[PATCH net-next 1/3] net: devmem: support single IOV with sendmsg

[PATCH net-next 1/3] net: devmem: support single IOV with sendmsg

[Stanislav Fomichev]

sendmsg() with a single iov becomes ITER_UBUF, sendmsg() with multiple
iovs becomes ITER_IOVEC. iter_iov_len does not return correct
value for UBUF, so teach to treat UBUF differently.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Pavel Begunkov <asml.silence@gmail.com>
Cc: Mina Almasry <almasrymina@google.com>
Fixes: bd61848900bf ("net: devmem: Implement TX path")
Signed-off-by: Stanislav Fomichev <stfomichev@gmail.com>
---
 include/linux/uio.h | 8 +++++++-
 net/core/datagram.c | 3 ++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 49ece9e1888f..393d0622cc28 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -99,7 +99,13 @@ static inline const struct iovec *iter_iov(const struct iov_iter *iter)
 }
 
 #define iter_iov_addr(iter)	(iter_iov(iter)->iov_base + (iter)->iov_offset)
-#define iter_iov_len(iter)	(iter_iov(iter)->iov_len - (iter)->iov_offset)
+
+static inline size_t iter_iov_len(const struct iov_iter *i)
+{
+	if (i->iter_type == ITER_UBUF)
+		return i->count;
+	return iter_iov(i)->iov_len - i->iov_offset;
+}
 
 static inline enum iter_type iov_iter_type(const struct iov_iter *i)
 {
diff --git a/net/core/datagram.c b/net/core/datagram.c
index 9ef5442536f5..c44f1d2b70a4 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -706,7 +706,8 @@ zerocopy_fill_skb_from_devmem(struct sk_buff *skb, struct iov_iter *from,
 	 * iov_addrs are interpreted as an offset in bytes into the dma-buf to
 	 * send from. We do not support other iter types.
 	 */
-	if (iov_iter_type(from) != ITER_IOVEC)
+	if (iov_iter_type(from) != ITER_IOVEC &&
+	    iov_iter_type(from) != ITER_UBUF)
 		return -EFAULT;
 
 	while (length && iov_iter_count(from)) {
-- 
2.49.0

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

[Stanislav Fomichev]

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;
+			}
 
-		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;
+		}
 
 		msg.msg_iov = iov;
-		msg.msg_iovlen = 2;
+		provider->memcpy_to_device(mem, 0, line, line_size);
 
 		msg.msg_control = ctrl_data;
 		msg.msg_controllen = sizeof(ctrl_data);
@@ -934,7 +939,8 @@ static int do_client(struct memory_buffer *mem)
 		fprintf(stderr, "sendmsg_ret=%d\n", ret);
 
 		if (ret != line_size)
-			error(1, errno, "Did not send all bytes");
+			error(1, errno, "Did not send all bytes %d vs %zd", ret,
+			      line_size);
 
 		wait_compl(socket_fd);
 	}
@@ -956,7 +962,7 @@ int main(int argc, char *argv[])
 	int is_server = 0, opt;
 	int ret;
 
-	while ((opt = getopt(argc, argv, "ls:c:p:v:q:t:f:")) != -1) {
+	while ((opt = getopt(argc, argv, "ls:c:p:v:q:t:f:z:")) != -1) {
 		switch (opt) {
 		case 'l':
 			is_server = 1;
@@ -982,6 +988,9 @@ int main(int argc, char *argv[])
 		case 'f':
 			ifname = optarg;
 			break;
+		case 'z':
+			max_chunk = atoi(optarg);
+			break;
 		case '?':
 			fprintf(stderr, "unknown option: %c\n", optopt);
 			break;
-- 
2.49.0

[PATCH net-next 3/3] selftests: ncdevmem: add tx test with multiple IOVs

[Stanislav Fomichev]

Use prime 3 for length to make offset slowly drift away.

