From 32e0e40ddecceeb03045bb790c7f9e19f7b1709c Mon Sep 17 00:00:00 2001
From: Jonathan Campbell <jonathan@castus.tv>
Date: Mon, 21 Oct 2013 01:30:58 -0700
Subject: [PATCH] add mount option and support in INT 13h code for "reserved
 cylinder" emulation

---
 include/bios_disk.h      |  3 +++
 src/dos/dos_programs.cpp | 11 ++++++++++-
 src/ints/bios_disk.cpp   | 18 ++++++++++++++++++
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/include/bios_disk.h b/include/bios_disk.h
index 8818bf223..3405b023d 100644
--- a/include/bios_disk.h
+++ b/include/bios_disk.h
@@ -50,6 +50,8 @@ public:
 	Bit8u Read_AbsoluteSector(Bit32u sectnum, void * data);
 	Bit8u Write_AbsoluteSector(Bit32u sectnum, void * data);
 
+	void Set_Reserved_Cylinders(Bitu resCyl);
+	Bit32u Get_Reserved_Cylinders();
 	void Set_Geometry(Bit32u setHeads, Bit32u setCyl, Bit32u setSect, Bit32u setSectSize);
 	void Get_Geometry(Bit32u * getHeads, Bit32u *getCyl, Bit32u *getSect, Bit32u *getSectSize);
 	Bit8u GetBiosType(void);
@@ -65,6 +67,7 @@ public:
 
 	Bit32u sector_size;
 	Bit32u heads,cylinders,sectors;
+	Bit32u reserved_cylinders;
 	Bit64u current_fpos;
 };
 
diff --git a/src/dos/dos_programs.cpp b/src/dos/dos_programs.cpp
index dce036359..ff971bd51 100644
--- a/src/dos/dos_programs.cpp
+++ b/src/dos/dos_programs.cpp
@@ -1935,10 +1935,18 @@ public:
 		if (type=="floppy" || type=="hdd" || type=="iso") {
 			Bit16u sizes[4];
 			bool imgsizedetect=false;
-			
+			int reserved_cylinders=0;
+			std::string reservecyl;
 			std::string str_size;
 			mediaid=0xF8;
 
+			/* DOSBox-X: to please certain 32-bit drivers like Windows 3.1 WDCTRL, or to emulate older h/w configurations,
+			 *           we allow the user or script to specify the number of reserved cylinders. older BIOSes were known
+			 *           to subtract 1 or 2 additional cylinders from the total in the fixed disk param table. the -reservecyl
+			 *           option allows the number we subtract from the total in INT 13H to be set */
+			cmd->FindString("-reservecyl",reservecyl,true);
+			if (reservecyl != "") reserved_cylinders = atoi(reservecyl.c_str());
+
 			/* DOSBox-X: we allow "-ide" to allow controlling which IDE controller and slot to attach the hard disk/CD-ROM to */
 			cmd->FindString("-ide",ideattach,true);
 
@@ -2306,6 +2314,7 @@ public:
 
 				newImage = new imageDisk(newDisk, (Bit8u *)temp_line.c_str(), imagesize, (imagesize > 2880));
 				if(imagesize>2880) newImage->Set_Geometry(sizes[2],sizes[3],sizes[1],sizes[0]);
+				if (reserved_cylinders > 0) newImage->Set_Reserved_Cylinders(reserved_cylinders);
 			}
 		} else {
 			WriteOut(MSG_Get("PROGRAM_IMGMOUNT_TYPE_UNSUPPORTED"),type.c_str());
diff --git a/src/ints/bios_disk.cpp b/src/ints/bios_disk.cpp
index 24b78658c..6c9ffd8ed 100644
--- a/src/ints/bios_disk.cpp
+++ b/src/ints/bios_disk.cpp
@@ -201,11 +201,20 @@ Bit8u imageDisk::Write_AbsoluteSector(Bit32u sectnum, void *data) {
 
 }
 
+void imageDisk::Set_Reserved_Cylinders(Bitu resCyl) {
+	reserved_cylinders = resCyl;
+}
+
+Bit32u imageDisk::Get_Reserved_Cylinders() {
+	return reserved_cylinders;
+}
+
 imageDisk::imageDisk(FILE *imgFile, Bit8u *imgName, Bit32u imgSizeK, bool isHardDisk) {
 	heads = 0;
 	cylinders = 0;
 	sectors = 0;
 	sector_size = 512;
+	reserved_cylinders = 0;
 	diskimg = imgFile;
 	
 	memset(diskname,0,512);
@@ -519,6 +528,15 @@ static Bitu INT13_DiskHandler(void) {
 		else tmpcyl--;		// cylinder count -> max cylinder
 		if (tmpheads==0) LOG(LOG_BIOS,LOG_ERROR)("INT13 DrivParm: head count zero!");
 		else tmpheads--;	// head count -> max head
+
+		/* older BIOSes were known to subtract 1 or 2 additional "reserved" cylinders.
+		 * some code, such as Windows 3.1 WDCTRL, might assume that fact. emulate that here */
+		{
+			Bit32u reserv = imageDiskList[drivenum]->Get_Reserved_Cylinders();
+			if (tmpcyl > reserv) tmpcyl -= reserv;
+			else tmpcyl = 0;
+		}
+
 		reg_ch = (Bit8u)(tmpcyl & 0xff);
 		reg_cl = (Bit8u)(((tmpcyl >> 2) & 0xc0) | (tmpsect & 0x3f)); 
 		reg_dh = (Bit8u)tmpheads;