/*
   * VMware Balloon driver.
   *
   * Copyright (C) 2000-2010, VMware, Inc. All Rights Reserved.
   *
   * 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; version 2 of the License and no 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, GOOD TITLE or
   * NON INFRINGEMENT.  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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Maintained by: Dmitry Torokhov <dtor@vmware.com>
   */
  
  /*
   * This is VMware physical memory management driver for Linux. The driver
   * acts like a "balloon" that can be inflated to reclaim physical pages by
   * reserving them in the guest and invalidating them in the monitor,
   * freeing up the underlying machine pages so they can be allocated to
   * other guests.  The balloon can also be deflated to allow the guest to
   * use more physical memory. Higher level policies can control the sizes
   * of balloons in VMs in order to manage physical memory resources.
   */
  
  //#define DEBUG
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/types.h>
  #include <linux/kernel.h>
  #include <linux/mm.h>
  #include <linux/sched.h>
  #include <linux/module.h>
  #include <linux/workqueue.h>
  #include <linux/debugfs.h>
  #include <linux/seq_file.h>
  #include <asm/hypervisor.h>
  
  MODULE_AUTHOR("VMware, Inc.");
  MODULE_DESCRIPTION("VMware Memory Control (Balloon) Driver");
  MODULE_VERSION("1.2.1.3-k");
  MODULE_ALIAS("dmi:*:svnVMware*:*");
  MODULE_ALIAS("vmware_vmmemctl");
  MODULE_LICENSE("GPL");
  
  /*
   * Various constants controlling rate of inflaint/deflating balloon,
   * measured in pages.
   */
  
  /*
   * Rate of allocating memory when there is no memory pressure
   * (driver performs non-sleeping allocations).
   */
  #define VMW_BALLOON_NOSLEEP_ALLOC_MAX	16384U
  
  /*
   * Rates of memory allocaton when guest experiences memory pressure
   * (driver performs sleeping allocations).
   */
  #define VMW_BALLOON_RATE_ALLOC_MIN	512U
  #define VMW_BALLOON_RATE_ALLOC_MAX	2048U
  #define VMW_BALLOON_RATE_ALLOC_INC	16U
  
  /*
   * Rates for releasing pages while deflating balloon.
   */
  #define VMW_BALLOON_RATE_FREE_MIN	512U
  #define VMW_BALLOON_RATE_FREE_MAX	16384U
  #define VMW_BALLOON_RATE_FREE_INC	16U
  
  /*
   * When guest is under memory pressure, use a reduced page allocation
   * rate for next several cycles.
   */
  #define VMW_BALLOON_SLOW_CYCLES		4
  
  /*
   * Use __GFP_HIGHMEM to allow pages from HIGHMEM zone. We don't
   * allow wait (__GFP_WAIT) for NOSLEEP page allocations. Use
   * __GFP_NOWARN, to suppress page allocation failure warnings.
   */
  #define VMW_PAGE_ALLOC_NOSLEEP		(__GFP_HIGHMEM|__GFP_NOWARN)
  
  /*
   * Use GFP_HIGHUSER when executing in a separate kernel thread
   * context and allocation can sleep.  This is less stressful to
   * the guest memory system, since it allows the thread to block
   * while memory is reclaimed, and won't take pages from emergency
   * low-memory pools.
   */
  #define VMW_PAGE_ALLOC_CANSLEEP		(GFP_HIGHUSER)
  
  /* Maximum number of page allocations without yielding processor */
  #define VMW_BALLOON_YIELD_THRESHOLD	1024
  
  /* Maximum number of refused pages we accumulate during inflation cycle */
  #define VMW_BALLOON_MAX_REFUSED		16
  
  /*
   * Hypervisor communication port definitions.
   */
  #define VMW_BALLOON_HV_PORT		0x5670
  #define VMW_BALLOON_HV_MAGIC		0x456c6d6f
  #define VMW_BALLOON_PROTOCOL_VERSION	2
  #define VMW_BALLOON_GUEST_ID		1	/* Linux */
  
