1 files changed, 77 insertions, 0 deletions
diff --git a/lib/write_full.c b/lib/write_full.c
new file mode 100644
index 0000000..4ef902c
--- /dev/null
+++ b/lib/write_full.c
@@ -0,0 +1,77 @@
+/*
+ * SPDX-FileCopyrightText: 2023, Christian Göttsche <cgzones@googlemail.com>
+ * SPDX-FileCopyrightText: 2023, Alejandro Colomar <alx@kernel.org>
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+
+#include <config.h>
+
+#ident "$Id$"
+
+#include <errno.h>
+#include <unistd.h>
+
+#include "prototypes.h"
+
+
+/*
+ * SYNOPSIS
+ *	int write_full(int fd, const void *buf, size_t count);
+ *
+ * ARGUMENTS
+ *	fd	File descriptor.
+ *	buf	Source buffer to write(2) into 'fd'.
+ *	count	Size of 'buf'.
+ *
+ * DESCRIPTION
+ *	Write 'count' bytes from the buffer starting at 'buf' to the
+ *	file referred to by 'fd'.
+ *
+ *	This function is similar to write(2), except that it retries
+ *	in case of a short write.
+ *
+ *	Since this function either performs a full write, or fails, the
+ *	return value is simpler than for write(2).
+ *
+ * RETURN VALUE
+ *	0	On success.
+ *	-1	On error.
+ *
+ * ERRORS
+ *	See write(2).
+ *
+ * CAVEATS
+ *	This function can still perform partial writes: if the function
+ *	fails in the loop after one or more write(2) calls have
+ *	succeeded, it will report a failure, but some data may have been
+ *	written.  In such a case, it's the caller's responsibility to
+ *	make sure that the partial write is not problematic, and
+ *	remediate it if it is --maybe by trying to remove the file--.
+ */
+
+
+int
+write_full(int fd, const void *buf, size_t count)
+{
+	ssize_t              w;
+	const unsigned char  *p;
+
+	p = buf;
+
+	while (count > 0) {
+		w = write(fd, p, count);
+		if (w == -1) {
+			if (errno == EINTR)
+				continue;
+
+			return -1;
+		}
+
+		p += w;
+		count -= w;
+	}
+
+	return 0;
+}