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Diffstat (limited to 'drivers/block/lguest_blk.c')
-rw-r--r--drivers/block/lguest_blk.c421
1 files changed, 0 insertions, 421 deletions
diff --git a/drivers/block/lguest_blk.c b/drivers/block/lguest_blk.c
deleted file mode 100644
index fa8e42341b87..000000000000
--- a/drivers/block/lguest_blk.c
+++ /dev/null
@@ -1,421 +0,0 @@
1/*D:400
2 * The Guest block driver
3 *
4 * This is a simple block driver, which appears as /dev/lgba, lgbb, lgbc etc.
5 * The mechanism is simple: we place the information about the request in the
6 * device page, then use SEND_DMA (containing the data for a write, or an empty
7 * "ping" DMA for a read).
8 :*/
9/* Copyright 2006 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
10 *
11 * This program is free software; you can redistribute it and/or modify
12 * it under the terms of the GNU General Public License as published by
13 * the Free Software Foundation; either version 2 of the License, or
14 * (at your option) any later version.
15 *
16 * This program is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 * GNU General Public License for more details.
20 *
21 * You should have received a copy of the GNU General Public License
22 * along with this program; if not, write to the Free Software
23 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
24 */
25//#define DEBUG
26#include <linux/init.h>
27#include <linux/types.h>
28#include <linux/blkdev.h>
29#include <linux/interrupt.h>
30#include <linux/lguest_bus.h>
31
32static char next_block_index = 'a';
33
34/*D:420 Here is the structure which holds all the information we need about
35 * each Guest block device.
36 *
37 * I'm sure at this stage, you're wondering "hey, where was the adventure I was
38 * promised?" and thinking "Rusty sucks, I shall say nasty things about him on
39 * my blog". I think Real adventures have boring bits, too, and you're in the
40 * middle of one. But it gets better. Just not quite yet. */
41struct blockdev
42{
43 /* The block queue infrastructure wants a spinlock: it is held while it
44 * calls our block request function. We grab it in our interrupt
45 * handler so the responses don't mess with new requests. */
46 spinlock_t lock;
47
48 /* The disk structure registered with kernel. */
49 struct gendisk *disk;
50
51 /* The major device number for this disk, and the interrupt. We only
52 * really keep them here for completeness; we'd need them if we
53 * supported device unplugging. */
54 int major;
55 int irq;
56
57 /* The physical address of this device's memory page */
58 unsigned long phys_addr;
59 /* The mapped memory page for convenient acces. */
60 struct lguest_block_page *lb_page;
61
62 /* We only have a single request outstanding at a time: this is it. */
63 struct lguest_dma dma;
64 struct request *req;
65};
66
67/*D:495 We originally used end_request() throughout the driver, but it turns
68 * out that end_request() is deprecated, and doesn't actually end the request
69 * (which seems like a good reason to deprecate it!). It simply ends the first
70 * bio. So if we had 3 bios in a "struct request" we would do all 3,
71 * end_request(), do 2, end_request(), do 1 and end_request(): twice as much
72 * work as we needed to do.
73 *
74 * This reinforced to me that I do not understand the block layer.
75 *
76 * Nonetheless, Jens Axboe gave me this nice helper to end all chunks of a
77 * request. This improved disk speed by 130%. */
78static void end_entire_request(struct request *req, int uptodate)
79{
80 if (end_that_request_first(req, uptodate, req->hard_nr_sectors))
81 BUG();
82 add_disk_randomness(req->rq_disk);
83 blkdev_dequeue_request(req);
84 end_that_request_last(req, uptodate);
85}
86
87/* I'm told there are only two stories in the world worth telling: love and
88 * hate. So there used to be a love scene here like this:
89 *
90 * Launcher: We could make beautiful I/O together, you and I.
91 * Guest: My, that's a big disk!
