Re: Installing to NBD
Wouter Verhelst wrote: So, AIUI, there isn't really a way for me to do this, since all bootloader installers have hardcoded logic to decide they want to run; so if I want to make this work correctly (so that none of the bootloaders will attempt to write to disk by default), I'll have to patch each and every one of them myself. Hrmpf. There is a nobootloader package that can be made to run in preference to other bootloader installers. This can be enabled by setting grub-installer/skip, lilo-installer/skip, etc. seems to be pretty much in the same boat, in that each of the bootloader installers implements their own logic to come up with a reasonable kernel command line. They all call user-params, which uses debian-installer/add-kernel-opts. -- see shy jo signature.asc Description: Digital signature
Re: Installing to NBD
Hi, Some updates: On Tue, Jun 28, 2011 at 09:29:38PM +0200, Wouter Verhelst wrote: Hi, A while back, I blogged about success in installing to an NBD device[1]. Unfortunately, that was only partial success; that is, while it works perfectly well as far as partman is concerned (and therefore also the base-installer step), beyond that things go a bit wrong: - /usr/lib/finish-install.d has 50release-dhcp-lease and 95umount. Obviously, if /target is mounted over the network somehow (through NBD, but we might have support for installing to, say, NFS or iSCSI in the future too, which would run into the same problem), umount (and anything that wants to access anything under /target, really) is going to fail if there's no network anymore. This obviously means that whatever is between priority 50 and 95 that wants to access /target is going to fail too. I would like to fix this by moving release-dhcp-lease to priority 97, so it sits between umount and reboot. Any objections to that? If I hear none within the next few days, expect a commit to that effect near the end of the week (or sooner if I get a go-ahead :). I now have a locally patched netcfg that does the above, and it seems to work. Any objections if I commit? - Once the installatoin is complete, the installer will attempt to install grub to the local hard disk. If we've installed Debian to a network target, this is Wrong(TM); we've not touched the local hard disk for the rest of the installation, so I believe the boot loader shouldn't do so either. Indeed, if you're installing to an NBD device, you might not even *have* a local hard disk. So when the user installs to a network device, I believe the installer should default to nobootloader, rather than grub, lilo, or whatever boot loader is used on the architecture we're using; but if the user still wants to install a boot loader anyway, that should probably also be possible. Can this be done? If so, how do I do that? Also, note that this shouldn't be hardcoded; if we're installing to root-on-NBD we don't want to touch the local hard disk, but if we're doing, say, root on local hard disk but /usr on NBD, then we /do/ want to install the bootloader to the local hard disk. This is still an issue, and I'm not sure how to proceed. I've been thinking that suggesting to mount /boot on a separate filesystem (say, NFS or so) could be an option, and that I could then write a pxelinux.0 and a pxelinux.cfg there. That would only work for x86*, though. Or I could just unconditionally produce an error if /target is mounted on an NBD device, so that the user can then choose to either use the architecture's native boot loader (if that's what they want), or use nobootloader and figure out how to netboot the thing all by themselves. Input is welcome. - The nbd-client package has an extensive debconf configuration interface. Would it be considered good form to programmatically preseed the answers to that debconf interface from partman-nbd, or should I find another way? I've done this, and it seems to work; I don't think it's a serious problem. - Finally, in order for root-on-NBD to work properly, the kernel needs to specify an extra boot parameter that tells the nbd initramfs script where the server is. I couldn't find any interface to specify random extra kernel parameters for the installed system; did I miss something? I haven't found how to do this, yet. Anyone? At any rate, if I ignore the hang due to the network going down prematuraly, manually make sure the initrd is copied to my tftp server, and make sure to enter the correct values in the nbd-client debconf interface, the system will correctly boot off NBD to a login prompt, so I guess I'm almost there :-) For those who want to try, I've put an installer image for 2.6.39-2-amd64 up on http://people.debian.org/~wouter/d-i/initrd.gz[2]. Note that this is still slightly broken in that it doesn't run 'apt-install nbd-client' yet, but I'm working on that. That is fixed now, too. I've updated my initrd.gz, and beyond the above issues, it seems to work. I've moved the source to a git repository, and added it to the .mrconfig file, so if you run 'mr update' you should get it. Testing would be very welcome. (one caveat: poweroff on the installed system won't work properly, due to an issue with the initscripts package. I have a bug filed, so please ignore). -- The volume of a pizza of thickness a and radius z can be described by the following formula: pi zz a -- To UNSUBSCRIBE, email to debian-boot-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/20110629154912.gf20...@grep.be
