From 6458b08e5655dd6f3c89c83a4ef1e3d4f665733f Mon Sep 17 00:00:00 2001
From: Ian Abbott <abbotti@mev.co.uk>
Date: Thu, 12 May 2016 16:12:43 +0100
Subject: [PATCH] lib: remove some unnecessary setting of __comedi_errno

Since comedi_ioctl() calls libc_error() to set __comedi_errno to errno
(and possibly print an error message), there is no need for callers of
comedi_ioctl() to set __comedi_errno immediately afterwards.  But
comedi_command(), comedi_command_test(), and comedi_do_insnlist()
currently do that.  Remove the unneeded setting of __comedi_errno in
those functions.

Also, comedi_command() and comedi_command_test() check __comedi_errno
regardless of whether comedi_ioctl() returnis an error, and possibly
modify the error code to an internal comedi error.  Change them to only
do that if comedi_ioctl() returns an error, because __comedi_errno might
contain a stale value.
---
 lib/comedi.c | 27 +++++++++++++--------------
 1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/lib/comedi.c b/lib/comedi.c
index c5a7238..adb9294 100644
--- a/lib/comedi.c
+++ b/lib/comedi.c
@@ -164,11 +164,12 @@ int _comedi_command(comedi_t *it,comedi_cmd *t)
 	int ret;
 	if(!valid_dev(it)) return -1;
 	ret = comedi_ioctl(it->fd, COMEDI_CMD, t);
-	__comedi_errno = errno;
-	switch(__comedi_errno){
-	case EIO:
-		__comedi_errno = ECMDNOTSUPP;
-		break;
+	if(ret<0){
+		switch(__comedi_errno){
+		case EIO:
+			__comedi_errno = ECMDNOTSUPP;
+			break;
+		}
 	}
 	return ret;
 }
@@ -179,11 +180,12 @@ int _comedi_command_test(comedi_t *it,comedi_cmd *t)
 	int ret;
 	if(!valid_dev(it)) return -1;
 	ret = comedi_ioctl(it->fd, COMEDI_CMDTEST, t);
-	__comedi_errno = errno;
-	switch(__comedi_errno){
-	case EIO:
-		__comedi_errno = ECMDNOTSUPP;
-		break;
+	if(ret<0){
+		switch(__comedi_errno){
+		case EIO:
+			__comedi_errno = ECMDNOTSUPP;
+			break;
+		}
 	}
 	return ret;
 }
@@ -191,11 +193,8 @@ int _comedi_command_test(comedi_t *it,comedi_cmd *t)
 EXPORT_ALIAS_DEFAULT(_comedi_do_insnlist,comedi_do_insnlist,0.7.18);
 int _comedi_do_insnlist(comedi_t *it,comedi_insnlist *il)
 {
-	int ret;
 	if(!valid_dev(it)) return -1;
-	ret = comedi_ioctl(it->fd, COMEDI_INSNLIST, il);
-	__comedi_errno = errno;
-	return ret;
+	return comedi_ioctl(it->fd, COMEDI_INSNLIST, il);
 }
 
 EXPORT_ALIAS_DEFAULT(_comedi_do_insn,comedi_do_insn,0.7.18);