[PATCH net-next 0/2] net: rds: convert rds to getsockopt_iter

[PATCH net-next 0/2] net: rds: convert rds to getsockopt_iter

[Breno Leitao]

This series continues the conversion of the remaining proto_ops getsockopt
callbacks to the new getsockopt_iter callback introduced in commit
67fab22a7adc ("net: add getsockopt_iter callback to proto_ops"), this time
for RDS.

RDS is a little more involved than the protocols converted so far, because
the RDS_INFO_* options snapshot kernel state directly into the destination
buffer: the info producers memcpy into the pages under a spinlock via
kmap_atomic() and so must not fault.

The conversion preserves that model — it obtains the same page array and
starting offset from opt->iter_out with iov_iter_extract_pages(),
preallocating the array so the iterator fills it in place, and leaves
the rds_info_iterator / rds_info_copy machinery and all producer
callbacks unchanged; kernel (ITER_KVEC) buffers remain unsupported on
the RDS_INFO path, as before.

I've vibe-coded a kselftest exercising both the simple options and the
RDS_INFO_* snapshot path, feel free to drop it in case this is not
useful.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
Breno Leitao (2):
      rds: convert to getsockopt_iter
      selftests: net: rds: add getsockopt() conversion test

 net/rds/af_rds.c                             |  36 ++---
 net/rds/info.c                               |  70 +++++-----
 net/rds/info.h                               |   3 +-
 tools/testing/selftests/net/rds/.gitignore   |   1 +
 tools/testing/selftests/net/rds/Makefile     |   4 +
 tools/testing/selftests/net/rds/getsockopt.c | 201 +++++++++++++++++++++++++++
 6 files changed, 266 insertions(+), 49 deletions(-)
---
base-commit: b7bee4ca5688e30ca50fbc87b1b8f7eed7006c17
change-id: 20260603-getsock_more-46be8d1c56fd

Best regards,
-- 
Breno Leitao <leitao@debian.org>

[PATCH net-next 1/2] rds: convert to getsockopt_iter

[Breno Leitao]

Convert RDS socket's getsockopt implementation to use the new
getsockopt_iter callback with sockopt_t.

Key changes:
- Replace (char __user *optval, int __user *optlen) with sockopt_t *opt
- Use opt->optlen for buffer length (input) and returned size (output)
- Use copy_to_iter() instead of put_user()/copy_to_user()

The RDS_INFO_* snapshot path in rds_info_getsockopt() used to pin the
userspace buffer with pin_user_pages_fast() on the raw optval address;
the info producers then memcpy into those pages under a spinlock via
kmap_atomic() and so must not fault. Obtain the same page array and
starting offset from opt->iter_out with iov_iter_extract_pages(), which
pins for write because iter_out is ITER_DEST.

The page array is preallocated here (sized with iov_iter_npages()) and
passed in, so iov_iter_extract_pages() fills it in place rather than
allocating one for us; RDS therefore keeps ownership of the array on
every return path and frees it itself. The rds_info_iterator /
rds_info_copy machinery and all producer callbacks are unchanged.

Kernel buffers (ITER_KVEC) are not page-backed in a way the info
producers can use, so the RDS_INFO path returns -EOPNOTSUPP for them;
this matches the previous behaviour, where a kernel-buffer getsockopt
hit the WARN_ONCE() path in do_sock_getsockopt() and returned
-EOPNOTSUPP. The simple RDS_RECVERR and SO_RDS_TRANSPORT options keep
working for kernel buffers via copy_to_iter().

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 net/rds/af_rds.c | 36 ++++++++++++++++-------------
 net/rds/info.c   | 70 +++++++++++++++++++++++++++++++-------------------------
 net/rds/info.h   |  3 +--
 3 files changed, 60 insertions(+), 49 deletions(-)

diff --git a/net/rds/af_rds.c b/net/rds/af_rds.c
index 6f4f9cf352bd..d5defe9172e3 100644
--- a/net/rds/af_rds.c
+++ b/net/rds/af_rds.c
@@ -37,6 +37,7 @@
 #include <linux/in.h>
 #include <linux/ipv6.h>
 #include <linux/poll.h>
+#include <linux/uio.h>
 #include <net/sock.h>
 
 #include "rds.h"
@@ -485,35 +486,36 @@ static int rds_setsockopt(struct socket *sock, int level, int optname,
 }
 
 static int rds_getsockopt(struct socket *sock, int level, int optname,
-			  char __user *optval, int __user *optlen)
+			  sockopt_t *opt)
 {
 	struct rds_sock *rs = rds_sk_to_rs(sock->sk);
 	int ret = -ENOPROTOOPT, len;
 	int trans;
+	int val;
 
 	if (level != SOL_RDS)
 		goto out;
 
-	if (get_user(len, optlen)) {
-		ret = -EFAULT;
-		goto out;
-	}
+	len = opt->optlen;
 
 	switch (optname) {
 	case RDS_INFO_FIRST ... RDS_INFO_LAST:
-		ret = rds_info_getsockopt(sock, optname, optval,
-					  optlen);
+		ret = rds_info_getsockopt(sock, optname, opt);
 		break;
 
 	case RDS_RECVERR:
-		if (len < sizeof(int))
+		if (len < sizeof(int)) {
 			ret = -EINVAL;
-		else
-		if (put_user(rs->rs_recverr, (int __user *) optval) ||
-		    put_user(sizeof(int), optlen))
+			break;
+		}
+		val = rs->rs_recverr;
+		if (copy_to_iter(&val, sizeof(int), &opt->iter_out) !=
+		    sizeof(int)) {
 			ret = -EFAULT;
-		else
+		} else {
+			opt->optlen = sizeof(int);
 			ret = 0;
+		}
 		break;
 	case SO_RDS_TRANSPORT:
 		if (len < sizeof(int)) {
@@ -522,11 +524,13 @@ static int rds_getsockopt(struct socket *sock, int level, int optname,
 		}
 		trans = (rs->rs_transport ? rs->rs_transport->t_type :
 			 RDS_TRANS_NONE); /* unbound */
-		if (put_user(trans, (int __user *)optval) ||
-		    put_user(sizeof(int), optlen))
+		if (copy_to_iter(&trans, sizeof(int), &opt->iter_out) !=
+		    sizeof(int)) {
 			ret = -EFAULT;
-		else
+		} else {
+			opt->optlen = sizeof(int);
 			ret = 0;
+		}
 		break;
 	default:
 		break;
@@ -653,7 +657,7 @@ static const struct proto_ops rds_proto_ops = {
 	.listen =	sock_no_listen,
 	.shutdown =	sock_no_shutdown,
 	.setsockopt =	rds_setsockopt,
-	.getsockopt =	rds_getsockopt,
+	.getsockopt_iter =	rds_getsockopt,
 	.sendmsg =	rds_sendmsg,
 	.recvmsg =	rds_recvmsg,
 	.mmap =		sock_no_mmap,
diff --git a/net/rds/info.c b/net/rds/info.c
index f1b29994934a..171838782595 100644
--- a/net/rds/info.c
+++ b/net/rds/info.c
@@ -35,6 +35,7 @@
 #include <linux/slab.h>
 #include <linux/proc_fs.h>
 #include <linux/export.h>
+#include <linux/uio.h>
 