Signed-off-by: Stanislav Fomichev <stfomichev@gmail.com>
---
 .../testing/selftests/drivers/net/hw/devmem.py  | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/drivers/net/hw/devmem.py b/tools/testing/selftests/drivers/net/hw/devmem.py
index 7fc686cf47a2..d7f6a76eb2b7 100755
--- a/tools/testing/selftests/drivers/net/hw/devmem.py
+++ b/tools/testing/selftests/drivers/net/hw/devmem.py
@@ -49,12 +49,27 @@ from lib.py import ksft_disruptive
     ksft_eq(socat.stdout.strip(), "hello\nworld")
 
 
+@ksft_disruptive
+def check_tx_chunks(cfg) -> None:
+    cfg.require_ipver("6")
+    require_devmem(cfg)
+
+    port = rand_port()
+    listen_cmd = f"socat -U - TCP6-LISTEN:{port}"
+
+    with bkg(listen_cmd, exit_wait=True) as socat:
+        wait_port_listen(port)
+        cmd(f"echo -e \"hello\\nworld\"| {cfg.bin_remote} -f {cfg.ifname} -s {cfg.addr_v['6']} -p {port} -z 3", host=cfg.remote, shell=True)
+
+    ksft_eq(socat.stdout.strip(), "hello\nworld")
+
+
 def main() -> None:
     with NetDrvEpEnv(__file__) as cfg:
         cfg.bin_local = path.abspath(path.dirname(__file__) + "/ncdevmem")
         cfg.bin_remote = cfg.remote.deploy(cfg.bin_local)
 
-        ksft_run([check_rx, check_tx],
+        ksft_run([check_rx, check_tx, check_tx_chunks],
                  args=(cfg, ))
     ksft_exit()
 
-- 
2.49.0

Re: [PATCH net-next 1/3] net: devmem: support single IOV with sendmsg

[Mina Almasry]

On Tue, May 20, 2025 at 1:30 PM Stanislav Fomichev <stfomichev@gmail.com> wrote:
>
> sendmsg() with a single iov becomes ITER_UBUF, sendmsg() with multiple
> iovs becomes ITER_IOVEC. iter_iov_len does not return correct
> value for UBUF, so teach to treat UBUF differently.
>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Pavel Begunkov <asml.silence@gmail.com>
> Cc: Mina Almasry <almasrymina@google.com>
> Fixes: bd61848900bf ("net: devmem: Implement TX path")
> Signed-off-by: Stanislav Fomichev <stfomichev@gmail.com>
> ---
>  include/linux/uio.h | 8 +++++++-
>  net/core/datagram.c | 3 ++-
>  2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/uio.h b/include/linux/uio.h
> index 49ece9e1888f..393d0622cc28 100644
> --- a/include/linux/uio.h
> +++ b/include/linux/uio.h
> @@ -99,7 +99,13 @@ static inline const struct iovec *iter_iov(const struct iov_iter *iter)
>  }
>
>  #define iter_iov_addr(iter)    (iter_iov(iter)->iov_base + (iter)->iov_offset)
> -#define iter_iov_len(iter)     (iter_iov(iter)->iov_len - (iter)->iov_offset)
> +
> +static inline size_t iter_iov_len(const struct iov_iter *i)
> +{
> +       if (i->iter_type == ITER_UBUF)
> +               return i->count;
> +       return iter_iov(i)->iov_len - i->iov_offset;
> +}
>

This change looks good to me from devmem perspective, but aren't you
potentially breaking all these existing callers to iter_iov_len?

ackc -i iter_iov_len
fs/read_write.c
846:                                            iter_iov_len(iter), ppos);
849:                                            iter_iov_len(iter), ppos);
858:            if (nr != iter_iov_len(iter))

mm/madvise.c
1808:           size_t len_in = iter_iov_len(iter);
1838:           iov_iter_advance(iter, iter_iov_len(iter));

io_uring/rw.c
710:                    len = iter_iov_len(iter);

Or are you confident this change is compatible with these callers for
some reason?

Maybe better to handle this locally in zerocopy_fill_skb_from_devmem,
and then follow up with a more ambitious change that streamlines how
all the iters behave.


-- 
Thanks,
Mina

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

[Mina Almasry]

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?

> +                       }
>
> -               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?

