dmeventd protocol versioning mechanism

Hi,

the attached patch adds rudimentary versioning to the dmevend protocol, allowing us to detect the (protocol) version of the running dmeventd on the client side.

Right now this is only used in dmeventd -R.

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Yours,
Petr

id' Ash = Ash; id' Dust = Dust; id' _ = undefined

On 03/20/2011 11:10 AM, Petr Rockai wrote:
+/*
+ * You can (and have to) call this in place of
+ * daemon_talk(fifos, &msg, DM_EVENT_CMD_HELLO, NULL, NULL, 0, 0)
+ * -- this call will parse the version reply from dmeventd, in addition to
+ * above call. It is not safe to call this at any other place in the
+ * protocol.
+ */
+int dm_event_get_version(struct dm_event_fifos *fifos, int *version) {
+ char *p;
+ struct dm_event_daemon_message msg = { 0, 0, NULL };
+
+ if (daemon_talk(fifos, &msg, DM_EVENT_CMD_HELLO, NULL, NULL, 0, 0))
+ return 0;
+ p = msg.data;
+ *version = 0;
+
+ p = strchr(p, ' ') + 1; /* Message ID */
+ p = strchr(p, ' ') + 1; /* HELLO */
+ p = strchr(p, ' '); /* HELLO, once more */

Is this safe? I think it will segfault on malformed reply (no spaces). strchr(NULL, ...)

Milan

it is not (safe), on the other hand there's code in other places in libdevmapper-event that assumes correctly formatted messages and will segfault otherwise. Can be made safe fairly easy though (just adding if (p)'s) so I'll do that before checking it in.

Yours,
Petr

id' Ash = Ash; id' Dust = Dust; id' _ = undefined

Reminds me famous last words: "dmeventd cannot segfault" :-)

We should be more careful at least in new code, it should not hurt much to reject garbage on input.

Milan