 #include "rds.h"
 
@@ -144,60 +145,68 @@ void rds_info_copy(struct rds_info_iterator *iter, void *data,
 EXPORT_SYMBOL_GPL(rds_info_copy);
 
 /*
- * @optval points to the userspace buffer that the information snapshot
- * will be copied into.
- *
- * @optlen on input is the size of the buffer in userspace.  @optlen
- * on output is the size of the requested snapshot in bytes.
+ * @opt->iter_out describes the buffer that the information snapshot will be
+ * copied into, and @opt->optlen is the size of that buffer on input.  On
+ * output @opt->optlen is set to the size of the requested snapshot in bytes.
  *
  * This function returns -errno if there is a failure, particularly -ENOSPC
- * if the given userspace buffer was not large enough to fit the snapshot.
- * On success it returns the positive number of bytes of each array element
- * in the snapshot.
+ * if the given buffer was not large enough to fit the snapshot.  On success
+ * it returns the positive number of bytes of each array element in the
+ * snapshot.
  */
-int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
-			int __user *optlen)
+int rds_info_getsockopt(struct socket *sock, int optname, sockopt_t *opt)
 {
 	struct rds_info_iterator iter;
 	struct rds_info_lengths lens;
 	unsigned long nr_pages = 0;
-	unsigned long start;
 	rds_info_func func;
 	struct page **pages = NULL;
+	size_t offset0 = 0;
+	int npages = 0;
 	int ret;
 	int len;
 	int total;
 
-	if (get_user(len, optlen)) {
-		ret = -EFAULT;
-		goto out;
-	}
+	len = opt->optlen;
 
 	/* check for all kinds of wrapping and the like */
-	start = (unsigned long)optval;
-	if (len < 0 || len > INT_MAX - PAGE_SIZE + 1 || start + len < start) {
+	if (len < 0 || len > INT_MAX - PAGE_SIZE + 1) {
 		ret = -EINVAL;
 		goto out;
 	}
 
+	/* The info producers write into the pages with kmap_atomic() while
+	 * holding a spinlock, so they need a genuine page-backed user buffer.
+	 */
+	if (iov_iter_is_kvec(&opt->iter_out)) {
+		ret = -EOPNOTSUPP;
+		goto out;
+	}
+
 	/* a 0 len call is just trying to probe its length */
 	if (len == 0)
 		goto call_func;
 
-	nr_pages = (PAGE_ALIGN(start + len) - (start & PAGE_MASK))
-			>> PAGE_SHIFT;
-
-	pages = kmalloc_objs(struct page *, nr_pages);
+	/*
+	 * Preallocate the page array and pass it in so that
+	 * iov_iter_extract_pages() fills it in place rather than allocating
+	 * one for us.  Handing it a non-NULL array keeps ownership of the
+	 * array with us on every return path, instead of depending on the
+	 * iterator code to allocate and hand it back.
+	 */
+	npages = iov_iter_npages(&opt->iter_out, INT_MAX);
+	pages = kvmalloc_array(npages, sizeof(*pages), GFP_KERNEL);
 	if (!pages) {
 		ret = -ENOMEM;
 		goto out;
 	}
-	ret = pin_user_pages_fast(start, nr_pages, FOLL_WRITE, pages);
-	if (ret != nr_pages) {
-		if (ret > 0)
-			nr_pages = ret;
-		else
-			nr_pages = 0;
+
+	ret = iov_iter_extract_pages(&opt->iter_out, &pages, len, npages,
+				     0, &offset0);
+	if (ret < 0)
+		goto out;
+	nr_pages = DIV_ROUND_UP(offset0 + ret, PAGE_SIZE);
+	if (ret != len) {
 		ret = -EAGAIN; /* XXX ? */
 		goto out;
 	}
@@ -213,7 +222,7 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
 
 	iter.pages = pages;
 	iter.addr = NULL;
-	iter.offset = start & (PAGE_SIZE - 1);
+	iter.offset = offset0;
 
 	func(sock, len, &iter, &lens);
 	BUG_ON(lens.each == 0);
@@ -230,13 +239,12 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
 		ret = lens.each;
 	}
 
-	if (put_user(len, optlen))
-		ret = -EFAULT;
+	opt->optlen = len;
 
 out:
 	if (pages)
 		unpin_user_pages(pages, nr_pages);
-	kfree(pages);
+	kvfree(pages);
 
 	return ret;
 }
diff --git a/net/rds/info.h b/net/rds/info.h
index a069b51c4679..1aab62ab6d00 100644
--- a/net/rds/info.h
+++ b/net/rds/info.h
@@ -21,8 +21,7 @@ typedef void (*rds_info_func)(struct socket *sock, unsigned int len,
 
 void rds_info_register_func(int optname, rds_info_func func);
 void rds_info_deregister_func(int optname, rds_info_func func);
-int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
-			int __user *optlen);
+int rds_info_getsockopt(struct socket *sock, int optname, sockopt_t *opt);
 void rds_info_copy(struct rds_info_iterator *iter, void *data,
 		   unsigned long bytes);
 void rds_info_iter_unmap(struct rds_info_iterator *iter);

-- 
2.54.0

Re: [PATCH net-next 1/2] rds: convert to getsockopt_iter

[Allison Henderson]