>
>                 msg.msg_iov = iov;
> -               msg.msg_iovlen = 2;
> +               provider->memcpy_to_device(mem, 0, line, line_size);
>
>                 msg.msg_control = ctrl_data;
>                 msg.msg_controllen = sizeof(ctrl_data);
> @@ -934,7 +939,8 @@ static int do_client(struct memory_buffer *mem)
>                 fprintf(stderr, "sendmsg_ret=%d\n", ret);
>
>                 if (ret != line_size)
> -                       error(1, errno, "Did not send all bytes");
> +                       error(1, errno, "Did not send all bytes %d vs %zd", ret,
> +                             line_size);
>
>                 wait_compl(socket_fd);
>         }
> @@ -956,7 +962,7 @@ int main(int argc, char *argv[])
>         int is_server = 0, opt;
>         int ret;
>
> -       while ((opt = getopt(argc, argv, "ls:c:p:v:q:t:f:")) != -1) {
> +       while ((opt = getopt(argc, argv, "ls:c:p:v:q:t:f:z:")) != -1) {
>                 switch (opt) {
>                 case 'l':
>                         is_server = 1;
> @@ -982,6 +988,9 @@ int main(int argc, char *argv[])
>                 case 'f':
>                         ifname = optarg;
>                         break;
> +               case 'z':
> +                       max_chunk = atoi(optarg);
> +                       break;
>                 case '?':
>                         fprintf(stderr, "unknown option: %c\n", optopt);
>                         break;
> --
> 2.49.0
>


-- 
Thanks,
Mina

Re: [PATCH net-next 3/3] selftests: ncdevmem: add tx test with multiple IOVs

[Mina Almasry]

On Tue, May 20, 2025 at 1:30 PM Stanislav Fomichev <stfomichev@gmail.com> wrote:
>
> Use prime 3 for length to make offset slowly drift away.
>
> Signed-off-by: Stanislav Fomichev <stfomichev@gmail.com>
> ---
>  .../testing/selftests/drivers/net/hw/devmem.py  | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/drivers/net/hw/devmem.py b/tools/testing/selftests/drivers/net/hw/devmem.py
> index 7fc686cf47a2..d7f6a76eb2b7 100755
> --- a/tools/testing/selftests/drivers/net/hw/devmem.py
> +++ b/tools/testing/selftests/drivers/net/hw/devmem.py
> @@ -49,12 +49,27 @@ from lib.py import ksft_disruptive
>      ksft_eq(socat.stdout.strip(), "hello\nworld")
>
>
> +@ksft_disruptive
> +def check_tx_chunks(cfg) -> None:
> +    cfg.require_ipver("6")
> +    require_devmem(cfg)
> +
> +    port = rand_port()
> +    listen_cmd = f"socat -U - TCP6-LISTEN:{port}"
> +
> +    with bkg(listen_cmd, exit_wait=True) as socat:
> +        wait_port_listen(port)
> +        cmd(f"echo -e \"hello\\nworld\"| {cfg.bin_remote} -f {cfg.ifname} -s {cfg.addr_v['6']} -p {port} -z 3", host=cfg.remote, shell=True)
> +
> +    ksft_eq(socat.stdout.strip(), "hello\nworld")
> +
> +
>  def main() -> None:
>      with NetDrvEpEnv(__file__) as cfg:
>          cfg.bin_local = path.abspath(path.dirname(__file__) + "/ncdevmem")
>          cfg.bin_remote = cfg.remote.deploy(cfg.bin_local)
>
> -        ksft_run([check_rx, check_tx],
> +        ksft_run([check_rx, check_tx, check_tx_chunks],
>                   args=(cfg, ))
>      ksft_exit()
>
> --
> 2.49.0
>

I was hoping we'd add the test coverage without the need to add test
cases to the ksft. I was thinking maybe ncdevmem can do rand() each
sendmsg loop and send a different set of chunks, so that we don't need
a flag.

But it may be too hacky to have the test be non-deterministic, so up to you

Acked-by: Mina Almasry <almasrymina@google.com>


-- 
Thanks,
Mina

Re: [PATCH net-next 1/3] net: devmem: support single IOV with sendmsg

[Stanislav Fomichev]

