19.02.2020 19:59, Stephen Warren пишет: > On 2/19/20 9:27 AM, Christoph Hellwig wrote: >> On Wed, Feb 19, 2020 at 07:23:39PM +0300, Dmitry Osipenko wrote: >>> The gpt_sector=<sector> causes the GPT partition search to look at the >>> specified sector for a valid GPT header if the GPT is not found at the >>> beginning or the end of block device. >>> >>> In particular this is needed for NVIDIA Tegra consumer-grade Android >>> devices in order to make them usable with the upstream kernel because >>> these devices use a proprietary / closed-source partition table format >>> for the EMMC and it's impossible to change the partition's format. >>> Luckily >>> there is a GPT table in addition to the proprietary table, which is >>> placed >>> in uncommon location of the EMMC storage and bootloader passes the >>> location to kernel using "gpt gpt_sector=<sector>" cmdline parameters. >>> >>> This patch is based on the original work done by Colin Cross for the >>> downstream Android kernel. >> >> I don't think a magic command line is the way to go. The best would be >> to reverse-engineer the proprietary partition table format. If that is >> too hard we can at least key off the odd GPT location based of it's >> magic number. > > I thought that the backup GPT was always present in the standard > location; it's just the primary GPT that's in an odd location. So, this > kernel parameter just forces the kernel to look first for the primary > GPT in the unusual location, thus avoiding an error message when that's > not there, and the system falls back to the backup GPT. > > Or, do I misremember the layout, or the kernel's behaviour if primary > GPT is missing? The backup GPT not always presents in the standard location. For example Tegra30 ASUS Google Nexus 7 has a backup GPT in the proper location and this is what KMSG prints: [ 1.722888] Primary GPT is invalid, using alternate GPT. [ 1.723076] mmcblk1: p1 p2 p3 p4 p5 p6 p7 p8 p9 p10 But this doesn't work for Tegra20 Acer A500 and (IIRC) Tegra30 Ouya because both primary and backup GPTs are invalid at the standard locations.