On Wed, 2026-06-03 at 09:11 -0700, Breno Leitao wrote:
> Convert RDS socket's getsockopt implementation to use the new
> getsockopt_iter callback with sockopt_t.
> 
> Key changes:
> - Replace (char __user *optval, int __user *optlen) with sockopt_t *opt
> - Use opt->optlen for buffer length (input) and returned size (output)
> - Use copy_to_iter() instead of put_user()/copy_to_user()
> 
> The RDS_INFO_* snapshot path in rds_info_getsockopt() used to pin the
> userspace buffer with pin_user_pages_fast() on the raw optval address;
> the info producers then memcpy into those pages under a spinlock via
> kmap_atomic() and so must not fault. Obtain the same page array and
> starting offset from opt->iter_out with iov_iter_extract_pages(), which
> pins for write because iter_out is ITER_DEST.
> 
> The page array is preallocated here (sized with iov_iter_npages()) and
> passed in, so iov_iter_extract_pages() fills it in place rather than
> allocating one for us; RDS therefore keeps ownership of the array on
> every return path and frees it itself. The rds_info_iterator /
> rds_info_copy machinery and all producer callbacks are unchanged.
> 
> Kernel buffers (ITER_KVEC) are not page-backed in a way the info
> producers can use, so the RDS_INFO path returns -EOPNOTSUPP for them;
> this matches the previous behaviour, where a kernel-buffer getsockopt
> hit the WARN_ONCE() path in do_sock_getsockopt() and returned
> -EOPNOTSUPP. The simple RDS_RECVERR and SO_RDS_TRANSPORT options keep
> working for kernel buffers via copy_to_iter().
> 
> Signed-off-by: Breno Leitao <leitao@debian.org>

Hi Breno,

Thanks for working on this.  The conversions look mostly correct to me, just a few nits I noticed below:

> ---
>  net/rds/af_rds.c | 36 ++++++++++++++++-------------
>  net/rds/info.c   | 70 +++++++++++++++++++++++++++++++-------------------------
>  net/rds/info.h   |  3 +--
>  3 files changed, 60 insertions(+), 49 deletions(-)
> 
> diff --git a/net/rds/af_rds.c b/net/rds/af_rds.c
> index 6f4f9cf352bd..d5defe9172e3 100644
> --- a/net/rds/af_rds.c
> +++ b/net/rds/af_rds.c
> @@ -37,6 +37,7 @@
>  #include <linux/in.h>
>  #include <linux/ipv6.h>
>  #include <linux/poll.h>
> +#include <linux/uio.h>
>  #include <net/sock.h>
>  
>  #include "rds.h"
> @@ -485,35 +486,36 @@ static int rds_setsockopt(struct socket *sock, int level, int optname,
>  }
>  
>  static int rds_getsockopt(struct socket *sock, int level, int optname,
> -			  char __user *optval, int __user *optlen)
> +			  sockopt_t *opt)
>  {
>  	struct rds_sock *rs = rds_sk_to_rs(sock->sk);
>  	int ret = -ENOPROTOOPT, len;
>  	int trans;
> +	int val;
>  
>  	if (level != SOL_RDS)
>  		goto out;
>  
> -	if (get_user(len, optlen)) {
> -		ret = -EFAULT;
> -		goto out;
> -	}
> +	len = opt->optlen;
>  
>  	switch (optname) {
>  	case RDS_INFO_FIRST ... RDS_INFO_LAST:
> -		ret = rds_info_getsockopt(sock, optname, optval,
> -					  optlen);
> +		ret = rds_info_getsockopt(sock, optname, opt);
>  		break;
>  
>  	case RDS_RECVERR:
> -		if (len < sizeof(int))
> +		if (len < sizeof(int)) {
>  			ret = -EINVAL;
> -		else
> -		if (put_user(rs->rs_recverr, (int __user *) optval) ||
> -		    put_user(sizeof(int), optlen))
> +			break;
> +		}
> +		val = rs->rs_recverr;
> +		if (copy_to_iter(&val, sizeof(int), &opt->iter_out) !=
> +		    sizeof(int)) {
>  			ret = -EFAULT;
> -		else
> +		} else {
> +			opt->optlen = sizeof(int);
>  			ret = 0;
> +		}
>  		break;
>  	case SO_RDS_TRANSPORT:
>  		if (len < sizeof(int)) {
> @@ -522,11 +524,13 @@ static int rds_getsockopt(struct socket *sock, int level, int optname,
>  		}
>  		trans = (rs->rs_transport ? rs->rs_transport->t_type :
>  			 RDS_TRANS_NONE); /* unbound */
> -		if (put_user(trans, (int __user *)optval) ||
> -		    put_user(sizeof(int), optlen))
> +		if (copy_to_iter(&trans, sizeof(int), &opt->iter_out) !=
> +		    sizeof(int)) {
>  			ret = -EFAULT;
> -		else
> +		} else {
> +			opt->optlen = sizeof(int);
>  			ret = 0;
> +		}
>  		break;
>  	default:
>  		break;
> @@ -653,7 +657,7 @@ static const struct proto_ops rds_proto_ops = {
>  	.listen =	sock_no_listen,
>  	.shutdown =	sock_no_shutdown,
>  	.setsockopt =	rds_setsockopt,
> -	.getsockopt =	rds_getsockopt,
> +	.getsockopt_iter =	rds_getsockopt,
>  	.sendmsg =	rds_sendmsg,
>  	.recvmsg =	rds_recvmsg,
>  	.mmap =		sock_no_mmap,
> diff --git a/net/rds/info.c b/net/rds/info.c
> index f1b29994934a..171838782595 100644
> --- a/net/rds/info.c
> +++ b/net/rds/info.c
> @@ -35,6 +35,7 @@
>  #include <linux/slab.h>
>  #include <linux/proc_fs.h>
>  #include <linux/export.h>
> +#include <linux/uio.h>
>  
>  #include "rds.h"
>  
> @@ -144,60 +145,68 @@ void rds_info_copy(struct rds_info_iterator *iter, void *data,
>  EXPORT_SYMBOL_GPL(rds_info_copy);
>  
>  /*
> - * @optval points to the userspace buffer that the information snapshot
> - * will be copied into.
> - *
> - * @optlen on input is the size of the buffer in userspace.  @optlen
> - * on output is the size of the requested snapshot in bytes.
> + * @opt->iter_out describes the buffer that the information snapshot will be
> + * copied into, and @opt->optlen is the size of that buffer on input.  On
> + * output @opt->optlen is set to the size of the requested snapshot in bytes.
>   *
>   * This function returns -errno if there is a failure, particularly -ENOSPC
> - * if the given userspace buffer was not large enough to fit the snapshot.
> - * On success it returns the positive number of bytes of each array element
> - * in the snapshot.
> + * if the given buffer was not large enough to fit the snapshot.  On success
> + * it returns the positive number of bytes of each array element in the
> + * snapshot.
>   */
> -int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
> -			int __user *optlen)
> +int rds_info_getsockopt(struct socket *sock, int optname, sockopt_t *opt)
>  {
>  	struct rds_info_iterator iter;
>  	struct rds_info_lengths lens;
>  	unsigned long nr_pages = 0;
> -	unsigned long start;
>  	rds_info_func func;
>  	struct page **pages = NULL;
> +	size_t offset0 = 0;
> +	int npages = 0;
>  	int ret;
>  	int len;
>  	int total;
>  
> -	if (get_user(len, optlen)) {
> -		ret = -EFAULT;
> -		goto out;
> -	}
> +	len = opt->optlen;
>  
>  	/* check for all kinds of wrapping and the like */
> -	start = (unsigned long)optval;
> -	if (len < 0 || len > INT_MAX - PAGE_SIZE + 1 || start + len < start) {
> +	if (len < 0 || len > INT_MAX - PAGE_SIZE + 1) {
>  		ret = -EINVAL;
>  		goto out;
>  	}
>  
> +	/* The info producers write into the pages with kmap_atomic() while
> +	 * holding a spinlock, so they need a genuine page-backed user buffer.
> +	 */
I think !user_backed_iter() is more accurate for what you're meaning to do here?  Technically we only ever get kvecs or
ubufs since rds_info_getsockopt is only called by do_sock_getsockopt.  Those appear to be the only two types it passes,
so it works out.  But it means we're counting on that assumption from the caller and ideally we should filter anything
that's not user backed.  So, I'd replace the iov_iter_is_kvec check with:

	if (!user_backed_iter(&opt->iter_out)) {

> +	if (iov_iter_is_kvec(&opt->iter_out)) {
> +		ret = -EOPNOTSUPP;
> +		goto out;
> +	}
> +
>  	/* a 0 len call is just trying to probe its length */
>  	if (len == 0)
>  		goto call_func;
>  
> -	nr_pages = (PAGE_ALIGN(start + len) - (start & PAGE_MASK))
> -			>> PAGE_SHIFT;
> -
> -	pages = kmalloc_objs(struct page *, nr_pages);
> +	/*
> +	 * Preallocate the page array and pass it in so that
> +	 * iov_iter_extract_pages() fills it in place rather than allocating
> +	 * one for us.  Handing it a non-NULL array keeps ownership of the
> +	 * array with us on every return path, instead of depending on the
> +	 * iterator code to allocate and hand it back.
> +	 */
> +	npages = iov_iter_npages(&opt->iter_out, INT_MAX);
> +	pages = kvmalloc_array(npages, sizeof(*pages), GFP_KERNEL);
>  	if (!pages) {
>  		ret = -ENOMEM;
>  		goto out;
>  	}
> -	ret = pin_user_pages_fast(start, nr_pages, FOLL_WRITE, pages);
> -	if (ret != nr_pages) {
> -		if (ret > 0)
> -			nr_pages = ret;
> -		else
> -			nr_pages = 0;
> +
> +	ret = iov_iter_extract_pages(&opt->iter_out, &pages, len, npages,
> +				     0, &offset0);
> +	if (ret < 0)
> +		goto out;
> +	nr_pages = DIV_ROUND_UP(offset0 + ret, PAGE_SIZE);
> +	if (ret != len) {
>  		ret = -EAGAIN; /* XXX ? */
>  		goto out;
>  	}
> @@ -213,7 +222,7 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
>  
>  	iter.pages = pages;
>  	iter.addr = NULL;
> -	iter.offset = start & (PAGE_SIZE - 1);
> +	iter.offset = offset0;
>  
>  	func(sock, len, &iter, &lens);
>  	BUG_ON(lens.each == 0);
> @@ -230,13 +239,12 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
>  		ret = lens.each;
>  	}
>  
> -	if (put_user(len, optlen))
> -		ret = -EFAULT;
> +	opt->optlen = len;
>  
>  out:
The unpin here works, but it took me a little bit to trace out where the corresponding pin went since it is removed
earlier in the patch.  Pages are pinned on extract, but only for user pages. This works out since the only caller here
passes kvec or ubuf, and we error out on kvec iters.  Pages are assumed pinned if they're not null, but without the
!user_backed_iter check, it leans on this behavior from the caller.  Ideally I think iov_iter_extract_pages is supposed
to be paired with iov_iter_extract_will_pin.  A quick comment would help clarify too.  So the closing gate would look
something like this:

	/* unpin pages from ubuf iters */
	if (pages && iov_iter_extract_will_pin(&opt->iter_out))

>  	if (pages)
>  		unpin_user_pages(pages, nr_pages);

Having both checks is somewhat redundant, but it doesnt hurt anything either.  And I think it helps make it a little
more uniform and readable.  Other than that I think this patch is looking pretty good to me.

Thank you!
Allison

> -	kfree(pages);
> +	kvfree(pages);
>  
>  	return ret;
>  }
> diff --git a/net/rds/info.h b/net/rds/info.h
> index a069b51c4679..1aab62ab6d00 100644
> --- a/net/rds/info.h
> +++ b/net/rds/info.h
> @@ -21,8 +21,7 @@ typedef void (*rds_info_func)(struct socket *sock, unsigned int len,
>  
>  void rds_info_register_func(int optname, rds_info_func func);
>  void rds_info_deregister_func(int optname, rds_info_func func);
> -int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
> -			int __user *optlen);
> +int rds_info_getsockopt(struct socket *sock, int optname, sockopt_t *opt);
>  void rds_info_copy(struct rds_info_iterator *iter, void *data,
>  		   unsigned long bytes);
>  void rds_info_iter_unmap(struct rds_info_iterator *iter);
> 

Re: [PATCH net-next 1/2] rds: convert to getsockopt_iter

[Breno Leitao]

On Thu, Jun 04, 2026 at 07:20:24PM -0700, Allison Henderson wrote:
> Thanks for working on this.  The conversions look mostly correct to me, just a few nits I noticed below:

Thanks for the very detailed review.

> > +	/* The info producers write into the pages with kmap_atomic() while
> > +	 * holding a spinlock, so they need a genuine page-backed user buffer.
> > +	 */
> > +	if (iov_iter_is_kvec(&opt->iter_out)) {
> > +		ret = -EOPNOTSUPP;
> > +		goto out;
> I think !user_backed_iter() is more accurate for what you're meaning to do here?  Technically we only ever get kvecs or
> ubufs since rds_info_getsockopt is only called by do_sock_getsockopt.  Those appear to be the only two types it passes,
> so it works out.  But it means we're counting on that assumption from the caller and ideally we should filter anything
> that's not user backed.  So, I'd replace the iov_iter_is_kvec check with:
> 
> 	if (!user_backed_iter(&opt->iter_out)) {

Agreed, that's more accurate and doesn't lean on the caller only ever
handing us kvec or ubuf. Will switch to !user_backed_iter() in v2.