  #define VMW_BALLOON_CMD_START		0
  #define VMW_BALLOON_CMD_GET_TARGET	1
  #define VMW_BALLOON_CMD_LOCK		2
  #define VMW_BALLOON_CMD_UNLOCK		3
  #define VMW_BALLOON_CMD_GUEST_ID	4
  
  /* error codes */
  #define VMW_BALLOON_SUCCESS		0
  #define VMW_BALLOON_FAILURE		-1
  #define VMW_BALLOON_ERROR_CMD_INVALID	1
  #define VMW_BALLOON_ERROR_PPN_INVALID	2
  #define VMW_BALLOON_ERROR_PPN_LOCKED	3
  #define VMW_BALLOON_ERROR_PPN_UNLOCKED	4
  #define VMW_BALLOON_ERROR_PPN_PINNED	5
  #define VMW_BALLOON_ERROR_PPN_NOTNEEDED	6
  #define VMW_BALLOON_ERROR_RESET		7
  #define VMW_BALLOON_ERROR_BUSY		8
  
  #define VMWARE_BALLOON_CMD(cmd, data, result)		\
  ({							\
  	unsigned long __stat, __dummy1, __dummy2;	\
  	__asm__ __volatile__ ("inl %%dx" :		\
  		"=a"(__stat),				\
  		"=c"(__dummy1),				\
  		"=d"(__dummy2),				\
  		"=b"(result) :				\
  		"0"(VMW_BALLOON_HV_MAGIC),		\
  		"1"(VMW_BALLOON_CMD_##cmd),		\
  		"2"(VMW_BALLOON_HV_PORT),		\
  		"3"(data) :				\
  		"memory");				\
  	result &= -1UL;					\
  	__stat & -1UL;					\
  })
  
  #ifdef CONFIG_DEBUG_FS
  struct vmballoon_stats {
  	unsigned int timer;
  
  	/* allocation statistics */
  	unsigned int alloc;
  	unsigned int alloc_fail;
  	unsigned int sleep_alloc;
  	unsigned int sleep_alloc_fail;
  	unsigned int refused_alloc;
  	unsigned int refused_free;
  	unsigned int free;
  
  	/* monitor operations */
  	unsigned int lock;
  	unsigned int lock_fail;
  	unsigned int unlock;
  	unsigned int unlock_fail;
  	unsigned int target;
  	unsigned int target_fail;
  	unsigned int start;
  	unsigned int start_fail;
  	unsigned int guest_type;
  	unsigned int guest_type_fail;
  };
  
  #define STATS_INC(stat) (stat)++
  #else
  #define STATS_INC(stat)
  #endif
  
  struct vmballoon {
  
  	/* list of reserved physical pages */
  	struct list_head pages;
  
  	/* transient list of non-balloonable pages */
  	struct list_head refused_pages;
  	unsigned int n_refused_pages;
  
  	/* balloon size in pages */
  	unsigned int size;
  	unsigned int target;
  
  	/* reset flag */
  	bool reset_required;
  
  	/* adjustment rates (pages per second) */
  	unsigned int rate_alloc;
  	unsigned int rate_free;
  
  	/* slowdown page allocations for next few cycles */
  	unsigned int slow_allocation_cycles;
  
  #ifdef CONFIG_DEBUG_FS
  	/* statistics */
  	struct vmballoon_stats stats;
  
  	/* debugfs file exporting statistics */
  	struct dentry *dbg_entry;
  #endif
  
  	struct sysinfo sysinfo;
  
  	struct delayed_work dwork;
  };
  
  static struct vmballoon balloon;
  
  /*
   * Send "start" command to the host, communicating supported version
   * of the protocol.
   */
  static bool vmballoon_send_start(struct vmballoon *b)
  {
  	unsigned long status, dummy;
  
