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nbd: Improve server handling of shutdown requests 

NBD commit 6d34500b clarified how clients and servers are supposed
to behave before closing a connection. It added NBD_REP_ERR_SHUTDOWN
(for the server to announce it is about to go away during option
haggling, so the client should quit sending NBD_OPT_* other than
NBD_OPT_ABORT) and ESHUTDOWN (for the server to announce it is about
to go away during transmission, so the client should quit sending
NBD_CMD_* other than NBD_CMD_DISC).  It also clarified that
NBD_OPT_ABORT gets a reply, while NBD_CMD_DISC does not.

This patch merely adds the missing reply to NBD_OPT_ABORT and teaches
the client to recognize server errors.  Actually teaching the server
to send NBD_REP_ERR_SHUTDOWN or ESHUTDOWN would require knowing that
the server has been requested to shut down soon (maybe we could do
that by installing a SIGINT handler in qemu-nbd, which transitions
from RUNNING to a new state that waits for the client to react,
rather than just out-right quitting - but that's a bigger task for
another day).

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1476469998-28592-15-git-send-email-eblake@redhat.com>
[Move dummy ESHUTDOWN to include/qemu/osdep.h. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Eric Blake 2016-10-14 13:33:16 -05:00 committed by Paolo Bonzini
parent 8b34a9dbc3
commit b6f5d3b573
5 changed files with 41 additions and 4 deletions
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13
include/block/nbd.h
View File

@ -83,12 +83,17 @@ typedef struct NBDReply NBDReply;
#define NBD_FLAG_C_NO_ZEROES (1 << 1) /* End handshake without zeroes. */
/* Reply types. */
#define NBD_REP_ERR(value) ((UINT32_C(1) << 31) | (value))
#define NBD_REP_ACK (1) /* Data sending finished. */
#define NBD_REP_SERVER (2) /* Export description. */
#define NBD_REP_ERR_UNSUP ((UINT32_C(1) << 31) | 1) /* Unknown option. */
#define NBD_REP_ERR_POLICY ((UINT32_C(1) << 31) | 2) /* Server denied */
#define NBD_REP_ERR_INVALID ((UINT32_C(1) << 31) | 3) /* Invalid length. */
#define NBD_REP_ERR_TLS_REQD ((UINT32_C(1) << 31) | 5) /* TLS required */
#define NBD_REP_ERR_UNSUP NBD_REP_ERR(1) /* Unknown option */
#define NBD_REP_ERR_POLICY NBD_REP_ERR(2) /* Server denied */
#define NBD_REP_ERR_INVALID NBD_REP_ERR(3) /* Invalid length */
#define NBD_REP_ERR_PLATFORM NBD_REP_ERR(4) /* Not compiled in */
#define NBD_REP_ERR_TLS_REQD NBD_REP_ERR(5) /* TLS required */
#define NBD_REP_ERR_SHUTDOWN NBD_REP_ERR(7) /* Server shutting down */
/* Request flags, sent from client to server during transmission phase */
#define NBD_CMD_FLAG_FUA (1 << 0)

3
include/qemu/osdep.h
View File

@ -128,6 +128,9 @@ extern int daemon(int, int);
#if !defined(EMEDIUMTYPE)
#define EMEDIUMTYPE 4098
#endif
#if !defined(ESHUTDOWN)
#define ESHUTDOWN 4099
#endif
#ifndef TIME_MAX
#define TIME_MAX LONG_MAX
#endif

18
nbd/client.c
View File

@ -40,6 +40,9 @@ static int nbd_errno_to_system_errno(int err)
case NBD_ENOSPC:
ret = ENOSPC;
break;
case NBD_ESHUTDOWN:
ret = ESHUTDOWN;
break;
default:
TRACE("Squashing unexpected error %d to EINVAL", err);
/* fallthrough */
@ -239,11 +242,21 @@ static int nbd_handle_reply_err(QIOChannel *ioc, nbd_opt_reply *reply,
reply->option);
break;
case NBD_REP_ERR_PLATFORM:
error_setg(errp, "Server lacks support for option %" PRIx32,
reply->option);
break;
case NBD_REP_ERR_TLS_REQD:
error_setg(errp, "TLS negotiation required before option %" PRIx32,
reply->option);
break;
case NBD_REP_ERR_SHUTDOWN:
error_setg(errp, "Server shutting down before option %" PRIx32,
reply->option);
break;
default:
error_setg(errp, "Unknown error code when asking for option %" PRIx32,
reply->option);
@ -785,6 +798,11 @@ ssize_t nbd_receive_reply(QIOChannel *ioc, NBDReply *reply)
reply->error = nbd_errno_to_system_errno(reply->error);
if (reply->error == ESHUTDOWN) {
/* This works even on mingw which lacks a native ESHUTDOWN */
LOG("server shutting down");
return -EINVAL;
}
TRACE("Got reply: { magic = 0x%" PRIx32 ", .error = % " PRId32
", handle = %" PRIu64" }",
magic, reply->error, reply->handle);

1
nbd/nbd-internal.h
View File

@ -92,6 +92,7 @@
#define NBD_ENOMEM 12
#define NBD_EINVAL 22
#define NBD_ENOSPC 28
#define NBD_ESHUTDOWN 108
static inline ssize_t read_sync(QIOChannel *ioc, void *buffer, size_t size)
{

10
nbd/server.c
View File

@ -39,6 +39,8 @@ static int system_errno_to_nbd_errno(int err)
case EFBIG:
case ENOSPC:
return NBD_ENOSPC;
case ESHUTDOWN:
return NBD_ESHUTDOWN;
case EINVAL:
default:
return NBD_EINVAL;
@ -527,6 +529,10 @@ static int nbd_negotiate_options(NBDClient *client)
if (ret < 0) {
return ret;
}
/* Let the client keep trying, unless they asked to quit */
if (clientflags == NBD_OPT_ABORT) {
return -EINVAL;
}
break;
}
} else if (fixedNewstyle) {
@ -539,6 +545,10 @@ static int nbd_negotiate_options(NBDClient *client)
break;
case NBD_OPT_ABORT:
/* NBD spec says we must try to reply before
* disconnecting, but that we must also tolerate
* guests that don't wait for our reply. */
nbd_negotiate_send_rep(client->ioc, NBD_REP_ACK, clientflags);
return -EINVAL;
case NBD_OPT_EXPORT_NAME: