Hi Dan,
On 04/03/2012 15:24, Daniel V. Klein wrote:
> Jonathan-
>
> Looking naively at FnCallNow() in evalfunction.c, I believe you are correct
> in your suspicion that cf-agent uses the start time as "now". Now, I say
> "naively" because I am not that familiar with the Cfengine core code, and I
> have a not-quite up-to-date version. For a long-running agent, this is
> possibly a mistake, and I suggest the developers look at it (and either
> change the code or the documentation, because it is not a true bug, it is
> merely a confusing feature).
Thanks for looking into this.
> However, there being two sides to every coin (and sometimes three or four), I
> notice that you are using mtime in your file_select body, which is the
> modification time of the file. In this case, I think that you need to add
> ctime into the mix. If you change the contents of a file, you change both
> the ctime and mtime, but if you just change the permissions, you only change
> the ctime. Do you want the time a file was changed? Or created/perm-changed?
Well, I'm mostly interested in there not being unexpected behavior in
CFEngine, but I am indeed interested in the mtime - when the contents of
the file changed.
> The third side of the coin is that I don't see how either "bug" will cause
> your problem. Unless you started cf-agent 30 days ago, your
> currently-being-modified files should not be selected (and even though
> cf-execd may be old, each run of cf-agent starts anew).
I think that the "sloppy" selection may happen at the other end of the
interval. Note the expression in the select_files body: "between 'now'
and 30 days ago". So consider CFEngine starts running at 01:40. This
statement would then be roughly equivalent to "mtime < 01:40 Today &&
mtime < 01:40 30 days ago". But, what if cf-agent takes several minutes
to run, and my file is changed at the same time. It's mtime is then
01:41, so not "< 01:40" ! I think this maybe where the use of 'now' is
confusing.
Thinking about a possible fix, maybe the code could only use the "if
mtime < 30 days ago" part, and ignore the "mtime < now" part, as this
should always be in the case. I have no idea how to go about this, for
now anyway, though.
> Finally, with the fourth side bringing us from coins to Euclidean solids,
> look at your file_select body. What you have is legal and I think correct,
> but I feel it would be clearer as what follows (changing the easy to miss
> negation, and changing the mtime range):
>
> body file_select date_pattern(age, pattern)
> {
> mtime => irange(0, ago(0,0,"$(age)",0,0,0));
> leaf_name => { "$(pattern)" };
>
> file_result => "leaf_name.mtime";
> }
>
> This might change the behavior, but I don't think so. At least I hope not.
> But try it, and let me know...
Agreed, but I don't think it should change the behaviour, either. I'll
give it a try.
Thanks for considering this!
Jonathan
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