[CRIU] [PATCH 3/5] compel: Make struct seize_task_status be possible to be extensible

[Kirill Tkhai]

Sometimes get_status() callback in compel_wait_task()
may want to collect additional fields, e.g. NSpid and
friends. When compel_wait_task() goes to the second
turn to try_again, such fields must be freed, because
we're going to call get_status() once again, and it
rewrites the previous collected data.

So, allow get_status() to collect what it wants, and
also allow struct seize_task_status to be extensible:
on an extension of this structure users may safely
recompile their programs without any code changes.

Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 compel/include/uapi/infect.h |    2 ++
 compel/src/lib/infect.c      |   24 +++++++++++++++++++++---
 criu/seize.c                 |    8 +++++++-
 3 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/compel/include/uapi/infect.h b/compel/include/uapi/infect.h
index da0ca3a69..1e744c62a 100644
--- a/compel/include/uapi/infect.h
+++ b/compel/include/uapi/infect.h
@@ -21,11 +21,13 @@ struct seize_task_status {
 	unsigned long long	sigpnd;
 	unsigned long long	shdpnd;
 	int			seccomp_mode;
+	/* Add new members to the bottom and do not change existing */
 };
 
 extern int compel_wait_task(int pid, int ppid,
 		int (*get_status)(int pid, struct seize_task_status *),
 		struct seize_task_status *st);
+extern void compel_consume_seize_task_status(struct seize_task_status *ss);
 
 extern int compel_stop_task(int pid);
 extern int compel_resume_task(pid_t pid, int orig_state, int state);
diff --git a/compel/src/lib/infect.c b/compel/src/lib/infect.c
index 7f6d2f3f1..e0aaf7720 100644
--- a/compel/src/lib/infect.c
+++ b/compel/src/lib/infect.c
@@ -102,12 +102,15 @@ static int parse_pid_status(int pid, struct seize_task_status *ss)
 
 int compel_stop_task(int pid)
 {
-	int ret;
 	struct seize_task_status ss;
+	int ret;
 
 	ret = compel_interrupt_task(pid);
-	if (ret == 0)
+	if (ret == 0) {
 		ret = compel_wait_task(pid, -1, parse_pid_status, &ss);
+		if (ret != -1)
+			compel_consume_seize_task_status(&ss);
+	}
 	return ret;
 }
 
@@ -184,6 +187,17 @@ static int skip_sigstop(int pid, int nr_signals)
 	return 0;
 }
 
+/* Init dynamically allocated fields in NULL and do not touch other */
+static void init_seize_task_status(struct seize_task_status *ss)
+{
+}
+
+/* Free dynamically allocated fields in compel_wait_task() and do not touch other */
+void compel_consume_seize_task_status(struct seize_task_status *ss)
+{
+	init_seize_task_status(ss);
+}
+
 /*
  * This routine seizes task putting it into a special
  * state where we can manipulate the task via ptrace
@@ -207,6 +221,7 @@ int compel_wait_task(int pid, int ppid,
 	 */
 
 try_again:
+	init_seize_task_status(ss);
 
 	ret = wait4(pid, &status, __WALL, NULL);
 	if (ret < 0) {
@@ -231,7 +246,7 @@ int compel_wait_task(int pid, int ppid,
 			else
 				pr_err("Unseizable non-zombie %d found, state %c, err %d/%d\n",
 						pid, ss->state, ret, wait_errno);
-			return -1;
+			goto err_free;
 		}
 
 		if (ret < 0)
@@ -271,6 +286,7 @@ int compel_wait_task(int pid, int ppid,
 		}
 
 		ret = 0;
+		compel_consume_seize_task_status(ss);
 		goto try_again;
 	}
 
@@ -304,6 +320,8 @@ int compel_wait_task(int pid, int ppid,
 err:
 	if (ptrace(PTRACE_DETACH, pid, NULL, NULL))
 		pr_perror("Unable to detach from %d", pid);
+err_free:
+	compel_consume_seize_task_status(ss);
 	return -1;
 }
 
diff --git a/criu/seize.c b/criu/seize.c
index 5727b8ff8..718880679 100644
--- a/criu/seize.c
+++ b/criu/seize.c
@@ -518,6 +518,7 @@ static int collect_children(struct pstree_item *item)
 
 		/* Here is a recursive call (Depth-first search) */
 		ret = collect_task(c);
+		compel_consume_seize_task_status(&creds->s);
 		if (ret < 0)
 			goto free;
 	}
@@ -742,15 +743,19 @@ static int collect_threads(struct pstree_item *item)
 
 		if (ret == TASK_DEAD) {
 			pr_err("Zombie thread not supported\n");
+			compel_consume_seize_task_status(&t_creds.s);
 			goto err;
 		}
 
-		if (!creds_dumpable(dmpi(item)->pi_creds, &t_creds))
+		if (!creds_dumpable(dmpi(item)->pi_creds, &t_creds)) {
+			compel_consume_seize_task_status(&t_creds.s);
 			goto err;
+		}
 
 		if (ret == TASK_STOPPED) {
 			nr_stopped++;
 		}
+		compel_consume_seize_task_status(&t_creds.s);
 	}
 
 	if (nr_stopped && nr_stopped != nr_inprogress) {
@@ -871,6 +876,7 @@ int collect_pstree(void)
 	dmpi(root_item)->pi_creds = creds;
 
 	ret = collect_task(root_item);
+	compel_consume_seize_task_status(&creds->s);
 	if (ret < 0)
 		goto err;