[PATCH kexec-tools] x86: use old screen_info if needed

[Dave Young]

With modern drm/kms graphic driver kexec-tools does not setup screen_info
correctly so one will only see screen output after those drm drivers
reinitializing after rebooting. Copying the old screen info from original
boot_params will help during my test, although it could not work for some
potential cases, but it is not worse than before.  This has been used in
the kernel kexec_file_load.

Signed-off-by: Dave Young <dyoung at redhat.com>
---
 kexec/arch/i386/x86-linux-setup.c |   21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

--- kexec-tools.orig/kexec/arch/i386/x86-linux-setup.c
+++ kexec-tools/kexec/arch/i386/x86-linux-setup.c
@@ -27,6 +27,7 @@
 #include <fcntl.h>
 #include <sys/ioctl.h>
 #include <linux/fb.h>
+#include <linux/screen_info.h>
 #include <unistd.h>
 #include <dirent.h>
 #include <mntent.h>
@@ -122,7 +123,7 @@ void setup_linux_bootloader_parameters_h
 	cmdline_ptr[cmdline_len - 1] = '\0';
 }
 
-int setup_linux_vesafb(struct x86_linux_param_header *real_mode)
+static int setup_linux_vesafb(struct x86_linux_param_header *real_mode)
 {
 	struct fb_fix_screeninfo fix;
 	struct fb_var_screeninfo var;
@@ -826,6 +827,8 @@ out:
 void setup_linux_system_parameters(struct kexec_info *info,
 				   struct x86_linux_param_header *real_mode)
 {
+	int err;
+
 	/* get subarch from running kernel */
 	setup_subarch(real_mode);
 	if (bzImage_support_efi_boot && !arch_options.noefi)
@@ -841,8 +844,22 @@ void setup_linux_system_parameters(struc
 	real_mode->orig_video_ega_bx = 0;
 	real_mode->orig_video_isVGA = 1;
 	real_mode->orig_video_points = 16;
-	setup_linux_vesafb(real_mode);
 
+	/* setup vesa fb if possible, or just use original screen_info */
+	err = setup_linux_vesafb(real_mode);
+	if (err) {
+		uint16_t cl_magic, cl_offset;
+
+		/* save and restore the old cmdline param if needed */
+		cl_magic = real_mode->cl_magic;
+		cl_offset = real_mode->cl_offset;
+
+		err = get_bootparam(real_mode, 0, sizeof(struct screen_info));
+		if (!err) {
+			real_mode->cl_magic = cl_magic;
+			real_mode->cl_offset = cl_offset;
+		}
+	}
 	/* Fill in the memsize later */
 	real_mode->ext_mem_k = 0;
 	real_mode->alt_mem_k = 0;