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docs: netlink: Correct buffer sizing info

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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

Signed-off-by: Konstantin Shabanov <mail@etehtsea.me>
Link: https://patch.msgid.link/20260512103101.1076173-1-mail@etehtsea.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Konstantin Shabanov
2026-05-15 15:52:18 -07:00
committed by Jakub Kicinski
parent 822d4a8e39
commit 55834f0d74
1 changed files with 2 additions and 2 deletions
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Documentation/userspace-api/netlink/intro.rst
+2 -2
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@@ -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).