![Rusty Russell](/assets/img/avatar_default.png)
The lguest block device only requests one minor, which means partitions don't work (eg "root=/dev/lgba1"). Let's follow the crowd and ask for 16. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
424 lines
14 KiB
C
424 lines
14 KiB
C
/*D:400
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* The Guest block driver
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*
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* This is a simple block driver, which appears as /dev/lgba, lgbb, lgbc etc.
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* The mechanism is simple: we place the information about the request in the
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* device page, then use SEND_DMA (containing the data for a write, or an empty
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* "ping" DMA for a read).
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:*/
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/* Copyright 2006 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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//#define DEBUG
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#include <linux/init.h>
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#include <linux/types.h>
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#include <linux/blkdev.h>
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#include <linux/interrupt.h>
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#include <linux/lguest_bus.h>
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static char next_block_index = 'a';
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/*D:420 Here is the structure which holds all the information we need about
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* each Guest block device.
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*
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* I'm sure at this stage, you're wondering "hey, where was the adventure I was
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* promised?" and thinking "Rusty sucks, I shall say nasty things about him on
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* my blog". I think Real adventures have boring bits, too, and you're in the
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* middle of one. But it gets better. Just not quite yet. */
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struct blockdev
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{
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/* The block queue infrastructure wants a spinlock: it is held while it
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* calls our block request function. We grab it in our interrupt
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* handler so the responses don't mess with new requests. */
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spinlock_t lock;
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/* The disk structure registered with kernel. */
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struct gendisk *disk;
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/* The major device number for this disk, and the interrupt. We only
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* really keep them here for completeness; we'd need them if we
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* supported device unplugging. */
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int major;
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int irq;
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/* The physical address of this device's memory page */
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unsigned long phys_addr;
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/* The mapped memory page for convenient acces. */
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struct lguest_block_page *lb_page;
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/* We only have a single request outstanding at a time: this is it. */
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struct lguest_dma dma;
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struct request *req;
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};
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/*D:495 We originally used end_request() throughout the driver, but it turns
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* out that end_request() is deprecated, and doesn't actually end the request
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* (which seems like a good reason to deprecate it!). It simply ends the first
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* bio. So if we had 3 bios in a "struct request" we would do all 3,
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* end_request(), do 2, end_request(), do 1 and end_request(): twice as much
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* work as we needed to do.
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*
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* This reinforced to me that I do not understand the block layer.
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*
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* Nonetheless, Jens Axboe gave me this nice helper to end all chunks of a
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* request. This improved disk speed by 130%. */
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static void end_entire_request(struct request *req, int uptodate)
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{
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if (end_that_request_first(req, uptodate, req->hard_nr_sectors))
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BUG();
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add_disk_randomness(req->rq_disk);
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blkdev_dequeue_request(req);
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end_that_request_last(req, uptodate);
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}
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/* I'm told there are only two stories in the world worth telling: love and
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* hate. So there used to be a love scene here like this:
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*
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* Launcher: We could make beautiful I/O together, you and I.
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* Guest: My, that's a big disk!
