2008-07-17 22:59:04

by NeilBrown

[permalink] [raw]
Subject: Re: [PATCH] sm-notify: perform DNS lookup in the background.

On Thursday July 17, [email protected] wrote:
> > What the code is doing is taking the first addrinfo from the host->ai
> > list, and moving it to the end - effectively rotating the list.
> > This shouldn't change what freeaddrinfo will do.
> >
> > One of us is missing something.
> Even after staring at this for half an hour last week, it looked to me
> like you were chopping off the last addrinfo in the list each time
> through the "retries" loop. I could hope for something a little more
> straightforward to do the address rotation.

I assume from your use of the past-tense (looked) that you can see how
it works now?
I guess you could argue that it has been over-optimised, and that
something like:

struct addrinfo *first = host->ai;
struct addrinfo **next = &host->ai;

/* remove the first entry from the list */
host->ai = first->ai_next;
first->ai_next = NULL;
/* find the end of the list */
next = &host->ai;
while ( *next )
next = & (*next)->ai_next;
/* put first entry at end */
*next = first;
memcpy(&host->addr, first->ai_addr, first->ai_addrlen);
addr_set_port(&host->addr, 0);
host->retries = 0;

might be a little clearer?

> It would be nice to consolidate the acquisition and freeing of the
> addrinfo structs for each host so the lifetime of the results is made
> clear. Moving the host_lookup() into notify_host() does help with
> that.
> There is another addrinfo leak in notify(), I think. In the "Bind
> source IP if provided on command line" paragraph, host_lookup() is
> called and the address is copied, but that list of addrinfo structs is
> never freed, is it?

Yes, that is theoretically a leak, though as it is only called once in
a program with a limited lifetime it isn't a serious leak.

The reality with this program, is that it:
allocated lots of data structures
processes them and frees them

as the exit will implicitly free everything, all the other calls to
free allocated memory are fairly moot. But I would have no objection
to putting a freeaddrinfo call into that part of notify().