ptrace: Fix ptrace_regset() comments and diagnose errors specifically

Return -EINVAL for the bad size and for unrecognized NT_* type in
ptrace_regset() instead of -EIO.

Also update the comments for this ptrace interface with more clarifications.

Requested-by: Roland McGrath <roland@redhat.com>
Requested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <20100222225240.397523600@sbs-t61.sc.intel.com>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

include/linux/ptrace.h

@@ -30,6 +30,11 @@
 /*
  * Generic ptrace interface that exports the architecture specific regsets
  * using the corresponding NT_* types (which are also used in the core dump).
+ * Please note that the NT_PRSTATUS note type in a core dump contains a full
+ * 'struct elf_prstatus'. But the user_regset for NT_PRSTATUS contains just the
+ * elf_gregset_t that is the pr_reg field of 'struct elf_prstatus'. For all the
+ * other user_regset flavors, the user_regset layout and the ELF core dump note
+ * payload are exactly the same layout.
  *
  * This interface usage is as follows:
  *	struct iovec iov = { buf, len};

kernel/ptrace.c

@@ -537,7 +537,7 @@ static int ptrace_regset(struct task_struct *task, int req, unsigned int type,
 	int regset_no;
 
 	if (!regset || (kiov->iov_len % regset->size) != 0)
-		return -EIO;
+		return -EINVAL;
 
 	regset_no = regset - view->regsets;
 	kiov->iov_len = min(kiov->iov_len,