Re: Adding aliases to mmc

Hi,

On Sat, Sep 21, 2013 at 09:42:38AM +0200, Sascha Hauer wrote:

On Sat, Sep 21, 2013 at 07:23:27AM +0200, Dirk Behme wrote:

quoted

Am 20.09.2013 19:03, schrieb Stephen Warren:

quoted

On 09/20/2013 10:37 AM, Dirk Behme wrote:

quoted

Am 20.09.2013 18:05, schrieb Stephen Warren:

quoted

On 09/18/2013 11:22 PM, Dirk Behme wrote:
...

quoted

If you have an embedded system were you just care a little about boot
time you don't want to do anything like U-Boot's "part uuid" every time
you boot. Or even worse, you just have a minimalistic boot loader (e.g.
U-Boot's SPL) which doesn't know anything about UUIDs and file systems.

As mentioned above, no I don't think UUIDs work for production embedded
systems.

As I said above, whatever generates the filesystem image can easily
embed the appropriate UUID in the system's boot scripts or bootloader
environment. There's no need to run the "part" command at run-time if
there's a more appropriate flow for your situation.

Using a simple boot loader as an example, there are no boot scripts or
boot loader environment. The only thing the boot loader does is loading
the device tree and the kernel into RAM. Where do you want to embed an
UUID in such a product?

I think the initrd would be typical.

An embedded system typically doesn't have an initrd. The kernel
boots directly into the rootfs on SD/eMMC.

quoted

quoted

To my understanding, the UUID is different for each SD card/eMMC, correct?

Yes by default.

Although for an embedded product with a fixed eMMC, there's no reason
you couldn't make every device have the same UUID for the fixed device.

How do you make the eMMC on 1000 boards have the same UUID?

The same way you ensure an identical partition table in these 1000
boards. The disk signature is just a four byte value at offset 440 in
the MBR. Set this to your birthday or whatever on all boards, pass
root=PARTUUID=<yourbirthday>-01 on all boards and you're done.

Until someone inserts a SD-Card with the same disk signature...

Always booting from eMMC is a quite important use case for embedded
systems. And so far the only reliable solution seems to be an initrd. And
using an initrd is not acceptable in many cases. Certainly not just to
figure out where the rootfs is.

Regards,
Michael

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