"ps -e" without procfs(5)

[Kostik Belousov]

On Tue, Nov 08, 2011 at 11:47:54PM +0200, Mikolaj Golub wrote:
> 
> On Sun, 6 Nov 2011 20:10:41 +0200 Kostik Belousov wrote:
> 
>  KB> On Sat, Nov 05, 2011 at 10:37:46PM +0200, Mikolaj Golub wrote:
>  >> 
>  >> http://people.freebsd.org/~trociny/env.sys.3.patch
> 
>  KB> Oops, I missed this in the previous review. You cannot use fubyte in
>  KB> proc_read_mem(). fubyte reads a byte from the address space of the current
>  KB> process. The fix is easy, use proc_rwmem for 1 byte.
> 
>  KB> I do not think that fall back to single byte read is warranted for
>  KB> proc_read_mem calls e.g. for ps_strings. Add a flag to indicate whether
>  KB> the proc_read_mem should fall back to byte read ?
> 
>  KB> I would prefer using sizeof(uint64_t) and sizeof(uint32_t) instead of 8
>  KB> and 4 constants in the align checks.
> 
>  KB> Might be, add PROC_ASSERT_HELD() to get_ps_string() ?
> 
>  KB> procfs patch looks good.
> 
> Thanks. The updated version:
> 
> http://people.freebsd.org/~trociny/env.sys.4.patch
> 
> Investigating cases when EFAULT was returned and if the fallback was
> successful I noticed that most of the cases were when p->p_comm changed during
> the read, so the process was in exec in that time. In order to avoid this
> error I added a check for P_INEXEC flag.
And now you return success and nothing gets copied out for the process
in P_INEXEC state. Either you should return an error like EAGAIN, or
consider the P_INEXEC state as transitional and wait till process
leaves it. Or, ignore the state as it was before, and return whatever
error proc_rwmem generated (my preference).

> 
> After this I observed EFAULT (very rarely) only when reading arg or env
> strings and fallback was successful for those cases. So I modified the patch
> to do fallback only when reading strings (as it was in one of my earlier
> versions but with wrong fubyte), and returned your comment which explains why
> it may happen :-)
> 
> Also in the procfs patch I have added the check for process state.
> 
> The userland part has not been changed since my first report:
> 
> http://people.freebsd.org/~trociny/env.user.patch
> 
> -- 
> Mikolaj Golub
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