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Subject[PATCH -V18 05/13] vfs: Support null pathname in readlink
Date
From: NeilBrown <neilb@suse.de>

This enables to use readlink to get the link target name
from a file descriptor point to the link. This can be used
with open_by_handle syscall that returns a file descriptor for a link.
We can then use this file descriptor to get the target name.

This is similar to utimensat(2) interface

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
fs/stat.c | 30 ++++++++++++++++++++++--------
1 files changed, 22 insertions(+), 8 deletions(-)
diff --git a/fs/stat.c b/fs/stat.c
index 12e90e2..3723a9f 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -289,26 +289,40 @@ SYSCALL_DEFINE2(newfstat, unsigned int, fd, struct stat __user *, statbuf)
SYSCALL_DEFINE4(readlinkat, int, dfd, const char __user *, pathname,
char __user *, buf, int, bufsiz)
{
- struct path path;
- int error;
+ int error = 0, fput_needed;
+ struct path path, *pp;
+ struct file *file = NULL;

if (bufsiz <= 0)
return -EINVAL;

- error = user_path_at(dfd, pathname, 0, &path);
+ if (pathname == NULL && dfd != AT_FDCWD) {
+ file = fget_light(dfd, &fput_needed);
+
+ if (file)
+ pp = &file->f_path;
+ else
+ error = -EBADF;
+ } else {
+ error = user_path_at(dfd, pathname, 0, &path);
+ pp = &path;
+ }
if (!error) {
- struct inode *inode = path.dentry->d_inode;
+ struct inode *inode = pp->dentry->d_inode;

error = -EINVAL;
if (inode->i_op->readlink) {
- error = security_inode_readlink(path.dentry);
+ error = security_inode_readlink(pp->dentry);
if (!error) {
- touch_atime(path.mnt, path.dentry);
- error = inode->i_op->readlink(path.dentry,
+ touch_atime(pp->mnt, pp->dentry);
+ error = inode->i_op->readlink(pp->dentry,
buf, bufsiz);
}
}
- path_put(&path);
+ if (file)
+ fput_light(file, fput_needed);
+ else
+ path_put(&path);
}
return error;
}
--
1.7.0.4


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