92 *
93 * Unfortunately, it was just too raunchy for our otherwise-gentle tale. */
94
95/*D:490 This is the interrupt handler, called when a block read or write has
96 * been completed for us. */
97static irqreturn_t lgb_irq(int irq, void *_bd)
98{
99 /* We handed our "struct blockdev" as the argument to request_irq(), so
100 * it is passed through to us here. This tells us which device we're
101 * dealing with in case we have more than one. */
102 struct blockdev *bd = _bd;
103 unsigned long flags;
104
105 /* We weren't doing anything? Strange, but could happen if we shared
106 * interrupts (we don't!). */
107 if (!bd->req) {
108 pr_debug("No work!\n");
109 return IRQ_NONE;
110 }
111
112 /* Not done yet? That's equally strange. */
113 if (!bd->lb_page->result) {
114 pr_debug("No result!\n");
115 return IRQ_NONE;
116 }
117
118 /* We have to grab the lock before ending the request. */
119 spin_lock_irqsave(&bd->lock, flags);
120 /* "result" is 1 for success, 2 for failure: end_entire_request() wants
121 * to know whether this succeeded or not. */
122 end_entire_request(bd->req, bd->lb_page->result == 1);
123 /* Clear out request, it's done. */
124 bd->req = NULL;
125 /* Reset incoming DMA for next time. */
126 bd->dma.used_len = 0;
127 /* Ready for more reads or writes */
128 blk_start_queue(bd->disk->queue);
129 spin_unlock_irqrestore(&bd->lock, flags);
130
131 /* The interrupt was for us, we dealt with it. */
132 return IRQ_HANDLED;
133}
134
135/*D:480 The block layer's "struct request" contains a number of "struct bio"s,
136 * each of which contains "struct bio_vec"s, each of which contains a page, an
137 * offset and a length.
138 *
139 * Fortunately there are iterators to help us walk through the "struct
140 * request". Even more fortunately, there were plenty of places to steal the
141 * code from. We pack the "struct request" into our "struct lguest_dma" and
142 * return the total length. */
143static unsigned int req_to_dma(struct request *req, struct lguest_dma *dma)
144{
145 unsigned int i = 0, len = 0;
146 struct req_iterator iter;
147 struct bio_vec *bvec;
148
149 rq_for_each_segment(bvec, req, iter) {
150 /* We told the block layer not to give us too many. */
151 BUG_ON(i == LGUEST_MAX_DMA_SECTIONS);
152 /* If we had a zero-length segment, it would look like
153 * the end of the data referred to by the "struct
154 * lguest_dma", so make sure that doesn't happen. */
155 BUG_ON(!bvec->bv_len);
156 /* Convert page & offset to a physical address */
157 dma->addr[i] = page_to_phys(bvec->bv_page)
158 + bvec->bv_offset;
159 dma->len[i] = bvec->bv_len;
160 len += bvec->bv_len;
161 i++;
162 }
163 /* If the array isn't full, we mark the end with a 0 length */
164 if (i < LGUEST_MAX_DMA_SECTIONS)
165 dma->len[i] = 0;
166 return len;
167}
168
169/* This creates an empty DMA, useful for prodding the Host without sending data
170 * (ie. when we want to do a read) */
171static void empty_dma(struct lguest_dma *dma)
172{
173 dma->len[0] = 0;
174}
175
176/*D:470 Setting up a request is fairly easy: */
177static void setup_req(struct blockdev *bd,
178 int type, struct request *req, struct lguest_dma *dma)
179{
180 /* The type is 1 (write) or 0 (read). */
181 bd->lb_page->type = type;
182 /* The sector on disk where the read or write starts. */
183 bd->lb_page->sector = req->sector;
184 /* The result is initialized to 0 (unfinished). */
185 bd->lb_page->result = 0;
186 /* The current request (so we can end it in the interrupt handler). */
187 bd->req = req;
188 /* The number of bytes: returned as a side-effect of req_to_dma(),
189 * which packs the block layer's "struct request" into our "struct
190 * lguest_dma" */
191 bd->lb_page->bytes = req_to_dma(req, dma);
192}
193
194/*D:450 Write is pretty straightforward: we pack the request into a "struct
195 * lguest_dma", then use SEND_DMA to send the request. */
196static void do_write(struct blockdev *bd, struct request *req)
197{
198 struct lguest_dma send;
199
200 pr_debug("lgb: WRITE sector %li\n", (long)req->sector);
201 setup_req(bd, 1, req, &send);
202
203 lguest_send_dma(bd->phys_addr, &send);
204}
205
206/* Read is similar to write, except we pack the request into our receive
207 * "struct lguest_dma" and send through an empty DMA just to tell the Host that
