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Commit e2c97843 authored by Rusty Russell's avatar Rusty Russell Committed by Linus Torvalds
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lguest: documentation III: Drivers 

Documentation: The Drivers
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b2b47c21
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drivers/block/lguest_blk.c
View file @ e2c97843
/* 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
......@@ -25,27 +31,50 @@
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))
......@@ -55,30 +84,62 @@ static void end_entire_request(struct request *req, int uptodate)
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;
......@@ -87,8 +148,13 @@ static unsigned int req_to_dma(struct request *req, struct lguest_dma *dma)
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;
......@@ -96,26 +162,39 @@ static unsigned int req_to_dma(struct request *req, struct lguest_dma *dma)
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;
......@@ -126,6 +205,9 @@ static void do_write(struct blockdev *bd, struct request *req)
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;
......@@ -137,21 +219,30 @@ static void do_read(struct blockdev *bd, struct request *req)
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++;
......@@ -164,20 +255,31 @@ static void do_lgb_request(struct request_queue *q)
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;
......@@ -187,59 +289,100 @@ static int lguestblk_probe(struct lguest_device *lgdev)
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;
......@@ -258,6 +401,8 @@ static int lguestblk_probe(struct lguest_device *lgdev)
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,
......
drivers/char/hvc_lguest.c
View file @ e2c97843
/* 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
......@@ -21,49 +34,81 @@
#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)
......@@ -73,21 +118,46 @@ static int __init cons_init(void)
}
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,
......@@ -95,6 +165,7 @@ static struct lguest_driver lguestcons_drv = {
.probe = lguestcons_probe,
};
/* The standard init function */
static int __init hvc_lguest_init(void)
{
return register_lguest_driver(&lguestcons_drv);
......
drivers/lguest/lguest_bus.c
View file @ e2c97843
......@@ -46,6 +46,10 @@ static struct device_attribute lguest_dev_attrs[] = {
__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);
......@@ -53,6 +57,7 @@ static int lguest_dev_match(struct device *_dev, struct device_driver *_drv)
return (drv->device_type == lguest_devices[dev->index].type);
}
/*:*/
struct lguest_bus {
struct bus_type bus;
......@@ -71,11 +76,24 @@ static struct lguest_bus lguest_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;
struct lguest_device *dev = container_of(_dev,struct lguest_device,dev);
struct lguest_driver *drv = container_of(dev->dev.driver,
struct lguest_device*dev = container_of(_dev,struct lguest_device,dev);
struct lguest_driver*drv = container_of(dev->dev.driver,
struct lguest_driver, drv);
lguest_devices[dev->index].status |= LGUEST_DEVICE_S_DRIVER;
......@@ -85,6 +103,10 @@ static int lguest_dev_probe(struct device *_dev)
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)
......@@ -97,12 +119,36 @@ int register_lguest_driver(struct lguest_driver *drv)
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) {
......@@ -111,12 +157,17 @@ static void add_lguest_device(unsigned int index)
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;
......@@ -124,6 +175,9 @@ static void add_lguest_device(unsigned int index)
}
}
/*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;
......@@ -133,12 +187,23 @@ static void scan_devices(void)
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
......@@ -148,4 +213,5 @@ static int __init lguest_bus_init(void)
scan_devices();
return 0;
}
/* Do this after core stuff, before devices. */
postcore_initcall(lguest_bus_init);
drivers/net/lguest_net.c
View file @ e2c97843
/* A simple network driver for lguest.
/*D:500
* The Guest network driver.
*
* Copyright 2006 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
* This is very simple a virtual network driver, and our last Guest driver.
* The only trick is that it can talk directly to multiple other recipients
* (ie. other Guests on the same network). It can also be used with only the
* Host on the network.
