arch/um/kernel/irq.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2017 - Cambridge Greys Ltd
  * Copyright (C) 2011 - 2014 Cisco Systems Inc
  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Derived (i.e. mostly copied) from arch/i386/kernel/irq.c:
  *	Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
  */

 #include <linux/cpumask.h>
 #include <linux/hardirq.h>
 #include <linux/interrupt.h>
 #include <linux/kernel_stat.h>
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <linux/seq_file.h>
 #include <linux/slab.h>
 #include <as-layout.h>
 #include <kern_util.h>
 #include <os.h>
 #include <irq_user.h>


 extern void free_irqs(void);

 /* When epoll triggers we do not know why it did so
  * we can also have different IRQs for read and write.
  * This is why we keep a small irq_fd array for each fd -
  * one entry per IRQ type
  */

 struct irq_entry {
 	struct irq_entry *next;
 	int fd;
 	struct irq_fd *irq_array[MAX_IRQ_TYPE + 1];
 };

 static struct irq_entry *active_fds;

 static DEFINE_SPINLOCK(irq_lock);

 static void irq_io_loop(struct irq_fd *irq, struct uml_pt_regs *regs)
 {
 /*
  * irq->active guards against reentry
  * irq->pending accumulates pending requests
  * if pending is raised the irq_handler is re-run
  * until pending is cleared
  */
 	if (irq->active) {
 		irq->active = false;
 		do {
 			irq->pending = false;
 			do_IRQ(irq->irq, regs);
 		} while (irq->pending && (!irq->purge));
 		if (!irq->purge)
 			irq->active = true;
 	} else {
 		irq->pending = true;
 	}
 }

 void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
 {
 	struct irq_entry *irq_entry;
 	struct irq_fd *irq;

 	int n, i, j;

 	while (1) {
 		/* This is now lockless - epoll keeps back-referencesto the irqs
 		 * which have trigger it so there is no need to walk the irq
 		 * list and lock it every time. We avoid locking by turning off
 		 * IO for a specific fd by executing os_del_epoll_fd(fd) before
 		 * we do any changes to the actual data structures
 		 */
 		n = os_waiting_for_events_epoll();

 		if (n <= 0) {
 			if (n == -EINTR)
 				continue;
 			else
 				break;
 		}

 		for (i = 0; i < n ; i++) {
 			/* Epoll back reference is the entry with 3 irq_fd
 			 * leaves - one for each irq type.
 			 */
 			irq_entry = (struct irq_entry *)
 				os_epoll_get_data_pointer(i);
 			for (j = 0; j < MAX_IRQ_TYPE ; j++) {
 				irq = irq_entry->irq_array[j];
 				if (irq == NULL)
 					continue;
 				if (os_epoll_triggered(i, irq->events) > 0)
 					irq_io_loop(irq, regs);
 				if (irq->purge) {
 					irq_entry->irq_array[j] = NULL;
 					kfree(irq);
 				}
 			}
 		}
 	}

 	free_irqs();
 }

 static int assign_epoll_events_to_irq(struct irq_entry *irq_entry)
 {
 	int i;
 	int events = 0;
 	struct irq_fd *irq;

 	for (i = 0; i < MAX_IRQ_TYPE ; i++) {
 		irq = irq_entry->irq_array[i];
 		if (irq != NULL)
 			events = irq->events | events;
 	}
 	if (events > 0) {
 	/* os_add_epoll will call os_mod_epoll if this already exists */
 		return os_add_epoll_fd(events, irq_entry->fd, irq_entry);
 	}
 	/* No events - delete */
 	return os_del_epoll_fd(irq_entry->fd);
 }


 static int activate_fd(int irq, int fd, int type, void *dev_id)
 {
 	struct irq_fd *new_fd;
 	struct irq_entry *irq_entry;
 	int i, err, events;
 	unsigned long flags;

 	err = os_set_fd_async(fd);
 	if (err < 0)
 		goto out;

 	spin_lock_irqsave(&irq_lock, flags);

