chardev/char-socket: tcp_chr_recv: don't clobber errno

tcp_chr_recv communicates the specific error condition to the caller via
errno.  However, after setting it, it may call into some system calls or
library functions which can clobber the errno.

Avoid this by moving the errno assignment to the end of the function.

Signed-off-by: Roman Kagan <rvkagan@yandex-team.ru>
Message-Id: <20211111153354.18807-3-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

@@ -290,13 +290,6 @@ static ssize_t tcp_chr_recv(Chardev *chr, char *buf, size_t len)
                                      NULL);
     }
 
-    if (ret == QIO_CHANNEL_ERR_BLOCK) {
-        errno = EAGAIN;
-        ret = -1;
-    } else if (ret == -1) {
-        errno = EIO;
-    }
-
     if (msgfds_num) {
         /* close and clean read_msgfds */
         for (i = 0; i < s->read_msgfds_num; i++) {
@@ -325,6 +318,13 @@ static ssize_t tcp_chr_recv(Chardev *chr, char *buf, size_t len)
 #endif
     }
 
+    if (ret == QIO_CHANNEL_ERR_BLOCK) {
+        errno = EAGAIN;
+        ret = -1;
+    } else if (ret == -1) {
+        errno = EIO;
+    }
+
     return ret;
 }