Date: Mon, 26 Mar 2012 23:10:12 GMT From: Mike Kaganski <mikekaganski@mail.ru> To: freebsd-xen@FreeBSD.org Subject: Re: kern/165418: [xen] Problems mounting root filesystem from XENHVM Message-ID: <201203262310.q2QNACAX088120@freefall.freebsd.org>
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The following reply was made to PR kern/165418; it has been noted by GNATS. From: Mike Kaganski <mikekaganski@mail.ru> To: bug-followup@FreeBSD.org, stefan.witzel@zvw.uni-goettingen.de Cc: Subject: Re: kern/165418: [xen] Problems mounting root filesystem from XENHVM Date: Tue, 27 Mar 2012 10:00:04 +1100 > The Xen bootloader has problems with UFS2. > I'm only running PV guests, but pygrub doesn't recognise >UFS2 (and had to be patched for UFS). HVMs may have a similar issue Just to clarify things: 1. To boot a VM, *XEN* needs to start its kernel. In case of HVM, its job is simple: it considers the (virtual) boot disk as an opaque bytestream with a boot record in proper place, and it's the boot record's job to find and launch the kernel. In PV VMs, XEN needs to launch the kernel as its "native" program, so it needs to find the kernel file(s). Thus, either the kernel needs to be on a filesystem recognizable by XEN, or the kernel file(s) must be copied directly to dom0. 2. To work with a filesystem, the *VM kernel* needs to recognize it, thus its drivers must be accessible to the kernel before it starts using it. Thus, they need either to be compiled into the kernel itself, or to be placed somewhere on a different filesystem (and the kernel needs to know where to look for them). Generally, there is no need to patch XEN loader to use any new filesystem in case of PV domUs. The patching way may eventually lead to problems due to possible incompatibilities in different patches. It's better to just copy the properly compiled (with the required filesystem drivers compiled in) PV kernel to dom0 and configure its XEN startup parameters. The OP indeed has the HVM FreeBSD kernel started OK, but its configuration points to continue loading from a non-accessible device. It's not a "xen bootloader" issue. -- Best regards, Mike.
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