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*
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* Unfortunately, it was just too raunchy for our otherwise-gentle tale. */
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/*D:490 This is the interrupt handler, called when a block read or write has
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* been completed for us. */
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static irqreturn_t lgb_irq(int irq, void *_bd)
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{
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/* We handed our "struct blockdev" as the argument to request_irq(), so
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* it is passed through to us here. This tells us which device we're
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* dealing with in case we have more than one. */
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struct blockdev *bd = _bd;
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unsigned long flags;
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/* We weren't doing anything? Strange, but could happen if we shared
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* interrupts (we don't!). */
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if (!bd->req) {
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pr_debug("No work!\n");
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return IRQ_NONE;
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}
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/* Not done yet? That's equally strange. */
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if (!bd->lb_page->result) {
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pr_debug("No result!\n");
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return IRQ_NONE;
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}
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/* We have to grab the lock before ending the request. */
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spin_lock_irqsave(&bd->lock, flags);
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/* "result" is 1 for success, 2 for failure: end_entire_request() wants
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* to know whether this succeeded or not. */
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end_entire_request(bd->req, bd->lb_page->result == 1);
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/* Clear out request, it's done. */
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bd->req = NULL;
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/* Reset incoming DMA for next time. */
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bd->dma.used_len = 0;
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/* Ready for more reads or writes */
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blk_start_queue(bd->disk->queue);
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spin_unlock_irqrestore(&bd->lock, flags);
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/* The interrupt was for us, we dealt with it. */
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return IRQ_HANDLED;
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}
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/*D:480 The block layer's "struct request" contains a number of "struct bio"s,
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* each of which contains "struct bio_vec"s, each of which contains a page, an
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* offset and a length.
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*
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* Fortunately there are iterators to help us walk through the "struct
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* request". Even more fortunately, there were plenty of places to steal the
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* code from. We pack the "struct request" into our "struct lguest_dma" and
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* return the total length. */
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static unsigned int req_to_dma(struct request *req, struct lguest_dma *dma)
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{
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unsigned int i = 0, idx, len = 0;
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struct bio *bio;
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rq_for_each_bio(bio, req) {
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struct bio_vec *bvec;
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bio_for_each_segment(bvec, bio, idx) {
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/* We told the block layer not to give us too many. */
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BUG_ON(i == LGUEST_MAX_DMA_SECTIONS);
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/* If we had a zero-length segment, it would look like
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* the end of the data referred to by the "struct
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* lguest_dma", so make sure that doesn't happen. */
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BUG_ON(!bvec->bv_len);
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/* Convert page & offset to a physical address */
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dma->addr[i] = page_to_phys(bvec->bv_page)
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+ bvec->bv_offset;
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dma->len[i] = bvec->bv_len;
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len += bvec->bv_len;
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i++;
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}
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}
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/* If the array isn't full, we mark the end with a 0 length */
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if (i < LGUEST_MAX_DMA_SECTIONS)
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dma->len[i] = 0;
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return len;
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}
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/* This creates an empty DMA, useful for prodding the Host without sending data
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* (ie. when we want to do a read) */
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static void empty_dma(struct lguest_dma *dma)
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{
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dma->len[0] = 0;
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}
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/*D:470 Setting up a request is fairly easy: */
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static void setup_req(struct blockdev *bd,
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int type, struct request *req, struct lguest_dma *dma)
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{
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/* The type is 1 (write) or 0 (read). */
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bd->lb_page->type = type;
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/* The sector on disk where the read or write starts. */
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bd->lb_page->sector = req->sector;
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/* The result is initialized to 0 (unfinished). */
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bd->lb_page->result = 0;
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/* The current request (so we can end it in the interrupt handler). */
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bd->req = req;
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/* The number of bytes: returned as a side-effect of req_to_dma(),
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* which packs the block layer's "struct request" into our "struct
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* lguest_dma" */
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bd->lb_page->bytes = req_to_dma(req, dma);
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}
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/*D:450 Write is pretty straightforward: we pack the request into a "struct
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* lguest_dma", then use SEND_DMA to send the request. */
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static void do_write(struct blockdev *bd, struct request *req)
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{
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struct lguest_dma send;
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pr_debug("lgb: WRITE sector %li\n", (long)req->sector);
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setup_req(bd, 1, req, &send);
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lguest_send_dma(bd->phys_addr, &send);
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}
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/* Read is similar to write, except we pack the request into our receive
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* "struct lguest_dma" and send through an empty DMA just to tell the Host that
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* there's a request pending. */
