From 4a7b8740509205cb9a952c54bc4a9fdc9fcf1a19 Mon Sep 17 00:00:00 2001
From: Joseph Ferano <joseph@ferano.io>
Date: Sat, 12 Sep 2026 11:00:01 +0700
Subject: [PATCH] The limits test reads results through the seqlock that
 replaced the pointer

---
 test/dev_limits.c | 32 ++++++++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 4 deletions(-)

diff --git a/test/dev_limits.c b/test/dev_limits.c
index d4e444d..eb146d0 100644
--- a/test/dev_limits.c
+++ b/test/dev_limits.c
@@ -27,7 +27,31 @@ void **flan_dev_cell(const char *name);
 void flan_dev_result_begin(void);
 void flan_dev_emit(const uint8_t *bytes, int64_t len);
 void flan_dev_result_end(void);
-const char *flan_dev_result_get(uint64_t *gen, uint64_t *len);
+uint64_t flan_dev_result_cap(void);
+int flan_dev_result_read(char *dst, uint64_t cap, uint64_t *gen, uint64_t *len);
+
+/* [flan_dev_result_get] was replaced by a real seqlock, which copies into the
+ * caller's buffer rather than handing back a pointer into one being written.
+ * The buffer is sized from [flan_dev_result_cap] rather than from CAP below,
+ * which is this test's own expectation of the answer: sizing it from the
+ * number under test would make a wrong cap copy the wrong amount and agree
+ * with itself. */
+static char rbuf[1 << 16];
+
+static const char *result_read(uint64_t *gen, uint64_t *len) {
+  if (flan_dev_result_cap() > sizeof rbuf) {
+    printf("result buffer too small for cap %llu\n",
+           (unsigned long long)flan_dev_result_cap());
+    exit(2);
+  }
+  if (!flan_dev_result_read(rbuf, sizeof rbuf, gen, len)) {
+    /* Single-threaded here: the writer is this thread, so a failed read means
+     * the counter was left odd, not that a write was racing. */
+    printf("result read did not settle\n");
+    exit(2);
+  }
+  return rbuf;
+}
 void flan_rt_init(int32_t argc, char **argv);
 
 #define CAP 4096
@@ -45,7 +69,7 @@ static int cap(void) {
   memset(a, 'a', sizeof a);
   memset(b, 'b', sizeof b);
 
-  r = flan_dev_result_get(&gen0, &len);
+  r = result_read(&gen0, &len);
 
   flan_dev_result_begin();
   flan_dev_emit(a, (int64_t)sizeof a);
@@ -56,7 +80,7 @@ static int cap(void) {
   flan_dev_emit(b, (int64_t)sizeof b);
   flan_dev_result_end();
 
-  r = flan_dev_result_get(&gen1, &len);
+  r = result_read(&gen1, &len);
   printf("len %llu\n", (unsigned long long)len);
   printf("tail %.3s\n", len >= 3 ? r + len - 3 : "");
   printf("mid %c\n", len > 3500 ? r[3500] : '?');
@@ -68,7 +92,7 @@ static int cap(void) {
   flan_dev_result_begin();
   flan_dev_emit((const uint8_t *)"12", 2);
   flan_dev_result_end();
-  r = flan_dev_result_get(&gen1, &len);
+  r = result_read(&gen1, &len);
   printf("again %.*s\n", (int)len, r);
   return 0;
 }