linux-kernel - Re: [RFC 2/2] mmc: use SD/MMC host ID for block device name ID

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Message-ID: <837c304930e6ea74db848c14c6fa6313@agner.ch>
Date:	Tue, 01 Apr 2014 23:46:33 +0200
From:	Stefan Agner <stefan@...er.ch>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	chris@...ntf.net, linux-mmc@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux@....linux.org.uk,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/2] mmc: use SD/MMC host ID for block device name ID

Am 2014-04-01 22:47, Stephen Warren wrote:
> That's not true. There's no guarantee that a device name/ID gets
> released as soon as the SD card is removed; something might still have
> it mounted for example.
Yes. Also when booted there are other solutions to get static block
device name (e.g. /dev/disk/by-path), but the problem at hand aims for a
solution for the root file system.

Also, eMMC don't get removed, and those internal eMMC devices are the
reason of this thread... (see cover letter)

 
> The correct solution here is to use filesystem or partition UUIDs to
> identify the device/partition, not to attempt to assign static device IDs.
Yes, I'm aware of that solution. However, when recreating the partition
table, those UUIDs do change, which in turn needs a change of the kernel
arguments. Of course, one can use scripts to work around this, but its
easier to just boot from the block device at a given location (say eMMC,
first partition). Then, using UUID is also not as fast as using a device
name directly, since all block devices get scanned. This is not optimal
when trying to optimize boot speed, but might be negligible. I actually
never measured that. 

There are the /dev/disk/by-path/ which aim at a similar goal, but those
names are generated by udev. I'm open to suggestions solve this issue in
a more fashionable way...

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