From 05e2747bf2abd9e6bb301fd2b6884946833b06ed Mon Sep 17 00:00:00 2001
From: Alexander Moch <github@alexanderjulian.de>
Date: Tue, 2 Dec 2025 20:14:09 +0000
Subject: [PATCH] Provide loff_t via <fcntl.h> on musl-based Linux systems

Musl exposes loff_t only as a macro in <fcntl.h> when _GNU_SOURCE is
defined. Including <fcntl.h> ensures the type is available, and a
fallback typedef is provided when no macro is defined. This fixes build
failures on musl systems.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Rob Norris <robn@despairlabs.com>
Signed-off-by: Alexander Moch <mail@alexmoch.com>
Closes #18002
---
 lib/libspl/include/sys/types.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/lib/libspl/include/sys/types.h b/lib/libspl/include/sys/types.h
index 9af20d781..37cf1d241 100644
--- a/lib/libspl/include/sys/types.h
+++ b/lib/libspl/include/sys/types.h
@@ -54,4 +54,15 @@ typedef int		projid_t;
 typedef off_t loff_t;
 #endif
 
+/*
+ * On musl, loff_t is a macro within fcntl.h when _GNU_SOURCE is defined.
+ * If no macro is defined, a typedef fallback is provided.
+ */
+#if defined(__linux__) && !defined(__GLIBC__)
+#include <fcntl.h>
+#ifndef loff_t
+typedef off_t loff_t;
+#endif
+#endif
+
 #endif