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Date: Mon, 8 Apr 2013 13:49:56 -0700
From: Kent Overstreet <koverstreet@...gle.com>
To: Gabriel <g2p.code@...il.com>
Cc: linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
Gabriel <g2p.code+bcache@...il.com>
Subject: Re: [PATCH] bcache: Take data offset from the bdev superblock.
On Mon, Apr 08, 2013 at 12:11:06PM +0200, Gabriel wrote:
> Add a new superblock version, and consolidate related defines.
So, I think BDEV_WITH_OFFSET looks ok, but what's the use case for it? I
was going to add it way back but we decided not to implement the hack we
thought we needed it for - if you or someone is going to use it I'll go
ahead and apply it.
As for BCACHE_SB_VERSION_CDEV_WITH_UUID, can you explain why you added
that? I suspect it's needed but I can't remember why I didn't add it
when I added the new UUID format (or perhaps I just forgot)
>
> Signed-off-by: Gabriel de Perthuis <g2p.code+bcache@...il.com>
> ---
> drivers/md/bcache/bcache.h | 23 ++++++++++++++++++-----
> drivers/md/bcache/request.c | 2 +-
> drivers/md/bcache/super.c | 21 ++++++++++++++++-----
> 3 files changed, 35 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> index f057235..8a110e6 100644
> --- a/drivers/md/bcache/bcache.h
> +++ b/drivers/md/bcache/bcache.h
> @@ -223,11 +223,17 @@ struct bkey {
> #define BKEY_PADDED(key) \
> union { struct bkey key; uint64_t key ## _pad[BKEY_PAD]; }
>
> -/* Version 1: Backing device
> +/* Version 0: Cache device
> + * Version 1: Backing device
> * Version 2: Seed pointer into btree node checksum
> - * Version 3: New UUID format
> + * Version 3: Cache device with new UUID format
> + * Version 4: Backing device with data offset
> */
> -#define BCACHE_SB_VERSION 3
> +#define BCACHE_SB_VERSION_CDEV 0
> +#define BCACHE_SB_VERSION_BDEV 1
> +#define BCACHE_SB_VERSION_CDEV_WITH_UUID 3
> +#define BCACHE_SB_VERSION_BDEV_WITH_OFFSET 4
> +#define BCACHE_SB_MAX_VERSION 4
>
> #define SB_SECTOR 8
> #define SB_SIZE 4096
> @@ -236,13 +242,12 @@ struct bkey {
> /* SB_JOURNAL_BUCKETS must be divisible by BITS_PER_LONG */
> #define MAX_CACHES_PER_SET 8
>
> -#define BDEV_DATA_START 16 /* sectors */
> +#define BDEV_DATA_START_DEFAULT 16 /* sectors */
>
> struct cache_sb {
> uint64_t csum;
> uint64_t offset; /* sector where this sb was written */
> uint64_t version;
> -#define CACHE_BACKING_DEV 1
>
> uint8_t magic[16];
>
> @@ -485,6 +490,7 @@ struct cached_dev {
> * where it's at.
> */
> sector_t last_read;
> + sector_t data_start_sector;
>
> /* Number of writeback bios in flight */
> atomic_t in_flight;
> @@ -861,6 +867,13 @@ static inline bool key_merging_disabled(struct cache_set *c)
> #endif
> }
>
> +
> +static inline bool SB_IS_BDEV(const struct cache_sb *sb) {
> + return sb->version == BCACHE_SB_VERSION_BDEV
> + || sb->version == BCACHE_SB_VERSION_BDEV_WITH_OFFSET;
> +}
> +
> +
> struct bbio {
> unsigned submit_time_us;
> union {
> diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
> index 83731dc..9f74aff 100644
> --- a/drivers/md/bcache/request.c
> +++ b/drivers/md/bcache/request.c
> @@ -1220,7 +1220,7 @@ static void cached_dev_make_request(struct request_queue *q, struct bio *bio)
> part_stat_unlock();
>
> bio->bi_bdev = dc->bdev;
> - bio->bi_sector += BDEV_DATA_START;
> + bio->bi_sector += dc->data_start_sector;
>
> if (cached_dev_get(dc)) {
> s = search_alloc(bio, d);
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index 5fa3cd2..a409bb5 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -148,7 +148,7 @@ static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
> goto err;
>
> err = "Unsupported superblock version";
> - if (sb->version > BCACHE_SB_VERSION)
> + if (sb->version > BCACHE_SB_MAX_VERSION)
> goto err;
>
> err = "Bad block/bucket size";
> @@ -168,7 +168,7 @@ static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
> if (get_capacity(bdev->bd_disk) < sb->bucket_size * sb->nbuckets)
> goto err;
>
> - if (sb->version == CACHE_BACKING_DEV)
> + if (SB_IS_BDEV(sb))
> goto out;
>
> err = "Bad UUID";
> @@ -286,7 +286,7 @@ void bcache_write_super(struct cache_set *c)
> for_each_cache(ca, c, i) {
> struct bio *bio = &ca->sb_bio;
>
> - ca->sb.version = BCACHE_SB_VERSION;
> + ca->sb.version = BCACHE_SB_VERSION_CDEV_WITH_UUID;
> ca->sb.seq = c->sb.seq;
> ca->sb.last_mount = c->sb.last_mount;
>
> @@ -1047,9 +1047,20 @@ static const char *register_bdev(struct cache_sb *sb, struct page *sb_page,
> dc->bdev = bdev;
> dc->bdev->bd_holder = dc;
>
> + err = "bad start sector";
> + if (sb->version == BCACHE_SB_VERSION_BDEV) {
> + dc->data_start_sector = BDEV_DATA_START_DEFAULT;
> + } else {
> + if (sb->keys < 1)
> + goto err;
> + dc->data_start_sector = sb->d[0];
> + if (dc->data_start_sector < BDEV_DATA_START_DEFAULT)
> + goto err;
> + }
> +
> g = dc->disk.disk;
>
> - set_capacity(g, dc->bdev->bd_part->nr_sects - 16);
> + set_capacity(g, dc->bdev->bd_part->nr_sects - dc->data_start_sector);
>
> bch_cached_dev_request_init(dc);
>
> @@ -1802,7 +1813,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
> if (err)
> goto err_close;
>
> - if (sb->version == CACHE_BACKING_DEV) {
> + if (SB_IS_BDEV(sb)) {
> struct cached_dev *dc = kzalloc(sizeof(*dc), GFP_KERNEL);
>
> err = register_bdev(sb, sb_page, bdev, dc);
> --
> 1.8.2.rc3.7.g35aca0e
>
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