/*
 *  linux/kernel/vm86.c
 *
 *  Copyright (C) 1994  Linus Torvalds
 */
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/string.h>
#include <linux/ptrace.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>

#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/io.h>

/*
 * Known problems:
 *
 * Interrupt handling is not guaranteed:
 * - a real x86 will disable all interrupts for one instruction
 *   after a "mov ss,xx" to make stack handling atomic even without
 *   the 'lss' instruction. We can't guarantee this in v86 mode,
 *   as the next instruction might result in a page fault or similar.
 * - a real x86 will have interrupts disabled for one instruction
 *   past the 'sti' that enables them. We don't bother with all the
 *   details yet.
 *
 * Let's hope these problems do not actually matter for anything.
 */


#define KVM86	((struct kernel_vm86_struct *)regs)
#define VMPI 	KVM86->vm86plus


/*
 * 8- and 16-bit register defines..
 */
#define AL(regs)	(((unsigned char *)&((regs)->eax))[0])
#define AH(regs)	(((unsigned char *)&((regs)->eax))[1])
#define IP(regs)	(*(unsigned short *)&((regs)->eip))
#define SP(regs)	(*(unsigned short *)&((regs)->esp))

/*
 * virtual flags (16 and 32-bit versions)
 */
#define VFLAGS	(*(unsigned short *)&(current->tss.v86flags))
#define VEFLAGS	(current->tss.v86flags)

#define set_flags(X,new,mask) \
((X) = ((X) & ~(mask)) | ((new) & (mask)))

#define SAFE_MASK	(0xDD5)
#define RETURN_MASK	(0xDFF)

#define VM86_REGS_PART2 orig_eax
#define VM86_REGS_SIZE1 \
        ( (unsigned)( & (((struct kernel_vm86_regs *)0)->VM86_REGS_PART2) ) )
#define VM86_REGS_SIZE2 (sizeof(struct kernel_vm86_regs) - VM86_REGS_SIZE1)

asmlinkage struct pt_regs * FASTCALL(save_v86_state(struct kernel_vm86_regs * regs));
struct pt_regs * save_v86_state(struct kernel_vm86_regs * regs)
{
	struct pt_regs *ret;
	unsigned long tmp;

	lock_kernel();
	if (!current->tss.vm86_info) {
		printk("no vm86_info: BAD\n");
		do_exit(SIGSEGV);
	}
	set_flags(regs->eflags, VEFLAGS, VIF_MASK | current->tss.v86mask);
	tmp = copy_to_user(&current->tss.vm86_info->regs,regs, VM86_REGS_SIZE1);
	tmp += copy_to_user(&current->tss.vm86_info->regs.VM86_REGS_PART2,
		&regs->VM86_REGS_PART2, VM86_REGS_SIZE2);
	tmp += put_user(current->tss.screen_bitmap,&current->tss.vm86_info->screen_bitmap);
	if (tmp) {
		printk("vm86: could not access userspace vm86_info\n");
		do_exit(SIGSEGV);
	}
	current->tss.esp0 = current->tss.saved_esp0;
	current->tss.saved_esp0 = 0;
	ret = KVM86->regs32;
	unlock_kernel();
	return ret;
}

static void mark_screen_rdonly(struct task_struct * tsk)
{
	pgd_t *pgd;
	pmd_t *pmd;
	pte_t *pte;
	int i;

	pgd = pgd_offset(tsk->mm, 0xA0000);
	if (pgd_none(*pgd))
		return;
	if (pgd_bad(*pgd)) {
		printk("vm86: bad pgd entry [%p]:%08lx\n", pgd, pgd_val(*pgd));
		pgd_clear(pgd);
		return;
	}
	pmd = pmd_offset(pgd, 0xA0000);
	if (pmd_none(*pmd))
		return;
	if (pmd_bad(*pmd)) {
		printk("vm86: bad pmd entry [%p]:%08lx\n", pmd, pmd_val(*pmd));
		pmd_clear(pmd);
		return;
	}
	pte = pte_offset(pmd, 0xA0000);
	for (i = 0; i < 32; i++) {
		if (pte_present(*pte))
			set_pte(pte, pte_wrprotect(*pte));
		pte++;
	}
	flush_tlb();
}



