From: Roman Kagan <rvkagan@yandex-team.ru>

After the return from tcp_chr_recv, tcp_chr_sync_read calls into a
function which eventually makes a system call and may clobber errno.

Make a copy of errno right after tcp_chr_recv and restore the errno on
return from tcp_chr_sync_read.

Signed-off-by: Roman Kagan <rvkagan@yandex-team.ru>
Message-Id: <20211111153354.18807-4-rvkagan@yandex-team.ru>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 chardev/char-socket.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/chardev/char-socket.c b/chardev/char-socket.c
index 3ddd98ed49..fab2d791d4 100644
--- a/chardev/char-socket.c
+++ b/chardev/char-socket.c
@@ -525,6 +525,7 @@ static int tcp_chr_sync_read(Chardev *chr, const uint8_t *buf, int len)
 {
     SocketChardev *s = SOCKET_CHARDEV(chr);
     int size;
+    int saved_errno;
 
     if (s->state != TCP_CHARDEV_STATE_CONNECTED) {
         return 0;
@@ -532,6 +533,7 @@ static int tcp_chr_sync_read(Chardev *chr, const uint8_t *buf, int len)
 
     qio_channel_set_blocking(s->ioc, true, NULL);
     size = tcp_chr_recv(chr, (void *) buf, len);
+    saved_errno = errno;
     if (s->state != TCP_CHARDEV_STATE_DISCONNECTED) {
         qio_channel_set_blocking(s->ioc, false, NULL);
     }
@@ -540,6 +542,7 @@ static int tcp_chr_sync_read(Chardev *chr, const uint8_t *buf, int len)
         tcp_chr_disconnect(chr);
     }
 
+    errno = saved_errno;
     return size;
 }
 
-- 
MST