/*D:300 * The Guest console driver * * 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. :*/ /*M:002 The console can be flooded: while the Guest is processing input the * Host can send more. Buffering in the Host could alleviate this, but it is a * difficult problem in general. :*/ /* Copyright (C) 2006, 2007 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 * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */ #include <linux/err.h> #include <linux/init.h> #include <linux/virtio.h> #include <linux/virtio_console.h> #include "hvc_console.h" /*D:340 These represent our input and output console queues, and the virtio * operations for them. */ static struct virtqueue *in_vq, *out_vq; static struct virtio_device *vdev; /* This is our input buffer, and how much data is left in it. */ static unsigned int in_len; static char *in, *inbuf; /* The operations for our console. */ static struct hv_ops virtio_cons; /*D:310 The put_chars() callback is pretty straightforward. * * We turn the characters into a scatter-gather list, add it to the output * queue and then kick the Host. Then we sit here waiting for it to finish: * inefficient in theory, but in practice implementations will do it * immediately (lguest's Launcher does). */ static int put_chars(u32 vtermno, const char *buf, int count) { struct scatterlist sg[1]; unsigned int len; /* This is a convenient routine to initialize a single-elem sg list */ sg_init_one(sg, buf, count); /* add_buf wants a token to identify this buffer: we hand it any * non-NULL pointer, since there's only ever one buffer. */ if (out_vq->vq_ops->add_buf(out_vq, sg, 1, 0, (void *)1) == 0) { /* Tell Host to go! */ out_vq->vq_ops->kick(out_vq); /* Chill out until it's done with the buffer. */ while (!out_vq->vq_ops->get_buf(out_vq, &len)) cpu_relax(); } /* We're expected to return the amount of data we wrote: all of it. */ return count; } /* Create a scatter-gather list representing our input buffer and put it in the * queue. */ static void add_inbuf(void) { struct scatterlist sg[1]; sg_init_one(sg, inbuf, PAGE_SIZE); /* We should always be able to add one buffer to an empty queue. */ if (in_vq->vq_ops->add_buf(in_vq, sg, 0, 1, inbuf) != 0) BUG(); in_vq->vq_ops->kick(in_vq); } /*D:350 get_chars() is the callback from the hvc_console infrastructure when * an interrupt is received. * * Most of the code deals with the fact that the hvc_console() infrastructure * only asks us for 16 bytes at a time. We keep in_offset and in_used fields * for partially-filled buffers. */ static int get_chars(u32 vtermno, char *buf, int count) { /* If we don't have an input queue yet, we can't get input. */ BUG_ON(!in_vq); /* No buffer? Try to get one. */ if (!in_len) { in = in_vq->vq_ops->get_buf(in_vq, &in_len); if (!in) return 0; } /* You want more than we have to give? Well, try wanting less! */ if (in_len < count) count = in_len; /* Copy across to their buffer and increment offset. */ memcpy(buf, in, count); in += count; in_len -= count; /* Finished? Re-register buffer so Host will use it again. */ if (in_len == 0) add_inbuf(); return count; } /*:*/ /*D:320 Console drivers are initialized very early so boot messages can go out, * so we do things slightly differently from the generic virtio initialization * of the net and block drivers. * * At this stage, the console is output-only. It's too early to set up a * virtqueue, so we let the drivers do some boutique early-output thing. */ int __init virtio_cons_early_init(int (*put_chars)(u32, const char *, int)) { virtio_cons.put_chars = put_chars; return hvc_instantiate(0, 0, &virtio_cons); } /*D:370 Once we're further in boot, we get probed like any other virtio device. * At this stage we set up the output virtqueue. * * To set up and manage our virtual console, we call hvc_alloc(). Since we * never remove the console device we never need this pointer again. * * Finally we put our input buffer in the input queue, ready to receive. */ static int __devinit virtcons_probe(struct virtio_device *dev) { int err; struct hvc_struct *hvc; vdev = dev; /* This is the scratch page we use to receive console input */ inbuf = kmalloc(PAGE_SIZE, GFP_KERNEL); if (!inbuf) { err = -ENOMEM; goto fail; } /* Find the input queue. */ /* FIXME: This is why we want to wean off hvc: we do nothing * when input comes in. */ in_vq = vdev->config->find_vq(vdev, NULL); if (IS_ERR(in_vq)) { err = PTR_ERR(in_vq); goto free; } out_vq = vdev->config->find_vq(vdev, NULL); if (IS_ERR(out_vq)) { err = PTR_ERR(out_vq); goto free_in_vq; } /* Start using the new console output. */ virtio_cons.get_chars = get_chars; virtio_cons.put_chars = put_chars; /* The first argument of hvc_alloc() is the virtual console number, so * we use zero. The second argument is the interrupt number; we * currently leave this as zero: it would be better not to use the * hvc mechanism and fix this (FIXME!). * * 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 can do any size, so we put PAGE_SIZE here. */ hvc = hvc_alloc(0, 0, &virtio_cons, PAGE_SIZE); if (IS_ERR(hvc)) { err = PTR_ERR(hvc); goto free_out_vq; } /* Register the input buffer the first time. */ add_inbuf(); return 0; free_out_vq: vdev->config->del_vq(out_vq); free_in_vq: vdev->config->del_vq(in_vq); free: kfree(inbuf); fail: return err; } static struct virtio_device_id id_table[] = { { VIRTIO_ID_CONSOLE, VIRTIO_DEV_ANY_ID }, { 0 }, }; static struct virtio_driver virtio_console = { .driver.name = KBUILD_MODNAME, .driver.owner = THIS_MODULE, .id_table = id_table, .probe = virtcons_probe, }; static int __init init(void) { return register_virtio_driver(&virtio_console); } module_init(init); MODULE_DEVICE_TABLE(virtio, id_table); MODULE_DESCRIPTION("Virtio console driver"); MODULE_LICENSE("GPL");