On Thu, 11 Feb 2016 10:47:22 +0530
haris iqbal <haris.p...@gmail.com> wrote:
> Hello,
>
> I have understood a fair amount of working, how -e trace=option works.
>
> Through the init() --> qualify()
>
> for (p = strtok(copy, ","); p; p = strtok(NULL, ",")) {
> int n;
> if (opt->bitflag == QUAL_TRACE && (n = lookup_class(p)) > 0) {
> unsigned pers;
> for (pers = 0; pers < SUPPORTED_PERSONALITIES; pers++) {
> for (i = 0; i < nsyscall_vec[pers]; i++)
> if (sysent_vec[pers][i].sys_flags & n)
> qualify_one(i, opt->bitflag, not, pers);
> }
> continue;
> }
>
> This piece of code is doing the magic. Now the lookupclass() uses the
> bit set by the macros which is used to set the bits in qual_vec.
> through qualify_one().
>
> Although I am not understanding how the macros
>
> TRACE_FILE, TRACE_IPC, TRACE_NETWORK, etc which corresponds to the
> bits 001, 002, 004, work and set the particular system call bit in
> qual_vec. I mean what will be the bit if I want to add TRACE_OPEN_LIKE
> or something like that.
>
> Btw, I am still trying to understand how qual_vec is used to trace
> only particular system calls. May be the knowledge will help me
> contribute more.
You need to add another TRACE_* macro to defs.h, you should just find a
bit that is not used.
After that, you need to add in syscall.c the short name for your macro,
and use it in all the syscallent.h files.
> A Note. I saw at many critical places you are using wait4() system
> call to wait for the process. I read it is obsolete. Should we worry
> about it and think of changing it to waitpid() and getrusage() at
> places.
Imho this is not necessary, wait4() is will stay in the kernel anyway.
--
Gabriel Laskar
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