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: > > Am 20.09.2013 19:03, schrieb Stephen Warren: > > >On 09/20/2013 10:37 AM, Dirk Behme wrote: > > >>Am 20.09.2013 18:05, schrieb Stephen Warren: > > >>>On 09/18/2013 11:22 PM, Dirk Behme wrote: > > >>>... > > >>>>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. > > > > >>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 -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