static int do_vm86_irq_handling(int subfunction, int irqnumber);
static void do_sys_vm86(struct kernel_vm86_struct *info, struct task_struct *tsk);

asmlinkage int sys_vm86old(struct vm86_struct * v86)
{
	struct kernel_vm86_struct info; /* declare this _on top_,
					 * this avoids wasting of stack space.
					 * This remains on the stack until we
					 * return to 32 bit user space.
					 */
	struct task_struct *tsk;
	int tmp, ret = -EPERM;

	lock_kernel();
	tsk = current;
	if (tsk->tss.saved_esp0)
		goto out;
	tmp  = copy_from_user(&info, v86, VM86_REGS_SIZE1);
	tmp += copy_from_user(&info.regs.VM86_REGS_PART2, &v86->regs.VM86_REGS_PART2,
		(long)&info.vm86plus - (long)&info.regs.VM86_REGS_PART2);
	ret = -EFAULT;
	if (tmp)
		goto out;
	memset(&info.vm86plus, 0, (int)&info.regs32 - (int)&info.vm86plus);
	info.regs32 = (struct pt_regs *) &v86;
	tsk->tss.vm86_info = v86;
	do_sys_vm86(&info, tsk);
	ret = 0;	/* we never return here */
out:
	unlock_kernel();
	return ret;
}


asmlinkage int sys_vm86(unsigned long subfunction, struct vm86plus_struct * v86)
{
	struct kernel_vm86_struct info; /* declare this _on top_,
					 * this avoids wasting of stack space.
					 * This remains on the stack until we
					 * return to 32 bit user space.
					 */
	struct task_struct *tsk;
	int tmp, ret;

	lock_kernel();
	tsk = current;
	switch (subfunction) {
		case VM86_REQUEST_IRQ:
		case VM86_FREE_IRQ:
		case VM86_GET_IRQ_BITS:
		case VM86_GET_AND_RESET_IRQ:
			ret = do_vm86_irq_handling(subfunction,(int)v86);
			goto out;
		case VM86_PLUS_INSTALL_CHECK:
			/* NOTE: on old vm86 stuff this will return the error
			   from verify_area(), because the subfunction is
			   interpreted as (invalid) address to vm86_struct.
			   So the installation check works.
			 */
			ret = 0;
			goto out;
	}

	/* we come here only for functions VM86_ENTER, VM86_ENTER_NO_BYPASS */
	ret = -EPERM;
	if (tsk->tss.saved_esp0)
		goto out;
	tmp  = copy_from_user(&info, v86, VM86_REGS_SIZE1);
	tmp += copy_from_user(&info.regs.VM86_REGS_PART2, &v86->regs.VM86_REGS_PART2,
		(long)&info.regs32 - (long)&info.regs.VM86_REGS_PART2);
	ret = -EFAULT;
	if (tmp)
		goto out;
	info.regs32 = (struct pt_regs *) &subfunction;
	info.vm86plus.is_vm86pus = 1;
	tsk->tss.vm86_info = (struct vm86_struct *)v86;
	do_sys_vm86(&info, tsk);
	ret = 0;	/* we never return here */
out:
	unlock_kernel();
	return ret;
}


static void do_sys_vm86(struct kernel_vm86_struct *info, struct task_struct *tsk)
{
/*
 * make sure the vm86() system call doesn't try to do anything silly
 */
	info->regs.__null_ds = 0;
	info->regs.__null_es = 0;

/* we are clearing fs,gs later just before "jmp ret_from_sys_call",
 * because starting with Linux 2.1.x they aren't no longer saved/restored
 */

