On Thu, Jan 09, 2025 at 04:30:53PM +0100, Frantisek Rysanek wrote: > > Hi, > > > > The documentation on this feature[1] doesn't quite explain how the > > system should actually do a localboot. Is this for BIOS / x86 only? > > There was a recent discussion about this on the U-Boot mailing > > list[2]. > > > > Is someone able to help with how / if this should be implemented in > > U-Boot? > > > > Regards, > > Simon > > > > I feel that you actually understand the whole point :-) > > Syslinux is a bootloader for the PC's - those have a BIOS and > nowadays a Bios Boot Sequence (BBS). And, a specific member of the > syslinux family (package) is pxelinux, which loads from the LAN. > > The "local" boot means, that while the PC is trying to boot, in a > particular step of the BIOS Boot Sequence (= the order of bootable > devices) it has loaded PXElinux, and now the user has a choice, > either to chainload some "payload" (e.g. the Linux kernel + initrd or > some such via TFTP), or to hand over to the next entry in the "BIOS > Boot Sequence" - effectively by calling an "iret" at the top-level > function called by its respective BBS entry, which is effectively a > software interrupt... which will end up trying another boot media, > the next one up in the BBS. > > Yes this is specific to machines having a BIOS. > > Not sure about UEFI, the bootloader loading mechanism is different, > but Syslinux never quite got there with UEFI, so I believe this point > is moot. > I haven't actually tried this with iPXE, there doesn't seem to be an > explicit keyword for this. Possibly if you "let the ipxe boot script > fall off the end" or by calling an exit... or possibly not. > https://www.google.com/search?q=UEFI+exit+ipxe+and+try+the+next+boot+e > ntry%3F > > Now compare that to uBoot. Who typically has just a single purpose in > life, and a single option what to boot: the one kernel and initrd, > typically from a NAND flash MTD (or sometimes NOR flash for that > matter). You can possibly break normal boot and try loading something > via TFTP...
So the reason Simon is asking is that the syslinux / pxelinux file format is used outside of just the syslinux project, but it's a little unclear what the authoritative source is (systemd used to have a page, but that moved and then got dropped). We're hoping to find what the real intent of the keyword is, so that https://docs.u-boot.org/en/latest/develop/distro.html#boot-configuration-files can say the right thing, rather than the few stackoverflow examples of how people use "localboot" within U-Boot today. -- Tom
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