepend_path(path, &root, &b) > 1)
 		return ERR_PTR(-EINVAL);
-	return buflen >= 0 ? res : ERR_PTR(-ENAMETOOLONG);
+	return extract_string(&b);
 }
 
 static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
@@ -224,7 +234,7 @@ static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
  */
 char *d_path(const struct path *path, char *buf, int buflen)
 {
-	char *res = buf + buflen;
+	DECLARE_BUFFER(b, buf, buflen);
 	struct path root;
 
 	/*
@@ -245,13 +255,13 @@ char *d_path(const struct path *path, char *buf, int buflen)
 	rcu_read_lock();
 	get_fs_root_rcu(current->fs, &root);
 	if (unlikely(d_unlinked(path->dentry)))
-		prepend(&res, &buflen, " (deleted)", 11);
+		prepend(&b, " (deleted)", 11);
 	else
-		prepend(&res, &buflen, "", 1);
-	prepend_path(path, &root, &res, &buflen);
+		prepend(&b, "", 1);
+	prepend_path(path, &root, &b);
 	rcu_read_unlock();
 
-	return buflen >= 0 ? res : ERR_PTR(-ENAMETOOLONG);
+	return extract_string(&b);
 }
 EXPORT_SYMBOL(d_path);
 
@@ -278,36 +288,34 @@ char *dynamic_dname(struct dentry *dentry, char *buffer, int buflen,
 
 char *simple_dname(struct dentry *dentry, char *buffer, int buflen)
 {
-	char *end = buffer + buflen;
+	DECLARE_BUFFER(b, buffer, buflen);
 	/* these dentries are never renamed, so d_lock is not needed */
-	prepend(&end, &buflen, " (deleted)", 11);
-	prepend(&end, &buflen, dentry->d_name.name, dentry->d_name.len);
-	prepend(&end, &buflen, "/", 1);
-	return buflen >= 0 ? end : ERR_PTR(-ENAMETOOLONG);
+	prepend(&b, " (deleted)", 11);
+	prepend(&b, dentry->d_name.name, dentry->d_name.len);
+	prepend(&b, "/", 1);
+	return extract_string(&b);
 }
 
 /*
  * Write full pathname from the root of the filesystem into the buffer.
  */
-static char *__dentry_path(const struct dentry *d, char *p, int buflen)
+static char *__dentry_path(const struct dentry *d, struct prepend_buffer *p)
 {
 	const struct dentry *dentry;
-	char *end;
-	int len, seq = 0;
+	struct prepend_buffer b;
+	int seq = 0;
 
 	rcu_read_lock();
 restart:
 	dentry = d;
-	end = p;
-	len = buflen;
+	b = *p;
 	read_seqbegin_or_lock(&rename_lock, &seq);
 	while (!IS_ROOT(dentry)) {
 		const struct dentry *parent = dentry->d_parent;
 
 		prefetch(parent);
-		if (!prepend_name(&end, &len, &dentry->d_name))
+		if (!prepend_name(&b, &dentry->d_name))
 			break;
-
 		dentry = parent;
 	}
 	if (!(seq & 1))
@@ -317,28 +325,29 @@ restart:
 		goto restart;
 	}
 	done_seqretry(&rename_lock, seq);
-	if (len == buflen)
-		prepend(&end, &len, "/", 1);
-	return len >= 0 ? end : ERR_PTR(-ENAMETOOLONG);
+	if (b.len == p->len)
+		prepend(&b, "/", 1);
+	return extract_string(&b);
 }
 
 char *dentry_path_raw(const struct dentry *dentry, char *buf, int buflen)
 {
-	char *p = buf + buflen;
-	prepend(&p, &buflen, "", 1);
-	return __dentry_path(dentry, p, buflen);
+	DECLARE_BUFFER(b, buf, buflen);
+
+	prepend(&b, "", 1);
+	return __dentry_path(dentry, &b);
 }
 EXPORT_SYMBOL(dentry_path_raw);
 
 char *dentry_path(const struct dentry *dentry, char *buf, int buflen)
 {
-	char *p = buf + buflen;
+	DECLARE_BUFFER(b, buf, buflen);
 
 	if (unlikely(d_unlinked(dentry)))
-		prepend(&p, &buflen, "//deleted", 10);
+		prepend(&b, "//deleted", 10);
 	else
-		prepend(&p, &buflen, "", 1);
-	return __dentry_path(dentry, p, buflen);
+		prepend(&b, "", 1);
+	return __dentry_path(dentry, &b);
 }
 
 static void get_fs_root_and_pwd_rcu(struct fs_struct *fs, struct path *root,
@@ -386,24 +395,23 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
 	error = -ENOENT;
 	if (!d_unlinked(pwd.dentry)) {
 		unsigned long len;
-		char *cwd = page + PATH_MAX;
-		int buflen = PATH_MAX;
+		DECLARE_BUFFER(b, page, PATH_MAX);
 
-		prepend(&cwd, &buflen, "", 1);
-		if (prepend_path(&pwd, &root, &cwd, &buflen) > 0)
-			prepend(&cwd, &buflen, "(unreachable)", 13);
+		prepend(&b, "", 1);
+		if (prepend_path(&pwd, &root, &b) > 0)
+			prepend(&b, "(unreachable)", 13);
 		rcu_read_unlock();
 
-		if (buflen < 0) {
+		if (b.len < 0) {
 			error = -ENAMETOOLONG;
 			goto out;
 		}
 
 		error = -ERANGE;
-		len = PATH_MAX + page - cwd;
+		len = PATH_MAX - b.len;
 		if (len <= size) {
 			error = len;
-			if (copy_to_user(buf, cwd, len))
+			if (copy_to_user(buf, b.buf, len))
 				error = -EFAULT;
 		}
 	} else {