/*
 * The eflags register is also special: we cannot trust that the user
 * has set it up safely, so this makes sure interrupt etc flags are
 * inherited from protected mode.
 */
 	VEFLAGS = info->regs.eflags;
	info->regs.eflags &= SAFE_MASK;
	info->regs.eflags |= info->regs32->eflags & ~SAFE_MASK;
	info->regs.eflags |= VM_MASK;

	switch (info->cpu_type) {
		case CPU_286:
			tsk->tss.v86mask = 0;
			break;
		case CPU_386:
			tsk->tss.v86mask = NT_MASK | IOPL_MASK;
			break;
		case CPU_486:
			tsk->tss.v86mask = AC_MASK | NT_MASK | IOPL_MASK;
			break;
		default:
			tsk->tss.v86mask = ID_MASK | AC_MASK | NT_MASK | IOPL_MASK;
			break;
	}

/*
 * Save old state, set default return value (%eax) to 0
 */
	info->regs32->eax = 0;
	tsk->tss.saved_esp0 = tsk->tss.esp0;
	tsk->tss.esp0 = (unsigned long) &info->VM86_TSS_ESP0;

	tsk->tss.screen_bitmap = info->screen_bitmap;
	if (info->flags & VM86_SCREEN_BITMAP)
		mark_screen_rdonly(tsk);
	unlock_kernel();
	__asm__ __volatile__(
		"xorl %%eax,%%eax; movl %%ax,%%fs; movl %%ax,%%gs\n\t"
		"movl %0,%%esp\n\t"
		"jmp ret_from_sys_call"
		: /* no outputs */
		:"r" (&info->regs), "b" (tsk) : "ax");
	/* we never return here */
}

static inline void return_to_32bit(struct kernel_vm86_regs * regs16, int retval)
{
	struct pt_regs * regs32;

	regs32 = save_v86_state(regs16);
	regs32->eax = retval;
	unlock_kernel();
	__asm__ __volatile__("movl %0,%%esp\n\t"
		"jmp ret_from_sys_call"
		: : "r" (regs32), "b" (current));
}

static inline void set_IF(struct kernel_vm86_regs * regs)
{
	VEFLAGS |= VIF_MASK;
	if (VEFLAGS & VIP_MASK)
		return_to_32bit(regs, VM86_STI);
}

static inline void clear_IF(struct kernel_vm86_regs * regs)
{
	VEFLAGS &= ~VIF_MASK;
}

static inline void clear_TF(struct kernel_vm86_regs * regs)
{
	regs->eflags &= ~TF_MASK;
}

static inline void set_vflags_long(unsigned long eflags, struct kernel_vm86_regs * regs)
{
	set_flags(VEFLAGS, eflags, current->tss.v86mask);
	set_flags(regs->eflags, eflags, SAFE_MASK);
	if (eflags & IF_MASK)
		set_IF(regs);
}

static inline void set_vflags_short(unsigned short flags, struct kernel_vm86_regs * regs)
{
	set_flags(VFLAGS, flags, current->tss.v86mask);
	set_flags(regs->eflags, flags, SAFE_MASK);
	if (flags & IF_MASK)
		set_IF(regs);
}

static inline unsigned long get_vflags(struct kernel_vm86_regs * regs)
{
	unsigned long flags = regs->eflags & RETURN_MASK;

	if (VEFLAGS & VIF_MASK)
		flags |= IF_MASK;
	return flags | (VEFLAGS & current->tss.v86mask);
}

static inline int is_revectored(int nr, struct revectored_struct * bitmap)
{
	__asm__ __volatile__("btl %2,%1\n\tsbbl %0,%0"
		:"=r" (nr)
		:"m" (*bitmap),"r" (nr));
	return nr;
}

