[gPXE] [RFC] gPXE fw_cfg file interface support
Stefan Hajnoczi
stefanha at gmail.com
Wed Jan 27 04:42:07 EST 2010
This patch makes it possible for gPXE under QEMU/KVM to fetch files from the
host using the fw_cfg file interface. This means gPXE in the guest can fetch an
exposed file from the host without using networking.
I believe this feature will be useful to management software so that
network boot
configuration can be managed alongside with the virtual machine configuration,
not on a remote TFTP server.
Any interest in this feature? I imagine libvirt could use this to set
up iSCSI or
other network boot settings.
Images are fetched from the hypervisor using the fw_cfg interface provided by
QEMU/KVM. The URI syntax is as follows:
gPXE> imgfetch fw_cfg:genroms/static.gpxe
where 'fw_cfg' is the new URI scheme this patch adds and 'genroms/static.gpxe'
is the filename exported from QEMU/KVM via the fw_cfg interface.
Note that the URI uses a single colon ':', not '://', since there is no
hostname.
Current QEMU/KVM builds can be (ab)used to expose arbitrary files
like this:
qemu -option-rom path/to/file [...]
The file will appear as 'genroms/file'. Use the 'fw_cfg:genroms/file' URI to
reference it in gPXE.
The fw_cfg file interface is a recent addition to QEMU/KVM. You may need to
build QEMU/KVM from source in order to get this feature.
Note that this patch only adds the fw_cfg file interface mechanism, it does not
automatically probe for a special file when gPXE starts. You will
need to manually
"chain fw_cfg:genroms/file".
Any comments?
Stefan
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