Simplify imsg_write, msgbuf_write and ibuf_write return codes.

Return 0 on success or when a temporary error happened (EAGAIN, ENOBUFS).
Return -1 on error and set errno otherwise.
Kill the old 0 return for EOF. This is not how write operations work.

OK tb@

4 files changed, 69 insertions, 43 deletions

diff --git a/lib/libutil/ibuf_add.3 b/lib/libutil/ibuf_add.3
index e8486aa7324..5445c9a972a 100644
--- a/lib/libutil/ibuf_add.3
+++ b/lib/libutil/ibuf_add.3
@@ -1,4 +1,4 @@
-.\" $OpenBSD: ibuf_add.3,v 1.2 2024/11/21 12:42:14 claudio Exp $
+.\" $OpenBSD: ibuf_add.3,v 1.3 2024/11/21 12:49:58 claudio Exp $
 .\"
 .\" Copyright (c) 2023 Claudio Jeker <claudio@openbsd.org>
 .\" Copyright (c) 2010 Nicholas Marriott <nicm@openbsd.org>
@@ -469,11 +469,19 @@ routine transmits as many pending buffers as possible from
 .Fa msgbuf
 using
 .Xr writev 2 .
-It returns 1 if it succeeds, \-1 on error and 0 when no buffers were
-pending or an EOF condition on the socket is detected.
-Temporary resource shortages are returned with errno
-.Er EAGAIN
-and require the application to retry again in the future.
+It returns 0 if it succeeds, -1 on error and the global variable
+.Va errno
+is set to indicate the error.
+The errors
+.Er EINTR ,
+.Er EAGAIN ,
+and
+.Er ENOBUFS
+are treated as follows.
+.Er EINTR
+will automatically retry the write operation while the other errors are
+ignored with a 0 return.
+The application will then retry the operation at a later stage.
 .Pp
 The
 .Fn msgbuf_init
@@ -500,11 +508,19 @@ routine calls
 .Xr sendmsg 2
 to transmit buffers queued in
 .Fa msgbuf .
-It returns 1 if it succeeds, \-1 on error, and 0 when the queue was empty
-or an EOF condition on the socket is detected.
-Temporary resource shortages are returned with errno
-.Er EAGAIN
-and require the application to retry again in the future.
+It returns 0 if it succeeds, -1 on error and the global variable
+.Va errno
+is set to indicate the error.
+The errors
+.Er EINTR ,
+.Er EAGAIN ,
+and
+.Er ENOBUFS
+are treated as follows.
+.Er EINTR
+will automatically retry the write operation while the other errors are
+ignored with a 0 return.
+The application will then retry the operation at a later stage.
 .Sh SEE ALSO
 .Xr socketpair 2 ,
 .Xr imsg_init 3 ,
diff --git a/lib/libutil/imsg-buffer.c b/lib/libutil/imsg-buffer.c
index 0a824c63bd8..537e52d6f99 100644
--- a/lib/libutil/imsg-buffer.c
+++ b/lib/libutil/imsg-buffer.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: imsg-buffer.c,v 1.22 2024/11/21 12:44:06 claudio Exp $	*/
+/*	$OpenBSD: imsg-buffer.c,v 1.23 2024/11/21 12:49:58 claudio Exp $	*/
 
 /*
  * Copyright (c) 2023 Claudio Jeker <claudio@openbsd.org>
@@ -569,24 +569,21 @@ ibuf_write(struct msgbuf *msgbuf)
 		iov[i].iov_len = ibuf_size(buf);
 		i++;
 	}
+	if (i == 0)
+		return (0);	/* nothing queued */
 
 again:
 	if ((n = writev(msgbuf->fd, iov, i)) == -1) {
 		if (errno == EINTR)
 			goto again;
-		if (errno == ENOBUFS)
-			errno = EAGAIN;
+		if (errno == EAGAIN || errno == ENOBUFS)
+			/* lets retry later again */
+			return (0);
 		return (-1);
 	}
 
-	if (n == 0) {			/* connection closed */
-		errno = 0;
-		return (0);
-	}
-
 	msgbuf_drain(msgbuf, n);
-
-	return (1);
+	return (0);
 }
 
 void
@@ -653,6 +650,9 @@ msgbuf_write(struct msgbuf *msgbuf)
 			buf0 = buf;
 	}
 
+	if (i == 0)
+		return (0);	/* nothing queued */
+
 	msg.msg_iov = iov;
 	msg.msg_iovlen = i;
 