/*
 * Boy are these ugly, but we need to do the correct 16-bit arithmetic.
 * Gcc makes a mess of it, so we do it inline and use non-obvious calling
 * conventions..
 * FIXME: is VM86_UNKNOWN really the correct return code?
 */
#define pushb(base, ptr, val, regs) \
	do { \
		int err; \
		__asm__ __volatile__(				\
			"decw %w0\n\t"				\
			"1: movb %3,0(%2,%0)\n\t"		\
			"xor %1,%1\n\t"				\
			"2:\n"					\
			".section .fixup,\"ax\"\n\t"		\
			"3:	movl $1,%1\n\t"			\
			"	jmp 2b\n\t"			\
			".previous\n"				\
			".section __ex_table,\"a\"\n"		\
			"	.align 4\n"			\
			"	.long 1b,3b\n"			\
			".previous"				\
			: "=r" (ptr), "=r" (err)		\
			: "r" (base), "q" (val), "0" (ptr));	\
		if (err) \
			return_to_32bit(regs, VM86_UNKNOWN); \
	} while(0)

#define pushw(base, ptr, val, regs) \
	do { \
		int err; \
		__asm__ __volatile__(				\
			"decw %w0\n\t"				\
			"1: movb %h3,0(%2,%0)\n\t"		\
			"decw %w0\n\t"				\
			"2: movb %b3,0(%2,%0)\n\t"		\
			"xor %1,%1\n\t"				\
			"3:\n"					\
			".section .fixup,\"ax\"\n\t"		\
			"4:	movl $1,%1\n\t"			\
			"	jmp 3b\n\t"			\
			".previous\n"				\
			".section __ex_table,\"a\"\n"		\
			"	.align 4\n"			\
			"	.long 1b,4b\n"			\
			"	.long 2b,4b\n"			\
			".previous"				\
			: "=r" (ptr), "=r" (err)		\
			: "r" (base), "q" (val), "0" (ptr));	\
		if (err) \
			return_to_32bit(regs, VM86_UNKNOWN); \
	} while(0)

#define pushl(base, ptr, val, regs) \
	do { \
		int err; \
		__asm__ __volatile__(				\
			"decw %w0\n\t"				\
			"rorl $16,%3\n\t"			\
			"1: movb %h3,0(%2,%0)\n\t"		\
			"decw %w0\n\t"				\
			"2: movb %b3,0(%2,%0)\n\t"		\
			"decw %w0\n\t"				\
			"rorl $16,%3\n\t"			\
			"3: movb %h3,0(%2,%0)\n\t"		\
			"decw %w0\n\t"				\
			"4: movb %b3,0(%2,%0)\n\t"		\
			"xor %1,%1\n\t"				\
			"5:\n"					\
			".section .fixup,\"ax\"\n\t"		\
			"6:	movl $1,%1\n\t"			\
			"	jmp 5b\n\t"			\
			".previous\n"				\
			".section __ex_table,\"a\"\n"		\
			"	.align 4\n"			\
			"	.long 1b,6b\n"			\
			"	.long 2b,6b\n"			\
			"	.long 3b,6b\n"			\
			"	.long 4b,6b\n"			\
			".previous"				\
			: "=r" (ptr), "=r" (err)		\
			: "r" (base), "q" (val), "0" (ptr));	\
		if (err) \
			return_to_32bit(regs, VM86_UNKNOWN); \
	} while(0)

#define popb(base, ptr, regs) \
	({ \
	 	unsigned long __res; \
	 	unsigned int err; \
		__asm__ __volatile__( \
			"1:movb 0(%1,%0),%b2\n\t"		\
			"incw %w0\n\t"				\
			"xor %3,%3\n\t"				\
			"2:\n"					\
			".section .fixup,\"ax\"\n\t"		\
			"3:	movl $1,%1\n\t"			\
			"	jmp 2b\n\t"			\
			".previous\n"				\
			".section __ex_table,\"a\"\n"		\
			"	.align 4\n"			\
			"	.long 1b,3b\n"			\
			".previous"				\
			: "=r" (ptr), "=r" (base), "=q" (__res), \
				"=r" (err) \
			: "0" (ptr), "1" (base), "2" (0)); \
		if (err) \
			return_to_32bit(regs, VM86_UNKNOWN); \
		__res; \
	})

