linux-kernel - [PATCH net-next] net: netmem: remove NET_IOV_MAX from net_iov

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Message-Id: <20251024-b4-devmem-remove-niov-max-v1-1-ba72c68bc869@meta.com>
Date: Fri, 24 Oct 2025 11:02:56 -0700
From: Bobby Eshleman <bobbyeshleman@...il.com>
To: "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Mina Almasry <almasrymina@...gle.com>, Byungchul Park <byungchul@...com>, 
 Stanislav Fomichev <sdf@...ichev.me>, 
 Bobby Eshleman <bobbyeshleman@...a.com>
Subject: [PATCH net-next] net: netmem: remove NET_IOV_MAX from net_iov_type
 enum

From: Bobby Eshleman <bobbyeshleman@...a.com>

Remove the NET_IOV_MAX workaround from the net_iov_type enum. This entry
was previously added to force the enum size to unsigned long to satisfy
the NET_IOV_ASSERT_OFFSET static assertions.

After commit f3d85c9ee510 ("netmem: introduce struct netmem_desc
mirroring struct page") this approach became unnecessary by placing the
net_iov_type after the netmem_desc. Placing the net_iov_type after
netmem_desc results in the net_iov_type size having no effect on the
position or layout of the fields that mirror the struct page.

The layout before this patch:

struct net_iov {
	union {
		struct netmem_desc desc;                 /*     0    48 */
		struct {
			long unsigned int _flags;        /*     0     8 */
			long unsigned int pp_magic;      /*     8     8 */
			struct page_pool * pp;           /*    16     8 */
			long unsigned int _pp_mapping_pad; /*    24     8 */
			long unsigned int dma_addr;      /*    32     8 */
			atomic_long_t pp_ref_count;      /*    40     8 */
		};                                       /*     0    48 */
	};                                               /*     0    48 */
	struct net_iov_area *      owner;                /*    48     8 */
	enum net_iov_type          type;                 /*    56     8 */

	/* size: 64, cachelines: 1, members: 3 */
};

The layout after this patch:

struct net_iov {
	union {
		struct netmem_desc desc;                 /*     0    48 */
		struct {
			long unsigned int _flags;        /*     0     8 */
			long unsigned int pp_magic;      /*     8     8 */
			struct page_pool * pp;           /*    16     8 */
			long unsigned int _pp_mapping_pad; /*    24     8 */
			long unsigned int dma_addr;      /*    32     8 */
			atomic_long_t pp_ref_count;      /*    40     8 */
		};                                       /*     0    48 */
	};                                               /*     0    48 */
	struct net_iov_area *      owner;                /*    48     8 */
	enum net_iov_type          type;                 /*    56     4 */

	/* size: 64, cachelines: 1, members: 3 */
	/* padding: 4 */
};

Signed-off-by: Bobby Eshleman <bobbyeshleman@...a.com>
---
 include/net/netmem.h | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/include/net/netmem.h b/include/net/netmem.h
index 651e2c62d1dd..9e10f4ac50c3 100644
--- a/include/net/netmem.h
+++ b/include/net/netmem.h
@@ -68,10 +68,6 @@ DECLARE_STATIC_KEY_FALSE(page_pool_mem_providers);
 enum net_iov_type {
 	NET_IOV_DMABUF,
 	NET_IOV_IOURING,
-
-	/* Force size to unsigned long to make the NET_IOV_ASSERTS below pass.
-	 */
-	NET_IOV_MAX = ULONG_MAX
 };

 /* A memory descriptor representing abstract networking I/O vectors,

---
base-commit: f0a24b2547cfdd5ec85a131e386a2ce4ff9179cb
change-id: 20251024-b4-devmem-remove-niov-max-0d377187c9cb

Best regards,
-- 
Bobby Eshleman <bobbyeshleman@...a.com>