 	/* Check if we have an entry for this fd */

 	err = -EBUSY;
 	for (irq_entry = active_fds;
 		irq_entry != NULL; irq_entry = irq_entry->next) {
 		if (irq_entry->fd == fd)
 			break;
 	}

 	if (irq_entry == NULL) {
 		/* This needs to be atomic as it may be called from an
 		 * IRQ context.
 		 */
 		irq_entry = kmalloc(sizeof(struct irq_entry), GFP_ATOMIC);
 		if (irq_entry == NULL) {
 			printk(KERN_ERR
 				"Failed to allocate new IRQ entry\n");
 			goto out_unlock;
 		}
 		irq_entry->fd = fd;
 		for (i = 0; i < MAX_IRQ_TYPE; i++)
 			irq_entry->irq_array[i] = NULL;
 		irq_entry->next = active_fds;
 		active_fds = irq_entry;
 	}

 	/* Check if we are trying to re-register an interrupt for a
 	 * particular fd
 	 */

 	if (irq_entry->irq_array[type] != NULL) {
 		printk(KERN_ERR
 			"Trying to reregister IRQ %d FD %d TYPE %d ID %p\n",
 			irq, fd, type, dev_id
 		);
 		goto out_unlock;
 	} else {
 		/* New entry for this fd */

 		err = -ENOMEM;
 		new_fd = kmalloc(sizeof(struct irq_fd), GFP_ATOMIC);
 		if (new_fd == NULL)
 			goto out_unlock;

 		events = os_event_mask(type);

 		*new_fd = ((struct irq_fd) {
 			.id		= dev_id,
 			.irq		= irq,
 			.type		= type,
 			.events		= events,
 			.active		= true,
 			.pending	= false,
 			.purge		= false
 		});
 		/* Turn off any IO on this fd - allows us to
 		 * avoid locking the IRQ loop
 		 */
 		os_del_epoll_fd(irq_entry->fd);
 		irq_entry->irq_array[type] = new_fd;
 	}

 	/* Turn back IO on with the correct (new) IO event mask */
 	assign_epoll_events_to_irq(irq_entry);
 	spin_unlock_irqrestore(&irq_lock, flags);
 	maybe_sigio_broken(fd, (type != IRQ_NONE));

 	return 0;
 out_unlock:
 	spin_unlock_irqrestore(&irq_lock, flags);
 out:
 	return err;
 }

 /*
  * Walk the IRQ list and dispose of any unused entries.
  * Should be done under irq_lock.
  */

 static void garbage_collect_irq_entries(void)
 {
 	int i;
 	bool reap;
 	struct irq_entry *walk;
 	struct irq_entry *previous = NULL;
 	struct irq_entry *to_free;

 	if (active_fds == NULL)
 		return;
 	walk = active_fds;
 	while (walk != NULL) {
 		reap = true;
 		for (i = 0; i < MAX_IRQ_TYPE ; i++) {
 			if (walk->irq_array[i] != NULL) {
 				reap = false;
 				break;
 			}
 		}
 		if (reap) {
 			if (previous == NULL)
 				active_fds = walk->next;
 			else
 				previous->next = walk->next;
 			to_free = walk;
 		} else {
 			to_free = NULL;
 		}
 		walk = walk->next;
 		kfree(to_free);
 	}
 }

 /*
  * Walk the IRQ list and get the descriptor for our FD
  */

 static struct irq_entry *get_irq_entry_by_fd(int fd)
 {
 	struct irq_entry *walk = active_fds;

 	while (walk != NULL) {
 		if (walk->fd == fd)
 			return walk;
 		walk = walk->next;
 	}
 	return NULL;
 }


 /*
  * Walk the IRQ list and dispose of an entry for a specific
  * device, fd and number. Note - if sharing an IRQ for read
  * and writefor the same FD it will be disposed in either case.
  * If this behaviour is undesirable use different IRQ ids.
  */

 #define IGNORE_IRQ 1
 #define IGNORE_DEV (1<<1)

 static void do_free_by_irq_and_dev(
 	struct irq_entry *irq_entry,
 	unsigned int irq,
 	void *dev,
 	int flags
 )
 {
 	int i;
 	struct irq_fd *to_free;

 	for (i = 0; i < MAX_IRQ_TYPE ; i++) {
 		if (irq_entry->irq_array[i] != NULL) {
 			if (
 			((flags & IGNORE_IRQ) ||
 				(irq_entry->irq_array[i]->irq == irq)) &&
 			((flags & IGNORE_DEV) ||
 				(irq_entry->irq_array[i]->id == dev))
 			) {
 				/* Turn off any IO on this fd - allows us to
 				 * avoid locking the IRQ loop
 				 */
 				os_del_epoll_fd(irq_entry->fd);
 				to_free = irq_entry->irq_array[i];
 				irq_entry->irq_array[i] = NULL;
 				assign_epoll_events_to_irq(irq_entry);
 				if (to_free->active)
 					to_free->purge = true;
 				else
 					kfree(to_free);
 			}
 		}
 	}
 }

