From 327812ca96b7f9e6696af7e65cbd26de6aafe75a Mon Sep 17 00:00:00 2001
From: Carl Niklas Rydberg <carlniklasrydberg@gmail.com>
Date: Sun, 8 Feb 2026 08:46:06 +0100
Subject: [PATCH] Harden pointer head writes against ENOENT races

---
 src/adapters/asl_pointer_fs/asl_pointer_fs.c | 34 ++++++++++++++------
 1 file changed, 25 insertions(+), 9 deletions(-)

diff --git a/src/adapters/asl_pointer_fs/asl_pointer_fs.c b/src/adapters/asl_pointer_fs/asl_pointer_fs.c
index 2b3d1be..77cd140 100644
--- a/src/adapters/asl_pointer_fs/asl_pointer_fs.c
+++ b/src/adapters/asl_pointer_fs/asl_pointer_fs.c
@@ -471,6 +471,7 @@ static amduat_asl_pointer_error_t amduat_asl_pointer_write_head(
     const amduat_reference_t *prev_ref,
     bool has_prev) {
   char *tmp_path;
+  char *parent_dir = NULL;
   size_t tmp_len;
   int tmp_fd;
   FILE *fp;
@@ -511,9 +512,22 @@ static amduat_asl_pointer_error_t amduat_asl_pointer_write_head(
     free((void *)prev_bytes.data);
     return AMDUAT_ASL_POINTER_ERR_IO;
   }
+  parent_dir = amduat_asl_pointer_parent_dir(path);
+  if (parent_dir == NULL || !amduat_asl_pointer_ensure_directory(parent_dir)) {
+    free(parent_dir);
+    free(tmp_path);
+    free((void *)ref_bytes.data);
+    free((void *)prev_bytes.data);
+    return AMDUAT_ASL_POINTER_ERR_IO;
+  }
   snprintf(tmp_path, tmp_len, "%s.tmp.XXXXXX", path);
   tmp_fd = mkstemp(tmp_path);
+  if (tmp_fd < 0 && errno == ENOENT &&
+      amduat_asl_pointer_ensure_directory(parent_dir)) {
+    tmp_fd = mkstemp(tmp_path);
+  }
   if (tmp_fd < 0) {
+    free(parent_dir);
     free(tmp_path);
     free((void *)ref_bytes.data);
     free((void *)prev_bytes.data);
@@ -575,23 +589,25 @@ static amduat_asl_pointer_error_t amduat_asl_pointer_write_head(
   }
 
   if (err == AMDUAT_ASL_POINTER_OK && rename(tmp_path, path) != 0) {
-    err = AMDUAT_ASL_POINTER_ERR_IO;
+    if (errno == ENOENT && amduat_asl_pointer_ensure_directory(parent_dir) &&
+        rename(tmp_path, path) == 0) {
+      /* Recovered after recreating parent directory. */
+    } else {
+      err = AMDUAT_ASL_POINTER_ERR_IO;
+    }
   }
   if (err == AMDUAT_ASL_POINTER_OK) {
-    char *parent_dir = amduat_asl_pointer_parent_dir(path);
-    if (parent_dir != NULL) {
-      if (!amduat_asl_pointer_fsync_directory(parent_dir)) {
-        amduat_log(AMDUAT_LOG_WARN,
-                   "pointer fsync dir failed for %s", parent_dir);
-        err = AMDUAT_ASL_POINTER_ERR_IO;
-      }
-      free(parent_dir);
+    if (!amduat_asl_pointer_fsync_directory(parent_dir)) {
+      amduat_log(AMDUAT_LOG_WARN,
+                 "pointer fsync dir failed for %s", parent_dir);
+      err = AMDUAT_ASL_POINTER_ERR_IO;
     }
   }
   if (err != AMDUAT_ASL_POINTER_OK) {
     (void)remove(tmp_path);
   }
 
+  free(parent_dir);
   free(tmp_path);
   free((void *)ref_bytes.data);
   free((void *)prev_bytes.data);