/*
* Driver giving user-space access to the kernel's xenbus connection
* to xenstore.
*
* Copyright (c) 2005, Christian Limpach
* Copyright (c) 2005, 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 version 2
* as published by the Free Software Foundation; or, when distributed
* separately from the Linux kernel or incorporated into other
* software packages, subject to the following license:
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this source file (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use, copy, modify,
* merge, publish, distribute, sublicense, and/or sell copies of the Software,
* and to permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*
* Changes:
* 2008-10-07 Alex Zeffertt Replaced /proc/xen/xenbus with xenfs filesystem
* and /proc/xen compatibility mount point.
* Turned xenfs into a loadable module.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/uio.h>
#include <linux/notifier.h>
#include <linux/wait.h>
#include <linux/fs.h>
#include <linux/poll.h>
#include <linux/mutex.h>
#include <linux/sched.h>
#include <linux/spinlock.h>
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/uaccess.h>
#include <linux/init.h>
#include <linux/namei.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/miscdevice.h>
#include <linux/workqueue.h>
#include <xen/xenbus.h>
#include <xen/xen.h>
#include <asm/xen/hypervisor.h>
#include "xenbus.h"
unsigned int xb_dev_generation_id;
/*
* An element of a list of outstanding transactions, for which we're
* still waiting a reply.
*/
struct xenbus_transaction_holder {
struct list_head list;
struct xenbus_transaction handle;
unsigned int generation_id;
};
/*
* A buffer of data on the queue.
*/
struct read_buffer {
struct list_head list;
unsigned int cons;
unsigned int len;
char msg[] __counted_by(len);
};
struct xenbus_file_priv {
/*
* msgbuffer_mutex is held while partial requests are built up
* and complete requests are acted on. It therefore protects
* the "transactions" and "watches" lists, and the partial
* request length and buffer.
*
* reply_mutex protects the reply being built up to return to
* usermode. It nests inside msgbuffer_mutex but may be held
* alone during a watch callback.
*/
struct mutex msgbuffer_mutex;
/* In-progress transactions */
struct list_head transactions;
/* Active watches. */
struct list_head watches;
/* Partial request. */
unsigned int len;
union {
struct xsd_sockmsg msg;
char buffer[XENSTORE_PAYLOAD_MAX];
} u;
/* Response queue. */
struct mutex reply_mutex;
struct list_head read_buffers;
wait_queue_head_t read_waitq;
struct kref kref;
struct work_struct wq;
};
/* Read out any raw xenbus messages queued up. */
static ssize_t xenbus_file_read(struct file *filp,
char __user *ubuf,
size_t len, loff_t *ppos)
{
struct xenbus_file_priv *u = filp->private_data;
struct read_buffer *rb;
ssize_t i;
int ret;
mutex_lock(&u->reply_mutex);
again:
while (list_empty(&u->read_buffers)) {
mutex_unlock(&u->reply_mutex);
if (filp->f_flags & O_NONBLOCK)
return -EAGAIN;
ret = wait_event_interruptible(u->read_waitq,
!list_empty(&u->read_buffers));
if (ret)
return ret;
mutex_lock(&u->reply_mutex);
}
rb = list_entry(u->read_buffers.next, struct read_buffer, list);
i = 0;
while (i < len) {
size_t sz = min_t(size_t, len - i, rb->len - rb->cons);
ret = copy_to_user(ubuf + i, &rb->msg[rb->cons], sz);
i += sz - ret;
rb->cons += sz - ret;
if (ret != 0) {
if (i == 0)
i = -EFAULT;
goto out;
}
/* Clear out buffer if it has been consumed */
if (rb->cons == rb->len) {
list_del(&rb->list);
kfree(rb);
if (list_empty(&u->read_buffers))
break;
rb = list_entry(u->read_buffers.next,
struct read_buffer, list);
}
}
if (i == 0)
goto again;
out:
mutex_unlock(&u->reply_mutex);
return i;
}
/*
* Add a buffer to the queue. Caller must hold the appropriate lock
* if the queue is not local. (Commonly the caller will build up
* multiple queued buffers on a temporary local list, and then add it
* to the appropriate list under lock once all the buffers have een
* successfully allocated.)
*/
static int queue_reply(struct list_head *queue, const void *data, size_t len)
{
struct read_buffer *rb;
if (len == 0)
return 0;
if (len > XENSTORE_PAYLOAD_MAX)
return -EINVAL;
rb = kmalloc(struct_size(rb, msg, len), GFP_KERNEL);
if (rb == NULL)
return -ENOMEM;
rb->cons = 0;
rb->len = len;
memcpy(rb->msg, data, len);
list_add_tail(&rb->list, queue);
return 0;
}
/*
* Free all the read_buffer s on a list.