 void free_irq_by_fd(int fd)
 {
 	struct irq_entry *to_free;
 	unsigned long flags;

 	spin_lock_irqsave(&irq_lock, flags);
 	to_free = get_irq_entry_by_fd(fd);
 	if (to_free != NULL) {
 		do_free_by_irq_and_dev(
 			to_free,
 			-1,
 			NULL,
 			IGNORE_IRQ | IGNORE_DEV
 		);
 	}
 	garbage_collect_irq_entries();
 	spin_unlock_irqrestore(&irq_lock, flags);
 }
 EXPORT_SYMBOL(free_irq_by_fd);

 static void free_irq_by_irq_and_dev(unsigned int irq, void *dev)
 {
 	struct irq_entry *to_free;
 	unsigned long flags;

 	spin_lock_irqsave(&irq_lock, flags);
 	to_free = active_fds;
 	while (to_free != NULL) {
 		do_free_by_irq_and_dev(
 			to_free,
 			irq,
 			dev,
 			0
 		);
 		to_free = to_free->next;
 	}
 	garbage_collect_irq_entries();
 	spin_unlock_irqrestore(&irq_lock, flags);
 }


 void deactivate_fd(int fd, int irqnum)
 {
 	struct irq_entry *to_free;
 	unsigned long flags;

 	os_del_epoll_fd(fd);
 	spin_lock_irqsave(&irq_lock, flags);
 	to_free = get_irq_entry_by_fd(fd);
 	if (to_free != NULL) {
 		do_free_by_irq_and_dev(
 			to_free,
 			irqnum,
 			NULL,
 			IGNORE_DEV
 		);
 	}
 	garbage_collect_irq_entries();
 	spin_unlock_irqrestore(&irq_lock, flags);
 	ignore_sigio_fd(fd);
 }
 EXPORT_SYMBOL(deactivate_fd);

 /*
  * Called just before shutdown in order to provide a clean exec
  * environment in case the system is rebooting.  No locking because
  * that would cause a pointless shutdown hang if something hadn't
  * released the lock.
  */
 int deactivate_all_fds(void)
 {
 	struct irq_entry *to_free;

 	/* Stop IO. The IRQ loop has no lock so this is our
 	 * only way of making sure we are safe to dispose
 	 * of all IRQ handlers
 	 */
 	os_set_ioignore();
 	to_free = active_fds;
 	while (to_free != NULL) {
 		do_free_by_irq_and_dev(
 			to_free,
 			-1,
 			NULL,
 			IGNORE_IRQ | IGNORE_DEV
 		);
 		to_free = to_free->next;
 	}
 	/* don't garbage collect - we can no longer call kfree() here */
 	os_close_epoll_fd();
 	return 0;
 }

 /*
  * do_IRQ handles all normal device IRQs (the special
  * SMP cross-CPU interrupts have their own specific
  * handlers).
  */
 unsigned int do_IRQ(int irq, struct uml_pt_regs *regs)
 {
 	struct pt_regs *old_regs = set_irq_regs((struct pt_regs *)regs);
 	irq_enter();
 	generic_handle_irq(irq);
 	irq_exit();
 	set_irq_regs(old_regs);
 	return 1;
 }

 void um_free_irq(unsigned int irq, void *dev)
 {
 	free_irq_by_irq_and_dev(irq, dev);
 	free_irq(irq, dev);
 }
 EXPORT_SYMBOL(um_free_irq);

 int um_request_irq(unsigned int irq, int fd, int type,
 		   irq_handler_t handler,
 		   unsigned long irqflags, const char * devname,
 		   void *dev_id)
 {
 	int err;

 	if (fd != -1) {
 		err = activate_fd(irq, fd, type, dev_id);
 		if (err)
 			return err;
 	}

 	return request_irq(irq, handler, irqflags, devname, dev_id);
 }

 EXPORT_SYMBOL(um_request_irq);

 /*
  * irq_chip must define at least enable/disable and ack when
  * the edge handler is used.
  */
 static void dummy(struct irq_data *d)
 {
 }