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static void do_read(struct blockdev *bd, struct request *req)
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{
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struct lguest_dma ping;
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pr_debug("lgb: READ sector %li\n", (long)req->sector);
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setup_req(bd, 0, req, &bd->dma);
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empty_dma(&ping);
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lguest_send_dma(bd->phys_addr, &ping);
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}
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/*D:440 This where requests come in: we get handed the request queue and are
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* expected to pull a "struct request" off it until we've finished them or
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* we're waiting for a reply: */
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static void do_lgb_request(struct request_queue *q)
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{
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struct blockdev *bd;
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struct request *req;
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again:
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/* This sometimes returns NULL even on the very first time around. I
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* wonder if it's something to do with letting elves handle the request
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* queue... */
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req = elv_next_request(q);
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if (!req)
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return;
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/* We attached the struct blockdev to the disk: get it back */
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bd = req->rq_disk->private_data;
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/* Sometimes we get repeated requests after blk_stop_queue(), but we
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* can only handle one at a time. */
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if (bd->req)
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return;
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/* We only do reads and writes: no tricky business! */
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if (!blk_fs_request(req)) {
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pr_debug("Got non-command 0x%08x\n", req->cmd_type);
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req->errors++;
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end_entire_request(req, 0);
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goto again;
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}
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if (rq_data_dir(req) == WRITE)
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do_write(bd, req);
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else
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do_read(bd, req);
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/* We've put out the request, so stop any more coming in until we get
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* an interrupt, which takes us to lgb_irq() to re-enable the queue. */
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blk_stop_queue(q);
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}
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/*D:430 This is the "struct block_device_operations" we attach to the disk at
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* the end of lguestblk_probe(). It doesn't seem to want much. */
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static struct block_device_operations lguestblk_fops = {
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.owner = THIS_MODULE,
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};
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/*D:425 Setting up a disk device seems to involve a lot of code. I'm not sure
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* quite why. I do know that the IDE code sent two or three of the maintainers
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* insane, perhaps this is the fringe of the same disease?
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*
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* As in the console code, the probe function gets handed the generic
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* lguest_device from lguest_bus.c: */
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static int lguestblk_probe(struct lguest_device *lgdev)
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{
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struct blockdev *bd;
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int err;
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int irqflags = IRQF_SHARED;
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/* First we allocate our own "struct blockdev" and initialize the easy
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* fields. */
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bd = kmalloc(sizeof(*bd), GFP_KERNEL);
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if (!bd)
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return -ENOMEM;
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spin_lock_init(&bd->lock);
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bd->irq = lgdev_irq(lgdev);
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bd->req = NULL;
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bd->dma.used_len = 0;
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bd->dma.len[0] = 0;
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/* The descriptor in the lguest_devices array provided by the Host
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* gives the Guest the physical page number of the device's page. */
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bd->phys_addr = (lguest_devices[lgdev->index].pfn << PAGE_SHIFT);
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/* We use lguest_map() to get a pointer to the device page */
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bd->lb_page = lguest_map(bd->phys_addr, 1);
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if (!bd->lb_page) {
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err = -ENOMEM;
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goto out_free_bd;
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}
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/* We need a major device number: 0 means "assign one dynamically". */
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bd->major = register_blkdev(0, "lguestblk");
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if (bd->major < 0) {
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err = bd->major;
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goto out_unmap;
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}
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/* This allocates a "struct gendisk" where we pack all the information
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* about the disk which the rest of Linux sees. The argument is the
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* number of minor devices desired: we need one minor for the main
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* disk, and one for each partition. Of course, we can't possibly know
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* how many partitions are on the disk (add_disk does that).
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*/
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bd->disk = alloc_disk(16);
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if (!bd->disk) {
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err = -ENOMEM;
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goto out_unregister_blkdev;
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}
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/* Every disk needs a queue for requests to come in: we set up the
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* queue with a callback function (the core of our driver) and the lock
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* to use. */
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bd->disk->queue = blk_init_queue(do_lgb_request, &bd->lock);
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if (!bd->disk->queue) {
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err = -ENOMEM;
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goto out_put_disk;
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}
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/* We can only handle a certain number of pointers in our SEND_DMA
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* call, so we set that with blk_queue_max_hw_segments(). This is not
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* to be confused with blk_queue_max_phys_segments() of course! I
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* know, who could possibly confuse the two?