* Caller must have sole reference to list.
*/
static void queue_cleanup(struct list_head *list)
{
struct read_buffer *rb;
while (!list_empty(list)) {
rb = list_entry(list->next, struct read_buffer, list);
list_del(list->next);
kfree(rb);
}
}
struct watch_adapter {
struct list_head list;
struct xenbus_watch watch;
struct xenbus_file_priv *dev_data;
char *token;
};
static void free_watch_adapter(struct watch_adapter *watch)
{
kfree(watch->watch.node);
kfree(watch->token);
kfree(watch);
}
static struct watch_adapter *alloc_watch_adapter(const char *path,
const char *token)
{
struct watch_adapter *watch;
watch = kzalloc(sizeof(*watch), GFP_KERNEL);
if (watch == NULL)
goto out_fail;
watch->watch.node = kstrdup(path, GFP_KERNEL);
if (watch->watch.node == NULL)
goto out_free;
watch->token = kstrdup(token, GFP_KERNEL);
if (watch->token == NULL)
goto out_free;
return watch;
out_free:
free_watch_adapter(watch);
out_fail:
return NULL;
}
static void watch_fired(struct xenbus_watch *watch,
const char *path,
const char *token)
{
struct watch_adapter *adap;
struct xsd_sockmsg hdr;
const char *token_caller;
int path_len, tok_len, body_len;
int ret;
LIST_HEAD(staging_q);
adap = container_of(watch, struct watch_adapter, watch);
token_caller = adap->token;
path_len = strlen(path) + 1;
tok_len = strlen(token_caller) + 1;
body_len = path_len + tok_len;
hdr.type = XS_WATCH_EVENT;
hdr.len = body_len;
mutex_lock(&adap->dev_data->reply_mutex);
ret = queue_reply(&staging_q, &hdr, sizeof(hdr));
if (!ret)
ret = queue_reply(&staging_q, path, path_len);
if (!ret)
ret = queue_reply(&staging_q, token_caller, tok_len);
if (!ret) {
/* success: pass reply list onto watcher */
list_splice_tail(&staging_q, &adap->dev_data->read_buffers);
wake_up(&adap->dev_data->read_waitq);
} else
queue_cleanup(&staging_q);
mutex_unlock(&adap->dev_data->reply_mutex);
}
static void xenbus_worker(struct work_struct *wq)
{
struct xenbus_file_priv *u;
struct xenbus_transaction_holder *trans, *tmp;
struct watch_adapter *watch, *tmp_watch;
struct read_buffer *rb, *tmp_rb;
u = container_of(wq, struct xenbus_file_priv, wq);
/*
* No need for locking here because there are no other users,
* by definition.
*/
list_for_each_entry_safe(trans, tmp, &u->transactions, list) {
xenbus_transaction_end(trans->handle, 1);
list_del(&trans->list);
kfree(trans);
}
list_for_each_entry_safe(watch, tmp_watch, &u->watches, list) {
unregister_xenbus_watch(&watch->watch);
list_del(&watch->list);
free_watch_adapter(watch);
}
list_for_each_entry_safe(rb, tmp_rb, &u->read_buffers, list) {
list_del(&rb->list);
kfree(rb);
}
kfree(u);
}
static void xenbus_file_free(struct kref *kref)
{
struct xenbus_file_priv *u;
/*
* We might be called in xenbus_thread().
* Use workqueue to avoid deadlock.