 /* This is used for everything else than the timer. */
 static struct irq_chip normal_irq_type = {
 	.name = "SIGIO",
 	.irq_disable = dummy,
 	.irq_enable = dummy,
 	.irq_ack = dummy,
 	.irq_mask = dummy,
 	.irq_unmask = dummy,
 };

 static struct irq_chip SIGVTALRM_irq_type = {
 	.name = "SIGVTALRM",
 	.irq_disable = dummy,
 	.irq_enable = dummy,
 	.irq_ack = dummy,
 	.irq_mask = dummy,
 	.irq_unmask = dummy,
 };

 void __init init_IRQ(void)
 {
 	int i;

 	irq_set_chip_and_handler(TIMER_IRQ, &SIGVTALRM_irq_type, handle_edge_irq);


 	for (i = 1; i < NR_IRQS; i++)
 		irq_set_chip_and_handler(i, &normal_irq_type, handle_edge_irq);
 	/* Initialize EPOLL Loop */
 	os_setup_epoll();
 }

 /*
  * IRQ stack entry and exit:
  *
  * Unlike i386, UML doesn't receive IRQs on the normal kernel stack
  * and switch over to the IRQ stack after some preparation.  We use
  * sigaltstack to receive signals on a separate stack from the start.
  * These two functions make sure the rest of the kernel won't be too
  * upset by being on a different stack.  The IRQ stack has a
  * thread_info structure at the bottom so that current et al continue
  * to work.
  *
  * to_irq_stack copies the current task's thread_info to the IRQ stack
  * thread_info and sets the tasks's stack to point to the IRQ stack.
  *
  * from_irq_stack copies the thread_info struct back (flags may have
  * been modified) and resets the task's stack pointer.
  *
  * Tricky bits -
  *
  * What happens when two signals race each other?  UML doesn't block
  * signals with sigprocmask, SA_DEFER, or sa_mask, so a second signal
  * could arrive while a previous one is still setting up the
  * thread_info.
  *
  * There are three cases -
  *     The first interrupt on the stack - sets up the thread_info and
  * handles the interrupt
  *     A nested interrupt interrupting the copying of the thread_info -
  * can't handle the interrupt, as the stack is in an unknown state
  *     A nested interrupt not interrupting the copying of the
  * thread_info - doesn't do any setup, just handles the interrupt
  *
  * The first job is to figure out whether we interrupted stack setup.
  * This is done by xchging the signal mask with thread_info->pending.
  * If the value that comes back is zero, then there is no setup in
  * progress, and the interrupt can be handled.  If the value is
  * non-zero, then there is stack setup in progress.  In order to have
  * the interrupt handled, we leave our signal in the mask, and it will
  * be handled by the upper handler after it has set up the stack.
  *
  * Next is to figure out whether we are the outer handler or a nested
  * one.  As part of setting up the stack, thread_info->real_thread is
  * set to non-NULL (and is reset to NULL on exit).  This is the
  * nesting indicator.  If it is non-NULL, then the stack is already
  * set up and the handler can run.
  */

 static unsigned long pending_mask;

 unsigned long to_irq_stack(unsigned long *mask_out)
 {
 	struct thread_info *ti;
 	unsigned long mask, old;
 	int nested;

 	mask = xchg(&pending_mask, *mask_out);
 	if (mask != 0) {
 		/*
 		 * If any interrupts come in at this point, we want to
 		 * make sure that their bits aren't lost by our
 		 * putting our bit in.  So, this loop accumulates bits
 		 * until xchg returns the same value that we put in.
 		 * When that happens, there were no new interrupts,
 		 * and pending_mask contains a bit for each interrupt
 		 * that came in.
 		 */
 		old = *mask_out;
 		do {
 			old |= mask;
 			mask = xchg(&pending_mask, old);
 		} while (mask != old);
 		return 1;
 	}

 	ti = current_thread_info();
 	nested = (ti->real_thread != NULL);
 	if (!nested) {
 		struct task_struct *task;
 		struct thread_info *tti;

 		task = cpu_tasks[ti->cpu].task;
 		tti = task_thread_info(task);