> > @@ -230,13 +239,12 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
> >  		ret = lens.each;
> >  	}
> >  
> > -	if (put_user(len, optlen))
> > -		ret = -EFAULT;
> > +	opt->optlen = len;
> >  
> >  out:
> The unpin here works, but it took me a little bit to trace out where the corresponding pin went since it is removed
> earlier in the patch.  Pages are pinned on extract, but only for user pages. This works out since the only caller here
> passes kvec or ubuf, and we error out on kvec iters.  Pages are assumed pinned if they're not null, but without the
> !user_backed_iter check, it leans on this behavior from the caller.  Ideally I think iov_iter_extract_pages is supposed
> to be paired with iov_iter_extract_will_pin.  A quick comment would help clarify too.  So the closing gate would look
> something like this:
> 
> 	/* unpin pages from ubuf iters */
> 	if (pages && iov_iter_extract_will_pin(&opt->iter_out))
> 
> >  	if (pages)
> >  		unpin_user_pages(pages, nr_pages);
> 
> Having both checks is somewhat redundant, but it doesnt hurt anything either.  And I think it helps make it a little
> more uniform and readable.  Other than that I think this patch is looking pretty good to me.

Makes sense. In v2 I'll pair the extract with extract_will_pin and add a
comment so the pin/unpin contract is self-documenting:

  out:
              /*
               * iov_iter_extract_pages() pins only user-backed (ubuf)
               * iters; iov_iter_extract_will_pin() reports whether an
               * unpin is owed here.
               */
              if (pages && iov_iter_extract_will_pin(&opt->iter_out))
                      unpin_user_pages(pages, nr_pages);
              kvfree(pages);

Thanks for the review!
--breno

[PATCH net-next 2/2] selftests: net: rds: add getsockopt() conversion test

[Breno Leitao]

Add a kselftest that exercises the RDS getsockopt() paths converted to
the getsockopt_iter() / sockopt_t callback:

- RDS_RECVERR and SO_RDS_TRANSPORT, which return their int value through
  copy_to_iter() and report the written length in opt->optlen.

- RDS_INFO_*, which obtains the userspace buffer pages with
  iov_iter_extract_pages() (including a non-zero starting page offset)
  and lets the info producers copy the snapshot in under a spinlock.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 tools/testing/selftests/net/rds/.gitignore   |   1 +
 tools/testing/selftests/net/rds/Makefile     |   4 +
 tools/testing/selftests/net/rds/getsockopt.c | 201 +++++++++++++++++++++++++++
 3 files changed, 206 insertions(+)

diff --git a/tools/testing/selftests/net/rds/.gitignore b/tools/testing/selftests/net/rds/.gitignore
index 1c6f04e2aa11..7ca4b1440f51 100644
--- a/tools/testing/selftests/net/rds/.gitignore
+++ b/tools/testing/selftests/net/rds/.gitignore
@@ -1 +1,2 @@
 include.sh
+getsockopt
diff --git a/tools/testing/selftests/net/rds/Makefile b/tools/testing/selftests/net/rds/Makefile
index fe363be8e358..0700d8298eec 100644
--- a/tools/testing/selftests/net/rds/Makefile
+++ b/tools/testing/selftests/net/rds/Makefile
@@ -5,6 +5,8 @@ all:
 
 TEST_PROGS := run.sh
 
+TEST_GEN_PROGS := getsockopt
+
 TEST_FILES := \
 	include.sh \
 	settings \
@@ -16,4 +18,6 @@ EXTRA_CLEAN := \
 	/tmp/rds_logs \
 # end of EXTRA_CLEAN
 
