lguest: documentation III: Drivers

/* A simple block driver for lguest.

/*D:400

 * The Guest block driver

 *

 * Copyright 2006 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation

 * This is a simple block driver, which appears as /dev/lgba, lgbb, lgbc etc.

 * The mechanism is simple: we place the information about the request in the

 * device page, then use SEND_DMA (containing the data for a write, or an empty

 * "ping" DMA for a read).

 :*/

/* Copyright 2006 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

static char next_block_index = 'a';

/*D:420 Here is the structure which holds all the information we need about

 * each Guest block device.

 *

 * I'm sure at this stage, you're wondering "hey, where was the adventure I was

 * promised?" and thinking "Rusty sucks, I shall say nasty things about him on

 * my blog".  I think Real adventures have boring bits, too, and you're in the

 * middle of one.  But it gets better.  Just not quite yet. */

struct blockdev

{

	/* The block queue infrastructure wants a spinlock: it is held while it

	 * calls our block request function.  We grab it in our interrupt

	 * handler so the responses don't mess with new requests. */

	spinlock_t lock;

	/* The disk structure for the kernel. */

	/* The disk structure registered with kernel. */

	struct gendisk *disk;

	/* The major number for this disk. */

	/* The major device number for this disk, and the interrupt.  We only

	 * really keep them here for completeness; we'd need them if we

	 * supported device unplugging. */

	int major;

	int irq;

	/* The physical address of this device's memory page */

	unsigned long phys_addr;

	/* The mapped block page. */

	/* The mapped memory page for convenient acces. */

	struct lguest_block_page *lb_page;

	/* We only have a single request outstanding at a time. */

	/* We only have a single request outstanding at a time: this is it. */

	struct lguest_dma dma;

	struct request *req;

};

/* Jens gave me this nice helper to end all chunks of a request. */

/*D:495 We originally used end_request() throughout the driver, but it turns

 * out that end_request() is deprecated, and doesn't actually end the request

 * (which seems like a good reason to deprecate it!).  It simply ends the first

 * bio.  So if we had 3 bios in a "struct request" we would do all 3,

 * end_request(), do 2, end_request(), do 1 and end_request(): twice as much

 * work as we needed to do.

 *

 * This reinforced to me that I do not understand the block layer.

 *

 * Nonetheless, Jens Axboe gave me this nice helper to end all chunks of a

 * request.  This improved disk speed by 130%. */

static void end_entire_request(struct request *req, int uptodate)

{

	if (end_that_request_first(req, uptodate, req->hard_nr_sectors))

	end_that_request_last(req, uptodate);

}

/* I'm told there are only two stories in the world worth telling: love and

 * hate.  So there used to be a love scene here like this:

 *

 *  Launcher:	We could make beautiful I/O together, you and I.

 *  Guest:	My, that's a big disk!

 *

 * Unfortunately, it was just too raunchy for our otherwise-gentle tale. */

/*D:490 This is the interrupt handler, called when a block read or write has

 * been completed for us. */

static irqreturn_t lgb_irq(int irq, void *_bd)

{

	/* We handed our "struct blockdev" as the argument to request_irq(), so

	 * it is passed through to us here.  This tells us which device we're

	 * dealing with in case we have more than one. */

	struct blockdev *bd = _bd;

	unsigned long flags;

	/* We weren't doing anything?  Strange, but could happen if we shared

	 * interrupts (we don't!). */

	if (!bd->req) {

		pr_debug("No work!\n");

		return IRQ_NONE;

	}

	/* Not done yet?  That's equally strange. */

	if (!bd->lb_page->result) {

		pr_debug("No result!\n");

		return IRQ_NONE;

	}

	/* We have to grab the lock before ending the request. */

	spin_lock_irqsave(&bd->lock, flags);

	/* "result" is 1 for success, 2 for failure: end_entire_request() wants

	 * to know whether this succeeded or not. */

	end_entire_request(bd->req, bd->lb_page->result == 1);

	/* Clear out request, it's done. */

	bd->req = NULL;

	/* Reset incoming DMA for next time. */

	bd->dma.used_len = 0;

	/* Ready for more reads or writes */

	blk_start_queue(bd->disk->queue);

	spin_unlock_irqrestore(&bd->lock, flags);

	/* The interrupt was for us, we dealt with it. */

	return IRQ_HANDLED;

}

/*D:480 The block layer's "struct request" contains a number of "struct bio"s,

 * each of which contains "struct bio_vec"s, each of which contains a page, an

 * offset and a length.