  	STATS_INC(b->stats.start);
  
  	status = VMWARE_BALLOON_CMD(START, VMW_BALLOON_PROTOCOL_VERSION, dummy);
  	if (status == VMW_BALLOON_SUCCESS)
  		return true;
  
  	pr_debug("%s - failed, hv returns %ld
  ", __func__, status);
  	STATS_INC(b->stats.start_fail);
  	return false;
  }
  
  static bool vmballoon_check_status(struct vmballoon *b, unsigned long status)
  {
  	switch (status) {
  	case VMW_BALLOON_SUCCESS:
  		return true;
  
  	case VMW_BALLOON_ERROR_RESET:
  		b->reset_required = true;
  		/* fall through */
  
  	default:
  		return false;
  	}
  }
  
  /*
   * Communicate guest type to the host so that it can adjust ballooning
   * algorithm to the one most appropriate for the guest. This command
   * is normally issued after sending "start" command and is part of
   * standard reset sequence.
   */
  static bool vmballoon_send_guest_id(struct vmballoon *b)
  {
  	unsigned long status, dummy;
  
  	status = VMWARE_BALLOON_CMD(GUEST_ID, VMW_BALLOON_GUEST_ID, dummy);
  
  	STATS_INC(b->stats.guest_type);
  
  	if (vmballoon_check_status(b, status))
  		return true;
  
  	pr_debug("%s - failed, hv returns %ld
  ", __func__, status);
  	STATS_INC(b->stats.guest_type_fail);
  	return false;
  }
  
  /*
   * Retrieve desired balloon size from the host.
   */
  static bool vmballoon_send_get_target(struct vmballoon *b, u32 *new_target)
  {
  	unsigned long status;
  	unsigned long target;
  	unsigned long limit;
  	u32 limit32;
  
  	/*
  	 * si_meminfo() is cheap. Moreover, we want to provide dynamic
  	 * max balloon size later. So let us call si_meminfo() every
  	 * iteration.
  	 */
  	si_meminfo(&b->sysinfo);
  	limit = b->sysinfo.totalram;
  
  	/* Ensure limit fits in 32-bits */
  	limit32 = (u32)limit;
  	if (limit != limit32)
  		return false;
  
  	/* update stats */
  	STATS_INC(b->stats.target);
  
  	status = VMWARE_BALLOON_CMD(GET_TARGET, limit, target);
  	if (vmballoon_check_status(b, status)) {
  		*new_target = target;
  		return true;
  	}
  
  	pr_debug("%s - failed, hv returns %ld
  ", __func__, status);
  	STATS_INC(b->stats.target_fail);
  	return false;
  }
  
  /*
   * Notify the host about allocated page so that host can use it without
   * fear that guest will need it. Host may reject some pages, we need to
   * check the return value and maybe submit a different page.
   */
  static int vmballoon_send_lock_page(struct vmballoon *b, unsigned long pfn,
  				     unsigned int *hv_status)
  {
  	unsigned long status, dummy;
  	u32 pfn32;
  
  	pfn32 = (u32)pfn;
  	if (pfn32 != pfn)
  		return -1;
  
  	STATS_INC(b->stats.lock);
  
  	*hv_status = status = VMWARE_BALLOON_CMD(LOCK, pfn, dummy);
  	if (vmballoon_check_status(b, status))
  		return 0;
  
  	pr_debug("%s - ppn %lx, hv returns %ld
  ", __func__, pfn, status);
  	STATS_INC(b->stats.lock_fail);
  	return 1;
  }
  
  /*
   * Notify the host that guest intends to release given page back into
   * the pool of available (to the guest) pages.
   */
  static bool vmballoon_send_unlock_page(struct vmballoon *b, unsigned long pfn)
  {
  	unsigned long status, dummy;
  	u32 pfn32;
  
  	pfn32 = (u32)pfn;
  	if (pfn32 != pfn)
  		return false;
  
  	STATS_INC(b->stats.unlock);
  
  	status = VMWARE_BALLOON_CMD(UNLOCK, pfn, dummy);
  	if (vmballoon_check_status(b, status))
  		return true;
  
  	pr_debug("%s - ppn %lx, hv returns %ld
  ", __func__, pfn, status);
  	STATS_INC(b->stats.unlock_fail);
  	return false;
  }
  