+CFLAGS += $(KHDR_INCLUDES)
+
 include ../../lib.mk
diff --git a/tools/testing/selftests/net/rds/getsockopt.c b/tools/testing/selftests/net/rds/getsockopt.c
new file mode 100644
index 000000000000..a82ffe4871c2
--- /dev/null
+++ b/tools/testing/selftests/net/rds/getsockopt.c
@@ -0,0 +1,201 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Exercise the RDS getsockopt() paths that were converted to the
+ * getsockopt_iter() / sockopt_t callback.
+ *
+ * Three distinct paths are covered:
+ *
+ *   - RDS_RECVERR and SO_RDS_TRANSPORT, which now return their int value
+ *     through copy_to_iter() and report the written length in opt->optlen.
+ *
+ *   - RDS_INFO_*, which pins the userspace buffer with
+ *     iov_iter_extract_pages() (including a non-zero starting page offset)
+ *     and lets the info producers memcpy the snapshot in under a spinlock.
+ *
+ * The kvec (in-kernel buffer) -> -EOPNOTSUPP path of rds_info_getsockopt()
+ * is not reachable from a userspace getsockopt() and so is not tested here.
+ */
+#include <errno.h>
+#include <stdint.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <sys/socket.h>
+#include <linux/rds.h>
+
+#include "../../kselftest_harness.h"
+
+#ifndef AF_RDS
+#define AF_RDS 21
+#endif
+
+FIXTURE(rds) {
+	int fd;
+};
+
+FIXTURE_SETUP(rds)
+{
+	self->fd = socket(AF_RDS, SOCK_SEQPACKET, 0);
+	if (self->fd < 0)
+		SKIP(return, "AF_RDS unavailable (errno %d) - load the rds module",
+		     errno);
+}
+
+FIXTURE_TEARDOWN(rds)
+{
+	if (self->fd >= 0)
+		close(self->fd);
+}
+
+/* RDS_RECVERR defaults to 0 and is reported back as a 4-byte int. */
+TEST_F(rds, recverr_default)
+{
+	socklen_t len = sizeof(int);
+	int val = 0xdeadbeef;
+
+	ASSERT_EQ(0, getsockopt(self->fd, SOL_RDS, RDS_RECVERR, &val, &len));
+	EXPECT_EQ(sizeof(int), len);
+	EXPECT_EQ(0, val);
+}
+
+/* A value set via setsockopt() must be readable back unchanged. */
+TEST_F(rds, recverr_set_get)
+{
+	socklen_t len = sizeof(int);
+	int val = 1;
+
+	ASSERT_EQ(0, setsockopt(self->fd, SOL_RDS, RDS_RECVERR, &val, len));
+
+	val = 0;
+	ASSERT_EQ(0, getsockopt(self->fd, SOL_RDS, RDS_RECVERR, &val, &len));
+	EXPECT_EQ(sizeof(int), len);
+	EXPECT_EQ(1, val);
+}
+
+/* A buffer smaller than an int is rejected with EINVAL, not silently. */
+TEST_F(rds, recverr_short_buffer)
+{
+	socklen_t len = sizeof(int) - 1;
+	char buf[sizeof(int)];
+
+	EXPECT_EQ(-1, getsockopt(self->fd, SOL_RDS, RDS_RECVERR, buf, &len));
+	EXPECT_EQ(EINVAL, errno);
+}
+
+/* An unbound socket reports RDS_TRANS_NONE for SO_RDS_TRANSPORT. */
+TEST_F(rds, transport_unbound)
+{
+	socklen_t len = sizeof(int);
+	int val = 0;
+
+	ASSERT_EQ(0, getsockopt(self->fd, SOL_RDS, SO_RDS_TRANSPORT, &val,
+				&len));
+	EXPECT_EQ(sizeof(int), len);
+	EXPECT_EQ(RDS_TRANS_NONE, (unsigned int)val);
+}
+
+TEST_F(rds, transport_short_buffer)
+{
+	socklen_t len = sizeof(int) - 1;
+	char buf[sizeof(int)];
+
+	EXPECT_EQ(-1, getsockopt(self->fd, SOL_RDS, SO_RDS_TRANSPORT, buf,
+				 &len));
+	EXPECT_EQ(EINVAL, errno);
+}
+
+/*
+ * RDS_INFO_COUNTERS with a zero-length buffer is the "probe" call: it must
+ * fail with ENOSPC and report the required snapshot size in optlen.
+ */
+TEST_F(rds, info_counters_probe)
+{
+	socklen_t len = 0;
+
+	EXPECT_EQ(-1, getsockopt(self->fd, SOL_RDS, RDS_INFO_COUNTERS, NULL,
+				 &len));
+	EXPECT_EQ(ENOSPC, errno);
+	EXPECT_GT(len, 0);
+	/* The snapshot is an array of fixed-size counter records. */
+	EXPECT_EQ(0, len % (socklen_t)sizeof(struct rds_info_counter));
+}
+
+/*
+ * A real snapshot into an unaligned userspace buffer exercises the
+ * iov_iter_extract_pages() path, including the non-zero offset0 handling
+ * that the patch reworked. Place the buffer at a non-page-aligned address
+ * spanning into the next page to make sure multi-page pinning works too.
+ */
+TEST_F(rds, info_counters_snapshot)
+{
+	struct rds_info_counter *ctr;
+	socklen_t need = 0, len;
+	long pagesz = sysconf(_SC_PAGESIZE);
+	unsigned int i, n;
+	char *region, *buf;
+	int ret;
+
+	/* Probe for the required size. */
+	getsockopt(self->fd, SOL_RDS, RDS_INFO_COUNTERS, NULL, &need);
+	ASSERT_GT(need, 0);
+
+	region = mmap(NULL, 2 * pagesz, PROT_READ | PROT_WRITE,
+		      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	ASSERT_NE(MAP_FAILED, region);
+
+	/* Unaligned start that runs past the first page boundary. */
+	buf = region + pagesz - 64;
+	ASSERT_LE(need, (socklen_t)(pagesz + 64));
+
+	/*
+	 * On success the RDS_INFO path returns the positive per-element size
+	 * (lens.each) rather than 0, and writes the full snapshot length back
+	 * into optlen.
+	 */
+	len = need;
+	ret = getsockopt(self->fd, SOL_RDS, RDS_INFO_COUNTERS, buf, &len);
+	ASSERT_GE(ret, 0) {
+		TH_LOG("getsockopt snapshot failed: errno %d", errno);
+	}
+	EXPECT_EQ(sizeof(struct rds_info_counter), ret);
+	EXPECT_EQ(need, len);
+
+	/* The counter names must be NUL-terminated, non-empty strings. */
+	ctr = (struct rds_info_counter *)buf;
+	n = len / sizeof(*ctr);
+	ASSERT_GT(n, 0);
+	for (i = 0; i < n; i++) {
+		size_t namelen = strnlen((char *)ctr[i].name,
+					 sizeof(ctr[i].name));
+
+		EXPECT_GT(namelen, 0);
+		EXPECT_LT(namelen, sizeof(ctr[i].name));
+	}
+
+	munmap(region, 2 * pagesz);
+}
+
+/*
+ * A non-zero but too-small buffer must report ENOSPC and the full required
+ * length, without corrupting memory past the buffer.
+ */
+TEST_F(rds, info_counters_short_buffer)
+{
+	socklen_t need = 0, len;
+	char small[sizeof(struct rds_info_counter)];
+
+	getsockopt(self->fd, SOL_RDS, RDS_INFO_COUNTERS, NULL, &need);
+	ASSERT_GT(need, 0);
+
+	/* Ask with a buffer guaranteed smaller than the full snapshot. */
+	if (need <= (socklen_t)sizeof(small))
+		SKIP(return, "snapshot fits in one record; nothing to test");
+
+	len = 1; /* < sizeof(struct rds_info_counter) */
+	EXPECT_EQ(-1, getsockopt(self->fd, SOL_RDS, RDS_INFO_COUNTERS, small,
+				 &len));
+	EXPECT_EQ(ENOSPC, errno);
+	EXPECT_EQ(need, len);
+}
+
+TEST_HARNESS_MAIN

-- 
2.54.0

Re: [PATCH net-next 2/2] selftests: net: rds: add getsockopt() conversion test

[Allison Henderson]

On Wed, 2026-06-03 at 09:11 -0700, Breno Leitao wrote:
> Add a kselftest that exercises the RDS getsockopt() paths converted to
> the getsockopt_iter() / sockopt_t callback:
> 
> - RDS_RECVERR and SO_RDS_TRANSPORT, which return their int value through
>   copy_to_iter() and report the written length in opt->optlen.
> 
> - RDS_INFO_*, which obtains the userspace buffer pages with
>   iov_iter_extract_pages() (including a non-zero starting page offset)
>   and lets the info producers copy the snapshot in under a spinlock.
> 
> Signed-off-by: Breno Leitao <leitao@debian.org>

Hi Breno,

Thanks for working on this.  Your test covers a lot of socket behavior that the
existing packet test doesn't get into, so I definitely think it's worth adding.
I ran it locally under vng and it passes for me.  I did notice one nit below, but
otherwise I think it looks really good.


