(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