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*
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* Well, it's simple to tell them apart: this one seems to work and the
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* other one didn't. */
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blk_queue_max_hw_segments(bd->disk->queue, LGUEST_MAX_DMA_SECTIONS);
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/* Due to technical limitations of our Host (and simple coding) we
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* can't have a single buffer which crosses a page boundary. Tell it
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* here. This means that our maximum request size is 16
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* (LGUEST_MAX_DMA_SECTIONS) pages. */
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blk_queue_segment_boundary(bd->disk->queue, PAGE_SIZE-1);
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/* We name our disk: this becomes the device name when udev does its
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* magic thing and creates the device node, such as /dev/lgba.
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* next_block_index is a global which starts at 'a'. Unfortunately
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* this simple increment logic means that the 27th disk will be called
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* "/dev/lgb{". In that case, I recommend having at least 29 disks, so
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* your /dev directory will be balanced. */
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sprintf(bd->disk->disk_name, "lgb%c", next_block_index++);
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/* We look to the device descriptor again to see if this device's
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* interrupts are expected to be random. If they are, we tell the irq
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* subsystem. At the moment this bit is always set. */
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if (lguest_devices[lgdev->index].features & LGUEST_DEVICE_F_RANDOMNESS)
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irqflags |= IRQF_SAMPLE_RANDOM;
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/* Now we have the name and irqflags, we can request the interrupt; we
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* give it the "struct blockdev" we have set up to pass to lgb_irq()
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* when there is an interrupt. */
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err = request_irq(bd->irq, lgb_irq, irqflags, bd->disk->disk_name, bd);
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if (err)
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goto out_cleanup_queue;
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/* We bind our one-entry DMA pool to the key for this block device so
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* the Host can reply to our requests. The key is equal to the
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* physical address of the device's page, which is conveniently
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* unique. */
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err = lguest_bind_dma(bd->phys_addr, &bd->dma, 1, bd->irq);
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if (err)
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goto out_free_irq;
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/* We finish our disk initialization and add the disk to the system. */
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bd->disk->major = bd->major;
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bd->disk->first_minor = 0;
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bd->disk->private_data = bd;
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bd->disk->fops = &lguestblk_fops;
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/* This is initialized to the disk size by the Launcher. */
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set_capacity(bd->disk, bd->lb_page->num_sectors);
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add_disk(bd->disk);
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printk(KERN_INFO "%s: device %i at major %d\n",
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bd->disk->disk_name, lgdev->index, bd->major);
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/* We don't need to keep the "struct blockdev" around, but if we ever
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* implemented device removal, we'd need this. */
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lgdev->private = bd;
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return 0;
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out_free_irq:
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free_irq(bd->irq, bd);
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out_cleanup_queue:
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blk_cleanup_queue(bd->disk->queue);
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out_put_disk:
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put_disk(bd->disk);
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out_unregister_blkdev:
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unregister_blkdev(bd->major, "lguestblk");
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out_unmap:
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lguest_unmap(bd->lb_page);
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out_free_bd:
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kfree(bd);
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return err;
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}
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/*D:410 The boilerplate code for registering the lguest block driver is just
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* like the console: */
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static struct lguest_driver lguestblk_drv = {
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.name = "lguestblk",
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.owner = THIS_MODULE,
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.device_type = LGUEST_DEVICE_T_BLOCK,
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.probe = lguestblk_probe,
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};
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static __init int lguestblk_init(void)
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{
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return register_lguest_driver(&lguestblk_drv);
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}
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module_init(lguestblk_init);
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MODULE_DESCRIPTION("Lguest block driver");
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MODULE_LICENSE("GPL");
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