linux-kernel - Re: [GIT PULL] kdbus for 4.1-rc1

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Date:	Wed, 29 Apr 2015 16:51:37 +0200
From:	Richard Weinberger <richard@....at>
To:	Austin S Hemmelgarn <ahferroin7@...il.com>,
	Harald Hoyer <harald@...hat.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] kdbus for 4.1-rc1

Am 29.04.2015 um 16:46 schrieb Austin S Hemmelgarn:
> On 2015-04-29 10:11, Harald Hoyer wrote:
>> On 29.04.2015 16:04, Richard Weinberger wrote:
>>> Am 29.04.2015 um 16:01 schrieb Harald Hoyer:
>>>> On 29.04.2015 15:46, Richard Weinberger wrote:
>>>>> Am 29.04.2015 um 15:38 schrieb Harald Hoyer:
>>>>>> On 29.04.2015 15:33, Richard Weinberger wrote:
>>>>>>> It depends how you define "beginning". To me an initramfs is a *very* minimal
>>>>>>> tool to prepare the rootfs and nothing more (no udev, no systemd, no
>>>>>>> "mini distro").
>>>>>>> If the initramfs fails to do its job it can print to the console like
>>>>>>> the kernel does if it fails
>>>>>>> at a very early stage.
>>>>>>>
>>>>>>
>>>>>> Your solution might work for your small personal needs, but not for our customers.
>>>>>
>>>>> Correct, I don't know your customers, all I know are my customers. :-)
>>>>>
>>>>> What feature do your customers need?
>>>>> I mean, I fully agree with you that an initramfs must not fail silently
>>>>> but how does dbus help there? If it fails to mount the rootfs there is not
>>>>> much it can do.
>>>>>
>>>>> Thanks,
>>>>> //richard
>>>>>
>>>>
>>>> We don't handcraft the initramfs script for every our customers, therefore we
>>>> have to generically support hotplug, persistent device names, persistent
>>>> interface names, network connectivity in the initramfs, user input handling for
>>>> passwords, fonts, keyboard layouts, fips, fsck, repair tools for file systems,
>>>> raid assembly, LVM assembly, multipath, crypto devices, live images, iSCSI,
>>>> FCoE, all kinds of filesystems with their quirks, IBM z-series support, resume
>>>> from hibernation, […]
>>>
>>> This is correct. But which of these tools/features depend on dbus?
>>
>> I would love to add dbus support to all of them and use it, so I can connect
>> them all more easily. No need for them to invent their own version of IPC,
>> which can only be used by their own tool set.
>>
> Resume is built into the kernel, so no need for IPC there.  Keymaps, fonts, and fsck need no IPC either.  FIPS related stuff should need no IPC.  Anything to do with the Device
> Mapper and hotplug should just need uevents.  While I can kind of see you wanting to have lvmetad in the initramfs for use with LVM, I've seen all kinds of reports of issues caused
> by that.  I can also kind of understand wanting some kind of unified IPC for the netboot related stuff, DBus is still serious overkill for any of that IMHO.  As things stand
> currently, the few things in that list that I know actually use IPC for anything get by just fine (and much faster) using just UDS.

Even if dbus is really needed you can embed it into the initramfs.
What you need is a good bootstrap procedure between dbus/systemd within the initramfs and the real rootfs.

Thanks,
//richard
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