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nbd/client: Relax handling of large NBD_CMD_BLOCK_STATUS reply

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The NBD spec is proposing a relaxation of NBD_CMD_BLOCK_STATUS
where a server may have the final extent per context give a
length beyond the original request, if it can easily prove that
subsequent bytes have the same status, on the grounds that a
client can take advantage of this information for fewer block
status requests.  Since qemu 2.12 as a client always sends
NBD_CMD_FLAG_REQ_ONE, and rejects a server that sends extra
length, the upstream NBD spec will probably limit this behavior
to clients that don't request REQ_ONE semantics; but it doesn't
hurt to relax qemu to always be permissive of this server
behavior, even if it continues to use REQ_ONE.

CC: qemu-stable@nongnu.org
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20180503222626.1303410-1-eblake@redhat.com>
Reviewed-by:  Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
This commit is contained in:
Eric Blake 2018-05-03 17:26:26 -05:00
parent e475d108f1
commit acfd8f7a5f
1 changed files with 7 additions and 3 deletions
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10
block/nbd-client.c
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@ -259,14 +259,18 @@ static int nbd_parse_blockstatus_payload(NBDClientSession *client,
if (extent->length == 0 ||
(client->info.min_block && !QEMU_IS_ALIGNED(extent->length,
client->info.min_block)) ||
extent->length > orig_length)
{
client->info.min_block))) {
error_setg(errp, "Protocol error: server sent status chunk with "
"invalid length");
return -EINVAL;
}
/* The server is allowed to send us extra information on the final
* extent; just clamp it to the length we requested. */
if (extent->length > orig_length) {
extent->length = orig_length;
}
return 0;
}