On 05/21, Mina Almasry wrote:
> On Tue, May 20, 2025 at 1:30 PM Stanislav Fomichev <stfomichev@gmail.com> wrote:
> >
> > sendmsg() with a single iov becomes ITER_UBUF, sendmsg() with multiple
> > iovs becomes ITER_IOVEC. iter_iov_len does not return correct
> > value for UBUF, so teach to treat UBUF differently.
> >
> > Cc: Al Viro <viro@zeniv.linux.org.uk>
> > Cc: Pavel Begunkov <asml.silence@gmail.com>
> > Cc: Mina Almasry <almasrymina@google.com>
> > Fixes: bd61848900bf ("net: devmem: Implement TX path")
> > Signed-off-by: Stanislav Fomichev <stfomichev@gmail.com>
> > ---
> >  include/linux/uio.h | 8 +++++++-
> >  net/core/datagram.c | 3 ++-
> >  2 files changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/uio.h b/include/linux/uio.h
> > index 49ece9e1888f..393d0622cc28 100644
> > --- a/include/linux/uio.h
> > +++ b/include/linux/uio.h
> > @@ -99,7 +99,13 @@ static inline const struct iovec *iter_iov(const struct iov_iter *iter)
> >  }
> >
> >  #define iter_iov_addr(iter)    (iter_iov(iter)->iov_base + (iter)->iov_offset)
> > -#define iter_iov_len(iter)     (iter_iov(iter)->iov_len - (iter)->iov_offset)
> > +
> > +static inline size_t iter_iov_len(const struct iov_iter *i)
> > +{
> > +       if (i->iter_type == ITER_UBUF)
> > +               return i->count;
> > +       return iter_iov(i)->iov_len - i->iov_offset;
> > +}
> >
> 
> This change looks good to me from devmem perspective, but aren't you
> potentially breaking all these existing callers to iter_iov_len?
> 
> ackc -i iter_iov_len
> fs/read_write.c
> 846:                                            iter_iov_len(iter), ppos);
> 849:                                            iter_iov_len(iter), ppos);
> 858:            if (nr != iter_iov_len(iter))
> 
> mm/madvise.c
> 1808:           size_t len_in = iter_iov_len(iter);
> 1838:           iov_iter_advance(iter, iter_iov_len(iter));
> 
> io_uring/rw.c
> 710:                    len = iter_iov_len(iter);
> 
> Or are you confident this change is compatible with these callers for
> some reason?
 
Pavel did go over all callers, see:
https://lore.kernel.org/netdev/7f06216e-1e66-433e-a247-2445dac22498@gmail.com/

> Maybe better to handle this locally in zerocopy_fill_skb_from_devmem,
> and then follow up with a more ambitious change that streamlines how
> all the iters behave.

Yes, I can definitely do that, but it seems a bit strange that the
callers need to distinguish between IOVEC and UBUF (which is a 1-entry
IOVEC), so having working iter_iov_len seems a bit cleaner.

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

[Stanislav Fomichev]

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?

Re: [PATCH net-next 3/3] selftests: ncdevmem: add tx test with multiple IOVs

[Stanislav Fomichev]

On 05/21, Mina Almasry wrote:
> On Tue, May 20, 2025 at 1:30 PM Stanislav Fomichev <stfomichev@gmail.com> wrote:
> >
> > Use prime 3 for length to make offset slowly drift away.
> >
> > Signed-off-by: Stanislav Fomichev <stfomichev@gmail.com>
> > ---
> >  .../testing/selftests/drivers/net/hw/devmem.py  | 17 ++++++++++++++++-
> >  1 file changed, 16 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/testing/selftests/drivers/net/hw/devmem.py b/tools/testing/selftests/drivers/net/hw/devmem.py
> > index 7fc686cf47a2..d7f6a76eb2b7 100755
> > --- a/tools/testing/selftests/drivers/net/hw/devmem.py
> > +++ b/tools/testing/selftests/drivers/net/hw/devmem.py
> > @@ -49,12 +49,27 @@ from lib.py import ksft_disruptive
> >      ksft_eq(socat.stdout.strip(), "hello\nworld")
> >
> >
> > +@ksft_disruptive
> > +def check_tx_chunks(cfg) -> None:
> > +    cfg.require_ipver("6")
> > +    require_devmem(cfg)
> > +
> > +    port = rand_port()
> > +    listen_cmd = f"socat -U - TCP6-LISTEN:{port}"
> > +
> > +    with bkg(listen_cmd, exit_wait=True) as socat:
> > +        wait_port_listen(port)
> > +        cmd(f"echo -e \"hello\\nworld\"| {cfg.bin_remote} -f {cfg.ifname} -s {cfg.addr_v['6']} -p {port} -z 3", host=cfg.remote, shell=True)
> > +
> > +    ksft_eq(socat.stdout.strip(), "hello\nworld")
> > +
> > +
> >  def main() -> None:
> >      with NetDrvEpEnv(__file__) as cfg:
> >          cfg.bin_local = path.abspath(path.dirname(__file__) + "/ncdevmem")
> >          cfg.bin_remote = cfg.remote.deploy(cfg.bin_local)
> >
> > -        ksft_run([check_rx, check_tx],
> > +        ksft_run([check_rx, check_tx, check_tx_chunks],
> >                   args=(cfg, ))
> >      ksft_exit()
> >
> > --
> > 2.49.0
> >
> 
> I was hoping we'd add the test coverage without the need to add test
> cases to the ksft. I was thinking maybe ncdevmem can do rand() each
> sendmsg loop and send a different set of chunks, so that we don't need
> a flag.
> 
> But it may be too hacky to have the test be non-deterministic, so up to you
> 
> Acked-by: Mina Almasry <almasrymina@google.com>