Re: Installing to NBD
Hi, (I seem to be mostly talking to myself here -- anyone awake? ;-) On Wed, Jun 29, 2011 at 05:49:12PM +0200, Wouter Verhelst wrote: On Tue, Jun 28, 2011 at 09:29:38PM +0200, Wouter Verhelst wrote: - Once the installatoin is complete, the installer will attempt to install grub to the local hard disk. If we've installed Debian to a network target, this is Wrong(TM); we've not touched the local hard disk for the rest of the installation, so I believe the boot loader shouldn't do so either. Indeed, if you're installing to an NBD device, you might not even *have* a local hard disk. So when the user installs to a network device, I believe the installer should default to nobootloader, rather than grub, lilo, or whatever boot loader is used on the architecture we're using; but if the user still wants to install a boot loader anyway, that should probably also be possible. Can this be done? If so, how do I do that? Also, note that this shouldn't be hardcoded; if we're installing to root-on-NBD we don't want to touch the local hard disk, but if we're doing, say, root on local hard disk but /usr on NBD, then we /do/ want to install the bootloader to the local hard disk. This is still an issue, and I'm not sure how to proceed. I've been thinking that suggesting to mount /boot on a separate filesystem (say, NFS or so) could be an option, and that I could then write a pxelinux.0 and a pxelinux.cfg there. That would only work for x86*, though. Or I could just unconditionally produce an error if /target is mounted on an NBD device, so that the user can then choose to either use the architecture's native boot loader (if that's what they want), or use nobootloader and figure out how to netboot the thing all by themselves. Input is welcome. So, AIUI, there isn't really a way for me to do this, since all bootloader installers have hardcoded logic to decide they want to run; so if I want to make this work correctly (so that none of the bootloaders will attempt to write to disk by default), I'll have to patch each and every one of them myself. Hrmpf. Also, that other issue: [...] - Finally, in order for root-on-NBD to work properly, the kernel needs to specify an extra boot parameter that tells the nbd initramfs script where the server is. I couldn't find any interface to specify random extra kernel parameters for the installed system; did I miss something? I haven't found how to do this, yet. Anyone? seems to be pretty much in the same boat, in that each of the bootloader installers implements their own logic to come up with a reasonable kernel command line. So if I want to implement this properly, I'll have to patch each and every boot loader. I was hoping that that *wouldn't* be necessary. I believe, however, that this would be a good opportunity to modularize bootloader installers a bit. After all, they mostly all do the same thing: figure out which kernel to load, load it off the disk somehow, come up with a reasonable command line to pass to the kernel, and boot it. Whether the boot loader is lilo, uboot, grub, emile, aboot, or whathaveyou is just a detail, really. On top of that, having each and every boot loader come up with its own way of figuring out what the kernel command line should be sounds very much like a bad case of code duplication to me, so it might be a good idea regardless. So here's a suggestion for a way in which this could theoretically be implemented. It's not very well thought out yet, but I'm hoping it should get us in the right direction: Bootloaders generally exist in two flavours: those who hardcode the location of the kernel (either by copying it to a dedicated partition in the manner of yaboot, or by hardcoding the blocks on which the kernel is stored in the manner of lilo), and those who try to understand the filesystem on which the kernel is stored, and read it by reading the filesystem metadata. So there should be a way for a bootloader installer to specify things like 'I can boot off any filesystem, but the kernel must reside on one disk' (lilo), 'I can boot off any filesystem in this list' (grub), 'I don't care where the kernel is, I copy it to somewhere else' (yaboot/flash-kernel), etc. Similarly, there should be a standardized way for the installer to tell the bootloader this is the command line the kernel should receive when booting, this should be the default kernel, etc. It's probably a good idea to do this in a way that it can be preseeded, too. So I'm thinking the following: - Add a directory (say, /lib/bootloaders) that signal somehow (through flag files) what capabilities the different bootloaders available for the current (sub)architecture have available. This way, partman can provide warnings to the user if a particular configuration is not supported on the current subarchitecture, and main-menu can skip configuring a bootloader if it doesn't support the current
