Index: sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h
===================================================================
--- sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h	(revision 249431)
+++ sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h	(working copy)
@@ -591,6 +591,7 @@
  */
 #define	DMU_READ_PREFETCH	0 /* prefetch */
 #define	DMU_READ_NO_PREFETCH	1 /* don't prefetch */
+#define	DMU_READ_FAIL_SPARSE	2
 int dmu_read(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
 	void *buf, uint32_t flags);
 void dmu_write(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
Index: sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c
===================================================================
--- sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c	(revision 249431)
+++ sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c	(working copy)
@@ -412,12 +412,19 @@
 	zio = zio_root(dn->dn_objset->os_spa, NULL, NULL, ZIO_FLAG_CANFAIL);
 	blkid = dbuf_whichblock(dn, offset);
 	for (i = 0; i < nblks; i++) {
-		dmu_buf_impl_t *db = dbuf_hold(dn, blkid+i, tag);
-		if (db == NULL) {
-			rw_exit(&dn->dn_struct_rwlock);
-			dmu_buf_rele_array(dbp, nblks, tag);
-			zio_nowait(zio);
-			return (SET_ERROR(EIO));
+		dmu_buf_impl_t *db;
+		int dberr = dbuf_hold_impl(dn, 0, blkid + i,
+		    flags & DMU_READ_FAIL_SPARSE ? TRUE : FALSE, tag, &db);
+		if (dberr) {
+			if (dberr == ENOENT && flags & DMU_READ_FAIL_SPARSE && read) {
+				dbp[i] = NULL;
+				continue;
+			} else {
+				rw_exit(&dn->dn_struct_rwlock);
+				dmu_buf_rele_array(dbp, nblks, tag);
+				zio_nowait(zio);
+				return (SET_ERROR(EIO));
+			}
 		}
 		/* initiate async i/o */
 		if (read)
@@ -442,7 +449,7 @@
 
 	/* wait for other io to complete */
 	if (read) {
-		for (i = 0; i < nblks; i++) {
+		for (i = 0; i < nblks; i++) if (dbp[i]) {
 			dmu_buf_impl_t *db = (dmu_buf_impl_t *)dbp[i];
 			mutex_enter(&db->db_mtx);
 			while (db->db_state == DB_READ ||
@@ -981,21 +988,32 @@
 	dmu_buf_t **dbp;
 	int numbufs, i, err;
 	xuio_t *xuio = NULL;
+	dnode_t *dn;
+	uint32_t blocksize = 0;
+	uint64_t blkid;
 
+#ifdef UIO_XUIO
+	if (uio->uio_extflg == UIO_XUIO)
+		xuio = (xuio_t *)uio;
+#endif
+
+	err = dnode_hold(os, object, FTAG, &dn);
+	if (err)
+		return (err);
+
 	/*
 	 * NB: we could do this block-at-a-time, but it's nice
 	 * to be reading in parallel.
 	 */
-	err = dmu_buf_hold_array(os, object, uio->uio_loffset, size, TRUE, FTAG,
-	    &numbufs, &dbp);
-	if (err)
+	/* XXX - optimize sparse reads for xuio too? */
+	err = dmu_buf_hold_array_by_dnode(dn, uio->uio_loffset, size, TRUE,
+	    FTAG, &numbufs, &dbp,
+	    DMU_READ_PREFETCH | (xuio ? 0 : DMU_READ_FAIL_SPARSE));
+	if (err) {
+		dnode_rele(dn, FTAG);
 		return (err);
+	}
 
-#ifdef UIO_XUIO
-	if (uio->uio_extflg == UIO_XUIO)
-		xuio = (xuio_t *)uio;
-#endif
-
 	for (i = 0; i < numbufs; i++) {
 		int tocpy;
 		int bufoff;
@@ -1003,9 +1021,22 @@
 
 		ASSERT(size > 0);
 
-		bufoff = uio->uio_loffset - db->db_offset;
-		tocpy = (int)MIN(db->db_size - bufoff, size);
+		if (db) {
+			bufoff = uio->uio_loffset - db->db_offset;
+			tocpy = (int)MIN(db->db_size - bufoff, size);
+		} else { /* sparse optimization */
+			if (!blocksize) {
+				rw_enter(&dn->dn_struct_rwlock, RW_READER);
+				blocksize = dn->dn_datablksz;
+				blkid = dbuf_whichblock(dn, uio->uio_loffset) - i;
+				rw_exit(&dn->dn_struct_rwlock);
 
+				ASSERT(blocksize > 0);
+			}
+			bufoff = uio->uio_loffset - (blkid + i) * blocksize;
+			tocpy = (int)MIN(blocksize - bufoff, size);
+		}
+
 		if (xuio) {
 			dmu_buf_impl_t *dbi = (dmu_buf_impl_t *)db;
 			arc_buf_t *dbuf_abuf = dbi->db_buf;
@@ -1020,15 +1051,23 @@
 				XUIOSTAT_BUMP(xuiostat_rbuf_nocopy);
 			else
 				XUIOSTAT_BUMP(xuiostat_rbuf_copied);
-		} else {
+		} else if (db) {
 			err = uiomove((char *)db->db_data + bufoff, tocpy,
 			    UIO_READ, uio);
+		} else { /* sparse optimization */
+			void *zbuf = __DECONST(void *, zero_region);
+			do {
+				ssize_t len = MIN(tocpy, ZERO_REGION_SIZE);
+				err = uiomove(zbuf, len, UIO_READ, uio);
+				tocpy -= len;
+			} while (tocpy && !err);
 		}
 		if (err)
 			break;
 
 		size -= tocpy;
 	}
+	dnode_rele(dn, FTAG);
 	dmu_buf_rele_array(dbp, numbufs, FTAG);
 
 	return (err);