  /*
   * Quickly release all pages allocated for the balloon. This function is
   * called when host decides to "reset" balloon for one reason or another.
   * Unlike normal "deflate" we do not (shall not) notify host of the pages
   * being released.
   */
  static void vmballoon_pop(struct vmballoon *b)
  {
  	struct page *page, *next;
  	unsigned int count = 0;
  
  	list_for_each_entry_safe(page, next, &b->pages, lru) {
  		list_del(&page->lru);
  		__free_page(page);
  		STATS_INC(b->stats.free);
  		b->size--;
  
  		if (++count >= b->rate_free) {
  			count = 0;
  			cond_resched();
  		}
  	}
  }
  
  /*
   * Perform standard reset sequence by popping the balloon (in case it
   * is not  empty) and then restarting protocol. This operation normally
   * happens when host responds with VMW_BALLOON_ERROR_RESET to a command.
   */
  static void vmballoon_reset(struct vmballoon *b)
  {
  	/* free all pages, skipping monitor unlock */
  	vmballoon_pop(b);
  
  	if (vmballoon_send_start(b)) {
  		b->reset_required = false;
  		if (!vmballoon_send_guest_id(b))
  			pr_err("failed to send guest ID to the host
  ");
  	}
  }
  
  /*
   * Allocate (or reserve) a page for the balloon and notify the host.  If host
   * refuses the page put it on "refuse" list and allocate another one until host
   * is satisfied. "Refused" pages are released at the end of inflation cycle
   * (when we allocate b->rate_alloc pages).
   */
  static int vmballoon_reserve_page(struct vmballoon *b, bool can_sleep)
  {
  	struct page *page;
  	gfp_t flags;
  	unsigned int hv_status;
  	int locked;
  	flags = can_sleep ? VMW_PAGE_ALLOC_CANSLEEP : VMW_PAGE_ALLOC_NOSLEEP;
  
  	do {
  		if (!can_sleep)
  			STATS_INC(b->stats.alloc);
  		else
  			STATS_INC(b->stats.sleep_alloc);
  
  		page = alloc_page(flags);
  		if (!page) {
  			if (!can_sleep)
  				STATS_INC(b->stats.alloc_fail);
  			else
  				STATS_INC(b->stats.sleep_alloc_fail);
  			return -ENOMEM;
  		}
  
  		/* inform monitor */
  		locked = vmballoon_send_lock_page(b, page_to_pfn(page), &hv_status);
  		if (locked > 0) {
  			STATS_INC(b->stats.refused_alloc);
  
  			if (hv_status == VMW_BALLOON_ERROR_RESET ||
  			    hv_status == VMW_BALLOON_ERROR_PPN_NOTNEEDED) {
  				__free_page(page);
  				return -EIO;
  			}
  
  			/*
  			 * Place page on the list of non-balloonable pages
  			 * and retry allocation, unless we already accumulated
  			 * too many of them, in which case take a breather.
  			 */
  			list_add(&page->lru, &b->refused_pages);
  			if (++b->n_refused_pages >= VMW_BALLOON_MAX_REFUSED)
  				return -EIO;
  		}
  	} while (locked != 0);
  
  	/* track allocated page */
  	list_add(&page->lru, &b->pages);
  
  	/* update balloon size */
  	b->size++;
  
  	return 0;
  }
  
  /*
   * Release the page allocated for the balloon. Note that we first notify
   * the host so it can make sure the page will be available for the guest
   * to use, if needed.
   */
  static int vmballoon_release_page(struct vmballoon *b, struct page *page)
  {
  	if (!vmballoon_send_unlock_page(b, page_to_pfn(page)))
  		return -EIO;
  
  	list_del(&page->lru);
  
  	/* deallocate page */
  	__free_page(page);
  	STATS_INC(b->stats.free);
  
