waldo kitty wrote:
On 10/03/2015 02:30 PM, Bo Berglund wrote:
The program will probably be started by cron every minute to check if
it has anything to do and if so execute its data collection task and
quit. Otherwise just quit, but here maybe also check for an update on
the web?
But how could one exchange a running program on the pi from within
itself?
off the top of my head:
since you're running from cron and exiting, this could be pretty simple...
1. at start up, check if self is named known temp name. if yes, copy
self to normal name, spawn normal name and die.
2. at start up pull md5 checksum file from server and compare with own
md5 checksum.
Check size first in case somebody has inadvertently put up a binary with
a couple of dozen Mb debug info attached :-)
One way round this is to use (something like) Subversion at both ends of
the link, since this implements a fairly efficient check and is
generally OK for binaries.
3. if md5 sums are different, download new version to known temp name.
4. at end of execution, see if known temp name exists. if it does, spawn
it and die.
maybe something like that... of course, somewhere in there you'll still
do your required processing... the end of execution will wait for
everything to be done before doing step 4...
one might also use a special command line parameter to tell the known
temp name to copy itself over to the normal name in step 1.
i) Does the program need to detect changes while it's running?
ii) What provision is made for ensuring that a new version of the
program comes from the designated builder?
iii) Assuming that the program's not being rebuilt from source on the
machine it's to run on, does the binary name include the name of the
architecture etc.?
I've looked a bit at (i) for graphical programs. It can be done fairly
reliably using dynamically-linked libraries (.so files on unix) but not
IME quite reliably enough for remote sites. And while we're in the UK,
we have kit scattered around from Sweden to Turkey.
Code signing is not really implemented on Linux, so (ii) is a problem.
Considering (iii), Lazarus can be told to put the architecture etc. in
the name of a generated binary, but going further than that- and in
particular specifying subarchitectures like the HF on the RPi- is a
problem hardly helped by the fact that there's no provision for this in
the ELF header.
--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
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