vmas: Don't call stat on vm file twice

When parsing mappings in proc, we fstat vm file, later,
when dumping it, we stat it again to fill fd_parms.
The 2nd stat is not required, we can keep the stat in
vma_area.

This removed 35% of all stat calls on dump of basic container.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-dump.c

@@ -128,6 +128,8 @@ void free_mappings(struct vm_area_list *vma_area_list)
 
 	list_for_each_entry_safe(vma_area, p, &vma_area_list->h, list) {
 		close_vma_file(vma_area);
+		if (!vma_area->file_borrowed)
+			free(vma_area->st);
 		free(vma_area);
 	}
 
@@ -341,15 +343,14 @@ static int dump_task_rlims(int pid, struct cr_fdset *fds)
 	return 0;
 }
 
-static int dump_filemap(pid_t pid, VmaEntry *vma, int file_fd,
+static int dump_filemap(pid_t pid, struct vma_area *vma_area,
 		const struct cr_fdset *fdset)
 {
 	struct fd_parms p = FD_PARMS_INIT;
+	VmaEntry *vma = &vma_area->vma;
 
-	if (fstat(file_fd, &p.stat) < 0) {
-		pr_perror("Can't stat file for vma");
-		return -1;
-	}
+	BUG_ON(!vma_area->st);
+	p.stat = *vma_area->st;
 
 	if ((vma->prot & PROT_WRITE) && vma_entry_is(vma, VMA_FILE_SHARED))
 		p.flags = O_RDWR;
@@ -357,7 +358,7 @@ static int dump_filemap(pid_t pid, VmaEntry *vma, int file_fd,
 		p.flags = O_RDONLY;
 	vma->shmid = fd_id_generate_special();
 
-	return dump_one_reg_file(file_fd, vma->shmid, &p);
+	return dump_one_reg_file(vma_area->vm_file_fd, vma->shmid, &p);
 }
 
 static int check_sysvipc_map_dump(pid_t pid, VmaEntry *vma)
@@ -395,7 +396,7 @@ static int dump_task_mappings(pid_t pid, const struct vm_area_list *vma_area_lis
 			ret = add_shmem_area(pid, vma);
 		else if (vma_entry_is(vma, VMA_FILE_PRIVATE) ||
 				vma_entry_is(vma, VMA_FILE_SHARED))
-			ret = dump_filemap(pid, vma, vma_area->vm_file_fd, cr_fdset);
+			ret = dump_filemap(pid, vma_area, cr_fdset);
 		else if (vma_entry_is(vma, VMA_AREA_SOCKET))
 			ret = dump_socket_map(vma_area);
 		else

include/vma.h

@@ -27,6 +27,8 @@ struct vma_area {
 	unsigned long		premmaped_addr;
 
 	bool			file_borrowed;
+
+	struct stat		*st;
 };
 
 extern int collect_mappings(pid_t pid, struct vm_area_list *vma_area_list);

proc_parse.c

@@ -351,16 +351,21 @@ int parse_smaps(pid_t pid, struct vm_area_list *vma_area_list, bool use_map_file
 			vma_area->vma.flags |= (prev->vma.flags & MAP_ANONYMOUS);
 			vma_area->vma.status = prev->vma.status;
 			vma_area->vma.shmid = prev->vma.shmid;
+			vma_area->st = prev->st;
 		} else if (vma_area->vm_file_fd >= 0) {
-			struct stat st_buf;
+			struct stat *st_buf;
 
-			if (fstat(vma_area->vm_file_fd, &st_buf) < 0) {
+			st_buf = vma_area->st = xmalloc(sizeof(*st_buf));
+			if (!st_buf)
+				goto err;
+
+			if (fstat(vma_area->vm_file_fd, st_buf) < 0) {
 				pr_perror("Failed fstat on %d's map %lu", pid, start);
 				goto err;
 			}
 
-			if (!S_ISREG(st_buf.st_mode) &&
-			    !(S_ISCHR(st_buf.st_mode) && st_buf.st_rdev == DEVZERO)) {
+			if (!S_ISREG(st_buf->st_mode) &&
+			    !(S_ISCHR(st_buf->st_mode) && st_buf->st_rdev == DEVZERO)) {
 				pr_err("Can't handle non-regular mapping on %d's map %lu\n", pid, start);
 				goto err;
 			}
@@ -369,12 +374,12 @@ int parse_smaps(pid_t pid, struct vm_area_list *vma_area_list, bool use_map_file
 			 * /dev/zero stands for anon-shared mapping
 			 * otherwise it's some file mapping.
 			 */
-			if (is_anon_shmem_map(st_buf.st_dev)) {
+			if (is_anon_shmem_map(st_buf->st_dev)) {
 				if (!(vma_area->vma.flags & MAP_SHARED))
 					goto err_bogus_mapping;
 				vma_area->vma.flags  |= MAP_ANONYMOUS;
 				vma_area->vma.status |= VMA_ANON_SHARED;
-				vma_area->vma.shmid = st_buf.st_ino;
+				vma_area->vma.shmid = st_buf->st_ino;
 
 				if (!strcmp(file_path, "/SYSV")) {
 					pr_info("path: %s\n", file_path);