:*/
/* 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
......@@ -28,23 +35,28 @@
#define MAX_LANS 4
#define NUM_SKBS 8
/*D:530 The "struct lguestnet_info" contains all the information we need to
* know about the network device. */
struct lguestnet_info
{
/* The shared page(s). */
/* The mapped device page(s) (an array of "struct lguest_net"). */
struct lguest_net *peer;
/* The physical address of the device page(s) */
unsigned long peer_phys;
/* The size of the device page(s). */
unsigned long mapsize;
/* The lguest_device I come from */
struct lguest_device *lgdev;
/* My peerid. */
/* My peerid (ie. my slot in the array). */
unsigned int me;
/* Receive queue. */
/* Receive queue: the network packets waiting to be filled. */
struct sk_buff *skb[NUM_SKBS];
struct lguest_dma dma[NUM_SKBS];
};
/*:*/
/* How many bytes left in this page. */
static unsigned int rest_of_page(void *data)
......@@ -52,39 +64,82 @@ static unsigned int rest_of_page(void *data)
return PAGE_SIZE - ((unsigned long)data % PAGE_SIZE);
}
/* Simple convention: offset 4 * peernum. */
/*D:570 Each peer (ie. Guest or Host) on the network binds their receive
* buffers to a different key: we simply use the physical address of the
* device's memory page plus the peer number. The Host insists that all keys
* be a multiple of 4, so we multiply the peer number by 4. */
static unsigned long peer_key(struct lguestnet_info *info, unsigned peernum)
{
return info->peer_phys + 4 * peernum;
}
/* This is the routine which sets up a "struct lguest_dma" to point to a
* network packet, similar to req_to_dma() in lguest_blk.c. The structure of a
* "struct sk_buff" has grown complex over the years: it consists of a "head"
* linear section pointed to by "skb->data", and possibly an array of
* "fragments" in the case of a non-linear packet.
*
* Our receive buffers don't use fragments at all but outgoing skbs might, so
* we handle it. */
static void skb_to_dma(const struct sk_buff *skb, unsigned int headlen,
struct lguest_dma *dma)
{
unsigned int i, seg;
/* First, we put the linear region into the "struct lguest_dma". Each
* entry can't go over a page boundary, so even though all our packets
* are 1514 bytes or less, we might need to use two entries here: */
for (i = seg = 0; i < headlen; seg++, i += rest_of_page(skb->data+i)) {
dma->addr[seg] = virt_to_phys(skb->data + i);
dma->len[seg] = min((unsigned)(headlen - i),
rest_of_page(skb->data + i));
}
/* Now we handle the fragments: at least they're guaranteed not to go
* over a page. skb_shinfo(skb) returns a pointer to the structure
* which tells us about the number of fragments and the fragment
* array. */
for (i = 0; i < skb_shinfo(skb)->nr_frags; i++, seg++) {
const skb_frag_t *f = &skb_shinfo(skb)->frags[i];
/* Should not happen with MTU less than 64k - 2 * PAGE_SIZE. */
if (seg == LGUEST_MAX_DMA_SECTIONS) {
/* We will end up sending a truncated packet should
* this ever happen. Plus, a cool log message! */
printk("Woah dude! Megapacket!\n");
break;
}
dma->addr[seg] = page_to_phys(f->page) + f->page_offset;
dma->len[seg] = f->size;
}
/* If after all that we didn't use the entire "struct lguest_dma"
* array, we terminate it with a 0 length. */
if (seg < LGUEST_MAX_DMA_SECTIONS)
dma->len[seg] = 0;
}
/* We overload multicast bit to show promiscuous mode. */
/*
* Packet transmission.
*
* Our packet transmission is a little unusual. A real network card would just
* send out the packet and leave the receivers to decide if they're interested.
* Instead, we look through the network device memory page and see if any of
* the ethernet addresses match the packet destination, and if so we send it to
* that Guest.
*
* This is made a little more complicated in two cases. The first case is
* broadcast packets: for that we send the packet to all Guests on the network,
* one at a time. The second case is "promiscuous" mode, where a Guest wants
* to see all the packets on the network. We need a way for the Guest to tell
* us it wants to see all packets, so it sets the "multicast" bit on its
* published MAC address, which is never valid in a real ethernet address.
