/*
   * Copyright (C) 2006-2009 Red Hat, Inc.
   *
   * This file is released under the LGPL.
   */
  
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <net/sock.h>
  #include <linux/workqueue.h>
  #include <linux/connector.h>
  #include <linux/device-mapper.h>
  #include <linux/dm-log-userspace.h>
  
  #include "dm-log-userspace-transfer.h"
  
  static uint32_t dm_ulog_seq;
  
  /*
   * Netlink/Connector is an unreliable protocol.  How long should
   * we wait for a response before assuming it was lost and retrying?
   * (If we do receive a response after this time, it will be discarded
   * and the response to the resent request will be waited for.
   */
  #define DM_ULOG_RETRY_TIMEOUT (15 * HZ)
  
  /*
   * Pre-allocated space for speed
   */
  #define DM_ULOG_PREALLOCED_SIZE 512
  static struct cn_msg *prealloced_cn_msg;
  static struct dm_ulog_request *prealloced_ulog_tfr;
  
  static struct cb_id ulog_cn_id = {
  	.idx = CN_IDX_DM,
  	.val = CN_VAL_DM_USERSPACE_LOG
  };
  
  static DEFINE_MUTEX(dm_ulog_lock);
  
  struct receiving_pkg {
  	struct list_head list;
  	struct completion complete;
  
  	uint32_t seq;
  
  	int error;
  	size_t *data_size;
  	char *data;
  };
  
  static DEFINE_SPINLOCK(receiving_list_lock);
  static struct list_head receiving_list;
  
  static int dm_ulog_sendto_server(struct dm_ulog_request *tfr)
  {
  	int r;
  	struct cn_msg *msg = prealloced_cn_msg;
  
  	memset(msg, 0, sizeof(struct cn_msg));
  
  	msg->id.idx = ulog_cn_id.idx;
  	msg->id.val = ulog_cn_id.val;
  	msg->ack = 0;
  	msg->seq = tfr->seq;
  	msg->len = sizeof(struct dm_ulog_request) + tfr->data_size;
  
  	r = cn_netlink_send(msg, 0, gfp_any());
  
  	return r;
  }
  
  /*
   * Parameters for this function can be either msg or tfr, but not
   * both.  This function fills in the reply for a waiting request.
   * If just msg is given, then the reply is simply an ACK from userspace
   * that the request was received.
   *
   * Returns: 0 on success, -ENOENT on failure
   */
  static int fill_pkg(struct cn_msg *msg, struct dm_ulog_request *tfr)
  {
  	uint32_t rtn_seq = (msg) ? msg->seq : (tfr) ? tfr->seq : 0;
  	struct receiving_pkg *pkg;
  
  	/*
  	 * The 'receiving_pkg' entries in this list are statically
  	 * allocated on the stack in 'dm_consult_userspace'.
  	 * Each process that is waiting for a reply from the user
  	 * space server will have an entry in this list.
  	 *
  	 * We are safe to do it this way because the stack space
  	 * is unique to each process, but still addressable by
  	 * other processes.
  	 */
  	list_for_each_entry(pkg, &receiving_list, list) {
  		if (rtn_seq != pkg->seq)
  			continue;
  
  		if (msg) {
  			pkg->error = -msg->ack;
  			/*
  			 * If we are trying again, we will need to know our
  			 * storage capacity.  Otherwise, along with the
  			 * error code, we make explicit that we have no data.
  			 */
  			if (pkg->error != -EAGAIN)
  				*(pkg->data_size) = 0;
  		} else if (tfr->data_size > *(pkg->data_size)) {
  			DMERR("Insufficient space to receive package [%u] "
  			      "(%u vs %zu)", tfr->request_type,
  			      tfr->data_size, *(pkg->data_size));
  
  			*(pkg->data_size) = 0;
  			pkg->error = -ENOSPC;
  		} else {
  			pkg->error = tfr->error;
  			memcpy(pkg->data, tfr->data, tfr->data_size);
  			*(pkg->data_size) = tfr->data_size;
  		}
  		complete(&pkg->complete);
  		return 0;
  	}
  
  	return -ENOENT;
  }
  
  /*
   * This is the connector callback that delivers data
   * that was sent from userspace.
   */
  static void cn_ulog_callback(struct cn_msg *msg, struct netlink_skb_parms *nsp)
  {
  	struct dm_ulog_request *tfr = (struct dm_ulog_request *)(msg + 1);
  
  	if (!capable(CAP_SYS_ADMIN))
  		return;
  
  	spin_lock(&receiving_list_lock);
  	if (msg->len == 0)
  		fill_pkg(msg, NULL);
  	else if (msg->len < sizeof(*tfr))
  		DMERR("Incomplete message received (expected %u, got %u): [%u]",
  		      (unsigned)sizeof(*tfr), msg->len, msg->seq);
  	else
  		fill_pkg(NULL, tfr);
  	spin_unlock(&receiving_list_lock);
  }
  