 *

 * Fortunately there are iterators to help us walk through the "struct

 * request".  Even more fortunately, there were plenty of places to steal the

 * code from.  We pack the "struct request" into our "struct lguest_dma" and

 * return the total length. */

static unsigned int req_to_dma(struct request *req, struct lguest_dma *dma)

{

	unsigned int i = 0, idx, len = 0;

	rq_for_each_bio(bio, req) {

		struct bio_vec *bvec;

		bio_for_each_segment(bvec, bio, idx) {

			/* We told the block layer not to give us too many. */

			BUG_ON(i == LGUEST_MAX_DMA_SECTIONS);

			/* If we had a zero-length segment, it would look like

			 * the end of the data referred to by the "struct

			 * lguest_dma", so make sure that doesn't happen. */

			BUG_ON(!bvec->bv_len);

			/* Convert page & offset to a physical address */

			dma->addr[i] = page_to_phys(bvec->bv_page)

				+ bvec->bv_offset;

			dma->len[i] = bvec->bv_len;

			i++;

		}

	}

	/* If the array isn't full, we mark the end with a 0 length */

	if (i < LGUEST_MAX_DMA_SECTIONS)

		dma->len[i] = 0;

	return len;

}

/* This creates an empty DMA, useful for prodding the Host without sending data

 * (ie. when we want to do a read) */

static void empty_dma(struct lguest_dma *dma)

{

	dma->len[0] = 0;

}

/*D:470 Setting up a request is fairly easy: */

static void setup_req(struct blockdev *bd,

		      int type, struct request *req, struct lguest_dma *dma)

{

	/* The type is 1 (write) or 0 (read). */

	bd->lb_page->type = type;

	/* The sector on disk where the read or write starts. */

	bd->lb_page->sector = req->sector;

	/* The result is initialized to 0 (unfinished). */

	bd->lb_page->result = 0;

	/* The current request (so we can end it in the interrupt handler). */

	bd->req = req;

	/* The number of bytes: returned as a side-effect of req_to_dma(),

	 * which packs the block layer's "struct request" into our "struct

	 * lguest_dma" */

	bd->lb_page->bytes = req_to_dma(req, dma);

}

/*D:450 Write is pretty straightforward: we pack the request into a "struct

 * lguest_dma", then use SEND_DMA to send the request. */

static void do_write(struct blockdev *bd, struct request *req)

{

	struct lguest_dma send;

	lguest_send_dma(bd->phys_addr, &send);

}

/* Read is similar to write, except we pack the request into our receive

 * "struct lguest_dma" and send through an empty DMA just to tell the Host that

 * there's a request pending. */

static void do_read(struct blockdev *bd, struct request *req)

{

	struct lguest_dma ping;

	lguest_send_dma(bd->phys_addr, &ping);

}

/*D:440 This where requests come in: we get handed the request queue and are

 * expected to pull a "struct request" off it until we've finished them or

 * we're waiting for a reply: */

static void do_lgb_request(struct request_queue *q)

{

	struct blockdev *bd;

	struct request *req;

again:

	/* This sometimes returns NULL even on the very first time around.  I

	 * wonder if it's something to do with letting elves handle the request

	 * queue... */

	req = elv_next_request(q);

	if (!req)

		return;

	/* We attached the struct blockdev to the disk: get it back */

	bd = req->rq_disk->private_data;

	/* Sometimes we get repeated requests after blk_stop_queue. */

	/* Sometimes we get repeated requests after blk_stop_queue(), but we

	 * can only handle one at a time. */

	if (bd->req)

		return;

	/* We only do reads and writes: no tricky business! */

	if (!blk_fs_request(req)) {

		pr_debug("Got non-command 0x%08x\n", req->cmd_type);

		req->errors++;

	else

		do_read(bd, req);

	/* Wait for interrupt to tell us it's done. */

	/* We've put out the request, so stop any more coming in until we get

	 * an interrupt, which takes us to lgb_irq() to re-enable the queue. */

	blk_stop_queue(q);

}

/*D:430 This is the "struct block_device_operations" we attach to the disk at

 * the end of lguestblk_probe().  It doesn't seem to want much. */

static struct block_device_operations lguestblk_fops = {

	.owner = THIS_MODULE,

};

/*D:425 Setting up a disk device seems to involve a lot of code.  I'm not sure

 * quite why.  I do know that the IDE code sent two or three of the maintainers

 * insane, perhaps this is the fringe of the same disease?