> ---
>  tools/testing/selftests/net/rds/.gitignore   |   1 +
>  tools/testing/selftests/net/rds/Makefile     |   4 +
>  tools/testing/selftests/net/rds/getsockopt.c | 201 +++++++++++++++++++++++++++
>  3 files changed, 206 insertions(+)
> 
> diff --git a/tools/testing/selftests/net/rds/.gitignore b/tools/testing/selftests/net/rds/.gitignore
> index 1c6f04e2aa11..7ca4b1440f51 100644
> --- a/tools/testing/selftests/net/rds/.gitignore
> +++ b/tools/testing/selftests/net/rds/.gitignore
> @@ -1 +1,2 @@
>  include.sh
> +getsockopt
> diff --git a/tools/testing/selftests/net/rds/Makefile b/tools/testing/selftests/net/rds/Makefile
> index fe363be8e358..0700d8298eec 100644
> --- a/tools/testing/selftests/net/rds/Makefile
> +++ b/tools/testing/selftests/net/rds/Makefile
> @@ -5,6 +5,8 @@ all:
>  
>  TEST_PROGS := run.sh
>  
> +TEST_GEN_PROGS := getsockopt
> +
>  TEST_FILES := \
>  	include.sh \
>  	settings \
> @@ -16,4 +18,6 @@ EXTRA_CLEAN := \
>  	/tmp/rds_logs \
>  # end of EXTRA_CLEAN
>  
> +CFLAGS += $(KHDR_INCLUDES)
> +
>  include ../../lib.mk
> diff --git a/tools/testing/selftests/net/rds/getsockopt.c b/tools/testing/selftests/net/rds/getsockopt.c
> new file mode 100644
> index 000000000000..a82ffe4871c2
> --- /dev/null
> +++ b/tools/testing/selftests/net/rds/getsockopt.c
> @@ -0,0 +1,201 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Exercise the RDS getsockopt() paths that were converted to the
> + * getsockopt_iter() / sockopt_t callback.
> + *
> + * Three distinct paths are covered:
> + *
> + *   - RDS_RECVERR and SO_RDS_TRANSPORT, which now return their int value
> + *     through copy_to_iter() and report the written length in opt->optlen.
> + *
> + *   - RDS_INFO_*, which pins the userspace buffer with
> + *     iov_iter_extract_pages() (including a non-zero starting page offset)
> + *     and lets the info producers memcpy the snapshot in under a spinlock.
> + *
> + * The kvec (in-kernel buffer) -> -EOPNOTSUPP path of rds_info_getsockopt()
> + * is not reachable from a userspace getsockopt() and so is not tested here.
> + */
> +#include <errno.h>
> +#include <stdint.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <sys/mman.h>
> +#include <sys/socket.h>
> +#include <linux/rds.h>
> +
> +#include "../../kselftest_harness.h"
> +
> +#ifndef AF_RDS
> +#define AF_RDS 21
> +#endif
> +
> +FIXTURE(rds) {
> +	int fd;
> +};
> +
> +FIXTURE_SETUP(rds)
> +{
> +	self->fd = socket(AF_RDS, SOCK_SEQPACKET, 0);
> +	if (self->fd < 0)
> +		SKIP(return, "AF_RDS unavailable (errno %d) - load the rds module",
> +		     errno);
> +}
> +
> +FIXTURE_TEARDOWN(rds)
> +{
> +	if (self->fd >= 0)
> +		close(self->fd);
> +}
> +
> +/* RDS_RECVERR defaults to 0 and is reported back as a 4-byte int. */
> +TEST_F(rds, recverr_default)
> +{
> +	socklen_t len = sizeof(int);
> +	int val = 0xdeadbeef;
> +
> +	ASSERT_EQ(0, getsockopt(self->fd, SOL_RDS, RDS_RECVERR, &val, &len));
> +	EXPECT_EQ(sizeof(int), len);
> +	EXPECT_EQ(0, val);
> +}
> +
> +/* A value set via setsockopt() must be readable back unchanged. */
> +TEST_F(rds, recverr_set_get)
> +{
> +	socklen_t len = sizeof(int);
> +	int val = 1;
> +
> +	ASSERT_EQ(0, setsockopt(self->fd, SOL_RDS, RDS_RECVERR, &val, len));
> +
> +	val = 0;
> +	ASSERT_EQ(0, getsockopt(self->fd, SOL_RDS, RDS_RECVERR, &val, &len));
> +	EXPECT_EQ(sizeof(int), len);
> +	EXPECT_EQ(1, val);
> +}
> +
> +/* A buffer smaller than an int is rejected with EINVAL, not silently. */
> +TEST_F(rds, recverr_short_buffer)
> +{
> +	socklen_t len = sizeof(int) - 1;
> +	char buf[sizeof(int)];
> +
> +	EXPECT_EQ(-1, getsockopt(self->fd, SOL_RDS, RDS_RECVERR, buf, &len));
> +	EXPECT_EQ(EINVAL, errno);
> +}
> +
> +/* An unbound socket reports RDS_TRANS_NONE for SO_RDS_TRANSPORT. */
> +TEST_F(rds, transport_unbound)
> +{
> +	socklen_t len = sizeof(int);
> +	int val = 0;
> +
> +	ASSERT_EQ(0, getsockopt(self->fd, SOL_RDS, SO_RDS_TRANSPORT, &val,
> +				&len));
> +	EXPECT_EQ(sizeof(int), len);
> +	EXPECT_EQ(RDS_TRANS_NONE, (unsigned int)val);
> +}
> +
> +TEST_F(rds, transport_short_buffer)
> +{
> +	socklen_t len = sizeof(int) - 1;
> +	char buf[sizeof(int)];
> +
> +	EXPECT_EQ(-1, getsockopt(self->fd, SOL_RDS, SO_RDS_TRANSPORT, buf,
> +				 &len));
> +	EXPECT_EQ(EINVAL, errno);
> +}
> +
> +/*
> + * RDS_INFO_COUNTERS with a zero-length buffer is the "probe" call: it must
> + * fail with ENOSPC and report the required snapshot size in optlen.
> + */
> +TEST_F(rds, info_counters_probe)
> +{
> +	socklen_t len = 0;
> +
> +	EXPECT_EQ(-1, getsockopt(self->fd, SOL_RDS, RDS_INFO_COUNTERS, NULL,
> +				 &len));
> +	EXPECT_EQ(ENOSPC, errno);
> +	EXPECT_GT(len, 0);
> +	/* The snapshot is an array of fixed-size counter records. */
> +	EXPECT_EQ(0, len % (socklen_t)sizeof(struct rds_info_counter));
> +}
> +
> +/*
> + * A real snapshot into an unaligned userspace buffer exercises the
> + * iov_iter_extract_pages() path, including the non-zero offset0 handling
> + * that the patch reworked. Place the buffer at a non-page-aligned address
> + * spanning into the next page to make sure multi-page pinning works too.
> + */
> +TEST_F(rds, info_counters_snapshot)
> +{
> +	struct rds_info_counter *ctr;
> +	socklen_t need = 0, len;
> +	long pagesz = sysconf(_SC_PAGESIZE);
> +	unsigned int i, n;
> +	char *region, *buf;
> +	int ret;
> +
> +	/* Probe for the required size. */
> +	getsockopt(self->fd, SOL_RDS, RDS_INFO_COUNTERS, NULL, &need);
> +	ASSERT_GT(need, 0);
> +
> +	region = mmap(NULL, 2 * pagesz, PROT_READ | PROT_WRITE,
> +		      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);