 		*ti = *tti;
 		ti->real_thread = tti;
 		task->stack = ti;
 	}

 	mask = xchg(&pending_mask, 0);
 	*mask_out |= mask | nested;
 	return 0;
 }

 unsigned long from_irq_stack(int nested)
 {
 	struct thread_info *ti, *to;
 	unsigned long mask;

 	ti = current_thread_info();

 	pending_mask = 1;

 	to = ti->real_thread;
 	current->stack = to;
 	ti->real_thread = NULL;
 	*to = *ti;

 	mask = xchg(&pending_mask, 0);
 	return mask & ~1;
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Copyright (C) 2017 - Cambridge Greys Ltd
	* Copyright (C) 2011 - 2014 Cisco Systems Inc
	* Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
	* Derived (i.e. mostly copied) from arch/i386/kernel/irq.c:
	* Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
	*/

	#include <linux/cpumask.h>
	#include <linux/hardirq.h>
	#include <linux/interrupt.h>
	#include <linux/kernel_stat.h>
	#include <linux/module.h>
	#include <linux/sched.h>
	#include <linux/seq_file.h>
	#include <linux/slab.h>
	#include <as-layout.h>
	#include <kern_util.h>
	#include <os.h>
	#include <irq_user.h>


	extern void free_irqs(void);

	/* When epoll triggers we do not know why it did so
	* we can also have different IRQs for read and write.
	* This is why we keep a small irq_fd array for each fd -
	* one entry per IRQ type
	*/

	struct irq_entry {
	struct irq_entry *next;
	int fd;
	struct irq_fd *irq_array[MAX_IRQ_TYPE + 1];
	};

	static struct irq_entry *active_fds;

	static DEFINE_SPINLOCK(irq_lock);

	static void irq_io_loop(struct irq_fd irq, struct uml_pt_regs regs)
	{
	/*
	* irq->active guards against reentry
	* irq->pending accumulates pending requests
	* if pending is raised the irq_handler is re-run
	* until pending is cleared
	*/
	if (irq->active) {
	irq->active = false;
	do {
	irq->pending = false;
	do_IRQ(irq->irq, regs);
	} while (irq->pending && (!irq->purge));
	if (!irq->purge)
	irq->active = true;
	} else {
	irq->pending = true;
	}
	}

	void sigio_handler(int sig, struct siginfo unused_si, struct uml_pt_regs regs)
	{
	struct irq_entry *irq_entry;
	struct irq_fd *irq;

	int n, i, j;

	while (1) {
	/* This is now lockless - epoll keeps back-referencesto the irqs
	* which have trigger it so there is no need to walk the irq
	* list and lock it every time. We avoid locking by turning off
	* IO for a specific fd by executing os_del_epoll_fd(fd) before
	* we do any changes to the actual data structures
	*/
	n = os_waiting_for_events_epoll();

	if (n <= 0) {
	if (n == -EINTR)
	continue;
	else
	break;
	}

	for (i = 0; i < n ; i++) {
	/* Epoll back reference is the entry with 3 irq_fd
	* leaves - one for each irq type.
	*/
	irq_entry = (struct irq_entry *)
	os_epoll_get_data_pointer(i);
	for (j = 0; j < MAX_IRQ_TYPE ; j++) {
	irq = irq_entry->irq_array[j];
	if (irq == NULL)
	continue;
	if (os_epoll_triggered(i, irq->events) > 0)
	irq_io_loop(irq, regs);
	if (irq->purge) {
	irq_entry->irq_array[j] = NULL;
	kfree(irq);
	}
	}
	}
	}

	free_irqs();
	}

	static int assign_epoll_events_to_irq(struct irq_entry *irq_entry)
	{
	int i;
	int events = 0;
	struct irq_fd *irq;

	for (i = 0; i < MAX_IRQ_TYPE ; i++) {
	irq = irq_entry->irq_array[i];
	if (irq != NULL)
	events = irq->events \| events;
	}
	if (events > 0) {
	/* os_add_epoll will call os_mod_epoll if this already exists */
	return os_add_epoll_fd(events, irq_entry->fd, irq_entry);
	}
	/* No events - delete */
	return os_del_epoll_fd(irq_entry->fd);
	}



	static int activate_fd(int irq, int fd, int type, void *dev_id)
	{
	struct irq_fd *new_fd;
	struct irq_entry *irq_entry;
	int i, err, events;
	unsigned long flags;

	err = os_set_fd_async(fd);
	if (err < 0)
	goto out;

	spin_lock_irqsave(&irq_lock, flags);

