Am 02.10.2014 14:50, schrieb Tanya Brokhman: >> Consider the case where you have a board with a fastmap enabled bootloader >> and a Linux OS. >> The bootloader does a fastmap attach and boots the kernel from UBI and the >> kernel it self has the rootfs >> on UBI too. If you install a new kernel with your changes applied it will >> write the fastmap in a different >> format and the bootloader will fail badly. In worst case the board bricks, >> in best case the bootloader can fall back >> to scanning mode but it will be slow and the customer unhappy. >> > > Ok, I understand the problem now. I wanted to discuss a possible solution > before implementing it: > We have a "fastmap version" in fm_sb. At the moment UBI_FM_FMT_VERSION = 1 > and any other is not supported. We can use that; Add another fm version > (UBI_FM_FMT_VERSION_RD = 2) and > then decide according to it. Meaning, if during attach process we find fm > superblock we check it's version, if it's != UBI_FM_FMT_VERSION_RD, we fall > back to full scan. The next > fastmap will be written with the new layout (and new version number) so > second boot will attach from fastmap without any issues.
Yes, if we change the fastmap on-disk layout we need to change UBI_FM_FMT_VERSION. Then other fastmap implementations will notice the change and can hopefully recover. Implementations which do not evaluate UBI_FM_FMT_VERSION deserve breaking. ;-) That said, I'll not block a layout change but we have to be sure that it is *really* needed. I'm currently heavily working on fastmap and my local queue with fastmap fixes keeps growing. If I find a horror bug which needs a fastmap layout change I want to change the layout only once, not twice. Thanks, //richard -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
