kernel/accounting question ...

[William W. Austin]

(I know that this question might be more reasonable on a kernel list,  
but a while back I posted the question twice and got no answers.)

The acct struct is defined in /usr/include/sys/acct.h includes both  
ac_io and ac_rw for bytes transferred and blocks read or written,  
respectively.  Fair and good - works (on paper) similarly to unix,  
solaris, hp-ux, etc.

However, in the kernel code [kernel/acct.c], ac_io (char) and ac_rw  
(blocks) are always set to 0 by these two lines:

	ac.ac_io = encode_comp_t(0 /* current->io_usage */);
	ac.ac_rw = encode_comp_t(ac.ac_io / 1024);

For most purposes, this probably wouldn't be an issue, but I also do  
extensive performance analysis on several platforms and have written a  
fairly compresive accounting package (as a wraparound for psacct or as  
a standalone) including both an improved acctcom and a built-in  
reporter for it.

Does anyone know wby the kernel zero's out the bytes transferred data?  
(Overhead comes to mind.) Not that it makes a huge differnce for my  
purposes (I had to write some wraparound code to make a  
"best-guestimate" about the data I'm missing), but curiosity is bugging  
me now.  When I compile my program on other OS's I get useful data for  
char and block i/o and I'd like to find out whether there is something  
obvious that I'm just totally missing here...).

Thanks

-- 
william w. austin                               waustin at speakeasy.net
"life is just another phase i'm going through. this time, anyway ..."