sandbox: Add a way to map a file into memory

It is useful to map a file into memory so that it can be accessed using
simple pointers. Add a function to support this.

Signed-off-by: Simon Glass <sjg@chromium.org>

arch/sandbox/cpu/os.c

@@ -182,6 +182,35 @@ err:
 	return ret;
 }
 
+int os_map_file(const char *pathname, int os_flags, void **bufp, int *sizep)
+{
+	void *ptr;
+	int size;
+	int ifd;
+
+	ifd = os_open(pathname, os_flags);
+	if (ifd < 0) {
+		printf("Cannot open file '%s'\n", pathname);
+		return -EIO;
+	}
+	size = os_filesize(ifd);
+	if (size < 0) {
+		printf("Cannot get file size of '%s'\n", pathname);
+		return -EIO;
+	}
+
+	ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, ifd, 0);
+	if (ptr == MAP_FAILED) {
+		printf("Can't map file '%s': %s\n", pathname, strerror(errno));
+		return -EPERM;
+	}
+
+	*bufp = ptr;
+	*sizep = size;
+
+	return 0;
+}
+
 /* Restore tty state when we exit */
 static struct termios orig_term;
 static bool term_setup;

include/os.h

@@ -406,6 +406,19 @@ int os_write_file(const char *name, const void *buf, int size);
  */
 int os_read_file(const char *name, void **bufp, int *sizep);
 
+/**
+ * os_map_file() - Map a file from the host filesystem into memory
+ *
+ * This can be useful when to provide a backing store for an emulated device
+ *
+ * @pathname:	File pathname to map
+ * @os_flags:	Flags, like OS_O_RDONLY, OS_O_RDWR
+ * @bufp:	Returns buffer containing the file
+ * @sizep:	Returns size of data
+ * Return:	0 if OK, -ve on error
+ */
+int os_map_file(const char *pathname, int os_flags, void **bufp, int *sizep);
+
 /*
  * os_find_text_base() - Find the text section in this running process
  *