[PATCH 1/2] tools/nolibc: Add sendfile()

[Daniel Palmer <daniel@thingy.jp>]

This is useful because it allows copying data up to 2GB from one
fd to another without a buffer in userspace and with a single syscall.

For 32bit kernels we use the sendfile64 syscall to allow for 64bit
offsets to work.

Signed-off-by: Daniel Palmer <daniel@thingy.jp>
---
 tools/include/nolibc/Makefile       |  1 +
 tools/include/nolibc/nolibc.h       |  1 +
 tools/include/nolibc/sys/sendfile.h | 41 +++++++++++++++++++++++++++++
 3 files changed, 43 insertions(+)
 create mode 100644 tools/include/nolibc/sys/sendfile.h

diff --git a/tools/include/nolibc/Makefile b/tools/include/nolibc/Makefile
index 6d213d372bf8..668883f13cd6 100644
--- a/tools/include/nolibc/Makefile
+++ b/tools/include/nolibc/Makefile
@@ -59,6 +59,7 @@ all_files := \
 		sys/reboot.h \
 		sys/resource.h \
 		sys/select.h \
+		sys/sendfile.h \
 		sys/stat.h \
 		sys/syscall.h \
 		sys/sysmacros.h \
diff --git a/tools/include/nolibc/nolibc.h b/tools/include/nolibc/nolibc.h
index faa94f247281..352a207bbedc 100644
--- a/tools/include/nolibc/nolibc.h
+++ b/tools/include/nolibc/nolibc.h
@@ -106,6 +106,7 @@
 #include "sys/reboot.h"
 #include "sys/resource.h"
 #include "sys/select.h"
+#include "sys/sendfile.h"
 #include "sys/stat.h"
 #include "sys/syscall.h"
 #include "sys/sysmacros.h"
diff --git a/tools/include/nolibc/sys/sendfile.h b/tools/include/nolibc/sys/sendfile.h
new file mode 100644
index 000000000000..7136c0eee547
--- /dev/null
+++ b/tools/include/nolibc/sys/sendfile.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
+/*
+ * sendfile for NOLIBC
+ * Copyright (C) 2026 Daniel Palmer <daniel@thingy.jp>
+ */
+
+/* make sure to include all global symbols */
+#include "../nolibc.h"
+
+#ifndef _NOLIBC_SYS_SENDFILE_H
+#define _NOLIBC_SYS_SENDFILE_H
+
+#include "../sys.h"
+#include <linux/unistd.h>
+
+/*
+ * ssize_t sendfile(int out_fd, int in_fd, off_t *offset, size_t count);
+ */
+
+static __attribute__((unused))
+ssize_t _sys_sendfile(int out_fd, int in_fd, off_t *offset, size_t count)
+{
+	__nolibc_static_assert(sizeof(*offset) == sizeof(__kernel_loff_t));
+
+#ifdef __NR_sendfile64
+	/* 32bit kernels use sendfile64 so offset is treated as a __kernel_loff_t */
+	return __nolibc_syscall4(__NR_sendfile64, out_fd, in_fd, offset, count);
+#else
+	__nolibc_static_assert(sizeof(*offset) == sizeof(__kernel_off_t));
+
+	return __nolibc_syscall4(__NR_sendfile, out_fd, in_fd, offset, count);
+#endif
+}
+
+static __attribute__((unused))
+ssize_t sendfile(int out_fd, int in_fd, off_t *offset, size_t count)
+{
+	return __sysret(_sys_sendfile(out_fd, in_fd, offset, count));
+}
+
+#endif /* _NOLIBC_SYS_SENDFILE_H */
-- 
2.53.0