  	/* update balloon size */
  	b->size--;
  
  	return 0;
  }
  
  /*
   * Release pages that were allocated while attempting to inflate the
   * balloon but were refused by the host for one reason or another.
   */
  static void vmballoon_release_refused_pages(struct vmballoon *b)
  {
  	struct page *page, *next;
  
  	list_for_each_entry_safe(page, next, &b->refused_pages, lru) {
  		list_del(&page->lru);
  		__free_page(page);
  		STATS_INC(b->stats.refused_free);
  	}
  
  	b->n_refused_pages = 0;
  }
  
  /*
   * Inflate the balloon towards its target size. Note that we try to limit
   * the rate of allocation to make sure we are not choking the rest of the
   * system.
   */
  static void vmballoon_inflate(struct vmballoon *b)
  {
  	unsigned int goal;
  	unsigned int rate;
  	unsigned int i;
  	unsigned int allocations = 0;
  	int error = 0;
  	bool alloc_can_sleep = false;
  
  	pr_debug("%s - size: %d, target %d
  ", __func__, b->size, b->target);
  
  	/*
  	 * First try NOSLEEP page allocations to inflate balloon.
  	 *
  	 * If we do not throttle nosleep allocations, we can drain all
  	 * free pages in the guest quickly (if the balloon target is high).
  	 * As a side-effect, draining free pages helps to inform (force)
  	 * the guest to start swapping if balloon target is not met yet,
  	 * which is a desired behavior. However, balloon driver can consume
  	 * all available CPU cycles if too many pages are allocated in a
  	 * second. Therefore, we throttle nosleep allocations even when
  	 * the guest is not under memory pressure. OTOH, if we have already
  	 * predicted that the guest is under memory pressure, then we
  	 * slowdown page allocations considerably.
  	 */
  
  	goal = b->target - b->size;
  	/*
  	 * Start with no sleep allocation rate which may be higher
  	 * than sleeping allocation rate.
  	 */
  	rate = b->slow_allocation_cycles ?
  			b->rate_alloc : VMW_BALLOON_NOSLEEP_ALLOC_MAX;
  
  	pr_debug("%s - goal: %d, no-sleep rate: %d, sleep rate: %d
  ",
  		 __func__, goal, rate, b->rate_alloc);
  
  	for (i = 0; i < goal; i++) {
  
  		error = vmballoon_reserve_page(b, alloc_can_sleep);
  		if (error) {
  			if (error != -ENOMEM) {
  				/*
  				 * Not a page allocation failure, stop this
  				 * cycle. Maybe we'll get new target from
  				 * the host soon.
  				 */
  				break;
  			}
  
  			if (alloc_can_sleep) {
  				/*
  				 * CANSLEEP page allocation failed, so guest
  				 * is under severe memory pressure. Quickly
  				 * decrease allocation rate.
  				 */
  				b->rate_alloc = max(b->rate_alloc / 2,
  						    VMW_BALLOON_RATE_ALLOC_MIN);
  				break;
  			}
  
  			/*
  			 * NOSLEEP page allocation failed, so the guest is
  			 * under memory pressure. Let us slow down page
  			 * allocations for next few cycles so that the guest
  			 * gets out of memory pressure. Also, if we already
  			 * allocated b->rate_alloc pages, let's pause,
  			 * otherwise switch to sleeping allocations.
  			 */
  			b->slow_allocation_cycles = VMW_BALLOON_SLOW_CYCLES;
  
  			if (i >= b->rate_alloc)
  				break;
  
  			alloc_can_sleep = true;
  			/* Lower rate for sleeping allocations. */
  			rate = b->rate_alloc;
  		}
  
  		if (++allocations > VMW_BALLOON_YIELD_THRESHOLD) {
  			cond_resched();
  			allocations = 0;
  		}
  
  		if (i >= rate) {
  			/* We allocated enough pages, let's take a break. */
  			break;
  		}
  	}
  
