Part of the information hopped to a different thread, so it is possibly
better to split this question of to a separate thread:
For those who want to use the kernel hotplug helper mechanism, the
netlink interested are not affected by this.
The Problem:
The kernel spawns a separate process for each event, who gathers the
information for this event. The startup of those processes go into
parallel, when events arrive in bursts. This has the race condition, of
reordering the device node operations. Avoid such reordering, mdev uses
a special file to check a sequence number.
More description in doc/mdev.txt
Idea:
Splitting the gathering parts from the parser / handler, may allow to do
this checking in a slight different way, which would avoid massive
writing / reading a file.
When the hotplug helper (or netlink reader) gathers the event
information, the sequence number of this event can be send ahead of the
message to the parser. The parser may check this sequence number as
explained, but push the message in a backlist, when sequence is wrong.
Then parser continue with message reading, checking merging incoming
messages with the backlist, until it get a message of right sequence
number or some timeout, which will hop to the nearest sequence number in
the backlist.
When doing that carefully, we will be able to avoid actively waiting for
the message getting into the right sequence.
Before the parser exits, it has to write the sequence number in the file
and read it back (once) on next startup. No more polling until matching
sequence number.
I did not dig deeper into this, but I wont lose that idea, so I put this
into it's own thread for separate discussion.
Current state is pure idea, we could do this, but we can also stay at
current mdev sequence ordering solution. I did not dig into the details
yet, but will do that when it's the time for this.
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