implement short read/write, EOF handling (#415)

Report any short reads to callers as ECONNRESET, which is the closest we can
meaningfully get right now. This also fixes get_next_command(), which previously
wasn't checking for short reads at all.

When we fail to send or recv from the socket due to the client disappearing in
some manner, call into vfu_reset_ctx() to clean up the connection fd, allowing a
subsequent vfu_attach_ctx() to work.

If we get 0 bytes from recv[msg](), this is reported by the transport as ENOMSG,
and is a normal EOF condition.

We can also get ECONNRESET: this can happen when we've written unacknowledged
data to the socket, the client side socket is closed, and we try a subsequent
read.

Finally, we can get a short read or write. Our handling of these still has
issues, but for now we'll presume this means the client has gone too. It may
in fact be due to a client bug - if it failed to write enough data - but right
now, we can't easily tell that.

Signed-off-by: John Levon <john.levon@nutanix.com>
Reviewed-by: Thanos Makatos <thanos.makatos@nutanix.com>

1 files changed, 7 insertions, 7 deletions

diff --git a/lib/tran_sock.c b/lib/tran_sock.c
index 9a58570..ea01a68 100644
--- a/lib/tran_sock.c
+++ b/lib/tran_sock.c
@@ -173,6 +173,8 @@ get_msg(void *data, size_t len, int *fds, size_t *nr_fds, int sock_fd,
         return -errno;
     } else if (ret == 0) {
         return -ENOMSG;
+    } else if ((size_t)ret < len) {
+        return -ECONNRESET;
     }
 
     if (msg.msg_flags & MSG_CTRUNC || msg.msg_flags & MSG_TRUNC) {
@@ -222,9 +224,6 @@ tran_sock_recv_fds(int sock, struct vfio_user_header *hdr, bool is_reply,
     if (ret < 0) {
         return ret;
     }
-    if (ret < (int)sizeof(*hdr)) {
-        return -EINVAL;
-    }
 
     if (is_reply) {
         if (msg_id != NULL && hdr->msg_id != *msg_id) {
@@ -257,11 +256,12 @@ tran_sock_recv_fds(int sock, struct vfio_user_header *hdr, bool is_reply,
             return -errno;
         } else if (ret == 0) {
             return -ENOMSG;
-        } else if (*len != (size_t)ret) { /* FIXME we should allow receiving less */
-            return -EINVAL;
+        } else if (*len != (size_t)ret) {
+            return -ECONNRESET;
         }
         *len = ret;
     }
+
     return 0;
 }
 
@@ -318,7 +318,7 @@ tran_sock_recv_alloc(int sock, struct vfio_user_header *hdr, bool is_reply,
         return -ENOMSG;
     } else if (len != (size_t)ret) {
         free(data);
-        return -EINVAL;
+        return -ECONNRESET;
     }
 
     *datap = data;
@@ -818,7 +818,7 @@ tran_sock_recv_body(vfu_ctx_t *vfu_ctx, const struct vfio_user_header *hdr,
         vfu_log(vfu_ctx, LOG_ERR, "msg%#hx: short read: expected=%d, actual=%d",
                 hdr->msg_id, body_size, ret);
         free(data);
-        return -EINVAL;
+        return -ECONNRESET;
     }
 
     *datap = data;