*/
#define PROMISC_BIT 0x01
/* This is the callback which is summoned whenever the network device's
* multicast or promiscuous state changes. If the card is in promiscuous mode,
* we advertise that in our ethernet address in the device's memory. We do the
* same if Linux wants any or all multicast traffic. */
static void lguestnet_set_multicast(struct net_device *dev)
{
struct lguestnet_info *info = netdev_priv(dev);
......@@ -95,11 +150,14 @@ static void lguestnet_set_multicast(struct net_device *dev)
info->peer[info->me].mac[0] &= ~PROMISC_BIT;
}
/* A simple test function to see if a peer wants to see all packets.*/
static int promisc(struct lguestnet_info *info, unsigned int peer)
{
return info->peer[peer].mac[0] & PROMISC_BIT;
}
/* Another simple function to see if a peer's advertised ethernet address
* matches a packet's destination ethernet address. */
static int mac_eq(const unsigned char mac[ETH_ALEN],
struct lguestnet_info *info, unsigned int peer)
{
......@@ -109,6 +167,8 @@ static int mac_eq(const unsigned char mac[ETH_ALEN],
return memcmp(mac+1, info->peer[peer].mac+1, ETH_ALEN-1) == 0;
}
/* This is the function which actually sends a packet once we've decided a
* peer wants it: */
static void transfer_packet(struct net_device *dev,
struct sk_buff *skb,
unsigned int peernum)
......@@ -116,76 +176,134 @@ static void transfer_packet(struct net_device *dev,
struct lguestnet_info *info = netdev_priv(dev);
struct lguest_dma dma;
/* We use our handy "struct lguest_dma" packing function to prepare
* the skb for sending. */
skb_to_dma(skb, skb_headlen(skb), &dma);
pr_debug("xfer length %04x (%u)\n", htons(skb->len), skb->len);
/* This is the actual send call which copies the packet. */
lguest_send_dma(peer_key(info, peernum), &dma);
/* Check that the entire packet was transmitted. If not, it could mean
* that the other Guest registered a short receive buffer, but this
* driver should never do that. More likely, the peer is dead. */
if (dma.used_len != skb->len) {
dev->stats.tx_carrier_errors++;
pr_debug("Bad xfer to peer %i: %i of %i (dma %p/%i)\n",
peernum, dma.used_len, skb->len,
(void *)dma.addr[0], dma.len[0]);
} else {
/* On success we update the stats. */
dev->stats.tx_bytes += skb->len;
dev->stats.tx_packets++;
}
}
/* Another helper function to tell is if a slot in the device memory is unused.
* Since we always set the Local Assignment bit in the ethernet address, the
* first byte can never be 0. */
static int unused_peer(const struct lguest_net peer[], unsigned int num)
{
return peer[num].mac[0] == 0;
}
/* Finally, here is the routine which handles an outgoing packet. It's called
* "start_xmit" for traditional reasons. */
static int lguestnet_start_xmit(struct sk_buff *skb, struct net_device *dev)
{
unsigned int i;
int broadcast;
struct lguestnet_info *info = netdev_priv(dev);
/* Extract the destination ethernet address from the packet. */
const unsigned char *dest = ((struct ethhdr *)skb->data)->h_dest;
pr_debug("%s: xmit %02x:%02x:%02x:%02x:%02x:%02x\n",
dev->name, dest[0],dest[1],dest[2],dest[3],dest[4],dest[5]);
/* If it's a multicast packet, we broadcast to everyone. That's not
* very efficient, but there are very few applications which actually
* use multicast, which is a shame really.
*
* As etherdevice.h points out: "By definition the broadcast address is
* also a multicast address." So we don't have to test for broadcast
* packets separately. */
broadcast = is_multicast_ether_addr(dest);
/* Look through all the published ethernet addresses to see if we
* should send this packet. */
for (i = 0; i < info->mapsize/sizeof(struct lguest_net); i++) {
/* We don't send to ourselves (we actually can't SEND_DMA to
* ourselves anyway), and don't send to unused slots.*/
if (i == info->me || unused_peer(info->peer, i))
continue;
/* If it's broadcast we send it. If they want every packet we
* send it. If the destination matches their address we send
* it. Otherwise we go to the next peer. */
if (!broadcast && !promisc(info, i) && !mac_eq(dest, info, i))
continue;
pr_debug("lguestnet %s: sending from %i to %i\n",
dev->name, info->me, i);
/* Our routine which actually does the transfer. */
transfer_packet(dev, skb, i);
}
/* An xmit routine is expected to dispose of the packet, so we do. */
dev_kfree_skb(skb);
/* As per kernel convention, 0 means success. This is why I love
* networking: even if we never sent to anyone, that's still
* success! */
return 0;
}
/* Find a new skb to put in this slot in shared mem. */
/*D:560
* Packet receiving.
