Re: [PATCH net-next 2/3] selftests: ncdevmem: make chunking optional

On 05/21, Mina Almasry wrote:

On Tue, May 20, 2025 at 1:30 PM Stanislav Fomichev stfomichev@gmail.com wrote:

...

Add new -z argument to specify max IOV size. By default, use single large IOV.

Signed-off-by: Stanislav Fomichev stfomichev@gmail.com

.../selftests/drivers/net/hw/ncdevmem.c | 49 +++++++++++-------- 1 file changed, 29 insertions(+), 20 deletions(-)

diff --git a/tools/testing/selftests/drivers/net/hw/ncdevmem.c b/tools/testing/selftests/drivers/net/hw/ncdevmem.c index ca723722a810..fc7ba7d71502 100644 --- a/tools/testing/selftests/drivers/net/hw/ncdevmem.c +++ b/tools/testing/selftests/drivers/net/hw/ncdevmem.c @@ -82,6 +82,9 @@ #define MSG_SOCK_DEVMEM 0x2000000 #endif

+#define MAX_IOV 1024

+static size_t max_chunk; static char *server_ip; static char *client_ip; static char *port; @@ -834,10 +837,10 @@ static int do_client(struct memory_buffer *mem) struct sockaddr_in6 server_sin; struct sockaddr_in6 client_sin; struct ynl_sock *ys = NULL;

•   struct iovec iov[MAX_IOV];
    struct msghdr msg = {};
    ssize_t line_size = 0;
    struct cmsghdr *cmsg;
  

•   struct iovec iov[2];
    char *line = NULL;
    unsigned long mid;
    size_t len = 0;
  

@@ -893,27 +896,29 @@ static int do_client(struct memory_buffer *mem) if (line_size < 0) break;

•           mid = (line_size / 2) + 1;
  

•           iov[0].iov_base = (void *)1;
  

•           iov[0].iov_len = mid;
  

•           iov[1].iov_base = (void *)(mid + 2);
  

•           iov[1].iov_len = line_size - mid;
  

•           if (max_chunk) {
  

•                   msg.msg_iovlen =
  

•                           (line_size + max_chunk - 1) / max_chunk;
  

•                   if (msg.msg_iovlen > MAX_IOV)
  

•                           error(1, 0,
  

•                                 "can't partition %zd bytes into maximum of %d chunks",
  

•                                 line_size, MAX_IOV);
  
  

•           provider->memcpy_to_device(mem, (size_t)iov[0].iov_base, line,
  

•                                      iov[0].iov_len);
  

•           provider->memcpy_to_device(mem, (size_t)iov[1].iov_base,
  

•                                      line + iov[0].iov_len,
  

•                                      iov[1].iov_len);
  

•                   for (int i = 0; i < msg.msg_iovlen; i++) {
  

•                           iov[i].iov_base = (void *)(i * max_chunk);
  

•                           iov[i].iov_len = max_chunk;
  

Isn't the last iov going to be truncated in the case where line_size is not exactly divisible with max_chunk?

I have this for the last iov entry:

iov[msg.msg_iovlen - 1].iov_len = line_size - (msg.msg_iovlen - 1) * max_chunk;

I think that should correctly adjust it to the remaining 1..max_chunk len?

...

•                   }
  
  

•           fprintf(stderr,
  

•                   "read line_size=%ld iov[0].iov_base=%lu, iov[0].iov_len=%lu, iov[1].iov_base=%lu, iov[1].iov_len=%lu\n",
  

•                   line_size, (unsigned long)iov[0].iov_base,
  

•                   iov[0].iov_len, (unsigned long)iov[1].iov_base,
  

•                   iov[1].iov_len);
  

•                   iov[msg.msg_iovlen - 1].iov_len =
  

•                           line_size - (msg.msg_iovlen - 1) * max_chunk;
  

•           } else {
  

•                   iov[0].iov_base = 0;
  

•                   iov[0].iov_len = line_size;
  

•                   msg.msg_iovlen = 1;
  

•           }
  

Do you need to special case this? Shouldn't this be the same as max_chunk==1?

I might need a better name. max_chunk is the max size of the iov entry (max iov_len), not the max number of IOVs. And I use max_chunk==0 as "max size of the iov is not provided -> use line_size", so not sure I can't make it work without a special case?