@@ -670,16 +670,12 @@ again:
 	if ((n = sendmsg(msgbuf->fd, &msg, 0)) == -1) {
 		if (errno == EINTR)
 			goto again;
-		if (errno == ENOBUFS)
-			errno = EAGAIN;
+		if (errno == EAGAIN || errno == ENOBUFS)
+			/* lets retry later again */
+			return (0);
 		return (-1);
 	}
 
-	if (n == 0) {			/* connection closed */
-		errno = 0;
-		return (0);
-	}
-
 	/*
 	 * assumption: fd got sent if sendmsg sent anything
 	 * this works because fds are passed one at a time
@@ -691,7 +687,7 @@ again:
 
 	msgbuf_drain(msgbuf, n);
 
-	return (1);
+	return (0);
 }
 
 uint32_t
diff --git a/lib/libutil/imsg.c b/lib/libutil/imsg.c
index db43273f1c0..8ee07a2dfaf 100644
--- a/lib/libutil/imsg.c
+++ b/lib/libutil/imsg.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: imsg.c,v 1.27 2024/11/21 12:49:14 claudio Exp $	*/
+/*	$OpenBSD: imsg.c,v 1.28 2024/11/21 12:49:58 claudio Exp $	*/
 
 /*
  * Copyright (c) 2023 Claudio Jeker <claudio@openbsd.org>
@@ -429,7 +429,7 @@ int
 imsg_flush(struct imsgbuf *imsgbuf)
 {
 	while (imsgbuf->w.queued)
-		if (imsg_write(imsgbuf) <= 0 && errno != EAGAIN)
+		if (imsg_write(imsgbuf) == -1)
 			return (-1);
 	return (0);
 }
diff --git a/lib/libutil/imsg_init.3 b/lib/libutil/imsg_init.3
index 652e7be189e..96cfd71bbc5 100644
--- a/lib/libutil/imsg_init.3
+++ b/lib/libutil/imsg_init.3
@@ -1,4 +1,4 @@
-.\" $OpenBSD: imsg_init.3,v 1.35 2024/11/21 12:49:14 claudio Exp $
+.\" $OpenBSD: imsg_init.3,v 1.36 2024/11/21 12:49:58 claudio Exp $
 .\"
 .\" Copyright (c) 2023 Claudio Jeker <claudio@openbsd.org>
 .\" Copyright (c) 2010 Nicholas Marriott <nicm@openbsd.org>
@@ -21,6 +21,9 @@
 .Sh NAME
 .Nm imsg_init ,
 .Nm imsg_read ,
+.Nm imsg_write ,
+.Nm imsg_flush ,
+.Nm imsg_clear
 .Nm imsg_get ,
 .Nm imsg_get_ibuf ,
 .Nm imsg_get_data ,
@@ -36,9 +39,7 @@
 .Nm imsg_add ,
 .Nm imsg_close ,
 .Nm imsg_forward ,
-.Nm imsg_free ,
-.Nm imsg_flush ,
-.Nm imsg_clear
+.Nm imsg_free
 .Nd IPC messaging functions
 .Sh SYNOPSIS
 .In sys/queue.h
@@ -235,7 +236,9 @@ more than once per message.
 calls
 .Fn imsg_write
 in a loop until all imsgs in the output buffer are sent.
-It returns 0 if it succeeds, \-1 otherwise.
+It returns 0 if it succeeds, \-1 otherwise and the global variable
+.Va errno
+is set to indicate the error.
 .Pp
 The
 .Fn imsg_read
@@ -253,8 +256,19 @@ and renders it suitable only for passing to
 .Pp
 .Fn imsg_write
 writes out queued messages.
-It returns 1 if it succeeds, -1 on error, and 0 when the queue
-was empty or an EOF condition on the socket is detected.
+It returns 0 if it succeeds, -1 on error and the global variable
+.Va errno
+is set to indicate the error.
+The errors
+.Er EINTR ,
+.Er EAGAIN ,
+and
+.Er ENOBUFS
+are treated as follows.
+.Er EINTR
+will automatically retry the write operation while the other errors are
+ignored with a 0 return.
+The caller will then retry the operation at a later stage.
 .Fn imsg_get
 fills in an individual imsg pending on
 .Fa imsgbuf
@@ -377,11 +391,11 @@ library is used to monitor the socket file descriptor.
 When the socket is ready for writing, queued messages are transmitted with
 .Fn imsg_write :
 .Bd -literal -offset indent
-	if ((n = imsg_write(&imsgbuf-\*(Gtw)) == -1 && errno != EAGAIN) {
-		/* handle write failure */
-	}
-	if (n == 0) {
-		/* handle closed connection */
+	if (imsg_write(imsgbuf) == -1) {
+		if (errno == EPIPE)
+			/* handle closed connection */
+		else
+			/* handle write failure */
 	}
 .Ed
 .Pp