 *

 * As in the console code, the probe function gets handed the generic

 * lguest_device from lguest_bus.c: */

static int lguestblk_probe(struct lguest_device *lgdev)

{

	struct blockdev *bd;

	int err;

	int irqflags = IRQF_SHARED;

	/* First we allocate our own "struct blockdev" and initialize the easy

	 * fields. */

	bd = kmalloc(sizeof(*bd), GFP_KERNEL);

	if (!bd)

		return -ENOMEM;

	bd->req = NULL;

	bd->dma.used_len = 0;

	bd->dma.len[0] = 0;

	/* The descriptor in the lguest_devices array provided by the Host

	 * gives the Guest the physical page number of the device's page. */

	bd->phys_addr = (lguest_devices[lgdev->index].pfn << PAGE_SHIFT);

	/* We use lguest_map() to get a pointer to the device page */

	bd->lb_page = lguest_map(bd->phys_addr, 1);

	if (!bd->lb_page) {

		err = -ENOMEM;

		goto out_free_bd;

	}

	/* We need a major device number: 0 means "assign one dynamically". */

	bd->major = register_blkdev(0, "lguestblk");

	if (bd->major < 0) {

		err = bd->major;

		goto out_unmap;

	}

	/* This allocates a "struct gendisk" where we pack all the information

	 * about the disk which the rest of Linux sees.  We ask for one minor

	 * number; I do wonder if we should be asking for more. */

	bd->disk = alloc_disk(1);

	if (!bd->disk) {

		err = -ENOMEM;

		goto out_unregister_blkdev;

	}

	/* Every disk needs a queue for requests to come in: we set up the

	 * queue with a callback function (the core of our driver) and the lock

	 * to use. */

	bd->disk->queue = blk_init_queue(do_lgb_request, &bd->lock);

	if (!bd->disk->queue) {

		err = -ENOMEM;

		goto out_put_disk;

	}

	/* We can only handle a certain number of sg entries */

	/* We can only handle a certain number of pointers in our SEND_DMA

	 * call, so we set that with blk_queue_max_hw_segments().  This is not

	 * to be confused with blk_queue_max_phys_segments() of course!  I

	 * know, who could possibly confuse the two?

	 *

	 * Well, it's simple to tell them apart: this one seems to work and the

	 * other one didn't. */

	blk_queue_max_hw_segments(bd->disk->queue, LGUEST_MAX_DMA_SECTIONS);

	/* Buffers must not cross page boundaries */

	/* Due to technical limitations of our Host (and simple coding) we

	 * can't have a single buffer which crosses a page boundary.  Tell it

	 * here.  This means that our maximum request size is 16

	 * (LGUEST_MAX_DMA_SECTIONS) pages. */

	blk_queue_segment_boundary(bd->disk->queue, PAGE_SIZE-1);

	/* We name our disk: this becomes the device name when udev does its

	 * magic thing and creates the device node, such as /dev/lgba.

	 * next_block_index is a global which starts at 'a'.  Unfortunately

	 * this simple increment logic means that the 27th disk will be called

	 * "/dev/lgb{".  In that case, I recommend having at least 29 disks, so

	 * your /dev directory will be balanced. */

	sprintf(bd->disk->disk_name, "lgb%c", next_block_index++);

	/* We look to the device descriptor again to see if this device's

	 * interrupts are expected to be random.  If they are, we tell the irq

	 * subsystem.  At the moment this bit is always set. */

	if (lguest_devices[lgdev->index].features & LGUEST_DEVICE_F_RANDOMNESS)

		irqflags |= IRQF_SAMPLE_RANDOM;

	/* Now we have the name and irqflags, we can request the interrupt; we

	 * give it the "struct blockdev" we have set up to pass to lgb_irq()

	 * when there is an interrupt. */

	err = request_irq(bd->irq, lgb_irq, irqflags, bd->disk->disk_name, bd);

	if (err)

		goto out_cleanup_queue;