#define popw(base, ptr, regs) \
	({ \
	 	unsigned long __res; \
	 	unsigned int err; \
		__asm__ __volatile__( \
			"1:movb 0(%1,%0),%b2\n\t"		\
			"incw %w0\n\t"				\
			"2:movb 0(%1,%0),%h2\n\t"		\
			"incw %w0\n\t"				\
			"xor %3,%3\n\t"				\
			"3:\n"					\
			".section .fixup,\"ax\"\n\t"		\
			"4:	movl $1,%1\n\t"			\
			"	jmp 3b\n\t"			\
			".previous\n"				\
			".section __ex_table,\"a\"\n"		\
			"	.align 4\n"			\
			"	.long 1b,4b\n"			\
			"	.long 2b,4b\n"			\
			".previous"				\
			: "=r" (ptr), "=r" (base), "=q" (__res), \
				"=r" (err) \
			: "0" (ptr), "1" (base), "2" (0)); \
		if (err) \
			return_to_32bit(regs, VM86_UNKNOWN); \
		__res; \
	})

#define popl(base, ptr, regs) \
	({ \
	 	unsigned long __res; \
	 	unsigned int err; \
		__asm__ __volatile__( \
			"1:movb 0(%1,%0),%b2\n\t"		\
			"incw %w0\n\t"				\
			"2:movb 0(%1,%0),%h2\n\t"		\
			"incw %w0\n\t"				\
			"rorl $16,%2\n\t"			\
			"3:movb 0(%1,%0),%b2\n\t"		\
			"incw %w0\n\t"				\
			"4:movb 0(%1,%0),%h2\n\t"		\
			"incw %w0\n\t"				\
			"rorl $16,%2\n\t"			\
			"xor %3,%3\n\t"				\
			"5:\n"					\
			".section .fixup,\"ax\"\n\t"		\
			"6:	movl $1,%1\n\t"			\
			"	jmp 5b\n\t"			\
			".previous\n"				\
			".section __ex_table,\"a\"\n"		\
			"	.align 4\n"			\
			"	.long 1b,6b\n"			\
			"	.long 2b,6b\n"			\
			"	.long 3b,6b\n"			\
			"	.long 4b,6b\n"			\
			".previous"				\
			: "=r" (ptr), "=r" (base), "=q" (__res), \
				"=r" (err) \
			: "0" (ptr), "1" (base), "2" (0)); \
		if (err) \
			return_to_32bit(regs, VM86_UNKNOWN); \
		__res; \
	})

static void do_int(struct kernel_vm86_regs *regs, int i, unsigned char * ssp, unsigned long sp)
{
	unsigned long *intr_ptr, segoffs;

	if (regs->cs == BIOSSEG)
		goto cannot_handle;
	if (is_revectored(i, &KVM86->int_revectored))
		goto cannot_handle;
	if (i==0x21 && is_revectored(AH(regs),&KVM86->int21_revectored))
		goto cannot_handle;
	intr_ptr = (unsigned long *) (i << 2);
	if (get_user(segoffs, intr_ptr))
		goto cannot_handle;
	if ((segoffs >> 16) == BIOSSEG)
		goto cannot_handle;
	pushw(ssp, sp, get_vflags(regs), regs);
	pushw(ssp, sp, regs->cs, regs);
	pushw(ssp, sp, IP(regs), regs);
	regs->cs = segoffs >> 16;
	SP(regs) -= 6;
	IP(regs) = segoffs & 0xffff;
	clear_TF(regs);
	clear_IF(regs);
	return;

cannot_handle:
	return_to_32bit(regs, VM86_INTx + (i << 8));
}

/* This must be called with the kernel lock held. */
int handle_vm86_trap(struct kernel_vm86_regs * regs, long error_code, int trapno)
{
	if (VMPI.is_vm86pus) {
		if ( (trapno==3) || (trapno==1) )
			return_to_32bit(regs, VM86_TRAP + (trapno << 8));
		do_int(regs, trapno, (unsigned char *) (regs->ss << 4), SP(regs));
		return 0;
	}
	if (trapno !=1)
		return 1; /* we let this handle by the calling routine */
	if (current->ptrace & PT_PTRACED) {
		unsigned long flags;
		spin_lock_irqsave(&current->sigmask_lock, flags);
		sigdelset(&current->blocked, SIGTRAP);
		recalc_sigpending(current);
		spin_unlock_irqrestore(&current->sigmask_lock, flags);
	}
	send_sig(SIGTRAP, current, 1);
	current->tss.trap_no = trapno;
	current->tss.error_code = error_code;
	return 0;
}

