linux-kernel - Re: [PATCH v2] ptrace: Clarify PTRACE_GETREGSET/PTRACE

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Message-ID: <20140612180501.GB15795@redhat.com>
Date:	Thu, 12 Jun 2014 20:05:01 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:	Pedro Alves <palves@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, hpa@...or.com,
	suresh.b.siddha@...el.com
Subject: Re: [PATCH v2] ptrace: Clarify PTRACE_GETREGSET/PTRACE_SETREGSET,
	documentation in uapi header

On 06/12, Anshuman Khandual wrote:
>
> > --- a/include/uapi/linux/ptrace.h
> > +++ b/include/uapi/linux/ptrace.h
> > @@ -39,12 +39,17 @@
> >   * payload are exactly the same layout.
> >   *
> >   * This interface usage is as follows:
> > - *	struct iovec iov = { buf, len};
> > + *	struct iovec iov = { buf, len };
> >   *
> >   *	ret = ptrace(PTRACE_GETREGSET/PTRACE_SETREGSET, pid, NT_XXX_TYPE, &iov);
> >   *
> > - * On the successful completion, iov.len will be updated by the kernel,
> > - * specifying how much the kernel has written/read to/from the user's iov.buf.
> > + * On entry, iov describes the buffer's address and length.  The buffer's length
> > + * must be a multiple of the size of a single register in the register set.  The
> > + * kernel never reads or writes more than iov.len, and caps the buffer length to
> > + * the register set's size.  In other words, the kernel reads or writes
> > + * min(iov.len, regset size).

I think this should be self-obvious ;) otherwise why do we need to pass
the length of the buffer?

But of course I won't argue with the additional documentation, perhaps you
can re-send this patch to akpm? Usually ptrace changes are routed via -mm
tree.

But if we update the kernel header, then probably it would be more important
to update the man-page. To me the description of GETREGSET looks good, but
probably it could also mention that buflen should be multiple of regsize (as
you did above). Add Michael.

Oleg.

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