MFC r271536: MFV r271518:

Correctly report hole at end of file.

When asked to find a hole, the DMU sees that there are no holes in the
object, and returns ESRCH.  The ZPL interprets this as "no holes before
the end of the file", and therefore inserts the "virtual hole" at the
end of the file.  Because DMU and ZPL have different ideas of where the
end of an object/file is, we will end up returning the end of file,
which is generally larger, instead of returning the end of object.

The fix is to handle the "virtual hole" in the DMU. If no hole is found,
the DMU will return a hole at the end of the file, rather than an error.

Illumos issue:
    5139 SEEK_HOLE failed to report a hole at end of file

Approved by:	re (gjb)

2 files changed, 22 insertions, 10 deletions

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c
index 55bf895..0b19e76 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dnode.c
@@ -1948,6 +1948,15 @@ dnode_next_offset(dnode_t *dn, int flags, uint64_t *offset,
 		    flags, offset, lvl, blkfill, txg);
 	}
 
+	/*
+	 * There's always a "virtual hole" at the end of the object, even
+	 * if all BP's which physically exist are non-holes.
+	 */
+	if ((flags & DNODE_FIND_HOLE) && error == ESRCH && txg == 0 &&
+	    minlvl == 1 && blkfill == 1 && !(flags & DNODE_FIND_BACKWARDS)) {
+		error = 0;
+	}
+
 	if (error == 0 && (flags & DNODE_FIND_BACKWARDS ?
 	    initial_offset < *offset : initial_offset > *offset))
 		error = SET_ERROR(ESRCH);
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c
index d243b80..689a4a4 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c
@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2013, 2014 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
  * Copyright 2013 Nexenta Systems, Inc.  All rights reserved.
  */
 
@@ -266,16 +266,19 @@ zfs_holey(vnode_t *vp, u_long cmd, offset_t *off)
 
 	error = dmu_offset_next(zp->z_zfsvfs->z_os, zp->z_id, hole, &noff);
 
-	/* end of file? */
-	if ((error == ESRCH) || (noff > file_sz)) {
-		/*
-		 * Handle the virtual hole at the end of file.
-		 */
-		if (hole) {
-			*off = file_sz;
-			return (0);
-		}
+	if (error == ESRCH)
 		return (SET_ERROR(ENXIO));
+
+	/*
+	 * We could find a hole that begins after the logical end-of-file,
+	 * because dmu_offset_next() only works on whole blocks.  If the
+	 * EOF falls mid-block, then indicate that the "virtual hole"
+	 * at the end of the file begins at the logical EOF, rather than
+	 * at the end of the last block.
+	 */
+	if (noff > file_sz) {
+		ASSERT(hole);
+		noff = file_sz;
 	}
 
 	if (noff < *off)