Thanks! Let's spell it out explicitly for now. Doing it at random seems
like an option when we start sending more data (after your series
that converts the tests to -v).

Re: [PATCH net-next 1/3] net: devmem: support single IOV with sendmsg

[Mina Almasry]

On Wed, May 21, 2025 at 10:33 AM Stanislav Fomichev
<stfomichev@gmail.com> wrote:
>
> On 05/21, Mina Almasry wrote:
> > On Tue, May 20, 2025 at 1:30 PM Stanislav Fomichev <stfomichev@gmail.com> wrote:
> > >
> > > sendmsg() with a single iov becomes ITER_UBUF, sendmsg() with multiple
> > > iovs becomes ITER_IOVEC. iter_iov_len does not return correct
> > > value for UBUF, so teach to treat UBUF differently.
> > >
> > > Cc: Al Viro <viro@zeniv.linux.org.uk>
> > > Cc: Pavel Begunkov <asml.silence@gmail.com>
> > > Cc: Mina Almasry <almasrymina@google.com>
> > > Fixes: bd61848900bf ("net: devmem: Implement TX path")
> > > Signed-off-by: Stanislav Fomichev <stfomichev@gmail.com>
> > > ---
> > >  include/linux/uio.h | 8 +++++++-
> > >  net/core/datagram.c | 3 ++-
> > >  2 files changed, 9 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/include/linux/uio.h b/include/linux/uio.h
> > > index 49ece9e1888f..393d0622cc28 100644
> > > --- a/include/linux/uio.h
> > > +++ b/include/linux/uio.h
> > > @@ -99,7 +99,13 @@ static inline const struct iovec *iter_iov(const struct iov_iter *iter)
> > >  }
> > >
> > >  #define iter_iov_addr(iter)    (iter_iov(iter)->iov_base + (iter)->iov_offset)
> > > -#define iter_iov_len(iter)     (iter_iov(iter)->iov_len - (iter)->iov_offset)
> > > +
> > > +static inline size_t iter_iov_len(const struct iov_iter *i)
> > > +{
> > > +       if (i->iter_type == ITER_UBUF)
> > > +               return i->count;
> > > +       return iter_iov(i)->iov_len - i->iov_offset;
> > > +}
> > >
> >
> > This change looks good to me from devmem perspective, but aren't you
> > potentially breaking all these existing callers to iter_iov_len?
> >
> > ackc -i iter_iov_len
> > fs/read_write.c
> > 846:                                            iter_iov_len(iter), ppos);
> > 849:                                            iter_iov_len(iter), ppos);
> > 858:            if (nr != iter_iov_len(iter))
> >
> > mm/madvise.c
> > 1808:           size_t len_in = iter_iov_len(iter);
> > 1838:           iov_iter_advance(iter, iter_iov_len(iter));
> >
> > io_uring/rw.c
> > 710:                    len = iter_iov_len(iter);
> >
> > Or are you confident this change is compatible with these callers for
> > some reason?
>
> Pavel did go over all callers, see:
> https://lore.kernel.org/netdev/7f06216e-1e66-433e-a247-2445dac22498@gmail.com/
>

Thanks, I'm not confident enough in my understanding of the other call
sites of iter_iov_len to provide a reviewed-by, but this looks fine to
me for devmem TCP, so I think acked-by is appropriate.

Acked-by: Mina Almasry <almasrymina@google.com>

Thanks!

