[PATCH 5.10 134/145] bcache: introduce BCH_FEATURE_INCOMPAT_LOG_LARGE_BUCKET_SIZE for large bucket

Greg Kroah-Hartman
2021-01-11T13:20:47Z

From: Coly Li <colyli@suse.de>

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: ffa470327572 ("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>

---
drivers/md/bcache/features.c | 2 +-
drivers/md/bcache/features.h | 11 ++++++++---
drivers/md/bcache/super.c | 22 +++++++++++++++++++---
include/uapi/linux/bcache.h | 2 +-
4 files changed, 29 insertions(+), 8 deletions(-)

--- a/drivers/md/bcache/features.c
+++ b/drivers/md/bcache/features.c
@@ -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 },
};
--- a/drivers/md/bcache/features.h
+++ b/drivers/md/bcache/features.h
@@ -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_##n
~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)
{
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -64,9 +64,25 @@ static unsigned int get_bucket_size(stru
{
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;
}
--- a/include/uapi/linux/bcache.h
+++ b/include/uapi/linux/bcache.h
@@ -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 */
};

/*