[PATCH 09/17] bcache: use read_cache_page_gfp to read the superblock

colyli
2020-01-23T17:02:51Z

From: Christoph Hellwig <hch@lst.de>

Avoid a pointless dependency on buffer heads in bcache by simply open
coding reading a single page. Also add a SB_OFFSET define for the
byte offset of the superblock instead of using magic numbers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Coly Li <colyli@suse.de>
---
drivers/md/bcache/super.c | 16 +++++++---------
include/uapi/linux/bcache.h | 1 +
2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 5797c03f993e..3dea1d5acd5c 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -15,7 +15,6 @@
#include "writeback.h"

#include <linux/blkdev.h>
-#include <linux/buffer_head.h>
#include <linux/debugfs.h>
#include <linux/genhd.h>
#include <linux/idr.h>
@@ -64,13 +63,14 @@ static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
{
const char *err;
struct cache_sb_disk *s;
- struct buffer_head *bh = __bread(bdev, 1, SB_SIZE);
+ struct page *page;
unsigned int i;

- if (!bh)
+ page = read_cache_page_gfp(bdev->bd_inode->i_mapping,
+ SB_OFFSET >> PAGE_SHIFT, GFP_KERNEL);
+ if (IS_ERR(page))
return "IO error";
-
- s = (struct cache_sb_disk *)bh->b_data;
+ s = page_address(page) + offset_in_page(SB_OFFSET);

sb->offset = le64_to_cpu(s->offset);
sb->version = le64_to_cpu(s->version);
@@ -188,12 +188,10 @@ static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
}

sb->last_mount = (u32)ktime_get_real_seconds();
- err = NULL;
-
- get_page(bh->b_page);
*res = s;
+ return NULL;
err:
- put_bh(bh);
+ put_page(page);
return err;
}

diff --git a/include/uapi/linux/bcache.h b/include/uapi/linux/bcache.h
index 1d8b3a9fc080..9a1965c6c3d0 100644
--- a/include/uapi/linux/bcache.h
+++ b/include/uapi/linux/bcache.h
@@ -148,6 +148,7 @@ static inline struct bkey *bkey_idx(const struct bkey *k, unsigned int nr_keys)
#define BCACHE_SB_MAX_VERSION 4

#define SB_SECTOR 8
+#define SB_OFFSET (SB_SECTOR << SECTOR_SHIFT)
#define SB_SIZE 4096
#define SB_LABEL_SIZE 32
#define SB_JOURNAL_BUCKETS 256U
--
2.16.4