*
* First, here's a helper routine which fills one of our array of receive
* buffers: */
static int fill_slot(struct net_device *dev, unsigned int slot)
{
struct lguestnet_info *info = netdev_priv(dev);
/* Try to create and register a new one. */
/* We can receive ETH_DATA_LEN (1500) byte packets, plus a standard
* ethernet header of ETH_HLEN (14) bytes. */
info->skb[slot] = netdev_alloc_skb(dev, ETH_HLEN + ETH_DATA_LEN);
if (!info->skb[slot]) {
printk("%s: could not fill slot %i\n", dev->name, slot);
return -ENOMEM;
}
/* skb_to_dma() is a helper which sets up the "struct lguest_dma" to
* point to the data in the skb: we also use it for sending out a
* packet. */
skb_to_dma(info->skb[slot], ETH_HLEN + ETH_DATA_LEN, &info->dma[slot]);
/* This is a Write Memory Barrier: it ensures that the entry in the
* receive buffer array is written *before* we set the "used_len" entry
* to 0. If the Host were looking at the receive buffer array from a
* different CPU, it could potentially see "used_len = 0" and not see
* the updated receive buffer information. This would be a horribly
* nasty bug, so make sure the compiler and CPU know this has to happen
* first. */
wmb();
/* Now we tell hypervisor it can use the slot. */
/* Writing 0 to "used_len" tells the Host it can use this receive
* buffer now. */
info->dma[slot].used_len = 0;
return 0;
}
/* This is the actual receive routine. When we receive an interrupt from the
* Host to tell us a packet has been delivered, we arrive here: */
static irqreturn_t lguestnet_rcv(int irq, void *dev_id)
{
struct net_device *dev = dev_id;
struct lguestnet_info *info = netdev_priv(dev);
unsigned int i, done = 0;
/* Look through our entire receive array for an entry which has data
* in it. */
for (i = 0; i < ARRAY_SIZE(info->dma); i++) {
unsigned int length;
struct sk_buff *skb;
......@@ -194,10 +312,16 @@ static irqreturn_t lguestnet_rcv(int irq, void *dev_id)
if (length == 0)
continue;
/* We've found one! Remember the skb (we grabbed the length
* above), and immediately refill the slot we've taken it
* from. */
done++;
skb = info->skb[i];
fill_slot(dev, i);
/* This shouldn't happen: micropackets could be sent by a
* badly-behaved Guest on the network, but the Host will never
* stuff more data in the buffer than the buffer length. */
if (length < ETH_HLEN || length > ETH_HLEN + ETH_DATA_LEN) {
pr_debug(KERN_WARNING "%s: unbelievable skb len: %i\n",
dev->name, length);
......@@ -205,36 +329,72 @@ static irqreturn_t lguestnet_rcv(int irq, void *dev_id)
continue;
}
/* skb_put(), what a great function! I've ranted about this
* function before (http://lkml.org/lkml/1999/9/26/24). You
* call it after you've added data to the end of an skb (in
* this case, it was the Host which wrote the data). */
skb_put(skb, length);
/* The ethernet header contains a protocol field: we use the
* standard helper to extract it, and place the result in
* skb->protocol. The helper also sets up skb->pkt_type and
* eats up the ethernet header from the front of the packet. */
skb->protocol = eth_type_trans(skb, dev);
/* This is a reliable transport. */
/* If this device doesn't need checksums for sending, we also
* don't need to check the packets when they come in. */
if (dev->features & NETIF_F_NO_CSUM)
skb->ip_summed = CHECKSUM_UNNECESSARY;
/* As a last resort for debugging the driver or the lguest I/O
* subsystem, you can uncomment the "#define DEBUG" at the top
* of this file, which turns all the pr_debug() into printk()
* and floods the logs. */
pr_debug("Receiving skb proto 0x%04x len %i type %i\n",
ntohs(skb->protocol), skb->len, skb->pkt_type);
/* Update the packet and byte counts (visible from ifconfig,
* and good for debugging). */
dev->stats.rx_bytes += skb->len;
dev->stats.rx_packets++;
/* Hand our fresh network packet into the stack's "network
* interface receive" routine. That will free the packet
* itself when it's finished. */
netif_rx(skb);
}
/* If we found any packets, we assume the interrupt was for us. */
return done ? IRQ_HANDLED : IRQ_NONE;
}
/*D:550 This is where we start: when the device is brought up by dhcpd or
* ifconfig. At this point we advertise our MAC address to the rest of the
* network, and register receive buffers ready for incoming packets. */
static int lguestnet_open(struct net_device *dev)
{
int i;
struct lguestnet_info *info = netdev_priv(dev);
/* Set up our MAC address */
/* Copy our MAC address into the device page, so others on the network
* can find us. */
memcpy(info->peer[info->me].mac, dev->dev_addr, ETH_ALEN);
/* Turn on promisc mode if needed */
/* We might already be in promisc mode (dev->flags & IFF_PROMISC). Our
* set_multicast callback handles this already, so we call it now. */
lguestnet_set_multicast(dev);
/* Allocate packets and put them into our "struct lguest_dma" array.
