gfs2: Zero out fallocated blocks in fallocate_chunk

Instead of zeroing out fallocated blocks in gfs2_iomap_alloc, zero them
out in fallocate_chunk, much higher up the call stack.  This gets rid of
gfs2's abuse of the IOMAP_ZERO flag as well as the gfs2 specific zeronew
buffer flag.  I can't think of a reason why zeroing out the blocks in
gfs2_iomap_alloc would have any benefits: there is no additional locking
at that level that would add protection to the newly allocated blocks.

While at it, change fallocate over from gs2_block_map to gfs2_iomap_begin.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Acked-by: Christoph Hellwig <hch@lst.de>

fs/gfs2/bmap.c

@@ -491,14 +491,12 @@ static int gfs2_iomap_alloc(struct inode *inode, struct iomap *iomap,
 {
 	struct gfs2_inode *ip = GFS2_I(inode);
 	struct gfs2_sbd *sdp = GFS2_SB(inode);
-	struct super_block *sb = sdp->sd_vfs;
 	struct buffer_head *dibh = mp->mp_bh[0];
 	u64 bn;
 	unsigned n, i, blks, alloced = 0, iblks = 0, branch_start = 0;
 	unsigned dblks = 0;
 	unsigned ptrs_per_blk;
 	const unsigned end_of_metadata = mp->mp_fheight - 1;
-	int ret;
 	enum alloc_state state;
 	__be64 *ptr;
 	__be64 zero_bn = 0;
@@ -607,15 +605,6 @@ static int gfs2_iomap_alloc(struct inode *inode, struct iomap *iomap,
 			iomap->flags |= IOMAP_F_NEW;
 			while (n-- > 0)
 				*ptr++ = cpu_to_be64(bn++);
-			if (flags & IOMAP_ZERO) {
-				ret = sb_issue_zeroout(sb, iomap->addr >> inode->i_blkbits,
-						       dblks, GFP_NOFS);
-				if (ret) {
-					fs_err(sdp,
-					       "Failed to zero data buffers\n");
-					flags &= ~IOMAP_ZERO;
-				}
-			}
 			break;
 		}
 	} while (iomap->addr == IOMAP_NULL_ADDR);
@@ -846,8 +835,6 @@ int gfs2_block_map(struct inode *inode, sector_t lblock,
 
 	if (create)
 		flags |= IOMAP_WRITE;
-	if (buffer_zeronew(bh_map))
-		flags |= IOMAP_ZERO;
 	ret = gfs2_iomap_begin(inode, (loff_t)lblock << inode->i_blkbits,
 			       bh_map->b_size, flags, &iomap);
 	if (ret) {

fs/gfs2/file.c

@@ -729,11 +729,12 @@ static ssize_t gfs2_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 static int fallocate_chunk(struct inode *inode, loff_t offset, loff_t len,
 			   int mode)
 {
+	struct super_block *sb = inode->i_sb;
 	struct gfs2_inode *ip = GFS2_I(inode);
+	loff_t end = offset + len;
 	struct buffer_head *dibh;
+	struct iomap iomap;
 	int error;
-	unsigned int nr_blks;
-	sector_t lblock = offset >> inode->i_blkbits;
 
 	error = gfs2_meta_inode_buffer(ip, &dibh);
 	if (unlikely(error))
@@ -747,21 +748,19 @@ static int fallocate_chunk(struct inode *inode, loff_t offset, loff_t len,
 			goto out;
 	}
 
-	while (len) {
-		struct buffer_head bh_map = { .b_state = 0, .b_blocknr = 0 };
-		bh_map.b_size = len;
-		set_buffer_zeronew(&bh_map);
-
-		error = gfs2_block_map(inode, lblock, &bh_map, 1);
-		if (unlikely(error))
+	while (offset < end) {
+		error = gfs2_iomap_begin(inode, offset, end - offset,
+					 IOMAP_WRITE, &iomap);
+		if (error)
 			goto out;
-		len -= bh_map.b_size;
-		nr_blks = bh_map.b_size >> inode->i_blkbits;
-		lblock += nr_blks;
-		if (!buffer_new(&bh_map))
+		offset = iomap.offset + iomap.length;
+		if (iomap.type != IOMAP_HOLE)
 			continue;
-		if (unlikely(!buffer_zeronew(&bh_map))) {
-			error = -EIO;
+		error = sb_issue_zeroout(sb, iomap.addr >> inode->i_blkbits,
+					 iomap.length >> inode->i_blkbits,
+					 GFP_NOFS);
+		if (error) {
+			fs_err(GFS2_SB(inode), "Failed to zero data buffers\n");
 			goto out;
 		}
 	}

fs/gfs2/incore.h

@@ -130,15 +130,12 @@ static inline bool gfs2_rbm_eq(const struct gfs2_rbm *rbm1,
 enum gfs2_state_bits {
 	BH_Pinned = BH_PrivateStart,
 	BH_Escaped = BH_PrivateStart + 1,
-	BH_Zeronew = BH_PrivateStart + 2,
 };
 
 BUFFER_FNS(Pinned, pinned)
 TAS_BUFFER_FNS(Pinned, pinned)
 BUFFER_FNS(Escaped, escaped)
 TAS_BUFFER_FNS(Escaped, escaped)
-BUFFER_FNS(Zeronew, zeronew)
-TAS_BUFFER_FNS(Zeronew, zeronew)
 
 struct gfs2_bufdata {
 	struct buffer_head *bd_bh;