	/* Check if we have an entry for this fd */

	err = -EBUSY;
	for (irq_entry = active_fds;
	irq_entry != NULL; irq_entry = irq_entry->next) {
	if (irq_entry->fd == fd)
	break;
	}

	if (irq_entry == NULL) {
	/* This needs to be atomic as it may be called from an
	* IRQ context.
	*/
	irq_entry = kmalloc(sizeof(struct irq_entry), GFP_ATOMIC);
	if (irq_entry == NULL) {
	printk(KERN_ERR
	"Failed to allocate new IRQ entry\n");
	goto out_unlock;
	}
	irq_entry->fd = fd;
	for (i = 0; i < MAX_IRQ_TYPE; i++)
	irq_entry->irq_array[i] = NULL;
	irq_entry->next = active_fds;
	active_fds = irq_entry;
	}

	/* Check if we are trying to re-register an interrupt for a
	* particular fd
	*/

	if (irq_entry->irq_array[type] != NULL) {
	printk(KERN_ERR
	"Trying to reregister IRQ %d FD %d TYPE %d ID %p\n",
	irq, fd, type, dev_id
	);
	goto out_unlock;
	} else {
	/* New entry for this fd */

	err = -ENOMEM;
	new_fd = kmalloc(sizeof(struct irq_fd), GFP_ATOMIC);
	if (new_fd == NULL)
	goto out_unlock;

	events = os_event_mask(type);

	*new_fd = ((struct irq_fd) {
	.id = dev_id,
	.irq = irq,
	.type = type,
	.events = events,
	.active = true,
	.pending = false,
	.purge = false
	});
	/* Turn off any IO on this fd - allows us to
	* avoid locking the IRQ loop
	*/
	os_del_epoll_fd(irq_entry->fd);
	irq_entry->irq_array[type] = new_fd;
	}

	/* Turn back IO on with the correct (new) IO event mask */
	assign_epoll_events_to_irq(irq_entry);
	spin_unlock_irqrestore(&irq_lock, flags);
	maybe_sigio_broken(fd, (type != IRQ_NONE));

	return 0;
	out_unlock:
	spin_unlock_irqrestore(&irq_lock, flags);
	out:
	return err;
	}

	/*
	* Walk the IRQ list and dispose of any unused entries.
	* Should be done under irq_lock.
	*/

	static void garbage_collect_irq_entries(void)
	{
	int i;
	bool reap;
	struct irq_entry *walk;
	struct irq_entry *previous = NULL;
	struct irq_entry *to_free;

	if (active_fds == NULL)
	return;
	walk = active_fds;
	while (walk != NULL) {
	reap = true;
	for (i = 0; i < MAX_IRQ_TYPE ; i++) {
	if (walk->irq_array[i] != NULL) {
	reap = false;
	break;
	}
	}
	if (reap) {
	if (previous == NULL)
	active_fds = walk->next;
	else
	previous->next = walk->next;
	to_free = walk;
	} else {
	to_free = NULL;
	}
	walk = walk->next;
	kfree(to_free);
	}
	}

	/*
	* Walk the IRQ list and get the descriptor for our FD
	*/

	static struct irq_entry *get_irq_entry_by_fd(int fd)
	{
	struct irq_entry *walk = active_fds;

	while (walk != NULL) {
	if (walk->fd == fd)
	return walk;
	walk = walk->next;
	}
	return NULL;
	}


	/*
	* Walk the IRQ list and dispose of an entry for a specific
	* device, fd and number. Note - if sharing an IRQ for read
	* and writefor the same FD it will be disposed in either case.
	* If this behaviour is undesirable use different IRQ ids.
	*/

	#define IGNORE_IRQ 1
	#define IGNORE_DEV (1<<1)

	static void do_free_by_irq_and_dev(
	struct irq_entry *irq_entry,
	unsigned int irq,
	void *dev,
	int flags
	)
	{
	int i;
	struct irq_fd *to_free;

	for (i = 0; i < MAX_IRQ_TYPE ; i++) {
	if (irq_entry->irq_array[i] != NULL) {
	if (
	((flags & IGNORE_IRQ) \|\|
	(irq_entry->irq_array[i]->irq == irq)) &&
	((flags & IGNORE_DEV) \|\|
	(irq_entry->irq_array[i]->id == dev))
	) {
	/* Turn off any IO on this fd - allows us to
	* avoid locking the IRQ loop
	*/
	os_del_epoll_fd(irq_entry->fd);
	to_free = irq_entry->irq_array[i];
	irq_entry->irq_array[i] = NULL;
	assign_epoll_events_to_irq(irq_entry);
	if (to_free->active)
	to_free->purge = true;
	else
	kfree(to_free);
	}
	}
	}
	}

