On 12/6/24 3:49 AM, John Ousterhout wrote:
On Sun, Dec 1, 2024 at 7:51 PM D. Wythe <alibuda@xxxxxxxxxxxxxxxxx> wrote:
+int homa_setsockopt(struct sock *sk, int level, int optname, sockptr_t optval,
+ unsigned int optlen)
+{
+ struct homa_sock *hsk = homa_sk(sk);
+ struct homa_set_buf_args args;
+ int ret;
+
+ if (level != IPPROTO_HOMA || optname != SO_HOMA_SET_BUF ||
+ optlen != sizeof(struct homa_set_buf_args))
+ return -EINVAL;
SO_HOMA_SET_BUF is a bit odd here, maybe HOMA_RCVBUF ? which also can be
implemented in getsockopt.
I have changed it to HOMA_RCVBUF (and renamed struct homa_set_buf_args
to struct homa_rcvbuf_args). I also implemented getsockopt for
HOMA_RCVBUF.
+
+ if (copy_from_sockptr(&args, optval, optlen))
+ return -EFAULT;
+
+ /* Do a trivial test to make sure we can at least write the first
+ * page of the region.
+ */
+ if (copy_to_user((__force void __user *)args.start, &args, sizeof(args)))
+ return -EFAULT;
To share buffer between kernel and userspace, maybe you should refer to the implementation of
io_pin_pbuf_ring()
I'm not sure what you mean here. Are you suggesting that I look at the
code of io_pin_pbuf_ring to make sure I've done everything needed to
share buffers? I don't believe that Homa needs to do anything special
(e.g. it doesn't need to pin the user's buffers); it just saves the
address and makes copy_to_user calls later when needed (and these
calls are all done at syscall level in the context of the
application). Is there something I'm missing?
I just thought that since the received buffer is shared between kernel and user-space, if using
vmap() to map the very memory, so that we don't need to use such "copy_to_user" to transfer the data
from kernel to user-space, we can use memcpy() instead. This shall be more faster, but I had no
relevant data to prove it..
So I'm not going to insist on it, it ups to you.
D. Wythe
