From ea26c3662b37b92f6acd2330a81dfd2b72082e8a Mon Sep 17 00:00:00 2001
From: Laurent Bercot <ska-skaware@skarnet.org>
Date: Tue, 8 Apr 2025 06:39:59 +0000
Subject:  Add intake option

Signed-off-by: Laurent Bercot <ska@appnovation.com>
---
 doc/mdevd.html | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

(limited to 'doc/mdevd.html')

diff --git a/doc/mdevd.html b/doc/mdevd.html
index 983dbb5..ca39b02 100644
--- a/doc/mdevd.html
+++ b/doc/mdevd.html
@@ -49,7 +49,7 @@ to running mdevd over mdev. </li>
 <h2> Interface </h2>
 
 <pre>
-     mdevd [ -v <em>verbosity</em> ] [ -D <em>notif</em> ] [ -o <em>outputfd</em> ] [ -O <em>nlgroups</em> ] [ -b <em>kbufsz</em> ] [ -f <em>conffile</em> ] [ -n ] [ -s <em>slashsys</em> ] [ -d <em>slashdev</em> ] [ -F <em>fwbase</em> ] [ -C ]
+     mdevd [ -v <em>verbosity</em> ] [ -D <em>notif</em> ] [ -I <em>intake</em> ] [ -o <em>outputfd</em> ] [ -I <em>intake</em> ] [ -O <em>nlgroups</em> ] [ -b <em>kbufsz</em> ] [ -f <em>conffile</em> ] [ -n ] [ -s <em>slashsys</em> ] [ -d <em>slashdev</em> ] [ -F <em>fwbase</em> ] [ -C ]
 </pre>
 
 <ul>
@@ -104,11 +104,19 @@ character. The uevent is terminated by an additional null character.
 If for any reason, at any point, mdevd fails to write to <em>outputfd</em>,
 it stops writing, until it is restarted. (This is to preserve mdevd's memory
 stability guarantee.) By default, the uevents are not written anywhere. </li>
+ <li> <tt>-I</tt>&nbsp;<em>intake</em>&nbsp;: read the uevents from the netlink
+groups identified by the mask <em>intake</em>. The default is <strong>1</strong>,
+meaning the netlink group where the kernel sends its events, and it should not
+be changed unless you have a very particular and rare setting (namely, a chain
+of device managers reading events and rebroadcasting them to other netlink
+groups). </li>
  <li> <tt>-O</tt>&nbsp;<em>nlgroups</em>&nbsp;: after mdevd has handled the
 uevents, rebroadcast them to the netlink groups identified by the mask
-<em>nlgroups</em>. Bit 0 of <em>nlgroups</em> is always ignored (because
-netlink group 1 is the one used by the kernel to send the original uevents and
-that mdevd listens to, and we don't want to loopback on it). </li>
+<em>nlgroups</em>. If the bit 0 or the bits specified in <em>intake</em>
+(see above) are set in <em>nlgroups</em>, a warning is printed and these
+bits are ignored, in order to avoid causing a loop. (Yes, you can still
+cause a loop by chaining two separate instances of mdevd. mdevd will protect
+you against accidents, not against intentional stupidity.) </li>
  <li> <tt>-b</tt>&nbsp;<em>kbufsz</em>&nbsp;: try and reserve a kernel buffer of
 <em>kbufsz</em> bytes for the netlink queue. Too large a buffer wastes kernel memory;
 too small a buffer risks losing events. The default is <strong>512288</strong>,
-- 
cgit v1.3.1