um: ubd: Switch to the pthread-based helper

The ubd io thread and UML kernel thread share the same errno, which
can lead to conflicts when both call syscalls concurrently. Switch to
the pthread-based helper to address this issue.

Signed-off-by: Tiwei Bie <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Johannes Berg <[e-mail]>

arch/um/drivers/ubd.h

···
 #ifndef __UM_UBD_USER_H
 #define __UM_UBD_USER_H
 
-extern int start_io_thread(unsigned long sp, int *fds_out);
-extern int io_thread(void *arg);
+#include <os.h>
+
+int start_io_thread(struct os_helper_thread **td_out, int *fd_out);
+void *io_thread(void *arg);
 extern int kernel_fd;
 
 extern int ubd_read_poll(int timeout);

arch/um/drivers/ubd_kern.c

···
 }
 
 /* Only changed by ubd_init, which is an initcall. */
-static int io_pid = -1;
+static struct os_helper_thread *io_td;
 
 static void kill_io_thread(void)
 {
-	if(io_pid != -1)
-		os_kill_process(io_pid, 1);
+	if (io_td)
+		os_kill_helper_thread(io_td);
 }
 
 __uml_exitcall(kill_io_thread);
···
 
 late_initcall(ubd_init);
 
-static int __init ubd_driver_init(void){
-	unsigned long stack;
+static int __init ubd_driver_init(void)
+{
 	int err;
 
 	/* Set by CONFIG_BLK_DEV_UBD_SYNC or ubd=sync.*/
···
 		/* Letting ubd=sync be like using ubd#s= instead of ubd#= is
 		 * enough. So use anyway the io thread. */
 	}
-	stack = alloc_stack(0, 0);
-	io_pid = start_io_thread(stack + PAGE_SIZE, &thread_fd);
-	if(io_pid < 0){
+	err = start_io_thread(&io_td, &thread_fd);
+	if (err < 0) {
 		printk(KERN_ERR
 		       "ubd : Failed to start I/O thread (errno = %d) - "
-		       "falling back to synchronous I/O\n", -io_pid);
-		io_pid = -1;
+		       "falling back to synchronous I/O\n", -err);
 		return 0;
 	}
 	err = um_request_irq(UBD_IRQ, thread_fd, IRQ_READ, ubd_intr,
···
 /* Only changed by the io thread. XXX: currently unused. */
 static int io_count;
 
-int io_thread(void *arg)
+void *io_thread(void *arg)
 {
 	int n, count, written, res;
 
-	os_set_pdeathsig();
-	os_fix_helper_signals();
+	os_fix_helper_thread_signals();
 
 	while(1){
 		n = bulk_req_safe_read(
···
 		} while (written < n);
 	}
 
-	return 0;
+	return NULL;
 }

arch/um/drivers/ubd_user.c

···
 
 static struct pollfd kernel_pollfd;
 
-int start_io_thread(unsigned long sp, int *fd_out)
+int start_io_thread(struct os_helper_thread **td_out, int *fd_out)
 {
-	int pid, fds[2], err;
+	int fds[2], err;
 
 	err = os_pipe(fds, 1, 1);
 	if(err < 0){
···
 		goto out_close;
 	}
 
-	pid = clone(io_thread, (void *) sp, CLONE_FILES | CLONE_VM, NULL);
-	if(pid < 0){
-		err = -errno;
-		printk("start_io_thread - clone failed : errno = %d\n", errno);
+	err = os_run_helper_thread(td_out, io_thread, NULL);
+	if (err < 0) {
+		printk("%s - failed to run helper thread, err = %d\n",
+		       __func__, -err);
 		goto out_close;
 	}
 
-	return(pid);
+	return 0;
 
  out_close:
 	os_close_file(fds[0]);