wrapper: introduce writev(3p) wrappers

In the preceding commit we have added a compatibility wrapper for the
writev(3p) syscall. Introduce some generic wrappers for this function
that we nowadays take for granted in the Git codebase.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 41 insertions, 0 deletions

diff --git a/wrapper.c b/wrapper.c
index b794fb20e7..fa40f399b3 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -323,6 +323,47 @@ ssize_t write_in_full(int fd, const void *buf, size_t count)
 	return total;
 }
 
+ssize_t writev_in_full(int fd, struct iovec *iov, int iovcnt)
+{
+	ssize_t total_written = 0;
+
+	while (iovcnt) {
+		ssize_t bytes_written = writev(fd, iov, iovcnt);
+		if (bytes_written < 0) {
+			if (errno == EINTR || errno == EAGAIN)
+				continue;
+			return -1;
+		}
+		if (!bytes_written) {
+			errno = ENOSPC;
+			return -1;
+		}
+
+		total_written += bytes_written;
+
+		/*
+		 * We first need to discard any iovec entities that have been
+		 * fully written.
+		 */
+		while (iovcnt && (size_t)bytes_written >= iov->iov_len) {
+			bytes_written -= iov->iov_len;
+			iov++;
+			iovcnt--;
+		}
+
+		/*
+		 * Finally, we need to adjust the last iovec in case we have
+		 * performed a partial write.
+		 */
+		if (iovcnt && bytes_written) {
+			iov->iov_base = (char *) iov->iov_base + bytes_written;
+			iov->iov_len -= bytes_written;
+		}
+	}
+
+	return total_written;
+}
+
 ssize_t pread_in_full(int fd, void *buf, size_t count, off_t offset)
 {
 	char *p = buf;