/* This must be called with the kernel lock held. */
void handle_vm86_fault(struct kernel_vm86_regs * regs, long error_code)
{
	unsigned char *csp, *ssp;
	unsigned long ip, sp;

#define CHECK_IF_IN_TRAP \
	if (VMPI.vm86dbg_active && VMPI.vm86dbg_TFpendig) \
		pushw(ssp,sp,popw(ssp,sp, regs) | TF_MASK, regs);
#define VM86_FAULT_RETURN \
	if (VMPI.force_return_for_pic  && (VEFLAGS & IF_MASK)) \
		return_to_32bit(regs, VM86_PICRETURN); \
	return;
	                                   
	csp = (unsigned char *) (regs->cs << 4);
	ssp = (unsigned char *) (regs->ss << 4);
	sp = SP(regs);
	ip = IP(regs);

	switch (popb(csp, ip, regs)) {

	/* operand size override */
	case 0x66:
		switch (popb(csp, ip, regs)) {

		/* pushfd */
		case 0x9c:
			SP(regs) -= 4;
			IP(regs) += 2;
			pushl(ssp, sp, get_vflags(regs), regs);
			VM86_FAULT_RETURN;

		/* popfd */
		case 0x9d:
			SP(regs) += 4;
			IP(regs) += 2;
			CHECK_IF_IN_TRAP
			set_vflags_long(popl(ssp, sp, regs), regs);
			VM86_FAULT_RETURN;

		/* iretd */
		case 0xcf:
			SP(regs) += 12;
			IP(regs) = (unsigned short)popl(ssp, sp, regs);
			regs->cs = (unsigned short)popl(ssp, sp, regs);
			CHECK_IF_IN_TRAP
			set_vflags_long(popl(ssp, sp, regs), regs);
			VM86_FAULT_RETURN;
		/* need this to avoid a fallthrough */
		default:
			return_to_32bit(regs, VM86_UNKNOWN);
		}

	/* pushf */
	case 0x9c:
		SP(regs) -= 2;
		IP(regs)++;
		pushw(ssp, sp, get_vflags(regs), regs);
		VM86_FAULT_RETURN;

	/* popf */
	case 0x9d:
		SP(regs) += 2;
		IP(regs)++;
		CHECK_IF_IN_TRAP
		set_vflags_short(popw(ssp, sp, regs), regs);
		VM86_FAULT_RETURN;

	/* int xx */
	case 0xcd: {
	        int intno=popb(csp, ip, regs);
		IP(regs) += 2;
		if (VMPI.vm86dbg_active) {
			if ( (1 << (intno &7)) & VMPI.vm86dbg_intxxtab[intno >> 3] )
				return_to_32bit(regs, VM86_INTx + (intno << 8));
		}
		do_int(regs, intno, ssp, sp);
		return;
	}

	/* iret */
	case 0xcf:
		SP(regs) += 6;
		IP(regs) = popw(ssp, sp, regs);
		regs->cs = popw(ssp, sp, regs);
		CHECK_IF_IN_TRAP
		set_vflags_short(popw(ssp, sp, regs), regs);
		VM86_FAULT_RETURN;

	/* cli */
	case 0xfa:
		IP(regs)++;
		clear_IF(regs);
		VM86_FAULT_RETURN;

	/* sti */
	/*
	 * Damn. This is incorrect: the 'sti' instruction should actually
	 * enable interrupts after the /next/ instruction. Not good.
	 *
	 * Probably needs some horsing around with the TF flag. Aiee..
	 */
	case 0xfb:
		IP(regs)++;
		set_IF(regs);
		VM86_FAULT_RETURN;

	default:
		return_to_32bit(regs, VM86_UNKNOWN);
	}
}

/* ---------------- vm86 special IRQ passing stuff ----------------- */

#define VM86_IRQNAME		"vm86irq"

static struct vm86_irqs {
	struct task_struct *tsk;
	int sig;
} vm86_irqs[16] = {{0},}; 
static int irqbits=0;