* If we fail to allocate all the packets we could still limp along,
* but it's a sign of real stress so we should probably give up now. */
for (i = 0; i < ARRAY_SIZE(info->dma); i++) {
if (fill_slot(dev, i) != 0)
goto cleanup;
}
/* Finally we tell the Host where our array of "struct lguest_dma"
* receive buffers is, binding it to the key corresponding to the
* device's physical memory plus our peerid. */
if (lguest_bind_dma(peer_key(info,info->me), info->dma,
NUM_SKBS, lgdev_irq(info->lgdev)) != 0)
goto cleanup;
......@@ -245,22 +405,29 @@ static int lguestnet_open(struct net_device *dev)
dev_kfree_skb(info->skb[i]);
return -ENOMEM;
}
/*:*/
/* The close routine is called when the device is no longer in use: we clean up
* elegantly. */
static int lguestnet_close(struct net_device *dev)
{
unsigned int i;
struct lguestnet_info *info = netdev_priv(dev);
/* Clear all trace: others might deliver packets, we'll ignore it. */
/* Clear all trace of our existence out of the device memory by setting
* the slot which held our MAC address to 0 (unused). */
memset(&info->peer[info->me], 0, sizeof(info->peer[info->me]));
/* Deregister sg lists. */
/* Unregister our array of receive buffers */
lguest_unbind_dma(peer_key(info, info->me), info->dma);
for (i = 0; i < ARRAY_SIZE(info->dma); i++)
dev_kfree_skb(info->skb[i]);
return 0;
}
/*D:510 The network device probe function is basically a standard ethernet
* device setup. It reads the "struct lguest_device_desc" and sets the "struct
* net_device". Oh, the line-by-line excitement! Let's skip over it. :*/
static int lguestnet_probe(struct lguest_device *lgdev)
{
int err, irqf = IRQF_SHARED;
......@@ -290,10 +457,16 @@ static int lguestnet_probe(struct lguest_device *lgdev)
dev->stop = lguestnet_close;
dev->hard_start_xmit = lguestnet_start_xmit;
/* Turning on/off promisc will call dev->set_multicast_list.
* We don't actually support multicast yet */
/* We don't actually support multicast yet, but turning on/off
* promisc also calls dev->set_multicast_list. */
dev->set_multicast_list = lguestnet_set_multicast;
SET_NETDEV_DEV(dev, &lgdev->dev);
/* The network code complains if you have "scatter-gather" capability
* if you don't also handle checksums (it seem that would be
* "illogical"). So we use a lie of omission and don't tell it that we
* can handle scattered packets unless we also don't want checksums,
* even though to us they're completely independent. */
if (desc->features & LGUEST_NET_F_NOCSUM)
dev->features = NETIF_F_SG|NETIF_F_NO_CSUM;
......@@ -325,6 +498,9 @@ static int lguestnet_probe(struct lguest_device *lgdev)
}
pr_debug("lguestnet: registered device %s\n", dev->name);
/* Finally, we put the "struct net_device" in the generic "struct
* lguest_device"s private pointer. Again, it's not necessary, but
* makes sure the cool kernel kids don't tease us. */
lgdev->private = dev;
return 0;
......@@ -352,3 +528,11 @@ module_init(lguestnet_init);
MODULE_DESCRIPTION("Lguest network driver");
MODULE_LICENSE("GPL");
/*D:580
* This is the last of the Drivers, and with this we have covered the many and
* wonderous and fine (and boring) details of the Guest.
*
* "make Launcher" beckons, where we answer questions like "Where do Guests
* come from?", and "What do you do when someone asks for optimization?"
*/
include/linux/lguest_bus.h
View file @ e2c97843
......@@ -15,11 +15,14 @@ struct lguest_device {
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);
......
include/linux/lguest_launcher.h
View file @ e2c97843
......@@ -9,14 +9,45 @@
/* How many devices? Assume each one wants up to two dma arrays per device. */
#define LGUEST_MAX_DEVICES (LGUEST_MAX_DMA/2)
/*D:200
* Lguest I/O
*
* The lguest I/O mechanism is the only way Guests can talk to devices. There
* are two hypercalls involved: SEND_DMA for output and BIND_DMA for input. In
* each case, "struct lguest_dma" describes the buffer: this contains 16
* addr/len pairs, and if there are fewer buffer elements the len array is
* terminated with a 0.
