From fc00c656c96528112d05cf0edf8631bd5eaea446 Mon Sep 17 00:00:00 2001
From: Kacper <kacper@mail.openlinux.dev>
Date: Sun, 7 Dec 2025 20:10:31 +0100
Subject: Add build system scaffolding and libc headers

---
 lib/libc/uio/writev.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)
 create mode 100644 lib/libc/uio/writev.c

(limited to 'lib/libc/uio/writev.c')

diff --git a/lib/libc/uio/writev.c b/lib/libc/uio/writev.c
new file mode 100644
index 00000000..4e304336
--- /dev/null
+++ b/lib/libc/uio/writev.c
@@ -0,0 +1,49 @@
+#include <unistd.h>
+#include <syscall.h>
+#include <errno.h>
+#include <string.h>
+#include <linux/uio.h>
+
+ssize_t writev(int fd, const struct iovec *iov, int iovcnt)
+{
+	ssize_t total = 0;
+
+	if (iovcnt < 0) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	while (iovcnt > 0) {
+		int chunk = iovcnt > UIO_MAXIOV ? UIO_MAXIOV : iovcnt;
+
+		struct iovec local[UIO_MAXIOV];
+		memcpy(local, iov, chunk * sizeof(struct iovec));
+
+		ssize_t ret = syscall(writev, fd, local, chunk);
+		if (ret < 0) {
+			if (total > 0 && (errno == EAGAIN || errno == EINTR))
+				return total;
+			return ret;
+		}
+
+		total += ret;
+
+		ssize_t remaining = ret;
+		while (remaining > 0 && iovcnt > 0) {
+			if ((size_t)remaining >= iov->iov_len) {
+				remaining -= iov->iov_len;
+				iov++;
+				iovcnt--;
+			} else {
+				struct iovec tmp = *iov;
+				tmp.iov_base = (char *)tmp.iov_base + remaining;
+				tmp.iov_len -= remaining;
+				memcpy(local, &tmp, sizeof(tmp));
+				remaining = 0;
+				break;
+			}
+		}
+	}
+
+	return total;
+}
-- 
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