[CRIU] [PATCH] dump: Show task comm early

[Cyrill Gorcunov]

When error happens on file dumping stage the only information about
the task we dumping is its PID. For debug purpose show task's @comm early,
including seizing stage.

Note @comm is small enough so I preferred it instead of @cmdline.

Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
---
 criu/cr-dump.c        |  6 +++---
 criu/include/ptrace.h |  3 +++
 criu/ptrace.c         | 48 ++++++++++++++++++++++++++++++++++++++++++++++--
 criu/seize.c          |  9 ++++++---
 4 files changed, 58 insertions(+), 8 deletions(-)

diff --git a/criu/cr-dump.c b/criu/cr-dump.c
index 9e2a33ec6b38..2b956d0676f6 100644
--- a/criu/cr-dump.c
+++ b/criu/cr-dump.c
@@ -1124,7 +1124,7 @@ static int pre_dump_one_task(struct pstree_item *item)
 	vmas.nr = 0;
 
 	pr_info("========================================\n");
-	pr_info("Pre-dumping task (pid: %d)\n", pid);
+	pr_info("Pre-dumping task (pid: %d comm: %s)\n", pid, __task_comm_info(pid));
 	pr_info("========================================\n");
 
 	if (item->pid.state == TASK_STOPPED) {
@@ -1200,7 +1200,7 @@ static int dump_one_task(struct pstree_item *item)
 	vmas.nr = 0;
 
 	pr_info("========================================\n");
-	pr_info("Dumping task (pid: %d)\n", pid);
+	pr_info("Dumping task (pid: %d comm: %s)\n", pid, __task_comm_info(pid));
 	pr_info("========================================\n");
 
 	if (item->pid.state == TASK_DEAD)
@@ -1643,7 +1643,7 @@ int cr_dump_tasks(pid_t pid)
 	int ret = -1;
 
 	pr_info("========================================\n");
-	pr_info("Dumping processes (pid: %d)\n", pid);
+	pr_info("Dumping processes (pid: %d comm: %s)\n", pid, __task_comm_info(pid));
 	pr_info("========================================\n");
 
 	root_item = alloc_pstree_item();
diff --git a/criu/include/ptrace.h b/criu/include/ptrace.h
index bf416b3ad00c..09585a1e3d3b 100644
--- a/criu/include/ptrace.h
+++ b/criu/include/ptrace.h
@@ -83,4 +83,7 @@ extern int ptrace_peek_area(pid_t pid, void *dst, void *addr, long bytes);
 extern int ptrace_poke_area(pid_t pid, void *src, void *addr, long bytes);
 extern int ptrace_swap_area(pid_t pid, void *dst, void *src, long bytes);
 
+extern char *task_comm_info(pid_t pid, char *comm, size_t size);
+extern char *__task_comm_info(pid_t pid);
+
 #endif /* __CR_PTRACE_H__ */
diff --git a/criu/ptrace.c b/criu/ptrace.c
index 45271c60e1c6..0ecc1665d65c 100644
--- a/criu/ptrace.c
+++ b/criu/ptrace.c
@@ -7,6 +7,7 @@
 #include <stdbool.h>
 #include <limits.h>
 #include <signal.h>
+#include <fcntl.h>
 
 #include <sys/ptrace.h>
 #include <sys/types.h>
@@ -23,6 +24,47 @@
 #include "seccomp.h"
 #include "cr_options.h"
 
+char *task_comm_info(pid_t pid, char *comm, size_t size)
+{
+	int ret = 0;
+
+	if (!pr_quelled(LOG_INFO)) {
+		int saved_errno = errno;
+		char path[64];
+		int fd;
+
+		snprintf(path, sizeof(path), "/proc/%d/comm", pid);
+		fd = open(path, O_RDONLY);
+		if (fd >= 0) {
+			ssize_t n = read(fd, comm, size);
+			if (n > 0)
+				comm[n-1] = '\0';
+			else
+				ret = -1;
+			close(fd);
+		} else {
+			pr_perror("Can't open %s\n", path);
+			ret = -1;
+		}
+
+		errno = saved_errno;
+	}
+
+	if (ret || (pr_quelled(LOG_INFO) && comm[0]))
+		comm[0] = '\0';
+
+	return comm;
+}
+
+/*
+ * NOTE: Don't run simultaneously, it uses local static buffer!
+ */
+char *__task_comm_info(pid_t pid)
+{
+	static char comm[32];
+	return task_comm_info(pid, comm, sizeof(comm));
+}
+
 int unseize_task(pid_t pid, int orig_st, int st)
 {
 	pr_debug("\tUnseizing %d into %d\n", pid, st);
@@ -79,7 +121,8 @@ int seize_catch_task(pid_t pid)
 		 * attaching to zombie from other errors.
 		 * All errors will be handled in seize_wait_task().
 		 */
-		pr_warn("Unable to interrupt task: %d (%s)\n", pid, strerror(errno));
+		pr_warn("Unable to interrupt task: %d (comm %s) (%s)\n",
+			pid, __task_comm_info(pid), strerror(errno));
 		return ret;
 	}
 
@@ -94,7 +137,8 @@ int seize_catch_task(pid_t pid)
 	 */
 	ret = ptrace(PTRACE_INTERRUPT, pid, NULL, NULL);
 	if (ret < 0) {
-		pr_warn("SEIZE %d: can't interrupt task: %s", pid, strerror(errno));
+		pr_warn("SEIZE %d (comm %s): can't interrupt task: %s",
+			pid, __task_comm_info(pid), strerror(errno));
 		if (ptrace(PTRACE_DETACH, pid, NULL, NULL))
 			pr_perror("Unable to detach from %d", pid);
 	}
diff --git a/criu/seize.c b/criu/seize.c
index fb78a0ba8a8b..0727f229c5bd 100644
--- a/criu/seize.c
+++ b/criu/seize.c
@@ -117,13 +117,15 @@ static int seize_cgroup_tree(char *root_path, const char *state)
 		if (ret == 0)
 			continue;
 		if (errno != ESRCH) {
-			pr_perror("Unexpected error");
+			pr_perror("Unexpected error for pid %d (comm %s)",
+				  pid, __task_comm_info(pid));
 			fclose(f);
 			return -1;
 		}
 
 		if (!seize_catch_task(pid)) {
-			pr_debug("SEIZE %d: success\n", pid);
+			pr_debug("SEIZE %d (comm %s): success\n",
+				 pid, __task_comm_info(pid));
 			processes_to_wait++;
 		} else if (state == frozen) {
 			char buf[] = "/proc/XXXXXXXXXX/exe";
@@ -135,7 +137,8 @@ static int seize_cgroup_tree(char *root_path, const char *state)
 				continue;
 
 			/* fails when meets a zombie */
-			pr_err("zombie found while seizing\n");
+			pr_err("zombie %d (comm %s) found while seizing\n",
+			       pid, __task_comm_info(pid));
 			fclose(f);
 			return -1;
 		}
-- 
2.7.4