[GFS2] Use a bio to read the superblock

This means that we don't need to create a special inode just to contain
a struct address_space in order to read a single disk block. Instead
we read the disk block directly. Its slightly faster, and uses slightly
less memory, but the real reason for doing this is that it removes a
special case from the glock code.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 59 insertions, 10 deletions

diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index f2d287660cc9..48fd4cb49c1e 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -14,6 +14,7 @@
 #include <linux/buffer_head.h>
 #include <linux/crc32.h>
 #include <linux/gfs2_ondisk.h>
+#include <linux/bio.h>
 
 #include "gfs2.h"
 #include "lm_interface.h"
@@ -157,6 +158,54 @@ int gfs2_check_sb(struct gfs2_sbd *sdp, struct gfs2_sb *sb, int silent)
         return 0;
 }
 
+
+static int end_bio_io_page(struct bio *bio, unsigned int bytes_done, int error)
+{
+        struct page *page = bio->bi_private;
+        if (bio->bi_size)
+                return 1;
+
+        if (!error)
+                SetPageUptodate(page);
+        unlock_page(page);
+        return 0;
+}
+
+static struct page *gfs2_read_super(struct super_block *sb, sector_t sector)
+{
+        struct page *page;
+        struct bio *bio;
+
+        page = alloc_page(GFP_KERNEL);
+        if (unlikely(!page))
+                return NULL;
+
+        ClearPageUptodate(page);
+        ClearPageDirty(page);
+        lock_page(page);
+
+        bio = bio_alloc(GFP_KERNEL, 1);
+        if (unlikely(!bio)) {
+                __free_page(page);
+                return NULL;
+        }
+
+        bio->bi_sector = sector;
+        bio->bi_bdev = sb->s_bdev;
+        bio_add_page(bio, page, PAGE_SIZE, 0);
+
+        bio->bi_end_io = end_bio_io_page;
+        bio->bi_private = page;
+        submit_bio(READ | BIO_RW_SYNC, bio);
+        wait_on_page_locked(page);
+        bio_put(bio);
+        if (!PageUptodate(page)) {
+                __free_page(page);
+                return NULL;
+        }
+        return page;
+}
+
 /**
  * gfs2_read_sb - Read super block
  * @sdp: The GFS2 superblock
@@ -167,23 +216,23 @@ int gfs2_check_sb(struct gfs2_sbd *sdp, struct gfs2_sb *sb, int silent)
 
 int gfs2_read_sb(struct gfs2_sbd *sdp, struct gfs2_glock *gl, int silent)
 {
-        struct buffer_head *bh;
         uint32_t hash_blocks, ind_blocks, leaf_blocks;
         uint32_t tmp_blocks;
         unsigned int x;
         int error;
+        struct page *page;
+        char *sb;
 
-        error = gfs2_meta_read(gl, GFS2_SB_ADDR >> sdp->sd_fsb2bb_shift,
-                               DIO_FORCE | DIO_START | DIO_WAIT, &bh);
-        if (error) {
+        page = gfs2_read_super(sdp->sd_vfs, GFS2_SB_ADDR >> sdp->sd_fsb2bb_shift);
+        if (!page) {
                 if (!silent)
                         fs_err(sdp, "can't read superblock\n");
-                return error;
+                return -EIO;
         }
-
-        gfs2_assert(sdp, sizeof(struct gfs2_sb) <= bh->b_size);
-        gfs2_sb_in(&sdp->sd_sb, bh->b_data);
-        brelse(bh);
+        sb = kmap(page);
+        gfs2_sb_in(&sdp->sd_sb, sb);
+        kunmap(page);
+        __free_page(page);
 
         error = gfs2_check_sb(sdp, &sdp->sd_sb, silent);
         if (error)
@@ -202,7 +251,7 @@ int gfs2_read_sb(struct gfs2_sbd *sdp, struct gfs2_glock *gl, int silent)
         sdp->sd_hash_ptrs = sdp->sd_hash_bsize / sizeof(uint64_t);
         sdp->sd_qc_per_block = (sdp->sd_sb.sb_bsize -
                                 sizeof(struct gfs2_meta_header)) /
-                               sizeof(struct gfs2_quota_change);
+                                sizeof(struct gfs2_quota_change);
 
         /* Compute maximum reservation required to add a entry to a directory */