  	/*
  	 * We reached our goal without failures so try increasing
  	 * allocation rate.
  	 */
  	if (error == 0 && i >= b->rate_alloc) {
  		unsigned int mult = i / b->rate_alloc;
  
  		b->rate_alloc =
  			min(b->rate_alloc + mult * VMW_BALLOON_RATE_ALLOC_INC,
  			    VMW_BALLOON_RATE_ALLOC_MAX);
  	}
  
  	vmballoon_release_refused_pages(b);
  }
  
  /*
   * Decrease the size of the balloon allowing guest to use more memory.
   */
  static void vmballoon_deflate(struct vmballoon *b)
  {
  	struct page *page, *next;
  	unsigned int i = 0;
  	unsigned int goal;
  	int error;
  
  	pr_debug("%s - size: %d, target %d
  ", __func__, b->size, b->target);
  
  	/* limit deallocation rate */
  	goal = min(b->size - b->target, b->rate_free);
  
  	pr_debug("%s - goal: %d, rate: %d
  ", __func__, goal, b->rate_free);
  
  	/* free pages to reach target */
  	list_for_each_entry_safe(page, next, &b->pages, lru) {
  		error = vmballoon_release_page(b, page);
  		if (error) {
  			/* quickly decrease rate in case of error */
  			b->rate_free = max(b->rate_free / 2,
  					   VMW_BALLOON_RATE_FREE_MIN);
  			return;
  		}
  
  		if (++i >= goal)
  			break;
  	}
  
  	/* slowly increase rate if there were no errors */
  	b->rate_free = min(b->rate_free + VMW_BALLOON_RATE_FREE_INC,
  			   VMW_BALLOON_RATE_FREE_MAX);
  }
  
  /*
   * Balloon work function: reset protocol, if needed, get the new size and
   * adjust balloon as needed. Repeat in 1 sec.
   */
  static void vmballoon_work(struct work_struct *work)
  {
  	struct delayed_work *dwork = to_delayed_work(work);
  	struct vmballoon *b = container_of(dwork, struct vmballoon, dwork);
  	unsigned int target;
  
  	STATS_INC(b->stats.timer);
  
  	if (b->reset_required)
  		vmballoon_reset(b);
  
  	if (b->slow_allocation_cycles > 0)
  		b->slow_allocation_cycles--;
  
  	if (vmballoon_send_get_target(b, &target)) {
  		/* update target, adjust size */
  		b->target = target;
  
  		if (b->size < target)
  			vmballoon_inflate(b);
  		else if (b->size > target)
  			vmballoon_deflate(b);
  	}
  
  	/*
  	 * We are using a freezable workqueue so that balloon operations are
  	 * stopped while the system transitions to/from sleep/hibernation.
  	 */
  	queue_delayed_work(system_freezable_wq,
  			   dwork, round_jiffies_relative(HZ));
  }
  
  /*
   * DEBUGFS Interface
   */
  #ifdef CONFIG_DEBUG_FS
  
  static int vmballoon_debug_show(struct seq_file *f, void *offset)
  {
  	struct vmballoon *b = f->private;
  	struct vmballoon_stats *stats = &b->stats;
  
  	/* format size info */
  	seq_printf(f,
  		   "target:             %8d pages
  "
  		   "current:            %8d pages
  ",
  		   b->target, b->size);
  
  	/* format rate info */
  	seq_printf(f,
  		   "rateNoSleepAlloc:   %8d pages/sec
  "
  		   "rateSleepAlloc:     %8d pages/sec
  "
  		   "rateFree:           %8d pages/sec
  ",
  		   VMW_BALLOON_NOSLEEP_ALLOC_MAX,
  		   b->rate_alloc, b->rate_free);
  
