Staging: zram: Remove need for explicit device initialization

Currently, the user has to explicitly write a positive value to
initstate sysfs node before the device can be used. This event
triggers allocation of per-device metadata like memory pool,
table array and so on.

We do not pre-initialize all zram devices since the 'table' array,
mapping disk blocks to compressed chunks, takes considerable amount
of memory (8 bytes per page). So, pre-initializing all devices will
be quite wasteful if only few or none of the devices are actually
used.

This explicit device initialization from user is an odd requirement and
can be easily avoided. We now initialize the device when first write is
done to the device.
Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/zram/zram_drv.c

@@ -207,9 +207,15 @@ static int zram_read(struct zram *zram, struct bio *bio)
 	u32 index;
 	struct bio_vec *bvec;
 
-	zram_stat64_inc(zram, &zram->stats.num_reads);
+	if (unlikely(!zram->init_done)) {
+		set_bit(BIO_UPTODATE, &bio->bi_flags);
+		bio_endio(bio, 0);
+		return 0;
+	}
 
+	zram_stat64_inc(zram, &zram->stats.num_reads);
 	index = bio->bi_sector >> SECTORS_PER_PAGE_SHIFT;
+
 	bio_for_each_segment(bvec, bio, i) {
 		int ret;
 		size_t clen;
@@ -275,16 +281,20 @@ static int zram_read(struct zram *zram, struct bio *bio)
 
 static int zram_write(struct zram *zram, struct bio *bio)
 {
-	int i;
+	int i, ret;
 	u32 index;
 	struct bio_vec *bvec;
 
-	zram_stat64_inc(zram, &zram->stats.num_writes);
+	if (unlikely(!zram->init_done)) {
+		ret = zram_init_device(zram);
+		if (ret)
+			goto out;
+	}
 
+	zram_stat64_inc(zram, &zram->stats.num_writes);
 	index = bio->bi_sector >> SECTORS_PER_PAGE_SHIFT;
 
 	bio_for_each_segment(bvec, bio, i) {
-		int ret;
 		u32 offset;
 		size_t clen;
 		struct zobj_header *zheader;
@@ -425,11 +435,6 @@ static int zram_make_request(struct request_queue *queue, struct bio *bio)
 	int ret = 0;
 	struct zram *zram = queue->queuedata;
 
-	if (unlikely(!zram->init_done)) {
-		bio_io_error(bio);
-		return 0;
-	}
-
 	if (!valid_io_request(zram, bio)) {
 		zram_stat64_inc(zram, &zram->stats.invalid_io);
 		bio_io_error(bio);
@@ -453,7 +458,7 @@ void zram_reset_device(struct zram *zram)
 {
 	size_t index;
 
-	/* Do not accept any new I/O request */
+	mutex_lock(&zram->init_lock);
 	zram->init_done = 0;
 
 	/* Free various per-device buffers */
@@ -490,6 +495,7 @@ void zram_reset_device(struct zram *zram)
 	memset(&zram->stats, 0, sizeof(zram->stats));
 
 	zram->disksize = 0;
+	mutex_unlock(&zram->init_lock);
 }
 
 int zram_init_device(struct zram *zram)
@@ -497,9 +503,11 @@ int zram_init_device(struct zram *zram)
 	int ret;
 	size_t num_pages;
 
+	mutex_lock(&zram->init_lock);
+
 	if (zram->init_done) {
-		pr_info("Device already initialized!\n");
-		return -EBUSY;
+		mutex_unlock(&zram->init_lock);
+		return 0;
 	}
 
 	zram_set_disksize(zram, totalram_pages << PAGE_SHIFT);
@@ -542,11 +550,13 @@ int zram_init_device(struct zram *zram)
 	}
 
 	zram->init_done = 1;
+	mutex_unlock(&zram->init_lock);
 
 	pr_debug("Initialization done!\n");
 	return 0;
 
 fail:
+	mutex_unlock(&zram->init_lock);
 	zram_reset_device(zram);
 
 	pr_err("Initialization failed: err=%d\n", ret);
@@ -572,6 +582,7 @@ static int create_device(struct zram *zram, int device_id)
 	int ret = 0;
 
 	mutex_init(&zram->lock);
+	mutex_init(&zram->init_lock);
 	spin_lock_init(&zram->stat64_lock);
 
 	zram->queue = blk_alloc_queue(GFP_KERNEL);

drivers/staging/zram/zram_drv.h

@@ -108,6 +108,8 @@ struct zram {
 	struct request_queue *queue;
 	struct gendisk *disk;
 	int init_done;
+	/* Prevent concurrent execution of device init and reset */
+	struct mutex init_lock;
 	/*
 	 * This is the limit on amount of *uncompressed* worth of data
 	 * we can store in a disk.

drivers/staging/zram/zram_sysfs.c

@@ -58,8 +58,10 @@ static ssize_t disksize_store(struct device *dev,
 	int ret;
 	struct zram *zram = dev_to_zram(dev);
 
-	if (zram->init_done)
+	if (zram->init_done) {
+		pr_info("Cannot change disksize for initialized device\n");
 		return -EBUSY;
+	}
 
 	ret = strict_strtoull(buf, 10, &zram->disksize);
 	if (ret)
@@ -79,25 +81,6 @@ static ssize_t initstate_show(struct device *dev,
 	return sprintf(buf, "%u\n", zram->init_done);
 }
 
-static ssize_t initstate_store(struct device *dev,
-		struct device_attribute *attr, const char *buf, size_t len)
-{
-	int ret;
-	unsigned long do_init;
-	struct zram *zram = dev_to_zram(dev);
-
-	ret = strict_strtoul(buf, 10, &do_init);
-	if (ret)
-		return ret;
-
-	if (!do_init)
-		return -EINVAL;
-
-	zram_init_device(zram);
-
-	return len;
-}
-
 static ssize_t reset_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t len)
 {
@@ -208,8 +191,7 @@ static ssize_t mem_used_total_show(struct device *dev,
 
 static DEVICE_ATTR(disksize, S_IRUGO | S_IWUGO,
 		disksize_show, disksize_store);
-static DEVICE_ATTR(initstate, S_IRUGO | S_IWUGO,
-		initstate_show, initstate_store);
+static DEVICE_ATTR(initstate, S_IRUGO, initstate_show, NULL);
 static DEVICE_ATTR(reset, S_IWUGO, NULL, reset_store);
 static DEVICE_ATTR(num_reads, S_IRUGO, num_reads_show, NULL);
 static DEVICE_ATTR(num_writes, S_IRUGO, num_writes_show, NULL);