	/* We bind our one-entry DMA pool to the key for this block device so

	 * the Host can reply to our requests.  The key is equal to the

	 * physical address of the device's page, which is conveniently

	 * unique. */

	err = lguest_bind_dma(bd->phys_addr, &bd->dma, 1, bd->irq);

	if (err)

		goto out_free_irq;

	/* We finish our disk initialization and add the disk to the system. */

	bd->disk->major = bd->major;

	bd->disk->first_minor = 0;

	bd->disk->private_data = bd;

	bd->disk->fops = &lguestblk_fops;

	/* This is initialized to the disk size by the other end. */

	/* This is initialized to the disk size by the Launcher. */

	set_capacity(bd->disk, bd->lb_page->num_sectors);

	add_disk(bd->disk);

	printk(KERN_INFO "%s: device %i at major %d\n",

	       bd->disk->disk_name, lgdev->index, bd->major);

	/* We don't need to keep the "struct blockdev" around, but if we ever

	 * implemented device removal, we'd need this. */

	lgdev->private = bd;

	return 0;

	return err;

}

/*D:410 The boilerplate code for registering the lguest block driver is just

 * like the console: */

static struct lguest_driver lguestblk_drv = {

	.name = "lguestblk",

	.owner = THIS_MODULE,

/* Simple console for lguest.

/*D:300

 * The Guest console driver

 *

 * Copyright (C) 2006 Rusty Russell, IBM Corporation

 * This is a trivial console driver: we use lguest's DMA mechanism to send

 * bytes out, and register a DMA buffer to receive bytes in.  It is assumed to

 * be present and available from the very beginning of boot.

 *

 * Writing console drivers is one of the few remaining Dark Arts in Linux.

 * Fortunately for us, the path of virtual consoles has been well-trodden by

 * the PowerPC folks, who wrote "hvc_console.c" to generically support any

 * virtual console.  We use that infrastructure which only requires us to write

 * the basic put_chars and get_chars functions and call the right register

 * functions.

 :*/

/* Copyright (C) 2006 Rusty Russell, IBM Corporation

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

#include <linux/lguest_bus.h>

#include "hvc_console.h"

/*D:340 This is our single console input buffer, with associated "struct

 * lguest_dma" referring to it.  Note the 0-terminated length array, and the

 * use of physical address for the buffer itself. */

static char inbuf[256];

static struct lguest_dma cons_input = { .used_len = 0,

					.addr[0] = __pa(inbuf),

					.len[0] = sizeof(inbuf),

					.len[1] = 0 };

/*D:310 The put_chars() callback is pretty straightforward.

 *

 * First we put the pointer and length in a "struct lguest_dma": we only have

 * one pointer, so we set the second length to 0.  Then we use SEND_DMA to send

 * the data to (Host) buffers attached to the console key.  Usually a device's

 * key is a physical address within the device's memory, but because the

 * console device doesn't have any associated physical memory, we use the

 * LGUEST_CONSOLE_DMA_KEY constant (aka 0). */

static int put_chars(u32 vtermno, const char *buf, int count)

{

	struct lguest_dma dma;

	/* FIXME: what if it's over a page boundary? */

	/* FIXME: DMA buffers in a "struct lguest_dma" are not allowed

	 * to go over page boundaries.  This never seems to happen,

	 * but if it did we'd need to fix this code. */

	dma.len[0] = count;

	dma.len[1] = 0;

	dma.addr[0] = __pa(buf);

	lguest_send_dma(LGUEST_CONSOLE_DMA_KEY, &dma);

	/* We're expected to return the amount of data we wrote: all of it. */

	return count;

}

/*D:350 get_chars() is the callback from the hvc_console infrastructure when

 * an interrupt is received.

 *

 * Firstly we see if our buffer has been filled: if not, we return.  The rest

 * of the code deals with the fact that the hvc_console() infrastructure only

 * asks us for 16 bytes at a time.  We keep a "cons_offset" variable for

 * partially-read buffers. */

static int get_chars(u32 vtermno, char *buf, int count)

{

	static int cons_offset;

	/* Nothing left to see here... */

	if (!cons_input.used_len)

		return 0;

	/* You want more than we have to give?  Well, try wanting less! */

	if (cons_input.used_len - cons_offset < count)

		count = cons_input.used_len - cons_offset;

	/* Copy across to their buffer and increment offset. */

	memcpy(buf, inbuf + cons_offset, count);

	cons_offset += count;

