Re: [PATCH] Let gcore use ptrace interface rather than the procfs

On Thu, 19 Nov 2009, Attilio Rao wrote:

> 2009/11/17 Robert N. M. Watson <rwatson_at_freebsd.org>:
>>
>> On 17 Nov 2009, at 14:17, Ed Maste wrote:
>>
>>> Our original motivation for doing this was to make gcore work with 
>>> threaded apps, not avoiding procfs, but that's a useful side-effect of the 
>>> work.  Note though that for that purpose it isn't complete; procfs is 
>>> still used in readmap to read the process' memory map.  It looks like we 
>>> need to find a way to implement readmap without procfs.
>>
>> Are the sysctls used for procstat -v sufficient for this purpose?
>
> This patch should address the arised concerns by both of you: 
> http://www.freebsd.org/~attilio/Sandvine/STABLE_8/gcore/gcore2.diff
>
> and additively fix elf_getstatus() to not use procfs, so that gcore is 
> completely procfs independent now. Comments, reviews and testing are 
> welcome.

If you add the missing include of sys/wait.h, elfcore.c generates an error 
instead of a warning on this non-traditional use of wait(2):

+	wait();

Something like this may be preferred:

         if (waitpid(pid, NULL, 0) < 0)
                 err(1, "waitpid");

This further persisting reference to procfs can be replaced with a sysctl/kvm 
interface:

gcore.c:  asprintf(&binfile, "/proc/%d/file", pid);

See the implementation of "procstat -b" which returns the path to the binary 
using the same underlying mechanism (vn_fullpath on the process image vnode).

I think that kills the last of the procfs dependencies, in which case perhaps 
we can remove the procfs.h include from elfcore.c, which requires defining a 
local version of a summary data structure borrowed from procfs.  It's worth 
trying with procfs unmounted, however, to make sure they're really all gone 
(which is how I ran into the above problem).

Robert N M Watson
Computer Laboratory
University of Cambridge