208 * there's a request pending. */
209static void do_read(struct blockdev *bd, struct request *req)
210{
211 struct lguest_dma ping;
212
213 pr_debug("lgb: READ sector %li\n", (long)req->sector);
214 setup_req(bd, 0, req, &bd->dma);
215
216 empty_dma(&ping);
217 lguest_send_dma(bd->phys_addr, &ping);
218}
219
220/*D:440 This where requests come in: we get handed the request queue and are
221 * expected to pull a "struct request" off it until we've finished them or
222 * we're waiting for a reply: */
223static void do_lgb_request(struct request_queue *q)
224{
225 struct blockdev *bd;
226 struct request *req;
227
228again:
229 /* This sometimes returns NULL even on the very first time around. I
230 * wonder if it's something to do with letting elves handle the request
231 * queue... */
232 req = elv_next_request(q);
233 if (!req)
234 return;
235
236 /* We attached the struct blockdev to the disk: get it back */
237 bd = req->rq_disk->private_data;
238 /* Sometimes we get repeated requests after blk_stop_queue(), but we
239 * can only handle one at a time. */
240 if (bd->req)
241 return;
242
243 /* We only do reads and writes: no tricky business! */
244 if (!blk_fs_request(req)) {
245 pr_debug("Got non-command 0x%08x\n", req->cmd_type);
246 req->errors++;
247 end_entire_request(req, 0);
248 goto again;
249 }
250
251 if (rq_data_dir(req) == WRITE)
252 do_write(bd, req);
253 else
254 do_read(bd, req);
255
256 /* We've put out the request, so stop any more coming in until we get
257 * an interrupt, which takes us to lgb_irq() to re-enable the queue. */
258 blk_stop_queue(q);
259}
260
261/*D:430 This is the "struct block_device_operations" we attach to the disk at
262 * the end of lguestblk_probe(). It doesn't seem to want much. */
263static struct block_device_operations lguestblk_fops = {
264 .owner = THIS_MODULE,
265};
266
267/*D:425 Setting up a disk device seems to involve a lot of code. I'm not sure
268 * quite why. I do know that the IDE code sent two or three of the maintainers
269 * insane, perhaps this is the fringe of the same disease?
270 *
271 * As in the console code, the probe function gets handed the generic
272 * lguest_device from lguest_bus.c: */
273static int lguestblk_probe(struct lguest_device *lgdev)
274{
275 struct blockdev *bd;
276 int err;
277 int irqflags = IRQF_SHARED;
278
279 /* First we allocate our own "struct blockdev" and initialize the easy
280 * fields. */
281 bd = kmalloc(sizeof(*bd), GFP_KERNEL);
282 if (!bd)
283 return -ENOMEM;
284
285 spin_lock_init(&bd->lock);
286 bd->irq = lgdev_irq(lgdev);
287 bd->req = NULL;
288 bd->dma.used_len = 0;
289 bd->dma.len[0] = 0;
290 /* The descriptor in the lguest_devices array provided by the Host
291 * gives the Guest the physical page number of the device's page. */
292 bd->phys_addr = (lguest_devices[lgdev->index].pfn << PAGE_SHIFT);
293
294 /* We use lguest_map() to get a pointer to the device page */
295 bd->lb_page = lguest_map(bd->phys_addr, 1);
296 if (!bd->lb_page) {
297 err = -ENOMEM;
298 goto out_free_bd;
299 }
300
301 /* We need a major device number: 0 means "assign one dynamically". */
302 bd->major = register_blkdev(0, "lguestblk");
303 if (bd->major < 0) {
304 err = bd->major;
305 goto out_unmap;
306 }
307
308 /* This allocates a "struct gendisk" where we pack all the information
309 * about the disk which the rest of Linux sees. The argument is the
310 * number of minor devices desired: we need one minor for the main
311 * disk, and one for each partition. Of course, we can't possibly know
312 * how many partitions are on the disk (add_disk does that).
313 */
314 bd->disk = alloc_disk(16);
315 if (!bd->disk) {
316 err = -ENOMEM;
317 goto out_unregister_blkdev;
318 }
319
320 /* Every disk needs a queue for requests to come in: we set up the
321 * queue with a callback function (the core of our driver) and the lock
322 * to use. */
323 bd->disk->queue = blk_init_queue(do_lgb_request, &bd->lock);
324 if (!bd->disk->queue) {
325 err = -ENOMEM;
326 goto out_put_disk;
327 }
328
329 /* We can only handle a certain number of pointers in our SEND_DMA
330 * call, so we set that with blk_queue_max_hw_segments(). This is not
331 * to be confused with blk_queue_max_phys_segments() of course! I
332 * know, who could possibly confuse the two?