	void free_irq_by_fd(int fd)
	{
	struct irq_entry *to_free;
	unsigned long flags;

	spin_lock_irqsave(&irq_lock, flags);
	to_free = get_irq_entry_by_fd(fd);
	if (to_free != NULL) {
	do_free_by_irq_and_dev(
	to_free,
	-1,
	NULL,
	IGNORE_IRQ \| IGNORE_DEV
	);
	}
	garbage_collect_irq_entries();
	spin_unlock_irqrestore(&irq_lock, flags);
	}
	EXPORT_SYMBOL(free_irq_by_fd);

	static void free_irq_by_irq_and_dev(unsigned int irq, void *dev)
	{
	struct irq_entry *to_free;
	unsigned long flags;

	spin_lock_irqsave(&irq_lock, flags);
	to_free = active_fds;
	while (to_free != NULL) {
	do_free_by_irq_and_dev(
	to_free,
	irq,
	dev,
	0
	);
	to_free = to_free->next;
	}
	garbage_collect_irq_entries();
	spin_unlock_irqrestore(&irq_lock, flags);
	}


	void deactivate_fd(int fd, int irqnum)
	{
	struct irq_entry *to_free;
	unsigned long flags;

	os_del_epoll_fd(fd);
	spin_lock_irqsave(&irq_lock, flags);
	to_free = get_irq_entry_by_fd(fd);
	if (to_free != NULL) {
	do_free_by_irq_and_dev(
	to_free,
	irqnum,
	NULL,
	IGNORE_DEV
	);
	}
	garbage_collect_irq_entries();
	spin_unlock_irqrestore(&irq_lock, flags);
	ignore_sigio_fd(fd);
	}
	EXPORT_SYMBOL(deactivate_fd);

	/*
	* Called just before shutdown in order to provide a clean exec
	* environment in case the system is rebooting. No locking because
	* that would cause a pointless shutdown hang if something hadn't
	* released the lock.
	*/
	int deactivate_all_fds(void)
	{
	struct irq_entry *to_free;

	/* Stop IO. The IRQ loop has no lock so this is our
	* only way of making sure we are safe to dispose
	* of all IRQ handlers
	*/
	os_set_ioignore();
	to_free = active_fds;
	while (to_free != NULL) {
	do_free_by_irq_and_dev(
	to_free,
	-1,
	NULL,
	IGNORE_IRQ \| IGNORE_DEV
	);
	to_free = to_free->next;
	}
	/* don't garbage collect - we can no longer call kfree() here */
	os_close_epoll_fd();
	return 0;
	}

	/*
	* do_IRQ handles all normal device IRQs (the special
	* SMP cross-CPU interrupts have their own specific
	* handlers).
	*/
	unsigned int do_IRQ(int irq, struct uml_pt_regs *regs)
	{
	struct pt_regs old_regs = set_irq_regs((struct pt_regs )regs);
	irq_enter();
	generic_handle_irq(irq);
	irq_exit();
	set_irq_regs(old_regs);
	return 1;
	}

	void um_free_irq(unsigned int irq, void *dev)
	{
	free_irq_by_irq_and_dev(irq, dev);
	free_irq(irq, dev);
	}
	EXPORT_SYMBOL(um_free_irq);

	int um_request_irq(unsigned int irq, int fd, int type,
	irq_handler_t handler,
	unsigned long irqflags, const char * devname,
	void *dev_id)
	{
	int err;

	if (fd != -1) {
	err = activate_fd(irq, fd, type, dev_id);
	if (err)
	return err;
	}

	return request_irq(irq, handler, irqflags, devname, dev_id);
	}

	EXPORT_SYMBOL(um_request_irq);

	/*
	* irq_chip must define at least enable/disable and ack when
	* the edge handler is used.
	*/
	static void dummy(struct irq_data *d)
	{
	}