	/* Finished?  Zero offset, and reset cons_input so Host will use it

	 * again. */

	if (cons_offset == cons_input.used_len) {

		cons_offset = 0;

		cons_input.used_len = 0;

	}

	return count;

}

/*:*/

static struct hv_ops lguest_cons = {

	.get_chars = get_chars,

	.put_chars = put_chars,

};

/*D:320 Console drivers are initialized very early so boot messages can go

 * out.  At this stage, the console is output-only.  Our driver checks we're a

 * Guest, and if so hands hvc_instantiate() the console number (0), priority

 * (0), and the struct hv_ops containing the put_chars() function. */

static int __init cons_init(void)

{

	if (strcmp(paravirt_ops.name, "lguest") != 0)

}

console_initcall(cons_init);

/*D:370 To set up and manage our virtual console, we call hvc_alloc() and

 * stash the result in the private pointer of the "struct lguest_device".

 * Since we never remove the console device we never need this pointer again,

 * but using ->private is considered good form, and you never know who's going

 * to copy your driver.

 *

 * Once the console is set up, we bind our input buffer ready for input. */

static int lguestcons_probe(struct lguest_device *lgdev)

{

	int err;

	/* The first argument of hvc_alloc() is the virtual console number, so

	 * we use zero.  The second argument is the interrupt number.

	 *

	 * The third argument is a "struct hv_ops" containing the put_chars()

	 * and get_chars() pointers.  The final argument is the output buffer

	 * size: we use 256 and expect the Host to have room for us to send

	 * that much. */

	lgdev->private = hvc_alloc(0, lgdev_irq(lgdev), &lguest_cons, 256);

	if (IS_ERR(lgdev->private))

		return PTR_ERR(lgdev->private);

	/* We bind a single DMA buffer at key LGUEST_CONSOLE_DMA_KEY.

	 * "cons_input" is that statically-initialized global DMA buffer we saw

	 * above, and we also give the interrupt we want. */

	err = lguest_bind_dma(LGUEST_CONSOLE_DMA_KEY, &cons_input, 1,

			      lgdev_irq(lgdev));

	if (err)

		printk("lguest console: failed to bind buffer.\n");

	return err;

}

/* Note the use of lgdev_irq() for the interrupt number.  We tell hvc_alloc()

 * to expect input when this interrupt is triggered, and then tell

 * lguest_bind_dma() that is the interrupt to send us when input comes in. */

/*D:360 From now on the console driver follows standard Guest driver form:

 * register_lguest_driver() registers the device type and probe function, and

 * the probe function sets up the device.

 *

 * The standard "struct lguest_driver": */

static struct lguest_driver lguestcons_drv = {

	.name = "lguestcons",

	.owner = THIS_MODULE,

	.probe = lguestcons_probe,

};

/* The standard init function */

static int __init hvc_lguest_init(void)

{

	return register_lguest_driver(&lguestcons_drv);

	__ATTR_NULL

};

/*D:130 The generic bus infrastructure requires a function which says whether a

 * device matches a driver.  For us, it is simple: "struct lguest_driver"

 * contains a "device_type" field which indicates what type of device it can

 * handle, so we just cast the args and compare: */

static int lguest_dev_match(struct device *_dev, struct device_driver *_drv)

{

	struct lguest_device *dev = container_of(_dev,struct lguest_device,dev);

	return (drv->device_type == lguest_devices[dev->index].type);

}

/*:*/

struct lguest_bus {

	struct bus_type bus;

	}

};

/*D:140 This is the callback which occurs once the bus infrastructure matches

 * up a device and driver, ie. in response to add_lguest_device() calling

 * device_register(), or register_lguest_driver() calling driver_register().

 *

 * At the moment it's always the latter: the devices are added first, since

 * scan_devices() is called from a "core_initcall", and the drivers themselves

 * called later as a normal "initcall".  But it would work the other way too.

