kdat: Add fetching files stat

Will need it to unlimit the files allocation
for service fd reserving and later for parasite code run
(which is implemented in vz7 instance and soon will be
ported into vanilla).
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/include/kerndat.h

@@ -2,7 +2,6 @@
 #define __CR_KERNDAT_H__
 
 #include <stdbool.h>
-
 #include "int.h"
 #include "common/config.h"
 #ifdef CONFIG_VDSO
@@ -20,6 +19,7 @@ extern int kerndat_init(void);
 extern int kerndat_get_dirty_track(void);
 extern int kerndat_fdinfo_has_lock(void);
 extern int kerndat_loginuid(void);
+extern int kerndat_files_stat(bool early);
 
 enum pagemap_func {
 	PM_UNKNOWN,
@@ -66,6 +66,8 @@ struct kerndat_s {
 #endif
 	bool has_nsid;
 	bool has_link_nsid;
+	unsigned int sysctl_nr_open;
+	unsigned long files_stat_max_files;
 };
 
 extern struct kerndat_s kdat;

criu/kerndat.c

@@ -152,6 +152,74 @@ static void kerndat_mmap_min_addr(void)
 		 (unsigned long)kdat.mmap_min_addr);
 }
 
+int kerndat_files_stat(bool early)
+{
+	static const uint32_t NR_OPEN_DEFAULT = 1024 * 1024;
+	static const uint64_t MAX_FILES_DEFAULT = 8192;
+	uint64_t max_files;
+	uint32_t nr_open;
+
+	struct sysctl_req req[] = {
+		{
+			.name	= "fs/file-max",
+			.arg	= &max_files,
+			.type	= CTL_U64,
+		},
+		{
+			.name	= "fs/nr_open",
+			.arg	= &nr_open,
+			.type	= CTL_U32,
+		},
+	};
+
+	if (!early) {
+		if (sysctl_op(req, ARRAY_SIZE(req), CTL_READ, 0)) {
+			pr_warn("Can't fetch file_stat, using kernel defaults\n");
+			nr_open = NR_OPEN_DEFAULT;
+			max_files = MAX_FILES_DEFAULT;
+		}
+	} else {
+		char buf[64];
+		int fd1, fd2;
+		ssize_t ret;
+
+		fd1 = open("/proc/sys/fs/file-max", O_RDONLY);
+		fd2 = open("/proc/sys/fs/nr_open", O_RDONLY);
+
+		nr_open = NR_OPEN_DEFAULT;
+		max_files = MAX_FILES_DEFAULT;
+
+		if (fd1 < 0 || fd2 < 0) {
+			pr_warn("Can't fetch file_stat, using kernel defaults\n");
+		} else {
+			ret = read(fd1, buf, sizeof(buf) - 1);
+			if (ret > 0) {
+				buf[ret] = '\0';
+				max_files = atol(buf);
+			}
+			ret = read(fd2, buf, sizeof(buf));
+			if (ret > 0) {
+				buf[ret] = '\0';
+				nr_open = atol(buf);
+			}
+		}
+
+		if (fd1 >= 0)
+			close(fd1);
+		if (fd2 >= 0)
+			close(fd2);
+	}
+
+	kdat.sysctl_nr_open = nr_open;
+	kdat.files_stat_max_files = max_files;
+
+	pr_debug("files stat: %s %lu, %s %u\n",
+		 req[0].name, kdat.files_stat_max_files,
+		 req[1].name, kdat.sysctl_nr_open);
+
+	return 0;
+}
+
 static int kerndat_get_shmemdev(void)
 {
 	void *map;
@@ -909,6 +977,7 @@ int kerndat_init(void)
 
 	kerndat_lsm();
 	kerndat_mmap_min_addr();
+	kerndat_files_stat(false);
 
 	if (!ret)
 		kerndat_save_cache();