1 files changed, 58 insertions, 0 deletions
diff --git a/src/port/preadv.c b/src/port/preadv.c
new file mode 100644
index 0000000..eb153ca
--- /dev/null
+++ b/src/port/preadv.c
@@ -0,0 +1,58 @@
+/*-------------------------------------------------------------------------
+ *
+ * preadv.c
+ *	  Implementation of preadv(2) for platforms that lack one.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/port/preadv.c
+ *
+ * Note that this implementation changes the current file position, unlike
+ * the POSIX-like function, so we use the name pg_preadv().
+ *
+ *-------------------------------------------------------------------------
+ */
+
+
+#include "postgres.h"
+
+#ifdef WIN32
+#include <windows.h>
+#else
+#include <unistd.h>
+#endif
+
+#include "port/pg_iovec.h"
+
+ssize_t
+pg_preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset)
+{
+#ifdef HAVE_READV
+	if (iovcnt == 1)
+		return pg_pread(fd, iov[0].iov_base, iov[0].iov_len, offset);
+	if (lseek(fd, offset, SEEK_SET) < 0)
+		return -1;
+	return readv(fd, iov, iovcnt);
+#else
+	ssize_t		sum = 0;
+	ssize_t		part;
+
+	for (int i = 0; i < iovcnt; ++i)
+	{
+		part = pg_pread(fd, iov[i].iov_base, iov[i].iov_len, offset);
+		if (part < 0)
+		{
+			if (i == 0)
+				return -1;
+			else
+				return sum;
+		}
+		sum += part;
+		offset += part;
+		if (part < iov[i].iov_len)
+			return sum;
+	}
+	return sum;
+#endif
+}