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From: Konstantin Shabanov <mail@etehtsea.me>
To: linux-doc@vger.kernel.org
Cc: Konstantin Shabanov <mail@etehtsea.me>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Simon Horman <horms@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
	Shuah Khan <skhan@linuxfoundation.org>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] docs: netlink: Correct buffer sizing info
Date: Tue, 12 May 2026 17:30:53 +0700	[thread overview]
Message-ID: <20260512103101.1076173-1-mail@etehtsea.me> (raw)

Update the docs to match the code (include/linux/netlink.h):

  /*
   *	skb should fit one page. This choice is good for headerless malloc.
   *	But we should limit to 8K so that userspace does not have to
   *	use enormous buffer sizes on recvmsg() calls just to avoid
   *	MSG_TRUNC when PAGE_SIZE is very large.
  */
  #if PAGE_SIZE < 8192UL
  #define NLMSG_GOODSIZE	SKB_WITH_OVERHEAD(PAGE_SIZE)
  #else
  #define NLMSG_GOODSIZE	SKB_WITH_OVERHEAD(8192UL)
  #endif

Link: https://lore.kernel.org/all/20220819200221.422801-2-kuba@kernel.org/
Signed-off-by: Konstantin Shabanov <mail@etehtsea.me>
---
 Documentation/userspace-api/netlink/intro.rst | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Documentation/userspace-api/netlink/intro.rst b/Documentation/userspace-api/netlink/intro.rst
index aacffade8f84..ca60abe94e3d 100644
--- a/Documentation/userspace-api/netlink/intro.rst
+++ b/Documentation/userspace-api/netlink/intro.rst
@@ -526,8 +526,8 @@ of the recvmsg() system call, *not* a Netlink header).
 
 Upon truncation the remaining part of the message is discarded.
 
-Netlink expects that the user buffer will be at least 8kB or a page
-size of the CPU architecture, whichever is bigger. Particular Netlink
+Netlink expects that the user buffer will be at most 8kB or a page
+size of the CPU architecture, whichever is smaller. Particular Netlink
 families may, however, require a larger buffer. 32kB buffer is recommended
 for most efficient handling of dumps (larger buffer fits more dumped
 objects and therefore fewer recvmsg() calls are needed).

base-commit: 917719c412c48687d4a176965d1fa35320ec457c
-- 
2.53.0


             reply	other threads:[~2026-05-12 10:31 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-05-12 10:30 Konstantin Shabanov [this message]
2026-05-13  0:27 ` [PATCH] docs: netlink: Correct buffer sizing info Jakub Kicinski

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