plat/msdos86: implement close( ) function & proper errno setting

plat/msdos86/libsys/close.s

@@ -0,0 +1,23 @@
+#
+! $Source$
+! $State$
+! $Revision$
+
+! Declare segments (the order is important).
+
+.sect .text
+.sect .rom
+.sect .data
+.sect .bss
+
+.sect .text
+
+! Close a file.
+
+.define _close
+_close:
+	mov bx, sp
+	mov bx, 2(bx)
+	movb ah, 0x3E
+	int 0x21
+	jmp .sys_zret

plat/msdos86/libsys/errno.s

@@ -0,0 +1,28 @@
+#
+! $Source$
+! $State$
+! $Revision$
+
+! Declare segments (the order is important).
+
+.sect .text
+.sect .rom
+.sect .data
+.sect .bss
+
+#define D(e) .define e; e
+
+.sect .data
+
+! Define various ACK error numbers. Note that these are *not* ANSI C
+! errnos, and are used for different purposes.
+
+D(ERANGE)         = 1
+D(ESET)           = 2
+D(EIDIVZ)         = 6
+D(EHEAP)          = 17
+D(EILLINS)        = 18
+D(EODDZ)          = 19
+D(ECASE)          = 20
+D(EBADMON)        = 25
+

plat/msdos86/libsys/sys_seterrno.c

@@ -0,0 +1,45 @@
+/* $Source$
+ * $State$
+ * $Revision$
+ */
+
+#include <errno.h>
+
+static const signed char err_map[] =
+	{
+		0,			/* 0x00 no error */
+		EINVAL,			/* 0x01 function number invalid */
+		ENOENT,			/* 0x02 file not found */
+		ENOENT,			/* 0x03 path not found */
+		EMFILE,			/* 0x04 too many open files */
+		EACCES,			/* 0x05 access denied */
+		EBADF,			/* 0x06 invalid handle */
+		EFAULT,			/* 0x07 mem. control block destroyed */
+		ENOMEM,			/* 0x08 insufficient memory */
+		EFAULT,			/* 0x09 memory block address invalid */
+		E2BIG,			/* 0x0A environment invalid */
+		ENOEXEC,		/* 0x0B format invalid */
+		EINVAL,			/* 0x0C access code invalid */
+		EINVAL,			/* 0x0D data invalid */
+		ENOEXEC,		/* 0x0E (?) fixup overflow */
+		ENODEV,			/* 0x0F invalid drive */
+		EBUSY,			/* 0x10 attempt to remove curr. dir. */
+		EXDEV,			/* 0x11 not same device */
+		ENOENT,			/* 0x12 no more files */
+		EIO,			/* 0x13 disk write-protected */
+		EIO,			/* 0x14 unknown unit */
+		ENXIO,			/* 0x15 drive not ready */
+	};
+
+/*
+ * Map an MS-DOS 2+ system error code to an `errno' value and store that in
+ * `errno'.  Return -1.
+ */
+int _sys_seterrno(unsigned dos_err)
+{
+	if (dos_err < sizeof(err_map) / sizeof(err_map[0]))
+		errno = err_map[dos_err];
+	else
+		errno = EIO;
+	return -1;
+}

plat/msdos86/libsys/sys_xret.s

@@ -0,0 +1,35 @@
+#
+! $Source$
+! $State$
+! $Revision$
+
+! Declare segments (the order is important).
+
+.sect .text
+.sect .rom
+.sect .data
+.sect .bss
+
+.sect .text
+
+! .sys_zret: if the carry flag is set, then set `errno' from the DOS error
+! code in ax, and return -1.  If the carry flag is clear, just return zero.
+!
+! .sys_axret: if the carry flag is set, then set `errno' from the DOS error
+! code in ax, and return -1.  If the carry flag is clear, just return ax as
+! a return value.
+
+.extern .sys_zret
+.extern .sys_axret
+.sys_zret:
+	jc error
+	xor ax, ax
+no_error:
+	ret
+.sys_axret:
+	jnc no_error
+error:
+	push ax
+	call __sys_seterrno
+	pop cx
+	ret