[PATCH] ptrace: Fix PTRACE_GETREGSET/PTRACE_SETREGSET in code documentation

[Anshuman Khandual <khandual@linux.vnet.ibm.com>]

The current documentation is bit misleading and does not explicitly
specify that iov.len need to be initialized failing which kernel
may just ignore the ptrace request and never read from/write into
the user specified buffer. This patch fixes the documentation.

Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
---
 include/uapi/linux/ptrace.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
index cf1019e..e9d6b37 100644
--- a/include/uapi/linux/ptrace.h
+++ b/include/uapi/linux/ptrace.h
@@ -43,8 +43,12 @@
  *
  *	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.
+ * A non-zero value upto the max size of data expected to be written/read by the
+ * kernel in response to any NT_XXX_TYPE request type must be assigned to iov.len
+ * before initiating the ptrace call. If iov.len is 0, then kernel will neither
+ * read from or write into the user buffer specified. On 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.
  */
 #define PTRACE_GETREGSET	0x4204
 #define PTRACE_SETREGSET	0x4205
-- 
1.7.11.7