[PATCH teavpn2 3/3] arch/linux: syscall: Fix retval checking in libc syscall

[Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>]

The libc syscall wrappers mostly return -1 when they fail, then they
set the error code to the @errno variable. The current code seems to
be doing something wrong. We assume it errors when the return value
is negative. However, not all negative values are meant to be an
error indicator. On Linux, the only reserved error code is within
range [-4095, -1]. That means we still have a potential to get a
negative return value that is not an error.

I understand that most of them work fine here because of the nature
of the syscall itself that won't return a negative value upen
succcessful. But the above assumption about the negative value is
not correct.

Replace the error checking from (ret < 0) to (ret == -1) to reflect
the above fact.

Fixes: ca111cce3c05aed1d3a078c095c0111f3c48484f ("arch: Add generic arch syscalls from libc")
Cc: Ammar Faizi <ammarfaizi2@gmail.com>
Cc: Louvian Lyndal <louvianlyndal@gmail.com>
Cc: Michael Arminto <kohaku.mski@gmail.com>
Signed-off-by: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>
---
 src/teavpn2/arch/generic/linux.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/teavpn2/arch/generic/linux.h b/src/teavpn2/arch/generic/linux.h
index 42e7201..0dc12e8 100644
--- a/src/teavpn2/arch/generic/linux.h
+++ b/src/teavpn2/arch/generic/linux.h
@@ -20,21 +20,21 @@ static inline int __sys_epoll_wait(int epfd, struct epoll_event *events,
 {
 	int ret;
 	ret = epoll_wait(epfd, events, maxevents, timeout);
-	return unlikely(ret < 0) ? -errno : ret;
+	return unlikely(ret == -1) ? -errno : ret;
 }
 
 static inline ssize_t __sys_read(int fd, void *buf, size_t len)
 {
 	ssize_t ret;
 	ret = read(fd, buf, len);
-	return unlikely(ret < 0) ? (ssize_t) -errno : ret;
+	return unlikely(ret == -1) ? (ssize_t) -errno : ret;
 }
 
 static inline ssize_t __sys_write(int fd, const void *buf, size_t len)
 {
 	ssize_t ret;
 	ret = write(fd, buf, len);
-	return unlikely(ret < 0) ? (ssize_t) -errno : ret;
+	return unlikely(ret == -1) ? (ssize_t) -errno : ret;
 }
 
 static inline ssize_t __sys_recvfrom(int sockfd, void *buf, size_t len,
@@ -43,7 +43,7 @@ static inline ssize_t __sys_recvfrom(int sockfd, void *buf, size_t len,
 {
 	ssize_t ret;
 	ret = recvfrom(sockfd, buf, len, flags, src_addr, addrlen);
-	return unlikely(ret < 0) ? (ssize_t) -errno : ret;
+	return unlikely(ret == -1) ? (ssize_t) -errno : ret;
 }
 
 static inline ssize_t __sys_sendto(int sockfd, const void *buf, size_t len,
@@ -52,14 +52,14 @@ static inline ssize_t __sys_sendto(int sockfd, const void *buf, size_t len,
 {
 	ssize_t ret;
 	ret = sendto(sockfd, buf, len, flags, dest_addr, addrlen);
-	return unlikely(ret < 0) ? (ssize_t) -errno : ret;
+	return unlikely(ret == -1) ? (ssize_t) -errno : ret;
 }
 
 static inline int __sys_close(int fd)
 {
 	int ret;
 	ret = close(fd);
-	return unlikely(ret < 0) ? -errno : ret;
+	return unlikely(ret == -1) ? -errno : ret;
 }
 
 #endif /* #ifndef TEAVPN2__ARCH__GENERIC__LINUX_H */
-- 
Alviro Iskandar Setiawan