Hi!
> > Question for you was... Is the first 1KiB of each ext4 filesystem still
> > free and "reserved for a bootloader"?
>
> Yes.
>
> > If I needed more for bcache superblock (8KiB, IIRC), would that be
> > easy to accomplish on existing filesystem?
>
> Huh? Why would the bcache superblock matter when you're talking about
> the ext4 layout? The bcache superblock will be on the bcache
> device/partition, and the ext4 superblock will be on the ext4
> device/partition.
So this is what I came up with so far. With SSD in USB2 envelope (and
previous version of the patch), git diff goes from 9seconds to
3seconds; not too bad. git diff on (different) ssd is 1.5seconds.
Warning: this is rather dangerous, as it is easy to make cache go
out-of-sync with data partition. To solve that...
Is there some field in ext2 superblock that changes every time
filesystem is changed? Is mtime changed by fsck/badblocks/...?
Best regards,
Pavel
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index e57353e..f8c0aef 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -6,6 +6,7 @@
* Copyright 2012 Google, Inc.
*/
+#define DEBUG
#include "bcache.h"
#include "btree.h"
#include "debug.h"
@@ -67,7 +68,7 @@ static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
{
const char *err;
struct cache_sb *s;
- struct buffer_head *bh = __bread(bdev, 1, SB_SIZE);
+ struct buffer_head *bh = __bread(bdev, SB_SECTOR/8, SB_SIZE);
unsigned i;
if (!bh)
@@ -95,10 +96,11 @@ static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
pr_debug("read sb version %llu, flags %llu, seq %llu, journal size %u",
sb->version, sb->flags, sb->seq, sb->keys);
- err = "Not a bcache superblock";
+ err = "Not a bcache superblock: offset";
if (sb->offset != SB_SECTOR)
goto err;
+ err = "Not a bcache superblock: magic";
if (memcmp(sb->magic, bcache_magic, 16))
goto err;
@@ -124,7 +126,7 @@ static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
case BCACHE_SB_VERSION_BDEV:
sb->data_offset = BDEV_DATA_START_DEFAULT;
break;
- case BCACHE_SB_VERSION_BDEV_WITH_OFFSET:
+// case BCACHE_SB_VERSION_BDEV_WITH_OFFSET:
sb->data_offset = le64_to_cpu(s->data_offset);
err = "Bad data offset";
@@ -132,6 +134,15 @@ static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
goto err;
break;
+ case BCACHE_SB_VERSION_BDEV_WITH_OFFSET:
+ case BCACHE_SB_VERSION_BDEV_EXT4_LITE:
+ sb->data_offset = le64_to_cpu(s->data_offset);
+ printk("Size of sb is %d\n", sizeof(*sb));
+ WARN_ON(sizeof(*sb) > 1024);
+ if (sizeof(*sb) > 1024)
+ goto err;
+ break;
+
case BCACHE_SB_VERSION_CDEV:
case BCACHE_SB_VERSION_CDEV_WITH_UUID:
sb->nbuckets = le64_to_cpu(s->nbuckets);
diff --git a/include/uapi/linux/bcache.h b/include/uapi/linux/bcache.h
index e3bb063..b1ef80c 100644
--- a/include/uapi/linux/bcache.h
+++ b/include/uapi/linux/bcache.h
@@ -142,12 +142,13 @@ static inline struct bkey *bkey_idx(const struct bkey *k, unsigned nr_keys)
#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 BCACHE_SB_VERSION_BDEV_EXT4_LITE 5
+#define BCACHE_SB_MAX_VERSION 5
-#define SB_SECTOR 8
+#define SB_SECTOR 0
#define SB_SIZE 4096
#define SB_LABEL_SIZE 32
-#define SB_JOURNAL_BUCKETS 256U
+#define SB_JOURNAL_BUCKETS 64U
/* SB_JOURNAL_BUCKETS must be divisible by BITS_PER_LONG */
#define MAX_CACHES_PER_SET 8
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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