DLPX-88427 Fix estat metaslab-alloc: no data on 2026.3 engines + garbled names

bpf/estat/metaslab-alloc.c

@@ -12,9 +12,8 @@
 #define VD_NAME_SIZE 32
 typedef struct {
 	u64 ts;
-	u64 size;
+	u64 size;	/* psize from metaslab_alloc_dva_range_entry */
 	u64 asize;
-	u64 alloc_time;
 	char vd_name[VD_NAME_SIZE];
 } data_t;
 
@@ -40,9 +39,32 @@ equal_to_pool(char *str)
 	return (true);
 }
 
-// @@ kprobe|metaslab_alloc_dva|metaslab_alloc_dva_entry
+/*
+ * metaslab_alloc_dva_range() is the per-DVA entry point in the write path
+ * for ZFS versions that have it (Delphix 2026.3 / ZFS 2.4.99+).  It receives
+ * spa_t * as its first argument, making pool filtering straightforward.
+ *
+ * Call chain:
+ *   metaslab_alloc()
+ *     -> metaslab_alloc_range()
+ *       -> metaslab_alloc_dva_range()   <- outer probe (entry/exit)
+ *           -> metaslab_group_alloc()   <- inner probe (entry/exit)
+ *
+ * metaslab_alloc_dva_range() may call metaslab_group_alloc() multiple times
+ * (once per metaslab group tried).  We therefore emit a metric on each
+ * metaslab_group_alloc_exit and reset the per-group fields so the next
+ * attempt gets a fresh vdev name, leaving the outer entry alive until
+ * metaslab_alloc_dva_range_exit cleans it up.
+ *
+ * metaslab_alloc_dva() (the old outer entry point, now only used in
+ * vdev_removal.c) is no longer probed.  If this script is run on an older
+ * ZFS that lacks metaslab_alloc_dva_range, estat(8) will print a WARNING and
+ * skip those probes — no data will be collected.
+ */
+
+// @@ kprobe|metaslab_alloc_dva_range|metaslab_alloc_dva_range_entry
 int
-metaslab_alloc_dva_entry(struct pt_regs *ctx,
+metaslab_alloc_dva_range_entry(struct pt_regs *ctx,
     spa_t *spa, metaslab_class_t *mc, uint64_t psize)
 {
 	u32 tid = bpf_get_current_pid_tgid();
@@ -51,7 +73,7 @@ metaslab_alloc_dva_entry(struct pt_regs *ctx,
 	if (!equal_to_pool(spa->spa_name))
 		return (0);
 
-	data.ts = bpf_ktime_get_ns();
+	data.ts   = bpf_ktime_get_ns();
 	data.size = psize;
 
 	data_map.update(&tid, &data);
@@ -71,14 +93,14 @@ metaslab_group_alloc_entry(struct pt_regs *ctx,
 		return (0);
 
 	data->asize = asize;
-	data->alloc_time = bpf_ktime_get_ns();
 
 	if (mg->mg_vd->vdev_path != NULL) {
 		bpf_probe_read_str(data->vd_name,
 		    sizeof(data->vd_name), mg->mg_vd->vdev_path);
 	} else {
 		bpf_probe_read_str(data->vd_name,
-		    sizeof(data->vd_name), mg->mg_vd->vdev_ops->vdev_op_type);
+		    sizeof(data->vd_name),
+		    mg->mg_vd->vdev_ops->vdev_op_type);
 	}
 
 	return (0);
@@ -97,44 +119,72 @@ metaslab_group_alloc_exit(struct pt_regs *ctx)
 	if (data == NULL || data->ts == 0)
 		return (0);
 
-	if (PT_REGS_RC(ctx) == -1ULL) {
+	if (PT_REGS_RC(ctx) == 0) {
 		axis = failure;
 	} else {
 		axis = success;
 	}
 
+	/*
+	 * Guard against garbage in vd_name (DLPX-88427): a kernel bug on
+	 * some engine versions causes raw memory bytes to appear here.
+	 * A single non-printable byte anywhere in the string breaks JSON
+	 * output.  Scan all bytes up to the first NUL; replace the whole
+	 * name with "unknown" if empty or any byte is outside printable
+	 * ASCII (0x20-0x7e).
+	 */
+	bool vd_valid = (data->vd_name[0] != '\0');
+#pragma unroll
+	for (int _i = 0; _i < VD_NAME_SIZE; _i++) {
+		char _c = data->vd_name[_i];
+		if (_c == '\0')
+			break;
+		if (_c < 0x20 || _c > 0x7e)
+			vd_valid = false;
+	}
+	if (!vd_valid) {
+		char unknown[] = "unknown";
+		__builtin_memcpy(data->vd_name, unknown, sizeof(unknown));
+	}
+
 	AGGREGATE_DATA(data->vd_name, axis,
 		bpf_ktime_get_ns() - data->ts, data->asize);
 
-	data->asize = 0;
-	data->alloc_time = 0;
+	/*
+	 * Reset per-group fields so that if metaslab_alloc_dva_range retries
+	 * with another group, metaslab_group_alloc_entry gets a clean slate.
+	 * Leave the entry alive — metaslab_alloc_dva_range_exit owns cleanup.
+	 */
+	data->asize      = 0;
 	data->vd_name[0] = '\0';
 
 	return (0);
 }
 
-// @@ kretprobe|metaslab_alloc_dva|metaslab_alloc_dva_exit
+// @@ kretprobe|metaslab_alloc_dva_range|metaslab_alloc_dva_range_exit
 int
-metaslab_alloc_dva_exit(struct pt_regs *ctx,
-    spa_t *spa, metaslab_class_t *mc, uint64_t psize)
+metaslab_alloc_dva_range_exit(struct pt_regs *ctx)
 {
 	u32 tid = bpf_get_current_pid_tgid();
 	data_t *data = data_map.lookup(&tid);
 
 	if (data == NULL || data->ts == 0)
 		return (0);
 
-	if (PT_REGS_RC(ctx) == 0)
-		return (0);
-
-	char name[] = "allocation failures";
-	char axis = 0;
-	AGGREGATE_DATA(name, &axis,
-		bpf_ktime_get_ns() - data->ts, data->size);
+	/*
+	 * Non-zero return means the overall DVA allocation failed (no group
+	 * succeeded).  Emit an "allocation failures" metric using the psize
+	 * stored at entry time; the kretprobe argument registers may be
+	 * clobbered so we read from data->size instead.
+	 */
+	if (PT_REGS_RC(ctx) != 0) {
+		char name[] = "allocation failures";
+		char axis = 0;
+		AGGREGATE_DATA(name, &axis,
+			bpf_ktime_get_ns() - data->ts, data->size);
+	}
 
 	data->ts = 0;
-	data->size = 0;
-
 	data_map.delete(&tid);
 
 	return (0);