[PATCH -V18 07/13] vfs: Support null pathname in linkat

Aneesh Kumar K.V
2010-08-20T01:52:19Z

This enables to use linkat to create hardlinks from a
file descriptor pointing to the file. This can be used
with open_by_handle syscall that returns a file descriptor.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
fs/namei.c | 36 ++++++++++++++++++++++++++----------
1 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 2c79363..fd9febc 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2627,7 +2627,7 @@ int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_de
struct inode *inode = old_dentry->d_inode;
int error;

- if (!inode)
+ if (!inode || inode->i_nlink == 0)
return -ENOENT;

error = may_create(dir, new_dentry);
@@ -2673,16 +2673,28 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
{
struct dentry *new_dentry;
struct nameidata nd;
- struct path old_path;
- int error;
+ struct path old_path, *old_pathp;
+ struct file *file = NULL;
+ int error, fput_needed;
char *to;

if ((flags & ~AT_SYMLINK_FOLLOW) != 0)
return -EINVAL;

- error = user_path_at(olddfd, oldname,
- flags & AT_SYMLINK_FOLLOW ? LOOKUP_FOLLOW : 0,
- &old_path);
+ if (oldname == NULL && olddfd != AT_FDCWD) {
+ file = fget_light(olddfd, &fput_needed);
+ if (file) {
+ old_pathp = &file->f_path;
+ error = 0;
+ } else
+ error = -EBADF;
+ } else {
+ error = user_path_at(olddfd, oldname,
+ flags & AT_SYMLINK_FOLLOW ?
+ LOOKUP_FOLLOW : 0,
+ &old_path);
+ old_pathp = &old_path;
+ }
if (error)
return error;

@@ -2690,7 +2702,7 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
if (error)
goto out;
error = -EXDEV;
- if (old_path.mnt != nd.path.mnt)
+ if (old_pathp->mnt != nd.path.mnt)
goto out_release;
new_dentry = lookup_create(&nd, 0);
error = PTR_ERR(new_dentry);
@@ -2699,10 +2711,11 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
error = mnt_want_write(nd.path.mnt);
if (error)
goto out_dput;
- error = security_path_link(old_path.dentry, &nd.path, new_dentry);
+ error = security_path_link(old_pathp->dentry, &nd.path, new_dentry);
if (error)
goto out_drop_write;
- error = vfs_link(old_path.dentry, nd.path.dentry->d_inode, new_dentry);
+ error = vfs_link(old_pathp->dentry,
+ nd.path.dentry->d_inode, new_dentry);
out_drop_write:
mnt_drop_write(nd.path.mnt);
out_dput:
@@ -2713,7 +2726,10 @@ out_release:
path_put(&nd.path);
putname(to);
out:
- path_put(&old_path);
+ if (file)
+ fput_light(file, fput_needed);
+ else
+ path_put(&old_path);

return error;
}
--
1.7.0.4