  /**
   * dm_consult_userspace
   * @uuid: log's universal unique identifier (must be DM_UUID_LEN in size)
   * @luid: log's local unique identifier
   * @request_type:  found in include/linux/dm-log-userspace.h
   * @data: data to tx to the server
   * @data_size: size of data in bytes
   * @rdata: place to put return data from server
   * @rdata_size: value-result (amount of space given/amount of space used)
   *
   * rdata_size is undefined on failure.
   *
   * Memory used to communicate with userspace is zero'ed
   * before populating to ensure that no unwanted bits leak
   * from kernel space to user-space.  All userspace log communications
   * between kernel and user space go through this function.
   *
   * Returns: 0 on success, -EXXX on failure
   **/
  int dm_consult_userspace(const char *uuid, uint64_t luid, int request_type,
  			 char *data, size_t data_size,
  			 char *rdata, size_t *rdata_size)
  {
  	int r = 0;
  	size_t dummy = 0;
  	int overhead_size = sizeof(struct dm_ulog_request) + sizeof(struct cn_msg);
  	struct dm_ulog_request *tfr = prealloced_ulog_tfr;
  	struct receiving_pkg pkg;
  
  	/*
  	 * Given the space needed to hold the 'struct cn_msg' and
  	 * 'struct dm_ulog_request' - do we have enough payload
  	 * space remaining?
  	 */
  	if (data_size > (DM_ULOG_PREALLOCED_SIZE - overhead_size)) {
  		DMINFO("Size of tfr exceeds preallocated size");
  		return -EINVAL;
  	}
  
  	if (!rdata_size)
  		rdata_size = &dummy;
  resend:
  	/*
  	 * We serialize the sending of requests so we can
  	 * use the preallocated space.
  	 */
  	mutex_lock(&dm_ulog_lock);
  
  	memset(tfr, 0, DM_ULOG_PREALLOCED_SIZE - sizeof(struct cn_msg));
  	memcpy(tfr->uuid, uuid, DM_UUID_LEN);
  	tfr->version = DM_ULOG_REQUEST_VERSION;
  	tfr->luid = luid;
  	tfr->seq = dm_ulog_seq++;
  
  	/*
  	 * Must be valid request type (all other bits set to
  	 * zero).  This reserves other bits for possible future
  	 * use.
  	 */
  	tfr->request_type = request_type & DM_ULOG_REQUEST_MASK;
  
  	tfr->data_size = data_size;
  	if (data && data_size)
  		memcpy(tfr->data, data, data_size);
  
  	memset(&pkg, 0, sizeof(pkg));
  	init_completion(&pkg.complete);
  	pkg.seq = tfr->seq;
  	pkg.data_size = rdata_size;
  	pkg.data = rdata;
  	spin_lock(&receiving_list_lock);
  	list_add(&(pkg.list), &receiving_list);
  	spin_unlock(&receiving_list_lock);
  
  	r = dm_ulog_sendto_server(tfr);
  
  	mutex_unlock(&dm_ulog_lock);
  
  	if (r) {
  		DMERR("Unable to send log request [%u] to userspace: %d",
  		      request_type, r);
  		spin_lock(&receiving_list_lock);
  		list_del_init(&(pkg.list));
  		spin_unlock(&receiving_list_lock);
  
  		goto out;
  	}
  
  	r = wait_for_completion_timeout(&(pkg.complete), DM_ULOG_RETRY_TIMEOUT);
  	spin_lock(&receiving_list_lock);
  	list_del_init(&(pkg.list));
  	spin_unlock(&receiving_list_lock);
  	if (!r) {
  		DMWARN("[%s] Request timed out: [%u/%u] - retrying",
  		       (strlen(uuid) > 8) ?
  		       (uuid + (strlen(uuid) - 8)) : (uuid),
  		       request_type, pkg.seq);
  		goto resend;
  	}
  
  	r = pkg.error;
  	if (r == -EAGAIN)
  		goto resend;
  
  out:
  	return r;
  }
  
  int dm_ulog_tfr_init(void)
  {
  	int r;
  	void *prealloced;
  
  	INIT_LIST_HEAD(&receiving_list);
  
  	prealloced = kmalloc(DM_ULOG_PREALLOCED_SIZE, GFP_KERNEL);
  	if (!prealloced)
  		return -ENOMEM;
  
  	prealloced_cn_msg = prealloced;
  	prealloced_ulog_tfr = prealloced + sizeof(struct cn_msg);
  
  	r = cn_add_callback(&ulog_cn_id, "dmlogusr", cn_ulog_callback);
  	if (r) {
  		kfree(prealloced_cn_msg);
  		return r;
  	}
  
  	return 0;
  }
  
  void dm_ulog_tfr_exit(void)
  {
  	cn_del_callback(&ulog_cn_id);
  	kfree(prealloced_cn_msg);
  }