[PATCH net-next v9 2/8] netmem: introduce utility APIs to use struct netmem_desc
From: Byungchul Park <byungchul@sk.com>
Date: 2025-07-10 08:28:24
Also in:
bpf, linux-mm, linux-rdma, lkml
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
To eliminate the use of the page pool fields in struct page, the page
pool code should use netmem descriptor and APIs instead.
However, some code e.g. __netmem_to_page() is still used to access the
page pool fields e.g. ->pp via struct page, which should be changed so
as to access them via netmem descriptor, struct netmem_desc instead,
since the fields no longer will be available in struct page.
Introduce utility APIs to make them easy to use struct netmem_desc as
descriptor. The APIs are:
1. __netmem_to_nmdesc(), to convert netmem_ref to struct netmem_desc,
but unsafely without checking if it's net_iov or system memory.
2. netmem_to_nmdesc(), to convert netmem_ref to struct netmem_desc,
safely with checking if it's net_iov or system memory.
3. nmdesc_to_page(), to convert struct netmem_desc to struct page,
assuming struct netmem_desc overlays on struct page.
4. page_to_nmdesc(), to convert struct page to struct netmem_desc,
assuming struct netmem_desc overlays on struct page, allowing only
head page to be converted.
5. nmdesc_adress(), to get its virtual address corresponding to the
struct netmem_desc.
Signed-off-by: Byungchul Park <byungchul@sk.com>
---
include/net/netmem.h | 41 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)
diff --git a/include/net/netmem.h b/include/net/netmem.h
index 535cf17b9134..ad9444be229a 100644
--- a/include/net/netmem.h
+++ b/include/net/netmem.h@@ -198,6 +198,32 @@ static inline struct page *netmem_to_page(netmem_ref netmem) return __netmem_to_page(netmem); } +/** + * __netmem_to_nmdesc - unsafely get pointer to the &netmem_desc backing + * @netmem + * @netmem: netmem reference to convert + * + * Unsafe version of netmem_to_nmdesc(). When @netmem is always backed + * by system memory, performs faster and generates smaller object code + * (no check for the LSB, no WARN). When @netmem points to IOV, provokes + * undefined behaviour. + * + * Return: pointer to the &netmem_desc (garbage if @netmem is not backed + * by system memory). + */ +static inline struct netmem_desc *__netmem_to_nmdesc(netmem_ref netmem) +{ + return (__force struct netmem_desc *)netmem; +} + +static inline struct netmem_desc *netmem_to_nmdesc(netmem_ref netmem) +{ + if (WARN_ON_ONCE(netmem_is_net_iov(netmem))) + return NULL; + + return __netmem_to_nmdesc(netmem); +} + static inline struct net_iov *netmem_to_net_iov(netmem_ref netmem) { if (netmem_is_net_iov(netmem))
@@ -314,6 +340,21 @@ static inline netmem_ref netmem_compound_head(netmem_ref netmem) return page_to_netmem(compound_head(netmem_to_page(netmem))); } +#define nmdesc_to_page(nmdesc) (_Generic((nmdesc), \ + const struct netmem_desc * : (const struct page *)(nmdesc), \ + struct netmem_desc * : (struct page *)(nmdesc))) + +static inline struct netmem_desc *page_to_nmdesc(struct page *page) +{ + VM_BUG_ON_PAGE(PageTail(page), page); + return (struct netmem_desc *)page; +} + +static inline void *nmdesc_address(struct netmem_desc *nmdesc) +{ + return page_address(nmdesc_to_page(nmdesc)); +} + /** * __netmem_address - unsafely get pointer to the memory backing @netmem * @netmem: netmem reference to get the pointer for
--
2.17.1