new ->follow_link() and ->put_link() calling conventions

a) instead of storing the symlink body (via nd_set_link()) and returning
an opaque pointer later passed to ->put_link(), ->follow_link() _stores_
that opaque pointer (into void * passed by address by caller) and returns
the symlink body.  Returning ERR_PTR() on error, NULL on jump (procfs magic
symlinks) and pointer to symlink body for normal symlinks.  Stored pointer
is ignored in all cases except the last one.

Storing NULL for opaque pointer (or not storing it at all) means no call
of ->put_link().

b) the body used to be passed to ->put_link() implicitly (via nameidata).
Now only the opaque pointer is.  In the cases when we used the symlink body
to free stuff, ->follow_link() now should store it as opaque pointer in addition
to returning it.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

5 files changed, 27 insertions, 32 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 093ca14f5701..52652f86b187 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1380,7 +1380,7 @@ static int proc_exe_link(struct dentry *dentry, struct path *exe_path)
 		return -ENOENT;
 }
 
-static void *proc_pid_follow_link(struct dentry *dentry, struct nameidata *nd)
+static const char *proc_pid_follow_link(struct dentry *dentry, void **cookie, struct nameidata *nd)
 {
 	struct inode *inode = d_inode(dentry);
 	struct path path;
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 8272aaba1bb0..acd51d75387d 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -23,7 +23,6 @@
 #include <linux/slab.h>
 #include <linux/mount.h>
 #include <linux/magic.h>
-#include <linux/namei.h>
 
 #include <asm/uaccess.h>
 
@@ -394,16 +393,16 @@ static const struct file_operations proc_reg_file_ops_no_compat = {
 };
 #endif
 
-static void *proc_follow_link(struct dentry *dentry, struct nameidata *nd)
+static const char *proc_follow_link(struct dentry *dentry, void **cookie, struct nameidata *nd)
 {
 	struct proc_dir_entry *pde = PDE(d_inode(dentry));
 	if (unlikely(!use_pde(pde)))
 		return ERR_PTR(-EINVAL);
-	nd_set_link(nd, pde->data);
-	return pde;
+	*cookie = pde;
+	return pde->data;
 }
 
-static void proc_put_link(struct dentry *dentry, struct nameidata *nd, void *p)
+static void proc_put_link(struct dentry *dentry, void *p)
 {
 	unuse_pde(p);
 }
diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c
index e512642dbbdc..10d24dd096e8 100644
--- a/fs/proc/namespaces.c
+++ b/fs/proc/namespaces.c
@@ -30,7 +30,7 @@ static const struct proc_ns_operations *ns_entries[] = {
 	&mntns_operations,
 };
 
-static void *proc_ns_follow_link(struct dentry *dentry, struct nameidata *nd)
+static const char *proc_ns_follow_link(struct dentry *dentry, void **cookie, struct nameidata *nd)
 {
 	struct inode *inode = d_inode(dentry);
 	const struct proc_ns_operations *ns_ops = PROC_I(inode)->ns_ops;
diff --git a/fs/proc/self.c b/fs/proc/self.c
index 6195b4a7c3b1..ad333946b53a 100644
--- a/fs/proc/self.c
+++ b/fs/proc/self.c
@@ -1,5 +1,4 @@
 #include <linux/sched.h>
-#include <linux/namei.h>
 #include <linux/slab.h>
 #include <linux/pid_namespace.h>
 #include "internal.h"
@@ -19,21 +18,20 @@ static int proc_self_readlink(struct dentry *dentry, char __user *buffer,
 	return readlink_copy(buffer, buflen, tmp);
 }
 
-static void *proc_self_follow_link(struct dentry *dentry, struct nameidata *nd)
+static const char *proc_self_follow_link(struct dentry *dentry, void **cookie, struct nameidata *nd)
 {
 	struct pid_namespace *ns = dentry->d_sb->s_fs_info;
 	pid_t tgid = task_tgid_nr_ns(current, ns);
-	char *name = ERR_PTR(-ENOENT);
-	if (tgid) {
-		/* 11 for max length of signed int in decimal + NULL term */
-		name = kmalloc(12, GFP_KERNEL);
-		if (!name)
-			name = ERR_PTR(-ENOMEM);
-		else
-			sprintf(name, "%d", tgid);
-	}
-	nd_set_link(nd, name);
-	return NULL;
+	char *name;
+
+	if (!tgid)
+		return ERR_PTR(-ENOENT);
+	/* 11 for max length of signed int in decimal + NULL term */
+	name = kmalloc(12, GFP_KERNEL);
+	if (!name)
+		return ERR_PTR(-ENOMEM);
+	sprintf(name, "%d", tgid);
+	return *cookie = name;
 }
 
 static const struct inode_operations proc_self_inode_operations = {
diff --git a/fs/proc/thread_self.c b/fs/proc/thread_self.c
index a8371993b4fb..85c96e0d7aaa 100644
--- a/fs/proc/thread_self.c
+++ b/fs/proc/thread_self.c
@@ -1,5 +1,4 @@
 #include <linux/sched.h>
-#include <linux/namei.h>
 #include <linux/slab.h>
 #include <linux/pid_namespace.h>
 #include "internal.h"
@@ -20,21 +19,20 @@ static int proc_thread_self_readlink(struct dentry *dentry, char __user *buffer,
 	return readlink_copy(buffer, buflen, tmp);
 }
 
-static void *proc_thread_self_follow_link(struct dentry *dentry, struct nameidata *nd)
+static const char *proc_thread_self_follow_link(struct dentry *dentry, void **cookie, struct nameidata *nd)
 {
 	struct pid_namespace *ns = dentry->d_sb->s_fs_info;
 	pid_t tgid = task_tgid_nr_ns(current, ns);
 	pid_t pid = task_pid_nr_ns(current, ns);
-	char *name = ERR_PTR(-ENOENT);
-	if (pid) {
-		name = kmalloc(PROC_NUMBUF + 6 + PROC_NUMBUF, GFP_KERNEL);
-		if (!name)
-			name = ERR_PTR(-ENOMEM);
-		else
-			sprintf(name, "%d/task/%d", tgid, pid);
-	}
-	nd_set_link(nd, name);
-	return NULL;
+	char *name;
+
+	if (!pid)
+		return ERR_PTR(-ENOENT);
+	name = kmalloc(PROC_NUMBUF + 6 + PROC_NUMBUF, GFP_KERNEL);
+	if (!name)
+		return ERR_PTR(-ENOMEM);
+	sprintf(name, "%d/task/%d", tgid, pid);
+	return *cookie = name;
 }
 
 static const struct inode_operations proc_thread_self_inode_operations = {