linux-kernel - [PATCH net v2 2/2] net: clarify SO_DEVMEM

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Message-ID: <20241107210331.3044434-2-almasrymina@google.com>
Date: Thu,  7 Nov 2024 21:03:31 +0000
From: Mina Almasry <almasrymina@...gle.com>
To: netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>, 
	Eric Dumazet <edumazet@...gle.com>, Willem de Bruijn <willemb@...gle.com>, 
	"David S. Miller" <davem@...emloft.net>, Mina Almasry <almasrymina@...gle.com>, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Cc: Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Jonathan Corbet <corbet@....net>, Yi Lai <yi1.lai@...ux.intel.com>, 
	Stanislav Fomichev <sdf@...ichev.me>
Subject: [PATCH net v2 2/2] net: clarify SO_DEVMEM_DONTNEED behavior in documentation

Document new behavior when the number of frags passed is too big.

Signed-off-by: Mina Almasry <almasrymina@...gle.com>
---
 Documentation/networking/devmem.rst | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Documentation/networking/devmem.rst b/Documentation/networking/devmem.rst
index a55bf21f671c..d95363645331 100644
--- a/Documentation/networking/devmem.rst
+++ b/Documentation/networking/devmem.rst
@@ -225,6 +225,15 @@ The user must ensure the tokens are returned to the kernel in a timely manner.
 Failure to do so will exhaust the limited dmabuf that is bound to the RX queue
 and will lead to packet drops.
 
+The user must pass no more than 128 tokens, with no more than 1024 total frags
+among the token->token_count across all the tokens. If the user provides more
+than 1024 frags, the kernel will free up to 1024 frags and return early.
+
+The kernel returns the number of actual frags freed. The number of frags freed
+can be less than the tokens provided by the user in case of:
+
+(a) an internal kernel leak bug.
+(b) the user passed more than 1024 frags.
 
 Implementation & Caveats
 ========================
-- 
2.47.0.277.g8800431eea-goog