From: Al Viro > On Fri, Nov 21, 2014 at 05:42:55PM +0000, David Laight wrote: > > > Callers of kernel_send/recvmsg() could easily be using a wrapper > > function that creates the 'msghdr'. > > When the want to send the remaining part of a buffer the old iterator > > will no longer be available - just the original iov and the required offset. > > Er... So why not copy a struct iov_iter to/from msg->msg_iter, then? > It's not as it had been particulary large - 5 words isn't much... > > I'm not at all sure that _anything_ has valid reasons for draining iovecs. > Maintaining a struct iov_iter and modifying it is easy and actually faster... > > Right now the main examples outside of net/* are due to unfortunate > limitations of ->sendmsg() - until now it had no way to be told that > desired data starts at offset. With ->msg_iter it obviously becomes > possible... It may well be easier for code that only has to run in a new kernel. But for code that has run in old kernels as well you still need to modify the iov[]. This is also true of userspace - there is no way of completing a partial transfer without modifying the iov[] to allow for the partial transfer. Note that I'm not suggesting that any of the 'write' functions should ever modify an iov[]. David -- To unsubscribe from this list: send the line "unsubscribe target-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