 *

 * So now we have the happy couple, we add the status bit to indicate that we

 * found a driver.  If the driver truly loves the device, it will return

 * happiness from its probe function (ok, perhaps this wasn't my greatest

 * analogy), and we set the final "driver ok" bit so the Host sees it's all

 * green. */

static int lguest_dev_probe(struct device *_dev)

{

	int ret;

	return ret;

}

/* The last part of the bus infrastructure is the function lguest drivers use

 * to register themselves.  Firstly, we do nothing if there's no lguest bus

 * (ie. this is not a Guest), otherwise we fill in the embedded generic "struct

 * driver" fields and call the generic driver_register(). */

int register_lguest_driver(struct lguest_driver *drv)

{

	if (!lguest_devices)

	return driver_register(&drv->drv);

}

/* At the moment we build all the drivers into the kernel because they're so

 * simple: 8144 bytes for all three of them as I type this.  And as the console

 * really needs to be built in, it's actually only 3527 bytes for the network

 * and block drivers.

 *

 * If they get complex it will make sense for them to be modularized, so we

 * need to explicitly export the symbol.

 *

 * I don't think non-GPL modules make sense, so it's a GPL-only export.

 */

EXPORT_SYMBOL_GPL(register_lguest_driver);

/*D:120 This is the core of the lguest bus: actually adding a new device.

 * It's a separate function because it's neater that way, and because an

 * earlier version of the code supported hotplug and unplug.  They were removed

 * early on because they were never used.

 *

 * As Andrew Tridgell says, "Untested code is buggy code".

 *

 * It's worth reading this carefully: we start with an index into the array of

 * "struct lguest_device_desc"s indicating the device which is new: */

static void add_lguest_device(unsigned int index)

{

	struct lguest_device *new;

	/* Each "struct lguest_device_desc" has a "status" field, which the

	 * Guest updates as the device is probed.  In the worst case, the Host

	 * can look at these bits to tell what part of device setup failed,

	 * even if the console isn't available. */

	lguest_devices[index].status |= LGUEST_DEVICE_S_ACKNOWLEDGE;

	new = kmalloc(sizeof(struct lguest_device), GFP_KERNEL);

	if (!new) {

		return;

	}

	/* The "struct lguest_device" setup is pretty straight-forward example

	 * code. */

	new->index = index;

	new->private = NULL;

	memset(&new->dev, 0, sizeof(new->dev));

	new->dev.parent = &lguest_bus.dev;

	new->dev.bus = &lguest_bus.bus;

	sprintf(new->dev.bus_id, "%u", index);

	/* device_register() causes the bus infrastructure to look for a

	 * matching driver. */

	if (device_register(&new->dev) != 0) {

		printk(KERN_EMERG "Cannot register lguest device %u\n", index);

		lguest_devices[index].status |= LGUEST_DEVICE_S_FAILED;

	}

}

/*D:110 scan_devices() simply iterates through the device array.  The type 0

 * is reserved to mean "no device", and anything else means we have found a

 * device: add it. */

static void scan_devices(void)

{

	unsigned int i;

			add_lguest_device(i);

}

/*D:100 Fairly early in boot, lguest_bus_init() is called to set up the lguest

 * bus.  We check that we are a Guest by checking paravirt_ops.name: there are

 * other ways of checking, but this seems most obvious to me.

 *

 * So we can access the array of "struct lguest_device_desc"s easily, we map

 * that memory and store the pointer in the global "lguest_devices".  Then we

 * register the bus with the core.  Doing two registrations seems clunky to me,

 * but it seems to be the correct sysfs incantation.

 *

 * Finally we call scan_devices() which adds all the devices found in the

 * "struct lguest_device_desc" array. */

static int __init lguest_bus_init(void)

{

	if (strcmp(paravirt_ops.name, "lguest") != 0)

		return 0;

	/* Devices are in page above top of "normal" mem. */

	/* Devices are in a single page above top of "normal" mem */

	lguest_devices = lguest_map(max_pfn<<PAGE_SHIFT, 1);

	if (bus_register(&lguest_bus.bus) != 0

	scan_devices();

	return 0;

}

/* Do this after core stuff, before devices. */

postcore_initcall(lguest_bus_init);

	void *private;

};

/* By convention, each device can use irq index+1 if it wants to. */

/*D:380 Since interrupt numbers are arbitrary, we use a convention: each device

 * can use the interrupt number corresponding to its index.  The +1 is because

 * interrupt 0 is not usable (it's actually the timer interrupt). */

static inline int lgdev_irq(const struct lguest_device *dev)

{

	return dev->index + 1;

}

/*:*/

/* dma args must not be vmalloced! */

void lguest_send_dma(unsigned long key, struct lguest_dma *dma);