files: Kill file_desc_options::collect_fd()

The only user is fifo, but it uses collect_fd()
to do read only actions (the only change is
fifo_info::reg_d population, which may be easily
moved to open_fifo_fd()).

So, move the collect_special_file() functionality
from collect_fifo_fd() to open_fifo_fd() and
kill collect_fd method at all.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>

criu/fifo.c

@@ -33,7 +33,6 @@ struct fifo_info {
 	struct file_desc	d;
 	FifoEntry		*fe;
 	bool			restore_data;
-	struct file_desc	*reg_d;
 };
 
 static LIST_HEAD(fifo_head);
@@ -114,29 +113,22 @@ out:
 static int open_fifo_fd(struct file_desc *d, int *new_fd)
 {
 	struct fifo_info *info = container_of(d, struct fifo_info, d);
+	struct file_desc *reg_d;
 	int fd;
 
-	fd = open_path(info->reg_d, do_open_fifo, info);
+	reg_d = find_file_desc_raw(FD_TYPES__REG, info->fe->id);
+	BUG_ON(!reg_d);
+
+	fd = open_path(reg_d, do_open_fifo, info);
 	if (fd < 0)
 		return -1;
 	*new_fd = fd;
 	return 0;
 }
 
-static void collect_fifo_fd(struct file_desc *d,
-		struct fdinfo_list_entry *fle, struct rst_info *ri)
-{
-	struct fifo_info *info;
-
-	info = container_of(d, struct fifo_info, d);
-	info->reg_d = collect_special_file(info->fe->id);
-	BUG_ON(info->reg_d == NULL);
-}
-
 static struct file_desc_ops fifo_desc_ops = {
 	.type		= FD_TYPES__FIFO,
 	.open		= open_fifo_fd,
-	.collect_fd	= collect_fifo_fd,
 };
 
 static int collect_one_fifo(void *o, ProtobufCMessage *base, struct cr_img *i)

criu/files.c

@@ -731,9 +731,6 @@ int collect_fd(int pid, FdinfoEntry *e, struct rst_info *rst_info, bool fake)
 		if (pid_rst_prio(new_le->pid, le->pid))
 			break;
 
-	if (fdesc->ops->collect_fd)
-		fdesc->ops->collect_fd(fdesc, new_le, rst_info);
-
 	collect_task_fd(new_le, rst_info);
 
 	list_add_tail(&new_le->desc_list, &le->desc_list);

criu/include/files.h

@@ -106,13 +106,6 @@ struct file_desc_ops {
 	 * so it shouldn't be saved for any post-actions.
 	 */
 	int			(*open)(struct file_desc *d, int *new_fd);
-	/*
-	 * Called to collect a new fd before adding it on desc. Clients
-	 * may chose to collect it to some specific rst_info list. See
-	 * prepare_fds() for details.
-	 */
-	void			(*collect_fd)(struct file_desc *, struct fdinfo_list_entry *,
-						struct rst_info *);
 	char *			(*name)(struct file_desc *, char *b, size_t s);
 };