From 76fca90e9f3abc82114d9d02d8e14e0324a18ca2 Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@redhat.com>
Date: Fri, 9 Dec 2016 16:45:04 +0100
Subject: [PATCH] vfs: default to generic_readlink()
If i_op->readlink is NULL, but i_op->get_link is set then vfs_readlink()
defaults to calling generic_readlink().
The IOP_DEFAULT_READLINK flag indicates that the above conditions are met
and the default action can be taken.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
Documentation/filesystems/porting | 4 ++++
Documentation/filesystems/vfs.txt | 9 ++++++---
fs/namei.c | 15 ++++++++++++---
include/linux/fs.h | 1 +
4 files changed, 23 insertions(+), 6 deletions(-)
diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
index bdd025ceb763b..95280079c0b3a 100644
--- a/Documentation/filesystems/porting
+++ b/Documentation/filesystems/porting
@@ -596,3 +596,7 @@ in your dentry operations instead.
[mandatory]
->rename() has an added flags argument. Any flags not handled by the
filesystem should result in EINVAL being returned.
+--
+[recommended]
+ ->readlink is optional for symlinks. Don't set, unless filesystem needs
+ to fake something for readlink(2).
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index b5039a00caafa..038241123ca5a 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -451,9 +451,6 @@ otherwise noted.
exist; this is checked by the VFS. Unlike plain rename,
source and target may be of different type.
- readlink: called by the readlink(2) system call. Only required if
- you want to support reading symbolic links
-
get_link: called by the VFS to follow a symbolic link to the
inode it points to. Only required if you want to support
symbolic links. This method returns the symlink body
@@ -468,6 +465,12 @@ otherwise noted.
argument. If request can't be handled without leaving RCU mode,
have it return ERR_PTR(-ECHILD).
+ readlink: this is now just an override for use by readlink(2) for the
+ cases when ->get_link uses nd_jump_link() or object is not in
+ fact a symlink. Normally filesystems should only implement
+ ->get_link for symlinks and readlink(2) will automatically use
+ that.
+
permission: called by the VFS to check for access rights on a POSIX-like
filesystem.
diff --git a/fs/namei.c b/fs/namei.c
index 12a4159de72a9..b87465d67c60e 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4682,10 +4682,19 @@ int vfs_readlink(struct dentry *dentry, char __user *buffer, int buflen)
{
struct inode *inode = d_inode(dentry);
- if (!inode->i_op->readlink)
- return -EINVAL;
+ if (unlikely(!(inode->i_opflags & IOP_DEFAULT_READLINK))) {
+ if (unlikely(inode->i_op->readlink))
+ return inode->i_op->readlink(dentry, buffer, buflen);
+
+ if (!d_is_symlink(dentry))
+ return -EINVAL;
+
+ spin_lock(&inode->i_lock);
+ inode->i_opflags |= IOP_DEFAULT_READLINK;
+ spin_unlock(&inode->i_lock);
+ }
- return inode->i_op->readlink(dentry, buffer, buflen);
+ return generic_readlink(dentry, buffer, buflen);
}
EXPORT_SYMBOL(vfs_readlink);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index eba20d1c068d0..f6c206eae6ac2 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -595,6 +595,7 @@ is_uncached_acl(struct posix_acl *acl)
#define IOP_LOOKUP 0x0002
#define IOP_NOFOLLOW 0x0004
#define IOP_XATTR 0x0008
+#define IOP_DEFAULT_READLINK 0x0010
/*
* Keep mostly read-only and often accessed (especially for