[PATCH 2/2] [mmotm v2] ramzswap: add handlers for various swap events

[Nitin Gupta <ngupta@vflare.org>]

The SWAPON handler sets callback which frees memory associated
with given swap slot, eliminating any stale data in corresponding
ramzswap device.

v2: add calls to unregister all notifiers during module unload.

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
---
 drivers/staging/ramzswap/ramzswap_drv.c   |   73 +++++++++++++++++++++++++++++
 drivers/staging/ramzswap/ramzswap_drv.h   |    1 +
 drivers/staging/ramzswap/ramzswap_ioctl.h |    1 +
 3 files changed, 75 insertions(+), 0 deletions(-)

diff --git a/drivers/staging/ramzswap/ramzswap_drv.c b/drivers/staging/ramzswap/ramzswap_drv.c
index b839f05..fd4db0f 100644
--- a/drivers/staging/ramzswap/ramzswap_drv.c
+++ b/drivers/staging/ramzswap/ramzswap_drv.c
@@ -276,6 +276,7 @@ void ramzswap_ioctl_get_stats(struct ramzswap *rzs,
 	s->failed_reads = rs->failed_reads;
 	s->failed_writes = rs->failed_writes;
 	s->invalid_io = rs->invalid_io;
+	s->notify_free = rs->notify_free;
 	s->pages_zero = rs->pages_zero;
 
 	s->good_compress_pct = good_compress_perc;
@@ -1355,6 +1356,51 @@ static void create_device(struct ramzswap *rzs, int device_id)
 
 	rzs->init_done = 0;
 }
+static int ramzswap_slot_free_notify(struct notifier_block *self,
+			unsigned long index, void *swap_file)
+{
+	struct ramzswap *rzs;
+
+	rzs = ((struct file *)swap_file)->private_data;
+	ramzswap_free_page(rzs, index);
+	stat_inc(rzs->stats.notify_free);
+	return 0;
+}
+
+static struct notifier_block ramzswap_slot_free_nb = {
+	.notifier_call = ramzswap_slot_free_notify
+};
+
+static int ramzswap_swapon_notify(struct notifier_block *self,
+			unsigned long swap_id, void *swap_file)
+{
+	int ret = 0;
+	struct block_device *bdev;
+	struct file *file;
+	struct inode *inode;
+	struct ramzswap *rzs;
+
+	/* cache ramzswap struct associated with this swap_file */
+	file = (struct file *)swap_file;
+	inode = file->f_mapping->host;
+	bdev = I_BDEV(inode);
+	rzs = bdev->bd_disk->private_data;
+	file->private_data = rzs;
+
+	ret = register_swap_event_notifier(&ramzswap_slot_free_nb,
+				SWAP_EVENT_SLOT_FREE, swap_id);
+	if (ret)
+		pr_err("Error registering swap free notifier\n");
+	return ret;
+}
+
+static int ramzswap_swapoff_notify(struct notifier_block *self,
+			unsigned long swap_id, void *swap_file)
+{
+	unregister_swap_event_notifier(&ramzswap_slot_free_nb,
+				SWAP_EVENT_SLOT_FREE, swap_id);
+	return 0;
+}
 
 static void destroy_device(struct ramzswap *rzs)
 {
@@ -1367,6 +1413,14 @@ static void destroy_device(struct ramzswap *rzs)
 		blk_cleanup_queue(rzs->queue);
 }
 
+static struct notifier_block ramzswap_swapon_nb = {
+	.notifier_call = ramzswap_swapon_notify
+};
+
+static struct notifier_block ramzswap_swapoff_nb = {
+	.notifier_call = ramzswap_swapoff_notify
+};
+
 static int __init ramzswap_init(void)
 {
 	int i, ret;
@@ -1399,6 +1453,20 @@ static int __init ramzswap_init(void)
 	for (i = 0; i < num_devices; i++)
 		create_device(&devices[i], i);
 
+	ret = register_swap_event_notifier(&ramzswap_swapon_nb,
+				SWAP_EVENT_SWAPON, 0);
+	if (ret) {
+		pr_err("Error registering swapon notifier\n");
+		goto out;
+	}
+
+	ret = register_swap_event_notifier(&ramzswap_swapoff_nb,
+				SWAP_EVENT_SWAPOFF, 0);
+	if (ret) {
+		pr_err("Error registering swapoff notifier\n");
+		goto out;
+	}
+
 	return 0;
 out:
 	unregister_blkdev(ramzswap_major, "ramzswap");
@@ -1410,6 +1478,11 @@ static void __exit ramzswap_exit(void)
 	int i;
 	struct ramzswap *rzs;
 
+	unregister_swap_event_notifier(&ramzswap_swapon_nb,
+				SWAP_EVENT_SWAPON, 0);
+	unregister_swap_event_notifier(&ramzswap_swapoff_nb,
+				SWAP_EVENT_SWAPOFF, 0);
+
 	for (i = 0; i < num_devices; i++) {
 		rzs = &devices[i];
 
diff --git a/drivers/staging/ramzswap/ramzswap_drv.h b/drivers/staging/ramzswap/ramzswap_drv.h
index a6ea240..adc841a 100644
--- a/drivers/staging/ramzswap/ramzswap_drv.h
+++ b/drivers/staging/ramzswap/ramzswap_drv.h
@@ -124,6 +124,7 @@ struct ramzswap_stats {
 	u64 failed_reads;	/* can happen when memory is too low */
 	u64 failed_writes;	/* should NEVER! happen */
 	u64 invalid_io;		/* non-swap I/O requests */
+	u64 notify_free;	/* no. of swap slot free notifications */
 	u32 pages_zero;		/* no. of zero filled pages */
 	u32 pages_stored;	/* no. of pages currently stored */
 	u32 good_compress;	/* % of pages with compression ratio<=50% */
diff --git a/drivers/staging/ramzswap/ramzswap_ioctl.h b/drivers/staging/ramzswap/ramzswap_ioctl.h
index c713a09..ec50416 100644
--- a/drivers/staging/ramzswap/ramzswap_ioctl.h
+++ b/drivers/staging/ramzswap/ramzswap_ioctl.h
@@ -27,6 +27,7 @@ struct ramzswap_ioctl_stats {
 	u64 failed_reads;	/* can happen when memory is too low */
 	u64 failed_writes;	/* should NEVER! happen */
 	u64 invalid_io;		/* non-swap I/O requests */
+	u64 notify_free;	/* no. of swap slot free notifications */
 	u32 pages_zero;		/* no. of zero filled pages */
 	u32 good_compress_pct;	/* no. of pages with compression ratio<=50% */
 	u32 pages_expand_pct;	/* no. of incompressible pages */
-- 
1.6.2.5