#define ALLOWED_SIGS ( 1 /* 0 = don't send a signal */ \
	| (1 << SIGUSR1) | (1 << SIGUSR2) | (1 << SIGIO)  | (1 << SIGURG) \
	| (1 << SIGUNUSED) )
	
static void irq_handler(int intno, void *dev_id, struct pt_regs * regs) {
	int irq_bit;
	unsigned long flags;
	
	lock_kernel();
	save_flags(flags);
	cli();
	irq_bit = 1 << intno;
	if ((irqbits & irq_bit) || ! vm86_irqs[intno].tsk)
		goto out;
	irqbits |= irq_bit;
	if (vm86_irqs[intno].sig)
		send_sig(vm86_irqs[intno].sig, vm86_irqs[intno].tsk, 1);
	/* else user will poll for IRQs */
out:
	restore_flags(flags);
	unlock_kernel();
}

static inline void free_vm86_irq(int irqnumber)
{
	free_irq(irqnumber,0);
	vm86_irqs[irqnumber].tsk = 0;
	irqbits &= ~(1 << irqnumber);
}

static inline int task_valid(struct task_struct *tsk)
{
	struct task_struct *p;
	int ret = 0;

	read_lock(&tasklist_lock);
	for_each_task(p) {
		if ((p == tsk) && (p->sig)) {
			ret = 1;
			break;
		}
	}
	read_unlock(&tasklist_lock);
	return ret;
}

void release_x86_irqs(struct task_struct *task)
{
	int i;
	for (i=3; i<16; i++)
	    if (vm86_irqs[i].tsk == task)
		free_vm86_irq(i);
}

static inline void handle_irq_zombies(void)
{
	int i;
	for (i=3; i<16; i++) {
		if (vm86_irqs[i].tsk) {
			if (task_valid(vm86_irqs[i].tsk)) continue;
			free_vm86_irq(i);
		}
	}
}

static inline int get_and_reset_irq(int irqnumber)
{
	int bit;
	unsigned long flags;
	
	if ( (irqnumber<3) || (irqnumber>15) ) return 0;
	if (vm86_irqs[irqnumber].tsk != current) return 0;
	save_flags(flags);
	cli();
	bit = irqbits & (1 << irqnumber);
	irqbits &= ~bit;
	restore_flags(flags);
	return bit;
}


static int do_vm86_irq_handling(int subfunction, int irqnumber)
{
	int ret;
	switch (subfunction) {
		case VM86_GET_AND_RESET_IRQ: {
			return get_and_reset_irq(irqnumber);
		}
		case VM86_GET_IRQ_BITS: {
			return irqbits;
		}
		case VM86_REQUEST_IRQ: {
			int sig = irqnumber >> 8;
			int irq = irqnumber & 255;
			handle_irq_zombies();
			if (!capable(CAP_SYS_ADMIN)) return -EPERM;
			if (!((1 << sig) & ALLOWED_SIGS)) return -EPERM;
			if ( (irq<3) || (irq>15) ) return -EPERM;
			if (vm86_irqs[irq].tsk) return -EPERM;
			ret = request_irq(irq, &irq_handler, 0, VM86_IRQNAME, 0);
			if (ret) return ret;
			vm86_irqs[irq].sig = sig;
			vm86_irqs[irq].tsk = current;
			return irq;
		}
		case  VM86_FREE_IRQ: {
			handle_irq_zombies();
			if ( (irqnumber<3) || (irqnumber>15) ) return -EPERM;
			if (!vm86_irqs[irqnumber].tsk) return 0;
			if (vm86_irqs[irqnumber].tsk != current) return -EPERM;
			free_vm86_irq(irqnumber);
			return 0;
		}
	}
	return -EINVAL;
}