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bcache: introduce BCH_FEATURE_INCOMPAT_LOG_LARGE_BUCKET_SIZE for large bucket

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commit b16671e8f493e3df40b1fb0dff4078f391c5099a upstream.

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: ffa4703275 ("bcache: add bucket_size_hi into struct cache_sb_disk for large bucket")
Signed-off-by: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org # 5.9+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Coly Li 2021-01-04 15:41:21 +08:00 committed by Greg Kroah-Hartman
parent a9c413cd0c
commit a3601005de
4 changed files with 29 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/md/bcache/features.c
View File

@ -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 },
};

11
drivers/md/bcache/features.h
View File

@ -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)
{

22
drivers/md/bcache/super.c
View File

@ -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;
}

2
include/uapi/linux/bcache.h
View File

@ -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 */
};
/*