--- a/usr/src/uts/common/fs/zfs/zio.c	Fri Feb 16 12:27:32 2007 -0800
+++ b/usr/src/uts/common/fs/zfs/zio.c	Fri Feb 16 13:39:57 2007 -0800
@@ -64,6 +64,9 @@
 /* At or above this size, force gang blocking - for testing */
 uint64_t zio_gang_bang = SPA_MAXBLOCKSIZE + 1;
 
+/* Force an allocation failure when non-zero */
+uint16_t zio_zil_fail_shift = 0;
+
 typedef struct zio_sync_pass {
 	int	zp_defer_free;		/* defer frees after this pass */
 	int	zp_dontcompress;	/* don't compress after this pass */
@@ -1751,6 +1754,14 @@
 	}
 }
 
+static boolean_t
+zio_alloc_should_fail(void)
+{
+	static uint16_t	allocs = 0;
+
+	return (P2PHASE(allocs++, 1U<<zio_zil_fail_shift) == 0);
+}
+
 /*
  * Try to allocate an intent log block.  Return 0 on success, errno on failure.
  */
@@ -1762,6 +1773,11 @@
 
 	spa_config_enter(spa, RW_READER, FTAG);
 
+	if (zio_zil_fail_shift && zio_alloc_should_fail()) {
+		spa_config_exit(spa, FTAG);
+		return (ENOSPC);
+	}
+
 	/*
 	 * We were passed the previous log blocks dva_t in bp->blk_dva[0].
 	 */