linux-kernel - Re: [dm-devel] [PATCH v2 3/4] dm ioctl: Allow userspace to suppress uevent generation

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Message-ID: <364d626b-c3cf-8492-6c85-38417f2432b4@gmail.com>
Date:   Sun, 25 Jun 2023 19:13:15 +0200
From:   Milan Broz <gmazyland@...il.com>
To:     Demi Marie Obenour <demi@...isiblethingslab.com>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...nel.org>, dm-devel@...hat.com
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [dm-devel] [PATCH v2 3/4] dm ioctl: Allow userspace to suppress
 uevent generation

On 6/25/23 18:43, Demi Marie Obenour wrote:
> On Sun, Jun 25, 2023 at 06:33:33PM +0200, Milan Broz wrote:

...

>> BTW we use exactly this scenario in cryptsetup for years with existing flags
>> (DM_UDEV_DISABLE_SUBSYSTEM_RULES_FLAG | DM_UDEV_DISABLE_DISK_RULES_FLAG
>> DM_UDEV_DISABLE_OTHER_RULES_FLAG) - just rules are ignored while uevent is still
>> sent.
>> Anyway, not sure we need another way to disable it; I just asked do you need it.
> 
> How can one set these flags using the raw kernel ioctls?  The code I am
> working on does not use libdevmapper at all and just uses the kernel API
> directly.

IIRC you need to set cookie (kernel DM_COOKIE env), then default udev dm.rules decode
the flags from it.

(It is libdevmapper internal magic for me, the design is kind of complicated, but works.)

Better ask on LVM list (but the udev DM rules are pretty well inline documented).

Milan