diff --git a/commands/memset.c b/commands/memset.c
index f871e07..f99bf86 100644
--- a/commands/memset.c
+++ b/commands/memset.c
@@ -56,7 +56,7 @@
 	c = strtoull_suffix(argv[optind + 1], NULL, 0);
 	n = strtoull_suffix(argv[optind + 2], NULL, 0);
 
-	fd = open_and_lseek(file, mode | O_WRONLY, s);
+	fd = open_and_lseek(file, mode | O_WRONLY | O_CREAT, s);
 	if (fd < 0)
 		return 1;
 
diff --git a/commands/mm.c b/commands/mm.c
index 6d2a887..c7f62fc 100644
--- a/commands/mm.c
+++ b/commands/mm.c
@@ -53,7 +53,7 @@
 	value = simple_strtoull(argv[optind++], NULL, 0);
 	mask = simple_strtoull(argv[optind++], NULL, 0);
 
-	fd = open_and_lseek(filename, mode | O_RDWR, adr);
+	fd = open_and_lseek(filename, mode | O_RDWR | O_CREAT, adr);
 	if (fd < 0)
 		return 1;
 
diff --git a/commands/mw.c b/commands/mw.c
index 7ff589a..2912997 100644
--- a/commands/mw.c
+++ b/commands/mw.c
@@ -52,7 +52,7 @@
 
 	adr = strtoull_suffix(argv[optind++], NULL, 0);
 
-	fd = open_and_lseek(filename, mode | O_WRONLY, adr);
+	fd = open_and_lseek(filename, mode | O_WRONLY | O_CREAT, adr);
 	if (fd < 0)
 		return 1;
 
diff --git a/fs/ramfs.c b/fs/ramfs.c
index fb8d058..7548bda 100644
--- a/fs/ramfs.c
+++ b/fs/ramfs.c
@@ -109,7 +109,7 @@
 	if (!data)
 		return NULL;
 
-	data->data = malloc(CHUNK_SIZE);
+	data->data = calloc(CHUNK_SIZE, 1);
 	if (!data->data) {
 		free(data);
 		return NULL;
diff --git a/lib/libfile.c b/lib/libfile.c
index d22519b..0052e78 100644
--- a/lib/libfile.c
+++ b/lib/libfile.c
@@ -501,7 +501,7 @@
 {
 	int fd, ret;
 
-	fd = open(filename, mode | O_RDONLY);
+	fd = open(filename, mode);
 	if (fd < 0) {
 		perror("open");
 		return fd;
@@ -510,6 +510,24 @@
 	if (!pos)
 		return fd;
 
+	if (mode & (O_WRONLY | O_RDWR)) {
+		struct stat s;
+
+		ret = fstat(fd, &s);
+		if (ret) {
+			perror("fstat");
+			return ret;
+		}
+
+		if (s.st_size < pos) {
+			ret = ftruncate(fd, pos);
+			if (ret) {
+				perror("ftruncate");
+				return ret;
+			}
+		}
+	}
+
 	ret = lseek(fd, pos, SEEK_SET);
 	if (ret == -1) {
 		perror("lseek");