The 2-page mapping (and the ASSERT_LE guarding it) ties the test to the snapshot
fitting in two pages.  This works right now, but ideally the region here should
account for the number of counters that come back from RDS_INFO_COUNTERS so that
if the total number of counters were to grow later, we don't overrun a region
that's set to a fixed number of pages.  So in this case, we'd want the need + offset,
and then page align that so we can mmap it:

	offset	= pagesz - 64; 
	map_len	= ((offset + need + pagesz - 1) / pagesz) * pagesz;  /* round (off+need) up to whole pages */
	region  = mmap(NULL, map_len, ...);                 


> +	ASSERT_NE(MAP_FAILED, region);
> +
> +	/* Unaligned start that runs past the first page boundary. */
> +	buf = region + pagesz - 64;
Then this simplifies to:
	buf = region + offset;

> +	ASSERT_LE(need, (socklen_t)(pagesz + 64));
And then the ASSERT here can be removed

> +
> +	/*
> +	 * On success the RDS_INFO path returns the positive per-element size
> +	 * (lens.each) rather than 0, and writes the full snapshot length back
> +	 * into optlen.
> +	 */
> +	len = need;
> +	ret = getsockopt(self->fd, SOL_RDS, RDS_INFO_COUNTERS, buf, &len);
> +	ASSERT_GE(ret, 0) {
> +		TH_LOG("getsockopt snapshot failed: errno %d", errno);
> +	}
> +	EXPECT_EQ(sizeof(struct rds_info_counter), ret);
> +	EXPECT_EQ(need, len);
> +
> +	/* The counter names must be NUL-terminated, non-empty strings. */
> +	ctr = (struct rds_info_counter *)buf;
> +	n = len / sizeof(*ctr);
> +	ASSERT_GT(n, 0);
> +	for (i = 0; i < n; i++) {
> +		size_t namelen = strnlen((char *)ctr[i].name,
> +					 sizeof(ctr[i].name));
> +
> +		EXPECT_GT(namelen, 0);
> +		EXPECT_LT(namelen, sizeof(ctr[i].name));
> +	}
> +
> +	munmap(region, 2 * pagesz);

Finally this turns into:
        munmap(region, map_len);

That's the only thing that really stood out.  I think the rest of it looks really good.  Thanks for putting this
together!

Allison
> +}
> +
> +/*
> + * A non-zero but too-small buffer must report ENOSPC and the full required
> + * length, without corrupting memory past the buffer.
> + */
> +TEST_F(rds, info_counters_short_buffer)
> +{
> +	socklen_t need = 0, len;
> +	char small[sizeof(struct rds_info_counter)];
> +
> +	getsockopt(self->fd, SOL_RDS, RDS_INFO_COUNTERS, NULL, &need);
> +	ASSERT_GT(need, 0);
> +
> +	/* Ask with a buffer guaranteed smaller than the full snapshot. */
> +	if (need <= (socklen_t)sizeof(small))
> +		SKIP(return, "snapshot fits in one record; nothing to test");
> +
> +	len = 1; /* < sizeof(struct rds_info_counter) */
> +	EXPECT_EQ(-1, getsockopt(self->fd, SOL_RDS, RDS_INFO_COUNTERS, small,
> +				 &len));
> +	EXPECT_EQ(ENOSPC, errno);
> +	EXPECT_EQ(need, len);
> +}
> +
> +TEST_HARNESS_MAIN
> 

Re: [PATCH net-next 2/2] selftests: net: rds: add getsockopt() conversion test

[Breno Leitao]

On Fri, Jun 05, 2026 at 02:56:09AM -0700, Allison Henderson wrote:
> Hi Breno,
> 
> Thanks for working on this.  Your test covers a lot of socket behavior that the
> existing packet test doesn't get into, so I definitely think it's worth adding.
> I ran it locally under vng and it passes for me.  I did notice one nit below, but
> otherwise I think it looks really good.

Good, thanks for the direction and review!

> > +TEST_F(rds, info_counters_snapshot)
> > +{
> > +	struct rds_info_counter *ctr;
> > +	socklen_t need = 0, len;
> > +	long pagesz = sysconf(_SC_PAGESIZE);
> > +	unsigned int i, n;
> > +	char *region, *buf;
> > +	int ret;
> > +
> > +	/* Probe for the required size. */
> > +	getsockopt(self->fd, SOL_RDS, RDS_INFO_COUNTERS, NULL, &need);
> > +	ASSERT_GT(need, 0);
> > +
> > +	region = mmap(NULL, 2 * pagesz, PROT_READ | PROT_WRITE,
> > +		      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> 
> The 2-page mapping (and the ASSERT_LE guarding it) ties the test to the snapshot
> fitting in two pages.  This works right now, but ideally the region here should
> account for the number of counters that come back from RDS_INFO_COUNTERS so that
> if the total number of counters were to grow later, we don't overrun a region
> that's set to a fixed number of pages.  So in this case, we'd want the need + offset,
> and then page align that so we can mmap it:
> 
> 	offset	= pagesz - 64; 
> 	map_len	= ((offset + need + pagesz - 1) / pagesz) * pagesz;  /* round (off+need) up to whole pages */
> 	region  = mmap(NULL, map_len, ...);                 

Good point - sizing the mapping from the probed length keeps it correct if the
counter set ever grows. In v2 I'll derive map_len from need + offset and drop
the fixed 2-page assumption:

        long pagesz = sysconf(_SC_PAGESIZE);
        size_t offset, map_len;
        ...
        getsockopt(self->fd, SOL_RDS, RDS_INFO_COUNTERS, NULL, &need);
        ASSERT_GT(need, 0);

        /* Unaligned start that runs past the first page boundary. */
        offset  = pagesz - 64;
        map_len = ((offset + need + pagesz - 1) / pagesz) * pagesz;

        region = mmap(NULL, map_len, PROT_READ | PROT_WRITE,
                      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
        ASSERT_NE(MAP_FAILED, region);

        buf = region + offset;

with the ASSERT_LE() dropped and munmap(region, map_len) at the end.

Thanks for the review,
--breno