*
* I/O is organized by keys: BIND_DMA attaches buffers to a particular key, and
* SEND_DMA transfers to buffers bound to particular key. By convention, keys
* correspond to a physical address within the device's page. This means that
* devices will never accidentally end up with the same keys, and allows the
* Host use The Futex Trick (as we'll see later in our journey).
*
* SEND_DMA simply indicates a key to send to, and the physical address of the
* "struct lguest_dma" to send. The Host will write the number of bytes
* transferred into the "struct lguest_dma"'s used_len member.
*
* BIND_DMA indicates a key to bind to, a pointer to an array of "struct
* lguest_dma"s ready for receiving, the size of that array, and an interrupt
* to trigger when data is received. The Host will only allow transfers into
* buffers with a used_len of zero: it then sets used_len to the number of
* bytes transferred and triggers the interrupt for the Guest to process the
* new input. */
struct lguest_dma
{
/* 0 if free to be used, filled by hypervisor. */
/* 0 if free to be used, filled by the Host. */
u32 used_len;
unsigned long addr[LGUEST_MAX_DMA_SECTIONS];
u16 len[LGUEST_MAX_DMA_SECTIONS];
};
/*:*/
/*D:460 This is the layout of a block device memory page. The Launcher sets up
* the num_sectors initially to tell the Guest the size of the disk. The Guest
* puts the type, sector and length of the request in the first three fields,
* then DMAs to the Host. The Host processes the request, sets up the result,
* then DMAs back to the Guest. */
struct lguest_block_page
{
/* 0 is a read, 1 is a write. */
......@@ -28,27 +59,47 @@ struct lguest_block_page
u32 num_sectors; /* Disk length = num_sectors * 512 */
};
/* There is a shared page of these. */
/*D:520 The network device is basically a memory page where all the Guests on
* the network publish their MAC (ethernet) addresses: it's an array of "struct
* lguest_net": */
struct lguest_net
{
/* Simply the mac address (with multicast bit meaning promisc). */
unsigned char mac[6];
};
/*:*/
/* Where the Host expects the Guest to SEND_DMA console output to. */
#define LGUEST_CONSOLE_DMA_KEY 0
/* We have a page of these descriptors in the lguest_device page. */
/*D:010
* Drivers
*
* The Guest needs devices to do anything useful. Since we don't let it touch
* real devices (think of the damage it could do!) we provide virtual devices.
* We could emulate a PCI bus with various devices on it, but that is a fairly
* complex burden for the Host and suboptimal for the Guest, so we have our own
* "lguest" bus and simple drivers.
*
* Devices are described by an array of LGUEST_MAX_DEVICES of these structs,
* placed by the Launcher just above the top of physical memory:
*/
struct lguest_device_desc {
/* The device type: console, network, disk etc. */
u16 type;
#define LGUEST_DEVICE_T_CONSOLE 1
#define LGUEST_DEVICE_T_NET 2
#define LGUEST_DEVICE_T_BLOCK 3
/* The specific features of this device: these depends on device type
* except for LGUEST_DEVICE_F_RANDOMNESS. */
u16 features;
#define LGUEST_NET_F_NOCSUM 0x4000 /* Don't bother checksumming */
#define LGUEST_DEVICE_F_RANDOMNESS 0x8000 /* IRQ is fairly random */
/* This is how the Guest reports status of the device: the Host can set
* LGUEST_DEVICE_S_REMOVED to indicate removal, but the rest are only
* ever manipulated by the Guest, and only ever set. */
u16 status;
/* 256 and above are device specific. */
#define LGUEST_DEVICE_S_ACKNOWLEDGE 1 /* We have seen device. */
......@@ -58,9 +109,12 @@ struct lguest_device_desc {
#define LGUEST_DEVICE_S_REMOVED_ACK 16 /* Driver has been told. */
#define LGUEST_DEVICE_S_FAILED 128 /* Something actually failed */
/* Each device exists somewhere in Guest physical memory, over some
* number of pages. */
u16 num_pages;
u32 pfn;
};
/*:*/
/* Write command first word is a request. */
enum lguest_req
......
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