  	seq_printf(f,
  		   "
  "
  		   "timer:              %8u
  "
  		   "start:              %8u (%4u failed)
  "
  		   "guestType:          %8u (%4u failed)
  "
  		   "lock:               %8u (%4u failed)
  "
  		   "unlock:             %8u (%4u failed)
  "
  		   "target:             %8u (%4u failed)
  "
  		   "primNoSleepAlloc:   %8u (%4u failed)
  "
  		   "primCanSleepAlloc:  %8u (%4u failed)
  "
  		   "primFree:           %8u
  "
  		   "errAlloc:           %8u
  "
  		   "errFree:            %8u
  ",
  		   stats->timer,
  		   stats->start, stats->start_fail,
  		   stats->guest_type, stats->guest_type_fail,
  		   stats->lock,  stats->lock_fail,
  		   stats->unlock, stats->unlock_fail,
  		   stats->target, stats->target_fail,
  		   stats->alloc, stats->alloc_fail,
  		   stats->sleep_alloc, stats->sleep_alloc_fail,
  		   stats->free,
  		   stats->refused_alloc, stats->refused_free);
  
  	return 0;
  }
  
  static int vmballoon_debug_open(struct inode *inode, struct file *file)
  {
  	return single_open(file, vmballoon_debug_show, inode->i_private);
  }
  
  static const struct file_operations vmballoon_debug_fops = {
  	.owner		= THIS_MODULE,
  	.open		= vmballoon_debug_open,
  	.read		= seq_read,
  	.llseek		= seq_lseek,
  	.release	= single_release,
  };
  
  static int __init vmballoon_debugfs_init(struct vmballoon *b)
  {
  	int error;
  
  	b->dbg_entry = debugfs_create_file("vmmemctl", S_IRUGO, NULL, b,
  					   &vmballoon_debug_fops);
  	if (IS_ERR(b->dbg_entry)) {
  		error = PTR_ERR(b->dbg_entry);
  		pr_err("failed to create debugfs entry, error: %d
  ", error);
  		return error;
  	}
  
  	return 0;
  }
  
  static void __exit vmballoon_debugfs_exit(struct vmballoon *b)
  {
  	debugfs_remove(b->dbg_entry);
  }
  
  #else
  
  static inline int vmballoon_debugfs_init(struct vmballoon *b)
  {
  	return 0;
  }
  
  static inline void vmballoon_debugfs_exit(struct vmballoon *b)
  {
  }
  
  #endif	/* CONFIG_DEBUG_FS */
  
  static int __init vmballoon_init(void)
  {
  	int error;
  
  	/*
  	 * Check if we are running on VMware's hypervisor and bail out
  	 * if we are not.
  	 */
  	if (x86_hyper != &x86_hyper_vmware)
  		return -ENODEV;
  
  	INIT_LIST_HEAD(&balloon.pages);
  	INIT_LIST_HEAD(&balloon.refused_pages);
  
  	/* initialize rates */
  	balloon.rate_alloc = VMW_BALLOON_RATE_ALLOC_MAX;
  	balloon.rate_free = VMW_BALLOON_RATE_FREE_MAX;
  
  	INIT_DELAYED_WORK(&balloon.dwork, vmballoon_work);
  
  	/*
  	 * Start balloon.
  	 */
  	if (!vmballoon_send_start(&balloon)) {
  		pr_err("failed to send start command to the host
  ");
  		return -EIO;
  	}
  
  	if (!vmballoon_send_guest_id(&balloon)) {
  		pr_err("failed to send guest ID to the host
  ");
  		return -EIO;
  	}
  
  	error = vmballoon_debugfs_init(&balloon);
  	if (error)
  		return error;
  
  	queue_delayed_work(system_freezable_wq, &balloon.dwork, 0);
  
  	return 0;
  }
  module_init(vmballoon_init);
  
  static void __exit vmballoon_exit(void)
  {
  	cancel_delayed_work_sync(&balloon.dwork);
  
  	vmballoon_debugfs_exit(&balloon);
  
  	/*
  	 * Deallocate all reserved memory, and reset connection with monitor.
  	 * Reset connection before deallocating memory to avoid potential for
  	 * additional spurious resets from guest touching deallocated pages.
  	 */
  	vmballoon_send_start(&balloon);
  	vmballoon_pop(&balloon);
  }
  module_exit(vmballoon_exit);