[Cluster-devel] [PATCH 2/2] gfs2: Add support for IOMAP_ZERO

[Christoph Hellwig <hch@lst.de>]

Don't we actually need the write lock for zeroing as well?  Also
I think the alloc helper would be nice to keep, and a little use
of switch might clean things up.  How about something like this
instead?

diff --git a/fs/gfs2/bmap.c b/fs/gfs2/bmap.c
index f42718dd292f..8f5a25f507c3 100644
--- a/fs/gfs2/bmap.c
+++ b/fs/gfs2/bmap.c
@@ -1027,17 +1027,8 @@ static int gfs2_iomap_begin_write(struct inode *inode, loff_t pos,
 	bool unstuff, alloc_required;
 	int ret;
 
-	ret = gfs2_write_lock(inode);
-	if (ret)
-		return ret;
-
 	unstuff = gfs2_is_stuffed(ip) &&
 		  pos + length > gfs2_max_stuffed_size(ip);
-
-	ret = gfs2_iomap_get(inode, pos, length, flags, iomap, mp);
-	if (ret)
-		goto out_unlock;
-
 	alloc_required = unstuff || iomap->type == IOMAP_HOLE;
 
 	if (alloc_required || gfs2_is_jdata(ip))
@@ -1051,7 +1042,7 @@ static int gfs2_iomap_begin_write(struct inode *inode, loff_t pos,
 
 		ret = gfs2_quota_lock_check(ip, &ap);
 		if (ret)
-			goto out_unlock;
+			return ret;
 
 		ret = gfs2_inplace_reserve(ip, &ap);
 		if (ret)
@@ -1118,11 +1109,23 @@ static int gfs2_iomap_begin_write(struct inode *inode, loff_t pos,
 out_qunlock:
 	if (alloc_required)
 		gfs2_quota_unlock(ip);
-out_unlock:
-	gfs2_write_unlock(inode);
 	return ret;
 }
 
+static inline bool gfs2_iomap_need_write_lock(unsigned flags)
+{
+	switch (flags & (IOMAP_WRITE | IOMAP_ZERO)) {
+	case IOMAP_WRITE:
+		if (flags & IOMAP_DIRECT)
+			return false;
+		return true;
+	case IOMAP_ZERO:
+		return true;
+	default:
+		return false;
+	}
+}
+
 static int gfs2_iomap_begin(struct inode *inode, loff_t pos, loff_t length,
 			    unsigned flags, struct iomap *iomap)
 {
@@ -1133,20 +1136,48 @@ static int gfs2_iomap_begin(struct inode *inode, loff_t pos, loff_t length,
 	iomap->flags |= IOMAP_F_BUFFER_HEAD;
 
 	trace_gfs2_iomap_start(ip, pos, length, flags);
-	if ((flags & IOMAP_WRITE) && !(flags & IOMAP_DIRECT)) {
-		ret = gfs2_iomap_begin_write(inode, pos, length, flags, iomap, &mp);
-	} else {
-		ret = gfs2_iomap_get(inode, pos, length, flags, iomap, &mp);
 
-		/*
-		 * Silently fall back to buffered I/O for stuffed files or if
-		 * we've hot a hole (see gfs2_file_direct_write).
-		 */
-		if ((flags & IOMAP_WRITE) && (flags & IOMAP_DIRECT) &&
-		    iomap->type != IOMAP_MAPPED)
-			ret = -ENOTBLK;
+	if (gfs2_iomap_need_write_lock(flags)) {
+		ret = gfs2_write_lock(inode);
+		if (ret)
+			goto out;
 	}
+
+	ret = gfs2_iomap_get(inode, pos, length, flags, iomap, &mp);
+	if (ret)
+		goto out_unlock;
+
+	switch (flags & (IOMAP_WRITE | IOMAP_ZERO)) {
+	case 0:
+		goto out_unlock;
+	case IOMAP_WRITE:
+		if (flags & IOMAP_DIRECT) {
+			/*
+			 * Silently fall back to buffered I/O for stuffed files
+			 * or if we've got a hole (see gfs2_file_direct_write).
+			 */
+			if (iomap->type != IOMAP_MAPPED)
+				ret = -ENOTBLK;
+			goto out_unlock;
+		}
+		break;
+	case IOMAP_ZERO:
+		if (iomap->type == IOMAP_HOLE)
+			goto out_unlock;
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		ret = -EIO;
+		goto out_unlock;
+	}
+
+	ret = gfs2_iomap_begin_write(inode, pos, length, flags, iomap, &mp);
+
+out_unlock:
+	if (ret && gfs2_iomap_need_write_lock(flags))
+		gfs2_write_unlock(inode);
 	release_metapath(&mp);
+out:
 	trace_gfs2_iomap_end(ip, iomap, ret);
 	return ret;
 }
@@ -1157,8 +1188,21 @@ static int gfs2_iomap_end(struct inode *inode, loff_t pos, loff_t length,
 	struct gfs2_inode *ip = GFS2_I(inode);
 	struct gfs2_sbd *sdp = GFS2_SB(inode);
 
-	if ((flags & (IOMAP_WRITE | IOMAP_DIRECT)) != IOMAP_WRITE)
-		goto out;
+	switch (flags & (IOMAP_WRITE | IOMAP_ZERO)) {
+	case 0:
+		return 0;
+	case IOMAP_WRITE:
+		if (flags & IOMAP_DIRECT)
+			return 0;
+		break;
+	case IOMAP_ZERO:
+		if (iomap->type == IOMAP_HOLE)
+			return 0;
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		return -EIO;
+	}
 
 	if (!gfs2_is_stuffed(ip))
 		gfs2_ordered_add_inode(ip);
@@ -1183,8 +1227,6 @@ static int gfs2_iomap_end(struct inode *inode, loff_t pos, loff_t length,
 	if (ip->i_qadata && ip->i_qadata->qa_qd_num)
 		gfs2_quota_unlock(ip);
 	gfs2_write_unlock(inode);
-
-out:
 	return 0;
 }