333 *
334 * Well, it's simple to tell them apart: this one seems to work and the
335 * other one didn't. */
336 blk_queue_max_hw_segments(bd->disk->queue, LGUEST_MAX_DMA_SECTIONS);
337
338 /* Due to technical limitations of our Host (and simple coding) we
339 * can't have a single buffer which crosses a page boundary. Tell it
340 * here. This means that our maximum request size is 16
341 * (LGUEST_MAX_DMA_SECTIONS) pages. */
342 blk_queue_segment_boundary(bd->disk->queue, PAGE_SIZE-1);
343
344 /* We name our disk: this becomes the device name when udev does its
345 * magic thing and creates the device node, such as /dev/lgba.
346 * next_block_index is a global which starts at 'a'. Unfortunately
347 * this simple increment logic means that the 27th disk will be called
348 * "/dev/lgb{". In that case, I recommend having at least 29 disks, so
349 * your /dev directory will be balanced. */
350 sprintf(bd->disk->disk_name, "lgb%c", next_block_index++);
351
352 /* We look to the device descriptor again to see if this device's
353 * interrupts are expected to be random. If they are, we tell the irq
354 * subsystem. At the moment this bit is always set. */
355 if (lguest_devices[lgdev->index].features & LGUEST_DEVICE_F_RANDOMNESS)
356 irqflags |= IRQF_SAMPLE_RANDOM;
357
358 /* Now we have the name and irqflags, we can request the interrupt; we
359 * give it the "struct blockdev" we have set up to pass to lgb_irq()
360 * when there is an interrupt. */
361 err = request_irq(bd->irq, lgb_irq, irqflags, bd->disk->disk_name, bd);
362 if (err)
363 goto out_cleanup_queue;
364
365 /* We bind our one-entry DMA pool to the key for this block device so
366 * the Host can reply to our requests. The key is equal to the
367 * physical address of the device's page, which is conveniently
368 * unique. */
369 err = lguest_bind_dma(bd->phys_addr, &bd->dma, 1, bd->irq);
370 if (err)
371 goto out_free_irq;
372
373 /* We finish our disk initialization and add the disk to the system. */
374 bd->disk->major = bd->major;
375 bd->disk->first_minor = 0;
376 bd->disk->private_data = bd;
377 bd->disk->fops = &lguestblk_fops;
378 /* This is initialized to the disk size by the Launcher. */
379 set_capacity(bd->disk, bd->lb_page->num_sectors);
380 add_disk(bd->disk);
381
382 printk(KERN_INFO "%s: device %i at major %d\n",
383 bd->disk->disk_name, lgdev->index, bd->major);
384
385 /* We don't need to keep the "struct blockdev" around, but if we ever
386 * implemented device removal, we'd need this. */
387 lgdev->private = bd;
388 return 0;
389
390out_free_irq:
391 free_irq(bd->irq, bd);
392out_cleanup_queue:
393 blk_cleanup_queue(bd->disk->queue);
394out_put_disk:
395 put_disk(bd->disk);
396out_unregister_blkdev:
397 unregister_blkdev(bd->major, "lguestblk");
398out_unmap:
399 lguest_unmap(bd->lb_page);
400out_free_bd:
401 kfree(bd);
402 return err;
403}
404
405/*D:410 The boilerplate code for registering the lguest block driver is just
406 * like the console: */
407static struct lguest_driver lguestblk_drv = {
408 .name = "lguestblk",
409 .owner = THIS_MODULE,
410 .device_type = LGUEST_DEVICE_T_BLOCK,
411 .probe = lguestblk_probe,
412};
413
414static __init int lguestblk_init(void)
415{
416 return register_lguest_driver(&lguestblk_drv);
417}
418module_init(lguestblk_init);
419
420MODULE_DESCRIPTION("Lguest block driver");
421MODULE_LICENSE("GPL");
generated by cgit v1.2.2 (git 2.25.0) at 2025-12-27 23:25:48 -0500