um: Extract load file helper from initrd.c

The file loading support in initrd.c can be re-used for
loading devicetrees. Move it out of initrd.c.

Signed-off-by: Vincent Whitchurch <[e-mail]>
Signed-off-by: Richard Weinberger <[e-mail]>

arch/um/kernel/Makefile

···
 	physmem.o process.o ptrace.o reboot.o sigio.o \
 	signal.o sysrq.o time.o tlb.o trap.o \
 	um_arch.o umid.o maccess.o kmsg_dump.o capflags.o skas/
+obj-y += load_file.o
 
 obj-$(CONFIG_BLK_DEV_INITRD) += initrd.o
 obj-$(CONFIG_GPROF)	+= gprof_syms.o

arch/um/kernel/initrd.c

···
 #include <init.h>
 #include <os.h>
 
+#include "um_arch.h"
+
 /* Changed by uml_initrd_setup, which is a setup */
 static char *initrd __initdata = NULL;
-static int load_initrd(char *filename, void *buf, int size);
 
 int __init read_initrd(void)
 {
+	unsigned long long size;
 	void *area;
-	long long size;
-	int err;
 
-	if (initrd == NULL)
+	if (!initrd)
 		return 0;
 
-	err = os_file_size(initrd, &size);
-	if (err)
-		return 0;
-
-	/*
-	 * This is necessary because alloc_bootmem craps out if you
-	 * ask for no memory.
-	 */
-	if (size == 0) {
-		printk(KERN_ERR "\"%s\" is a zero-size initrd\n", initrd);
-		return 0;
-	}
-
-	area = memblock_alloc(size, SMP_CACHE_BYTES);
+	area = uml_load_file(initrd, &size);
 	if (!area)
-		panic("%s: Failed to allocate %llu bytes\n", __func__, size);
-
-	if (load_initrd(initrd, area, size) == -1)
 		return 0;
 
 	initrd_start = (unsigned long) area;
···
 "    This is used to boot UML from an initrd image.  The argument is the\n"
 "    name of the file containing the image.\n\n"
 );
-
-static int load_initrd(char *filename, void *buf, int size)
-{
-	int fd, n;
-
-	fd = os_open_file(filename, of_read(OPENFLAGS()), 0);
-	if (fd < 0) {
-		printk(KERN_ERR "Opening '%s' failed - err = %d\n", filename,
-		       -fd);
-		return -1;
-	}
-	n = os_read_file(fd, buf, size);
-	if (n != size) {
-		printk(KERN_ERR "Read of %d bytes from '%s' failed, "
-		       "err = %d\n", size,
-		       filename, -n);
-		return -1;
-	}
-
-	os_close_file(fd);
-	return 0;
-}

arch/um/kernel/load_file.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+#include <linux/memblock.h>
+#include <os.h>
+
+#include "um_arch.h"
+
+static int __init __uml_load_file(const char *filename, void *buf, int size)
+{
+	int fd, n;
+
+	fd = os_open_file(filename, of_read(OPENFLAGS()), 0);
+	if (fd < 0) {
+		printk(KERN_ERR "Opening '%s' failed - err = %d\n", filename,
+		       -fd);
+		return -1;
+	}
+	n = os_read_file(fd, buf, size);
+	if (n != size) {
+		printk(KERN_ERR "Read of %d bytes from '%s' failed, "
+		       "err = %d\n", size,
+		       filename, -n);
+		return -1;
+	}
+
+	os_close_file(fd);
+	return 0;
+}
+
+void *uml_load_file(const char *filename, unsigned long long *size)
+{
+	void *area;
+	int err;
+
+	*size = 0;
+
+	if (!filename)
+		return NULL;
+
+	err = os_file_size(filename, size);
+	if (err)
+		return NULL;
+
+	if (*size == 0) {
+		printk(KERN_ERR "\"%s\" is empty\n", filename);
+		return NULL;
+	}
+
+	area = memblock_alloc(*size, SMP_CACHE_BYTES);
+	if (!area)
+		panic("%s: Failed to allocate %llu bytes\n", __func__, *size);
+
+	if (__uml_load_file(filename, area, *size)) {
+		memblock_free(area, *size);
+		return NULL;
+	}
+
+	return area;
+}

arch/um/kernel/um_arch.h

···
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef __UML_ARCH_H__
+#define __UML_ARCH_H__
+
+extern void * __init uml_load_file(const char *filename, unsigned long long *size);
+
+#endif