[ale] compiled system calls versus shell scripts

[Christopher Bergeron]

Aahhh!  That explains why when I "time" each I get almost double results 
from the compiled binary.  I created a shell script and a binary that do 
the exact same thing and I got results that were opposite (as you 
described) from what I expected.  For those that don't know, you can 
"time" a command by simply running:  ' time whatever.sh ' or ' time 
binaryfilename '.  When the program is completed, you'll be presented 
with a timing calculation of the execution time.  As a result (of my 
result), I decided to post this thread to the list.  Thanks for sheding 
some light on it, Doug!!!

Does anyone know how to do the Make / Makefile thing at bootup?  How 
does one build the makefile, and where do you put it?

So many questions, such little time...

Thanks for all the help -
-cb



Doug McNash wrote:

>> void main() {
>>  system("modprobe whatever &");
>>  system("ifconfig eth0 192.168.0.4 &");
>> }
>>
>
> Ouch! That would be twice as slow since each system() would fork&exec 
> a sh which would then fork&exec the command.  Fork&exec is a long and 
> involved sequence of events == slow.
>
> What you might want to do is make the same system calls that ifconfig, 
> modprobe, and so on do in a C program and avoid the fork&exec.  Most 
> utilities boil down to doing one or two specific system calls.  Of 
> course, modprobe, for instance will open and parse modules.conf for 
> aliases and arguments and /lib/modules/2.X.x/modules.dep for 
> dependencies as well as sanity checks before doing the call. You could 
> do all that manually in the C program for everything you need to 
> setup.  It would be totally inflexible and very difficult to maintain 
> but would greatly speed your boot time. Plus you would have to figure 
> out all the system calls and arguments you need, a perhaps a serious 
> learning experience.
>
> Have you looked at busybox?  It provides a stripped down init scheme 
> as well as a one stop source for most of the utilities you would 
> need.  The LinkSys WRT54g uses it (as well as running an embedded 
> linux kernel).  This box also has a binary rc file like what I have 
> tried to described above and boots quite fast.  At least that's what I 
> think it is as I have not fully reverse engineered it yet.
>
> Check out http://www.seattlewireless.net/index.cgi/LinksysWrt54g
> It's a very interesting site. You might find some ideas there.  Sorry 
> I can't distill it further at the moment.
>
> This link will tell you how to recover the file system for the above.
> http://www.cs.helsinki.fi/linux/linux-kernel/2003-23/0035.html
> -- 
> Doug McNash <dmcnash at yahoo.com>
> _______________________________________________
> Ale mailing list
> Ale at ale.org
> http://www.ale.org/mailman/listinfo/ale
>
>