*/
u = container_of(kref, struct xenbus_file_priv, kref);
schedule_work(&u->wq);
}
static struct xenbus_transaction_holder *xenbus_get_transaction(
struct xenbus_file_priv *u, uint32_t tx_id)
{
struct xenbus_transaction_holder *trans;
list_for_each_entry(trans, &u->transactions, list)
if (trans->handle.id == tx_id)
return trans;
return NULL;
}
void xenbus_dev_queue_reply(struct xb_req_data *req)
{
struct xenbus_file_priv *u = req->par;
struct xenbus_transaction_holder *trans = NULL;
int rc;
LIST_HEAD(staging_q);
xs_request_exit(req);
mutex_lock(&u->msgbuffer_mutex);
if (req->type == XS_TRANSACTION_START) {
trans = xenbus_get_transaction(u, 0);
if (WARN_ON(!trans))
goto out;
if (req->msg.type == XS_ERROR) {
list_del(&trans->list);
kfree(trans);
} else {
rc = kstrtou32(req->body, 10, &trans->handle.id);
if (WARN_ON(rc))
goto out;
}
} else if (req->type == XS_TRANSACTION_END) {
trans = xenbus_get_transaction(u, req->msg.tx_id);
if (WARN_ON(!trans))
goto out;
list_del(&trans->list);
kfree(trans);
}
mutex_unlock(&u->msgbuffer_mutex);
mutex_lock(&u->reply_mutex);
rc = queue_reply(&staging_q, &req->msg, sizeof(req->msg));
if (!rc)
rc = queue_reply(&staging_q, req->body, req->msg.len);
if (!rc) {
list_splice_tail(&staging_q, &u->read_buffers);
wake_up(&u->read_waitq);
} else {
queue_cleanup(&staging_q);
}
mutex_unlock(&u->reply_mutex);
kfree(req->body);
kfree(req);
kref_put(&u->kref, xenbus_file_free);
return;
out:
mutex_unlock(&u->msgbuffer_mutex);
}
static int xenbus_command_reply(struct xenbus_file_priv *u,
unsigned int msg_type, const char *reply)
{
struct {
struct xsd_sockmsg hdr;
char body[16];
} msg;
int rc;
msg.hdr = u->u.msg;
msg.hdr.type = msg_type;
msg.hdr.len = strlen(reply) + 1;
if (msg.hdr.len > sizeof(msg.body))
return -E2BIG;
memcpy(&msg.body, reply, msg.hdr.len);
mutex_lock(&u->reply_mutex);
rc = queue_reply(&u->read_buffers, &msg, sizeof(msg.hdr) + msg.hdr.len);
wake_up(&u->read_waitq);
mutex_unlock(&u->reply_mutex);
if (!rc)
kref_put(&u->kref, xenbus_file_free);
return rc;
}
static int xenbus_write_transaction(unsigned msg_type,
struct xenbus_file_priv *u)
{
int rc;
struct xenbus_transaction_holder *trans = NULL;
struct {
struct xsd_sockmsg hdr;
char body[];
} *msg = (void *)u->u.buffer;
if (msg_type == XS_TRANSACTION_START) {
trans = kzalloc(sizeof(*trans), GFP_KERNEL);
if (!trans) {
rc = -ENOMEM;
goto out;
}
trans->generation_id = xb_dev_generation_id;
list_add(&trans->list, &u->transactions);
} else if (msg->hdr.tx_id != 0 &&
!xenbus_get_transaction(u, msg->hdr.tx_id))
return xenbus_command_reply(u, XS_ERROR, "ENOENT");
else if (msg_type == XS_TRANSACTION_END &&
!(msg->hdr.len == 2 &&
(!strcmp(msg->body, "T") || !strcmp(msg->body, "F"))))
return xenbus_command_reply(u, XS_ERROR, "EINVAL");
else if (msg_type == XS_TRANSACTION_END) {
trans = xenbus_get_transaction(u, msg->hdr.tx_id);
if (trans && trans->generation_id != xb_dev_generation_id) {
list_del(&trans->list);
kfree(trans);
if (!strcmp(msg->body, "T"))
return xenbus_command_reply(u, XS_ERROR,
"EAGAIN");
else
return xenbus_command_reply(u,
XS_TRANSACTION_END,
"OK");
}
}
rc = xenbus_dev_request_and_reply(&msg->hdr, u);
if (rc && trans) {
list_del(&trans->list);
kfree(trans);
}
out:
return rc;
}
static int xenbus_write_watch(unsigned msg_type, struct xenbus_file_priv *u)
{
struct watch_adapter *watch;
char *path, *token;
int err, rc;
path = u->u.buffer + sizeof(u->u.msg);
token = memchr(path, 0, u->u.msg.len);
if (token == NULL) {
rc = xenbus_command_reply(u, XS_ERROR, "EINVAL");
goto out;
}
token++;
if (memchr(token, 0, u->u.msg.len - (token - path)) == NULL) {
rc = xenbus_command_reply(u, XS_ERROR, "EINVAL");
goto out;
}
if (msg_type == XS_WATCH) {
watch = alloc_watch_adapter(path, token);
if (watch == NULL) {
rc = -ENOMEM;
goto out;
}
watch->watch.callback = watch_fired;
watch->dev_data = u;
err = register_xenbus_watch(&watch->watch);
if (err) {
free_watch_adapter(watch);
rc = err;
goto out;
}
list_add(&watch->list, &u->watches);
} else {
list_for_each_entry(watch, &u->watches, list) {
if (!strcmp(watch->token, token) &&
!strcmp(watch->watch.node, path)) {
unregister_xenbus_watch(&watch->watch);
list_del(&watch->list);
free_watch_adapter(watch);
break;
}
}
}
/* Success. Synthesize a reply to say all is OK. */
rc = xenbus_command_reply(u, msg_type, "OK");
out:
return rc;
}
static ssize_t xenbus_file_write(struct file *filp,
const char __user *ubuf,
size_t len, loff_t *ppos)
{
struct xenbus_file_priv *u = filp->private_data;
uint32_t msg_type;
int rc = len;
int ret;
/*
* We're expecting usermode to be writing properly formed
* xenbus messages. If they write an incomplete message we
* buffer it up. Once it is complete, we act on it.
