Understanding proc_rwmem

[Fernando Apesteguía]

2010/4/14 John Baldwin <jhb at freebsd.org>:
> On Wednesday 14 April 2010 4:22:56 pm Fernando Apesteguía wrote:
>> Hi all,
>>
>> I'm trying to read process memory other than the current process in
>> kernel. I was told to use the proc_rwmem function, however I can't get
>> it working properly. At first, I'm trying to read how many elements
>> the environment variables vector has. To do this I tried this from a
>> linprocfs filler function:
>>
>>
>>         struct iovec iov;
>>       struct uio tmp_uio;
>>       struct ps_strings *pss;
>>       int ret_code;
>>
>>       buff = malloc(sizeof(struct ps_strings), M_TEMP, M_WAITOK);
>>       memset(buff, 0, sizeof(struct ps_strings));
>>
>>       PROC_LOCK_ASSERT(td->td_proc, MA_NOTOWNED);
>>       iov.iov_base = (caddr_t) buff;
>>       iov.iov_len = sizeof(struct ps_strings);
>>       tmp_uio.uio_iov = &iov;
>>       tmp_uio.uio_iovcnt = 1;
>>       tmp_uio.uio_offset = (off_t)(p->p_sysent->sv_psstrings);
>>       tmp_uio.uio_resid = sizeof(struct ps_strings);
>>       tmp_uio.uio_segflg = UIO_USERSPACE;
>>       tmp_uio.uio_rw = UIO_READ;
>>       tmp_uio.uio_td = td;
>>       ret_code = proc_rwmem(td->td_proc, &tmp_uio);
>
> I think you want to use 'p' instead of 'td->td_proc' here.  As it is you are
> reading from the current process instead of the target process I believe.

Thank you. You are right.

I made the changes suggested by both you and Kostik. I still have
random data when reading.
I'm trying to to the same thing using kern/sys_generic.c::read and
kern/sys_process.c::kern_ptrace
as examples, but I'm missing something...
After reading with proc_rwmem, is it possible to do something like the
following?

if (ret_code == 0) {
		sbuf_printf(sb, "proc_rwmem successfully executed: %d\n", ret_code);
} else {
		sbuf_printf(sb, "Error in proc_rwmem: %d\n", ret_code);
}

pss = (struct ps_strings *)(iov.iov_base);
sbuf_printf(sb, "ps_nargvstr = %d\nps_nenvstr = %d\n",
pss->ps_nargvstr, pss->ps_nenvstr);

Thanks in advance.

>
> --
> John Baldwin
>