[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: NSteven Whitehouse <swhiteho@redhat.com>

fs/gfs2/glock.c

@@ -311,8 +311,7 @@ int gfs2_glock_get(struct gfs2_sbd *sdp, uint64_t number,
 	/* If this glock protects actual on-disk data or metadata blocks,
 	   create a VFS inode to manage the pages/buffers holding them. */
 	if (glops == &gfs2_inode_glops ||
-	    glops == &gfs2_rgrp_glops ||
-	    glops == &gfs2_meta_glops) {
+	    glops == &gfs2_rgrp_glops) {
 		gl->gl_aspace = gfs2_aspace_get(sdp);
 		if (!gl->gl_aspace) {
 			error = -ENOMEM;

fs/gfs2/glops.c

@@ -156,18 +156,6 @@ static void meta_go_inval(struct gfs2_glock *gl, int flags)
 	gl->gl_vn++;
 }
 
-/**
- * meta_go_demote_ok - Check to see if it's ok to unlock a glock
- * @gl: the glock
- *
- * Returns: 1 if we have no cached data; ok to demote meta glock
- */
-
-static int meta_go_demote_ok(struct gfs2_glock *gl)
-{
-	return !gl->gl_aspace->i_mapping->nrpages;
-}
-
 /**
  * inode_go_xmote_th - promote/demote a glock
  * @gl: the glock
@@ -338,11 +326,12 @@ static void inode_go_unlock(struct gfs2_holder *gh)
 	struct gfs2_glock *gl = gh->gh_gl;
 	struct gfs2_inode *ip = gl->gl_object;
 
-	if (ip && test_bit(GLF_DIRTY, &gl->gl_flags))
-		gfs2_inode_attr_in(ip);
+	if (ip) {
+		if (test_bit(GLF_DIRTY, &gl->gl_flags))
+			gfs2_inode_attr_in(ip);
 
-	if (ip)
 		gfs2_meta_cache_flush(ip);
+	}
 }
 
 /**
@@ -507,9 +496,6 @@ static int quota_go_demote_ok(struct gfs2_glock *gl)
 struct gfs2_glock_operations gfs2_meta_glops = {
 	.go_xmote_th = gfs2_glock_xmote_th,
 	.go_drop_th = gfs2_glock_drop_th,
-	.go_sync = meta_go_sync,
-	.go_inval = meta_go_inval,
-	.go_demote_ok = meta_go_demote_ok,
 	.go_type = LM_TYPE_META
 };
 

fs/gfs2/ops_fstype.c

@@ -310,11 +310,6 @@ static int init_sb(struct gfs2_sbd *sdp, int silent, int undo)
 		       sdp->sd_sb.sb_bsize, (unsigned int)PAGE_SIZE);
 		goto out;
 	}
-
-	/* Get rid of buffers from the original block size */
-	sb_gh.gh_gl->gl_ops->go_inval(sb_gh.gh_gl, DIO_METADATA | DIO_DATA);
-	sb_gh.gh_gl->gl_aspace->i_blkbits = sdp->sd_sb.sb_bsize_shift;
-
 	sb_set_blocksize(sb, sdp->sd_sb.sb_bsize);
 
 	/* Get the root inode */

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 */