	/* This is used for everything else than the timer. */
	static struct irq_chip normal_irq_type = {
	.name = "SIGIO",
	.irq_disable = dummy,
	.irq_enable = dummy,
	.irq_ack = dummy,
	.irq_mask = dummy,
	.irq_unmask = dummy,
	};

	static struct irq_chip SIGVTALRM_irq_type = {
	.name = "SIGVTALRM",
	.irq_disable = dummy,
	.irq_enable = dummy,
	.irq_ack = dummy,
	.irq_mask = dummy,
	.irq_unmask = dummy,
	};

	void __init init_IRQ(void)
	{
	int i;

	irq_set_chip_and_handler(TIMER_IRQ, &SIGVTALRM_irq_type, handle_edge_irq);


	for (i = 1; i < NR_IRQS; i++)
	irq_set_chip_and_handler(i, &normal_irq_type, handle_edge_irq);
	/* Initialize EPOLL Loop */
	os_setup_epoll();
	}

	/*
	* IRQ stack entry and exit:
	*
	* Unlike i386, UML doesn't receive IRQs on the normal kernel stack
	* and switch over to the IRQ stack after some preparation. We use
	* sigaltstack to receive signals on a separate stack from the start.
	* These two functions make sure the rest of the kernel won't be too
	* upset by being on a different stack. The IRQ stack has a
	* thread_info structure at the bottom so that current et al continue
	* to work.
	*
	* to_irq_stack copies the current task's thread_info to the IRQ stack
	* thread_info and sets the tasks's stack to point to the IRQ stack.
	*
	* from_irq_stack copies the thread_info struct back (flags may have
	* been modified) and resets the task's stack pointer.
	*
	* Tricky bits -
	*
	* What happens when two signals race each other? UML doesn't block
	* signals with sigprocmask, SA_DEFER, or sa_mask, so a second signal
	* could arrive while a previous one is still setting up the
	* thread_info.
	*
	* There are three cases -
	* The first interrupt on the stack - sets up the thread_info and
	* handles the interrupt
	* A nested interrupt interrupting the copying of the thread_info -
	* can't handle the interrupt, as the stack is in an unknown state
	* A nested interrupt not interrupting the copying of the
	* thread_info - doesn't do any setup, just handles the interrupt
	*
	* The first job is to figure out whether we interrupted stack setup.
	* This is done by xchging the signal mask with thread_info->pending.
	* If the value that comes back is zero, then there is no setup in
	* progress, and the interrupt can be handled. If the value is
	* non-zero, then there is stack setup in progress. In order to have
	* the interrupt handled, we leave our signal in the mask, and it will
	* be handled by the upper handler after it has set up the stack.
	*
	* Next is to figure out whether we are the outer handler or a nested
	* one. As part of setting up the stack, thread_info->real_thread is
	* set to non-NULL (and is reset to NULL on exit). This is the
	* nesting indicator. If it is non-NULL, then the stack is already
	* set up and the handler can run.
	*/

	static unsigned long pending_mask;

	unsigned long to_irq_stack(unsigned long *mask_out)
	{
	struct thread_info *ti;
	unsigned long mask, old;
	int nested;

	mask = xchg(&pending_mask, *mask_out);
	if (mask != 0) {
	/*
	* If any interrupts come in at this point, we want to
	* make sure that their bits aren't lost by our
	* putting our bit in. So, this loop accumulates bits
	* until xchg returns the same value that we put in.
	* When that happens, there were no new interrupts,
	* and pending_mask contains a bit for each interrupt
	* that came in.
	*/
	old = *mask_out;
	do {
	old \|= mask;
	mask = xchg(&pending_mask, old);
	} while (mask != old);
	return 1;
	}

	ti = current_thread_info();
	nested = (ti->real_thread != NULL);
	if (!nested) {
	struct task_struct *task;
	struct thread_info *tti;

	task = cpu_tasks[ti->cpu].task;
	tti = task_thread_info(task);

	ti = tti;
	ti->real_thread = tti;
	task->stack = ti;
	}

	mask = xchg(&pending_mask, 0);
	*mask_out \|= mask \| nested;
	return 0;
	}

	unsigned long from_irq_stack(int nested)
	{
	struct thread_info ti, to;
	unsigned long mask;

	ti = current_thread_info();

	pending_mask = 1;

	to = ti->real_thread;
	current->stack = to;
	ti->real_thread = NULL;
	to = ti;

	mask = xchg(&pending_mask, 0);
	return mask & ~1;
	}