[39/47] nbd/server: Don't complain on certain client disconnects

Commit Message

Michael Roth Dec. 15, 2021, 12:01 a.m. UTC

From: Eric Blake <[e-mail]>

When a client disconnects abruptly, but did not have any pending
requests (for example, when using nbdsh without calling h.shutdown),
we used to output the following message:

$ qemu-nbd -f raw file
$ nbdsh -u 'nbd://localhost:10809' -c 'h.trim(1,0)'
qemu-nbd: Disconnect client, due to: Failed to read request: Unexpected end-of-file before all bytes were read

Then in commit f148ae7, we refactored nbd_receive_request() to use
nbd_read_eof(); when this returns 0, we regressed into tracing
uninitialized memory (if tracing is enabled) and reporting a
less-specific:

qemu-nbd: Disconnect client, due to: Request handling failed in intermediate state

Note that with Unix sockets, we have yet another error message,
unchanged by the 6.0 regression:

$ qemu-nbd -k /tmp/sock -f raw file
$ nbdsh -u 'nbd+unix:///?socket=/tmp/sock' -c 'h.trim(1,0)'
qemu-nbd: Disconnect client, due to: Failed to send reply: Unable to write to socket: Broken pipe

But in all cases, the error message goes away if the client performs a
soft shutdown by using NBD_CMD_DISC, rather than a hard shutdown by
abrupt disconnect:

$ nbdsh -u 'nbd://localhost:10809' -c 'h.trim(1,0)' -c 'h.shutdown()'

This patch fixes things to avoid uninitialized memory, and in general
avoids warning about a client that does a hard shutdown when not in
the middle of a packet.  A client that aborts mid-request, or which
does not read the full server's reply, can still result in warnings,
but those are indeed much more unusual situations.

CC: [e-mail]
Fixes: f148ae7d36 ("nbd/server: Quiesce coroutines on context switch", v6.0.0)
Signed-off-by: Eric Blake <[e-mail]>
Reviewed-by: Vladimir Sementsov-Ogievskiy <[e-mail]>
[eblake: defer unrelated typo fixes to later patch]
Message-Id: <[e-mail]>
Signed-off-by: Eric Blake <[e-mail]>
(cherry picked from commit 1644cccea5c71b02b9cf8f78b780e7069a29b189)
Signed-off-by: Michael Roth <[e-mail]>
---
 nbd/server.c | 3 +++
 1 file changed, 3 insertions(+)

Patch

diff --git a/nbd/server.c b/nbd/server.c
index 3927f7789d..83aeed51c7 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1413,6 +1413,9 @@  static int nbd_receive_request(NBDClient *client, NBDRequest *request,
     if (ret < 0) {
         return ret;
     }
+    if (ret == 0) {
+        return -EIO;
+    }
 
     /* Request
        [ 0 ..  3]   magic   (NBD_REQUEST_MAGIC)