ceph: allow idmapped atomic_open inode op

Enable ceph_atomic_open() to handle idmapped mounts. This is just a
matter of passing down the mount's idmapping.

[ aleksandr.mikhalitsyn: adapted to 5fadbd99 ("ceph: rely on vfs for
  setgid stripping") ]
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/file.c

@@ -668,7 +668,9 @@ static int ceph_finish_async_create(struct inode *dir, struct inode *inode,
 	in.truncate_seq = cpu_to_le32(1);
 	in.truncate_size = cpu_to_le64(-1ULL);
 	in.xattr_version = cpu_to_le64(1);
-	in.uid = cpu_to_le32(from_kuid(&init_user_ns, current_fsuid()));
+	in.uid = cpu_to_le32(from_kuid(&init_user_ns,
+				       mapped_fsuid(req->r_mnt_idmap,
+						    &init_user_ns)));
 	if (dir->i_mode & S_ISGID) {
 		in.gid = cpu_to_le32(from_kgid(&init_user_ns, dir->i_gid));
 
@@ -676,7 +678,9 @@ static int ceph_finish_async_create(struct inode *dir, struct inode *inode,
 		if (S_ISDIR(mode))
 			mode |= S_ISGID;
 	} else {
-		in.gid = cpu_to_le32(from_kgid(&init_user_ns, current_fsgid()));
+		in.gid = cpu_to_le32(from_kgid(&init_user_ns,
+				     mapped_fsgid(req->r_mnt_idmap,
+						  &init_user_ns)));
 	}
 	in.mode = cpu_to_le32((u32)mode);
 
@@ -743,6 +747,7 @@ static int ceph_finish_async_create(struct inode *dir, struct inode *inode,
 int ceph_atomic_open(struct inode *dir, struct dentry *dentry,
 		     struct file *file, unsigned flags, umode_t mode)
 {
+	struct mnt_idmap *idmap = file_mnt_idmap(file);
 	struct ceph_fs_client *fsc = ceph_sb_to_fs_client(dir->i_sb);
 	struct ceph_client *cl = fsc->client;
 	struct ceph_mds_client *mdsc = fsc->mdsc;
@@ -802,6 +807,8 @@ int ceph_atomic_open(struct inode *dir, struct dentry *dentry,
 		mask |= CEPH_CAP_XATTR_SHARED;
 	req->r_args.open.mask = cpu_to_le32(mask);
 	req->r_parent = dir;
+	if (req->r_op == CEPH_MDS_OP_CREATE)
+		req->r_mnt_idmap = mnt_idmap_get(idmap);
 	ihold(dir);
 	if (IS_ENCRYPTED(dir)) {
 		set_bit(CEPH_MDS_R_FSCRYPT_FILE, &req->r_req_flags);