*/
/*
* Make sure concurrent writers can't stomp all over each
* other's messages and make a mess of our partial message
* buffer. We don't make any attemppt to stop multiple
* writers from making a mess of each other's incomplete
* messages; we're just trying to guarantee our own internal
* consistency and make sure that single writes are handled
* atomically.
*/
mutex_lock(&u->msgbuffer_mutex);
/* Get this out of the way early to avoid confusion */
if (len == 0)
goto out;
/* Can't write a xenbus message larger we can buffer */
if (len > sizeof(u->u.buffer) - u->len) {
/* On error, dump existing buffer */
u->len = 0;
rc = -EINVAL;
goto out;
}
ret = copy_from_user(u->u.buffer + u->len, ubuf, len);
if (ret != 0) {
rc = -EFAULT;
goto out;
}
/* Deal with a partial copy. */
len -= ret;
rc = len;
u->len += len;
/* Return if we haven't got a full message yet */
if (u->len < sizeof(u->u.msg))
goto out; /* not even the header yet */
/* If we're expecting a message that's larger than we can
possibly send, dump what we have and return an error. */
if ((sizeof(u->u.msg) + u->u.msg.len) > sizeof(u->u.buffer)) {
rc = -E2BIG;
u->len = 0;
goto out;
}
if (u->len < (sizeof(u->u.msg) + u->u.msg.len))
goto out; /* incomplete data portion */
/*
* OK, now we have a complete message. Do something with it.
*/
kref_get(&u->kref);
msg_type = u->u.msg.type;
switch (msg_type) {
case XS_WATCH:
case XS_UNWATCH:
/* (Un)Ask for some path to be watched for changes */
ret = xenbus_write_watch(msg_type, u);
break;
default:
/* Send out a transaction */
ret = xenbus_write_transaction(msg_type, u);
break;
}
if (ret != 0) {
rc = ret;
kref_put(&u->kref, xenbus_file_free);
}
/* Buffered message consumed */
u->len = 0;
out:
mutex_unlock(&u->msgbuffer_mutex);
return rc;
}
static int xenbus_file_open(struct inode *inode, struct file *filp)
{
struct xenbus_file_priv *u;
if (xen_store_evtchn == 0)
return -ENOENT;
stream_open(inode, filp);
u = kzalloc(sizeof(*u), GFP_KERNEL);
if (u == NULL)
return -ENOMEM;
kref_init(&u->kref);
INIT_LIST_HEAD(&u->transactions);
INIT_LIST_HEAD(&u->watches);
INIT_LIST_HEAD(&u->read_buffers);
init_waitqueue_head(&u->read_waitq);
INIT_WORK(&u->wq, xenbus_worker);
mutex_init(&u->reply_mutex);
mutex_init(&u->msgbuffer_mutex);
filp->private_data = u;
return 0;
}
static int xenbus_file_release(struct inode *inode, struct file *filp)
{
struct xenbus_file_priv *u = filp->private_data;
kref_put(&u->kref, xenbus_file_free);
return 0;
}
static __poll_t xenbus_file_poll(struct file *file, poll_table *wait)
{
struct xenbus_file_priv *u = file->private_data;
poll_wait(file, &u->read_waitq, wait);
if (!list_empty(&u->read_buffers))
return EPOLLIN | EPOLLRDNORM;
return 0;
}
const struct file_operations xen_xenbus_fops = {
.read = xenbus_file_read,
.write = xenbus_file_write,
.open = xenbus_file_open,
.release = xenbus_file_release,
.poll = xenbus_file_poll,
};
EXPORT_SYMBOL_GPL(xen_xenbus_fops);
static struct miscdevice xenbus_dev = {
.minor = MISC_DYNAMIC_MINOR,
.name = "xen/xenbus",
.fops = &xen_xenbus_fops,
};
static int __init xenbus_init(void)
{
int err;
if (!xen_domain())
return -ENODEV;
err = misc_register(&xenbus_dev);
if (err)
pr_err("Could not register xenbus frontend device\n");
return err;
}
device_initcall(xenbus_init);
Codebase Browser
linux