Date: Fri, 10 Aug 2012 11:14:11 +1000 From: Lawrence Stewart <lstewart@freebsd.org> To: "Andrey V. Elsukov" <ae@FreeBSD.org> Cc: "freebsd-fs@freebsd.org" <freebsd-fs@FreeBSD.org>, Marcel Moolenaar <marcel@FreeBSD.org> Subject: Re: gpart rewrites pmbr in a way which breaks Win 7 EFI bootloader Message-ID: <50246063.2080604@freebsd.org> In-Reply-To: <5023C723.90606@FreeBSD.org> References: <50237B73.9040301@freebsd.org> <5023979B.4010903@yandex.ru> <5023A907.7060800@freebsd.org> <5023C723.90606@FreeBSD.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On 08/10/12 00:20, Andrey V. Elsukov wrote: > On 09.08.2012 16:11, Lawrence Stewart wrote: >>>> - Should gpart be writing 0x80 (active) in the protective MBR entry? >>> >>> AFAIK, this was added because some BIOS could not boot without it. >> >> Makes sense if gpart is writing the pmbr out i.e. "gpart bootcode -b >> /boot/pmbr <geom>", but manipulating an existing pmbr for a GPT specific >> subcommand smells dodgy to me. > > When you create GPT it already has PMBR, because it is part of GPT > metadata. gpart's `bootcode' subcommand writes *bootcode* to specific > area in the PMBR. Right, I had a fundamental misunderstanding about the relationship between the pmbr and GPT. Thanks to you and Marcel for setting me straight on this. >>>> - Why is Windows EFI bootloader so sensitive to 0x80 in pmbr? >>> >>> This question you should ask to the Microsoft. :) >> >> Perhaps I should rephrase my question as: >> >> Is the MS bootloader's behaviour reasonable/unreasonable based on what >> people know of the relevant specs? My current guess why it behaves like >> this is that if it sees an MBR partition marked active, it simply >> assumes another OS is in charge and therefore bails out at the Windows >> EFI boot stage. > > In the EFI system partition might be several boot loaders, and this MS > bootloader's behaviour seems strange to me. > >> Can and should are two different things. I would argue it's a POLA >> violation at the very least to manipulate the pmbr when the user asked >> for something else. I certainly started my hunting expecting to find the >> GPT changing in some subtle way when FreeBSD wrote it out compared to >> what Windows writes. >> >> We have a specific gpart command to put a pmbr in place so I think it's >> reasonable to expect other GPT specific commands not to fiddle with the >> pmbr. > > Don't confuse bootcode in the PMBR and PMBR. Despite my misunderstanding about the relationship between the pmbr and GPT, I still stand by my assertion that gpart is not behaving very well here, but more on that in my follow up to Marcel. Cheers, Lawrence
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?50246063.2080604>