Re: Installing to NBD
On Wed, Jun 29, 2011 at 11:22:51PM +0200, Wouter Verhelst wrote: seems to be pretty much in the same boat, in that each of the bootloader installers implements their own logic to come up with a reasonable kernel command line. So if I want to implement this properly, I'll have to patch each and every boot loader. I was hoping that that *wouldn't* be necessary. I believe, however, that this would be a good opportunity to modularize bootloader installers a bit. After all, they mostly all do the same thing: figure out which kernel to load, load it off the disk somehow, come up with a reasonable command line to pass to the kernel, and boot it. Whether the boot loader is lilo, uboot, grub, emile, aboot, or whathaveyou is just a detail, really. On top of that, having each and every boot loader come up with its own way of figuring out what the kernel command line should be sounds very much like a bad case of code duplication to me, so it might be a good idea regardless. Grub2 is modular, and I think it is already to a large extent doing what you suggest. It supports many different system architectures (included being the complete firmware on some of them) and has modular plugins for filesystems and various OS kernel types. uboot supports a lot of architectures, but isn't modular in the same way as grub2. So here's a suggestion for a way in which this could theoretically be implemented. It's not very well thought out yet, but I'm hoping it should get us in the right direction: Bootloaders generally exist in two flavours: those who hardcode the location of the kernel (either by copying it to a dedicated partition in the manner of yaboot, or by hardcoding the blocks on which the kernel is stored in the manner of lilo), and those who try to understand the filesystem on which the kernel is stored, and read it by reading the filesystem metadata. That's the two common flavours on x86 PCs. I am not sure that is accurate for other systems. yaboot supports filesystem reads by the way. Some uboot installs have a hardcoded memory location in flash to load from, while other uboot installs read filesystems like grub. So there should be a way for a bootloader installer to specify things like 'I can boot off any filesystem, but the kernel must reside on one disk' (lilo), 'I can boot off any filesystem in this list' (grub), 'I don't care where the kernel is, I copy it to somewhere else' (yaboot/flash-kernel), etc. Similarly, there should be a standardized way for the installer to tell the bootloader this is the command line the kernel should receive when booting, this should be the default kernel, etc. It's probably a good idea to do this in a way that it can be preseeded, too. So I'm thinking the following: - Add a directory (say, /lib/bootloaders) that signal somehow (through flag files) what capabilities the different bootloaders available for the current (sub)architecture have available. This way, partman can provide warnings to the user if a particular configuration is not supported on the current subarchitecture, and main-menu can skip configuring a bootloader if it doesn't support the current configuration. Different boot loaders have vastly different feature sets. Some can only support one kernel at a time (essentially no config) while others provide the user with a menu and are sometimes even dynamic at supporting additional kernels and OSs. I don't know how you would make a universal interface to that. - Add a hidden debconf template (say, debian-installer/bootloader/arguments) that stores the arguments which should be specified to the kernel. Bootloades should use that template rather than their own logic. As an added bonus, this could allow a user to preseed the kernel command line, should the need arise. - Presumably the template may need to be split up to accomodate for bootloaders who care about the difference between arguments that specify the initrd, arguments that specify the root device (etc), and 'other arguments'. - Add new udeb (say, bootloader-support) that contains the generalized code to do all of the above, and reduce the bootloader installer packages' code to little more than read data and write boot record. Thoughts? Interesting question, but I don't know if it is even theoretically possible to do it, never mind practical. -- Len Sorensen -- To UNSUBSCRIBE, email to debian-boot-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/20110629213603.gg7...@caffeine.csclub.uwaterloo.ca
