proc_parse: fix vma file open mode recognition

WIth current code we have smth like

1) If file was opened with O_WRONLY, this mode is simply lost.
2) If file was opened with O_RDWR, but mapping is private, resulting mode will be O_RDONLY

The correct place to get fd open flags for file mappings is
/proc/<pid>/map_files.
An attempt tp speculate on "shared" and "maywrite" bits doesn't garantee,
that file will be opened with correct permissions on restore.
Here is an example:

Process mapping (read/write):

# cat /proc/481943/maps | grep 7f7108077000-7f7108078000
7f7108077000-7f7108078000 rw-p 00001000 00:35 7 <snip>

1) Before suspend:

# ls -l /proc/481427/map_files/7f7108077000-7f7108078000
lrw------- <snip> /proc/481427/map_files/7f7108077000-7f7108078000 -> <snip>

2) After restore:

# ls -l /proc/481943/map_files/7f7108077000-7f7108078000
lr-------- <snip> /proc/481943/map_files/7f7108077000-7f7108078000 -> <snip>

Write bit is lost.

This patch set vma->e->fdflags as /proc/<pid>/map_files/<vma> open mode.
Signed-off-by: Stanislav Kinsburskiy <skinsbursky@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/proc_parse.c

@@ -96,8 +96,6 @@ static bool is_vma_range_fmt(char *line)
 static int parse_vmflags(char *buf, struct vma_area *vma_area)
 {
 	char *tok;
-	bool shared = false;
-	bool maywrite = false;
 
 	if (!buf[0])
 		return 0;
@@ -109,12 +107,6 @@ static int parse_vmflags(char *buf, struct vma_area *vma_area)
 #define _vmflag_match(_t, _s) (_t[0] == _s[0] && _t[1] == _s[1])
 
 	do {
-		/* open() block */
-		if (_vmflag_match(tok, "sh"))
-			shared = true;
-		else if (_vmflag_match(tok, "mw"))
-			maywrite = true;
-
 		/* mmap() block */
 		if (_vmflag_match(tok, "gd"))
 			vma_area->e->flags |= MAP_GROWSDOWN;
@@ -158,12 +150,6 @@ static int parse_vmflags(char *buf, struct vma_area *vma_area)
 
 #undef _vmflag_match
 
-	if (shared && maywrite)
-		vma_area->e->fdflags = O_RDWR;
-	else
-		vma_area->e->fdflags = O_RDONLY;
-	vma_area->e->has_fdflags = true;
-
 	if (vma_area->e->madv)
 		vma_area->e->has_madv = true;
 
@@ -189,6 +175,34 @@ static inline int vfi_equal(struct vma_file_info *a, struct vma_file_info *b)
 			(a->dev_min ^ b->dev_min)) == 0;
 }
 
+static int vma_get_mapfile_flags(struct vma_area *vma, DIR *mfd, char *path)
+{
+	struct stat stat;
+
+	if (fstatat(dirfd(mfd), path, &stat, AT_SYMLINK_NOFOLLOW) < 0) {
+		if (errno == ENOENT) {
+			/* Just mapping w/o map_files link */
+			return 0;
+		}
+		pr_perror("Failed fstatat on map %"PRIx64"", vma->e->start);
+		return -1;
+	}
+
+	switch(stat.st_mode & 0600) {
+		case 0200:
+			vma->e->fdflags = O_WRONLY;
+			break;
+		case 0400:
+			vma->e->fdflags = O_RDONLY;
+			break;
+		case 0600:
+			vma->e->fdflags = O_RDWR;
+			break;
+	}
+	vma->e->has_fdflags = true;
+	return 0;
+}
+
 static int vma_get_mapfile(char *fname, struct vma_area *vma, DIR *mfd,
 			   struct vma_file_info *vfi,
 			   struct vma_file_info *prev_vfi,
@@ -197,6 +211,12 @@ static int vma_get_mapfile(char *fname, struct vma_area *vma, DIR *mfd,
 	char path[32];
 	int flags;
 
+	/* Figure out if it's file mapping */
+	snprintf(path, sizeof(path), "%"PRIx64"-%"PRIx64, vma->e->start, vma->e->end);
+
+	if (vma_get_mapfile_flags(vma, mfd, path))
+		return -1;
+
 	if (prev_vfi->vma && vfi_equal(vfi, prev_vfi)) {
 		struct vma_area *prev = prev_vfi->vma;
 
@@ -225,9 +245,6 @@ static int vma_get_mapfile(char *fname, struct vma_area *vma, DIR *mfd,
 	}
 	close_safe(vm_file_fd);
 
-	/* Figure out if it's file mapping */
-	snprintf(path, sizeof(path), "%"PRIx64"-%"PRIx64, vma->e->start, vma->e->end);
-
 	/*
 	 * Note that we "open" it in dumper process space
 	 * so later we might refer to it via /proc/self/fd/vm_file_fd

criu/util.c

@@ -161,12 +161,13 @@ void pr_vma(unsigned int loglevel, const struct vma_area *vma_area)
 		return;
 
 	vma_opt_str(vma_area, opt);
-	print_on_level(loglevel, "%#"PRIx64"-%#"PRIx64" (%"PRIi64"K) prot %#x flags %#x st %#x off %#"PRIx64" "
+	print_on_level(loglevel, "%#"PRIx64"-%#"PRIx64" (%"PRIi64"K) prot %#x flags %#x fdflags %#o st %#x off %#"PRIx64" "
 			"%s shmid: %#"PRIx64"\n",
 			vma_area->e->start, vma_area->e->end,
 			KBYTES(vma_area_len(vma_area)),
 			vma_area->e->prot,
 			vma_area->e->flags,
+			vma_area->e->fdflags,
 			vma_area->e->status,
 			vma_area->e->pgoff,
 			opt, vma_area->e->shmid);