Commit b16671e8 authored by Coly Li's avatar Coly Li Committed by Jens Axboe
Browse files

bcache: introduce BCH_FEATURE_INCOMPAT_LOG_LARGE_BUCKET_SIZE for large bucket 



When large bucket feature was added, BCH_FEATURE_INCOMPAT_LARGE_BUCKET
was introduced into the incompat feature set. It used bucket_size_hi
(which was added at the tail of struct cache_sb_disk) to extend current
16bit bucket size to 32bit with existing bucket_size in struct
cache_sb_disk.

This is not a good idea, there are two obvious problems,
- Bucket size is always value power of 2, if store log2(bucket size) in
  existing bucket_size of struct cache_sb_disk, it is unnecessary to add
  bucket_size_hi.
- Macro csum_set() assumes d[SB_JOURNAL_BUCKETS] is the last member in
  struct cache_sb_disk, bucket_size_hi was added after d[] which makes
  csum_set calculate an unexpected super block checksum.

To fix the above problems, this patch introduces a new incompat feature
bit BCH_FEATURE_INCOMPAT_LOG_LARGE_BUCKET_SIZE, when this bit is set, it
means bucket_size in struct cache_sb_disk stores the order of power-of-2
bucket size value. When user specifies a bucket size larger than 32768
sectors, BCH_FEATURE_INCOMPAT_LOG_LARGE_BUCKET_SIZE will be set to
incompat feature set, and bucket_size stores log2(bucket size) more
than store the real bucket size value.

The obsoleted BCH_FEATURE_INCOMPAT_LARGE_BUCKET won't be used anymore,
it is renamed to BCH_FEATURE_INCOMPAT_OBSO_LARGE_BUCKET and still only
recognized by kernel driver for legacy compatible purpose. The previous
bucket_size_hi is renmaed to obso_bucket_size_hi in struct cache_sb_disk
and not used in bcache-tools anymore.

For cache device created with BCH_FEATURE_INCOMPAT_LARGE_BUCKET feature,
bcache-tools and kernel driver still recognize the feature string and
display it as "obso_large_bucket".

With this change, the unnecessary extra space extend of bcache on-disk
super block can be avoided, and csum_set() may generate expected check
sum as well.

Fixes: ffa47032 ("bcache: add bucket_size_hi into struct cache_sb_disk for large bucket")
Signed-off-by: default avatarColy Li <colyli@suse.de>
Cc: stable@vger.kernel.org # 5.9+
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 1dfc0686

drivers/md/bcache/features.c

+1 −1
Original line number Diff line number Diff line
@@ -17,7 +17,7 @@ struct feature { 
};



static struct feature feature_list[] = {

	{BCH_FEATURE_INCOMPAT, BCH_FEATURE_INCOMPAT_LARGE_BUCKET,

	{BCH_FEATURE_INCOMPAT, BCH_FEATURE_INCOMPAT_LOG_LARGE_BUCKET_SIZE,

		"large_bucket"},

	{0, 0, 0 },

};

drivers/md/bcache/features.h

+8 −3
Original line number Diff line number Diff line
@@ -13,11 +13,15 @@ 


/* Feature set definition */

/* Incompat feature set */

#define BCH_FEATURE_INCOMPAT_LARGE_BUCKET	0x0001 /* 32bit bucket size */

/* 32bit bucket size, obsoleted */

#define BCH_FEATURE_INCOMPAT_OBSO_LARGE_BUCKET		0x0001

/* real bucket size is (1 << bucket_size) */

#define BCH_FEATURE_INCOMPAT_LOG_LARGE_BUCKET_SIZE	0x0002



#define BCH_FEATURE_COMPAT_SUPP		0

#define BCH_FEATURE_RO_COMPAT_SUPP	0

#define BCH_FEATURE_INCOMPAT_SUPP	BCH_FEATURE_INCOMPAT_LARGE_BUCKET

#define BCH_FEATURE_INCOMPAT_SUPP	(BCH_FEATURE_INCOMPAT_OBSO_LARGE_BUCKET| \

					 BCH_FEATURE_INCOMPAT_LOG_LARGE_BUCKET_SIZE)



#define BCH_HAS_COMPAT_FEATURE(sb, mask) \

		((sb)->feature_compat & (mask))
@@ -77,7 +81,8 @@ static inline void bch_clear_feature_##name(struct cache_sb *sb) \ 
		~BCH##_FEATURE_INCOMPAT_##flagname; \

}



BCH_FEATURE_INCOMPAT_FUNCS(large_bucket, LARGE_BUCKET);

BCH_FEATURE_INCOMPAT_FUNCS(obso_large_bucket, OBSO_LARGE_BUCKET);

BCH_FEATURE_INCOMPAT_FUNCS(large_bucket, LOG_LARGE_BUCKET_SIZE);



static inline bool bch_has_unknown_compat_features(struct cache_sb *sb)

{

drivers/md/bcache/super.c

+19 −3
Original line number Diff line number Diff line
@@ -64,9 +64,25 @@ static unsigned int get_bucket_size(struct cache_sb *sb, struct cache_sb_disk *s 
{

	unsigned int bucket_size = le16_to_cpu(s->bucket_size);



	if (sb->version >= BCACHE_SB_VERSION_CDEV_WITH_FEATURES &&

	     bch_has_feature_large_bucket(sb))

		bucket_size |= le16_to_cpu(s->bucket_size_hi) << 16;

	if (sb->version >= BCACHE_SB_VERSION_CDEV_WITH_FEATURES) {

		if (bch_has_feature_large_bucket(sb)) {

			unsigned int max, order;



			max = sizeof(unsigned int) * BITS_PER_BYTE - 1;

			order = le16_to_cpu(s->bucket_size);

			/*

			 * bcache tool will make sure the overflow won't

			 * happen, an error message here is enough.

			 */

			if (order > max)

				pr_err("Bucket size (1 << %u) overflows\n",

					order);

			bucket_size = 1 << order;

		} else if (bch_has_feature_obso_large_bucket(sb)) {

			bucket_size +=

				le16_to_cpu(s->obso_bucket_size_hi) << 16;

		}

	}



	return bucket_size;

}

include/uapi/linux/bcache.h

+1 −1
Original line number Diff line number Diff line
@@ -213,7 +213,7 @@ struct cache_sb_disk { 
		__le16		keys;

	};

	__le64			d[SB_JOURNAL_BUCKETS];	/* journal buckets */

	__le16			bucket_size_hi;

	__le16			obso_bucket_size_hi;	/* obsoleted */

};



/*