fds: Optimize fds draning (mem + cpu)

* Don't dumplicate array when sending to parasite
* Allocate necessary space in cr-dump for local fds/flags
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-dump.c

@@ -97,7 +97,7 @@ err:
 
 struct cr_fdset *glob_fdset;
 
-static int collect_fds(pid_t pid, int *fd, int *nr_fd)
+static int collect_fds(pid_t pid, struct parasite_drain_fd *dfds)
 {
 	struct dirent *de;
 	DIR *fd_dir;
@@ -118,12 +118,13 @@ static int collect_fds(pid_t pid, int *fd, int *nr_fd)
 		if (!strcmp(de->d_name, ".."))
 			continue;
 
-		if (n > *nr_fd - 1)
+		if (n > PARASITE_MAX_FDS - 1)
 			return -ENOMEM;
-		fd[n++] = atoi(de->d_name);
+
+		dfds->fds[n++] = atoi(de->d_name);
 	}
 
-	*nr_fd = n;
+	dfds->nr_fds = n;
 	pr_info("Found %d file descriptors\n", n);
 	pr_info("----------------------------------------\n");
 
@@ -312,7 +313,7 @@ static int dump_one_file(pid_t pid, int fd, int lfd, char fd_flags,
 }
 
 static int dump_task_files_seized(struct parasite_ctl *ctl, const struct cr_fdset *cr_fdset,
-				  int *fds, int nr_fds)
+		struct parasite_drain_fd *dfds)
 {
 	int *lfds;
 	char *flags;
@@ -322,20 +323,20 @@ static int dump_task_files_seized(struct parasite_ctl *ctl, const struct cr_fdse
 	pr_info("Dumping opened files (pid: %d)\n", ctl->pid);
 	pr_info("----------------------------------------\n");
 
-	lfds = xmalloc(PARASITE_MAX_FDS * sizeof(int));
+	lfds = xmalloc(dfds->nr_fds * sizeof(int));
 	if (!lfds)
 		goto err;
 
-	flags = xmalloc(PARASITE_MAX_FDS * sizeof(char));
+	flags = xmalloc(dfds->nr_fds * sizeof(char));
 	if (!flags)
 		goto err1;
 
-	ret = parasite_drain_fds_seized(ctl, fds, lfds, nr_fds, flags);
+	ret = parasite_drain_fds_seized(ctl, dfds, lfds, flags);
 	if (ret)
 		goto err2;
 
-	for (i = 0; i < nr_fds; i++) {
-		ret = dump_one_file(ctl->pid, fds[i], lfds[i], flags[i], cr_fdset);
+	for (i = 0; i < dfds->nr_fds; i++) {
+		ret = dump_one_file(ctl->pid, dfds->fds[i], lfds[i], flags[i], cr_fdset);
 		close(lfds[i]);
 		if (ret)
 			goto err2;
@@ -1346,16 +1347,14 @@ static int dump_one_task(struct pstree_item *item)
 	int ret = -1;
 	struct parasite_dump_misc misc;
 	struct cr_fdset *cr_fdset = NULL;
-
-	int nr_fds = PARASITE_MAX_FDS;
-	int *fds = NULL;
+	struct parasite_drain_fd *dfds;
 
 	pr_info("========================================\n");
 	pr_info("Dumping task (pid: %d)\n", pid);
 	pr_info("========================================\n");
 
-	fds = xmalloc(nr_fds * sizeof(int));
-	if (!fds)
+	dfds = xmalloc(sizeof(*dfds));
+	if (!dfds)
 		goto err_free;
 
 	if (item->state == TASK_STOPPED) {
@@ -1387,7 +1386,7 @@ static int dump_one_task(struct pstree_item *item)
 		goto err;
 	}
 
-	ret = collect_fds(pid, fds, &nr_fds);
+	ret = collect_fds(pid, dfds);
 	if (ret) {
 		pr_err("Collect fds (pid: %d) failed with %d\n", pid, ret);
 		goto err;
@@ -1415,7 +1414,7 @@ static int dump_one_task(struct pstree_item *item)
 	if (!cr_fdset)
 		goto err_cure;
 
-	ret = dump_task_files_seized(parasite_ctl, cr_fdset, fds, nr_fds);
+	ret = dump_task_files_seized(parasite_ctl, cr_fdset, dfds);
 	if (ret) {
 		pr_err("Dump files (pid: %d) failed with %d\n", pid, ret);
 		goto err_cure;
@@ -1480,7 +1479,7 @@ err:
 	close_pid_proc();
 err_free:
 	free_mappings(&vma_area_list);
-	xfree(fds);
+	xfree(dfds);
 	return ret;
 
 err_cure:

include/parasite-syscall.h

@@ -37,7 +37,9 @@ struct parasite_dump_tid_info;
 extern int parasite_dump_thread_seized(struct parasite_ctl *ctl, pid_t pid,
 					unsigned int **tid_add, u32 *tid);
 
-extern int parasite_drain_fds_seized(struct parasite_ctl *ctl, int *fds, int *lfds, int nr_fds, char *flags);
+struct parasite_drain_fd;
+extern int parasite_drain_fds_seized(struct parasite_ctl *ctl, struct parasite_drain_fd *dfds,
+		int *lfds, char *flags);
 
 extern int parasite_cure_seized(struct parasite_ctl *ctl);
 extern struct parasite_ctl *parasite_infect_seized(pid_t pid,

include/parasite.h

@@ -83,10 +83,15 @@ struct parasite_dump_tid_info {
 #define PARASITE_MAX_FDS	(PAGE_SIZE / sizeof(int))
 
 struct parasite_drain_fd {
-	int			fds[PARASITE_MAX_FDS];
 	int	nr_fds;
+	int	fds[PARASITE_MAX_FDS];
 };
 
+static inline int drain_fds_size(struct parasite_drain_fd *dfds)
+{
+	return sizeof(dfds->nr_fds) + dfds->nr_fds * sizeof(dfds->fds[0]);
+}
+
 /*
  * Some useful offsets
  */

parasite-syscall.c

@@ -601,32 +601,25 @@ out:
 	return ret;
 }
 
-int parasite_drain_fds_seized(struct parasite_ctl *ctl, int *fds, int *lfds, int nr_fds, char *flags)
+int parasite_drain_fds_seized(struct parasite_ctl *ctl,
+		struct parasite_drain_fd *dfds, int *lfds, char *flags)
 {
-	struct parasite_drain_fd *args;
 	int ret = -1;
 
-	args = xmalloc(sizeof(*args));
-	if (!args)
-		return -ENOMEM;
-
-	args->nr_fds = nr_fds;
-	memcpy(&args->fds, fds, sizeof(int) * nr_fds);
-
-	ret = parasite_execute(PARASITE_CMD_DRAIN_FDS, ctl, args, sizeof(*args));
+	ret = parasite_execute(PARASITE_CMD_DRAIN_FDS, ctl,
+			dfds, drain_fds_size(dfds));
 	if (ret) {
 		pr_err("Parasite failed to drain descriptors\n");
 		goto err;
 	}
 
-	ret = recv_fds(ctl->tsock, lfds, nr_fds, flags);
+	ret = recv_fds(ctl->tsock, lfds, dfds->nr_fds, flags);
 	if (ret) {
 		pr_err("Can't retrieve FDs from socket\n");
 		goto err;
 	}
 
 err:
-	xfree(args);
 	return ret;
 }