mainloop in nbd-server currently does this:
if (command==NBD_CMD_DISC) {
msg2(LOG_INFO, "Disconnect request received.");
...
}
len = ntohl(request.len);
if (request.magic != htonl(NBD_REQUEST_MAGIC))
err("Not enough magic.");
if (len > BUFSIZE - sizeof(struct nbd_reply)) {
currlen = BUFSIZE - sizeof(struct nbd_reply);
msg2(LOG_INFO, "oversized request (this is not a
problem)");
} else {
currlen = len;
}
[memcpy handle]
[check offset if appropriate]
[handle command with lots of "if"]
I tried to clear this up somewhat half-heartedly then reverted, but I may
have another go.
However, does the protocol *really* require that we check for
NBD_CMD_DISC prior to checking for a correct magic number? If not,
I think a more logical sequence would be:
if (request.magic != htonl(NBD_REQUEST_MAGIC))
err("Not enough magic.");
[memcpy handle]
len = ntohl(request.len);
[check offset if appropriate]
[handle command with switch, including disconnect]
[do oversize check in NBD_CMD_READ case: block]
This does mean we do a little work preparing a reply for NBD_DISCONNECT
which never gets sent (an 8 byte memcpy) but I think that's a small
price to pay for a more logical code flow.
--
Alex Bligh
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