Re: Installing to NBD
On Wed, Jun 29, 2011 at 05:36:03PM -0400, Lennart Sorensen wrote: On Wed, Jun 29, 2011 at 11:22:51PM +0200, Wouter Verhelst wrote: seems to be pretty much in the same boat, in that each of the bootloader installers implements their own logic to come up with a reasonable kernel command line. So if I want to implement this properly, I'll have to patch each and every boot loader. I was hoping that that *wouldn't* be necessary. I believe, however, that this would be a good opportunity to modularize bootloader installers a bit. After all, they mostly all do the same thing: figure out which kernel to load, load it off the disk somehow, come up with a reasonable command line to pass to the kernel, and boot it. Whether the boot loader is lilo, uboot, grub, emile, aboot, or whathaveyou is just a detail, really. On top of that, having each and every boot loader come up with its own way of figuring out what the kernel command line should be sounds very much like a bad case of code duplication to me, so it might be a good idea regardless. Grub2 is modular, and I think it is already to a large extent doing what you suggest. It supports many different system architectures (included being the complete firmware on some of them) and has modular plugins for filesystems and various OS kernel types. That's grub2, not grub-installer. I'm talking about d-i exclusively here. grub-installer will install grub or grub2 if we're on PC, depending on what makes most sense. uboot supports a lot of architectures, but isn't modular in the same way as grub2. So here's a suggestion for a way in which this could theoretically be implemented. It's not very well thought out yet, but I'm hoping it should get us in the right direction: Bootloaders generally exist in two flavours: those who hardcode the location of the kernel (either by copying it to a dedicated partition in the manner of yaboot, or by hardcoding the blocks on which the kernel is stored in the manner of lilo), and those who try to understand the filesystem on which the kernel is stored, and read it by reading the filesystem metadata. That's the two common flavours on x86 PCs. I am not sure that is accurate for other systems. yaboot supports filesystem reads by the way. Yes, but only if you use a particular kind of filesystem for /boot. If you don't, then yaboot will need a yaboot-specific filesystem that it copies the kernel to. Some uboot installs have a hardcoded memory location in flash to load from, while other uboot installs read filesystems like grub. So there should be a way for a bootloader installer to specify things like 'I can boot off any filesystem, but the kernel must reside on one disk' (lilo), 'I can boot off any filesystem in this list' (grub), 'I don't care where the kernel is, I copy it to somewhere else' (yaboot/flash-kernel), etc. Similarly, there should be a standardized way for the installer to tell the bootloader this is the command line the kernel should receive when booting, this should be the default kernel, etc. It's probably a good idea to do this in a way that it can be preseeded, too. So I'm thinking the following: - Add a directory (say, /lib/bootloaders) that signal somehow (through flag files) what capabilities the different bootloaders available for the current (sub)architecture have available. This way, partman can provide warnings to the user if a particular configuration is not supported on the current subarchitecture, and main-menu can skip configuring a bootloader if it doesn't support the current configuration. Different boot loaders have vastly different feature sets. Some can only support one kernel at a time (essentially no config) while others provide the user with a menu and are sometimes even dynamic at supporting additional kernels and OSs. I don't know how you would make a universal interface to that. It's not necessary to support the full feature set of all boot loaders with this interface; just the bits that could be relevant to d-i. - Add a hidden debconf template (say, debian-installer/bootloader/arguments) that stores the arguments which should be specified to the kernel. Bootloades should use that template rather than their own logic. As an added bonus, this could allow a user to preseed the kernel command line, should the need arise. - Presumably the template may need to be split up to accomodate for bootloaders who care about the difference between arguments that specify the initrd, arguments that specify the root device (etc), and 'other arguments'. - Add new udeb (say, bootloader-support) that contains the generalized code to do all of the above, and reduce the bootloader installer packages' code to little more than read data and write boot record. Thoughts? Interesting question, but I don't know if it is even theoretically