-- 
Thanks,
Mina

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

[Mina Almasry]

On Wed, May 21, 2025 at 10:39 AM Stanislav Fomichev
<stfomichev@gmail.com> wrote:
>
> 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?
>

Thanks, I missed that line.

Reviewed-by: Mina Almasry <almasrymina@google.com>

-- 
Thanks,
Mina

Re: [PATCH net-next 1/3] net: devmem: support single IOV with sendmsg

[Pavel Begunkov]

On 5/21/25 18:33, Stanislav Fomichev wrote:
> On 05/21, Mina Almasry wrote:
>> On Tue, May 20, 2025 at 1:30 PM Stanislav Fomichev <stfomichev@gmail.com> wrote:
>>>
>>> sendmsg() with a single iov becomes ITER_UBUF, sendmsg() with multiple
>>> iovs becomes ITER_IOVEC. iter_iov_len does not return correct
>>> value for UBUF, so teach to treat UBUF differently.
>>>
>>> Cc: Al Viro <viro@zeniv.linux.org.uk>
>>> Cc: Pavel Begunkov <asml.silence@gmail.com>
>>> Cc: Mina Almasry <almasrymina@google.com>
>>> Fixes: bd61848900bf ("net: devmem: Implement TX path")
>>> Signed-off-by: Stanislav Fomichev <stfomichev@gmail.com>
>>> ---
>>>   include/linux/uio.h | 8 +++++++-
>>>   net/core/datagram.c | 3 ++-
>>>   2 files changed, 9 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/include/linux/uio.h b/include/linux/uio.h
>>> index 49ece9e1888f..393d0622cc28 100644
>>> --- a/include/linux/uio.h
>>> +++ b/include/linux/uio.h
>>> @@ -99,7 +99,13 @@ static inline const struct iovec *iter_iov(const struct iov_iter *iter)
>>>   }
>>>
>>>   #define iter_iov_addr(iter)    (iter_iov(iter)->iov_base + (iter)->iov_offset)
>>> -#define iter_iov_len(iter)     (iter_iov(iter)->iov_len - (iter)->iov_offset)
>>> +
>>> +static inline size_t iter_iov_len(const struct iov_iter *i)
>>> +{
>>> +       if (i->iter_type == ITER_UBUF)
>>> +               return i->count;
>>> +       return iter_iov(i)->iov_len - i->iov_offset;
>>> +}
>>>
>>
>> This change looks good to me from devmem perspective, but aren't you
>> potentially breaking all these existing callers to iter_iov_len?
>>
>> ackc -i iter_iov_len
>> fs/read_write.c
>> 846:                                            iter_iov_len(iter), ppos);
>> 849:                                            iter_iov_len(iter), ppos);
>> 858:            if (nr != iter_iov_len(iter))
>>
>> mm/madvise.c
>> 1808:           size_t len_in = iter_iov_len(iter);
>> 1838:           iov_iter_advance(iter, iter_iov_len(iter));
>>
>> io_uring/rw.c
>> 710:                    len = iter_iov_len(iter);
>>
>> Or are you confident this change is compatible with these callers for
>> some reason?
>   
> Pavel did go over all callers, see:
> https://lore.kernel.org/netdev/7f06216e-1e66-433e-a247-2445dac22498@gmail.com/

Yes, the patch should work

Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>

> 
>> Maybe better to handle this locally in zerocopy_fill_skb_from_devmem,
>> and then follow up with a more ambitious change that streamlines how
>> all the iters behave.
> 
> Yes, I can definitely do that, but it seems a bit strange that the
> callers need to distinguish between IOVEC and UBUF (which is a 1-entry
> IOVEC), so having working iter_iov_len seems a bit cleaner.

It might be a good idea to rename it at some point to highlight that
it also works with ubufs (but not as a part of this fix).

-- 
Pavel Begunkov

Re: [PATCH net-next 1/3] net: devmem: support single IOV with sendmsg

[Jakub Kicinski]

On Tue, 20 May 2025 13:30:42 -0700 Stanislav Fomichev wrote:
> sendmsg() with a single iov becomes ITER_UBUF, sendmsg() with multiple
> iovs becomes ITER_IOVEC. iter_iov_len does not return correct
> value for UBUF, so teach to treat UBUF differently.

Looks like this has been merged (silently), thanks!