Add Azure Linux 4.0 PXE boot support for LiveOS images#826
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Add PXE (network) boot support for Azure Linux 4.0 LiveOS images. Azure Linux 4.0 boots via BLS (Boot Loader Specification) entries under boot/loader/entries, which grub cannot enumerate over TFTP, so a PXE-booted AZL4 image reached an empty grub menu. This expands the BLS Type #1 entries into explicit grub menuentry blocks when the PXE artifacts are built, so netboot works without grub reading the entries directory over TFTP. It is wired per distro through a new DistroHandler.UpdateLiveOSGrubCfgForPxe hook plus a shared BLS renderer, so other BLS distros benefit too. Tests (in support of the above): test_pxe.py adds bootstrap and full-OS PXE boot tests for AZL3 and AZL4 over a transient libvirt NAT network (dnsmasq DHCP and TFTP) plus an HTTP server over the extracted artifacts (pxe_server.py). They are skipped on Azure Linux hosts, whose edk2-ovmf lacks the UEFI network stack (EDK II NetworkPkg) and cannot netboot a VM, and run on Ubuntu hosts.
- Run the PXE HTTP server via multiprocessing.Process instead of a python -m http.server subprocess. - Extract PXE artifacts into a world-traversable /var/tmp directory and drop the chmod of ancestor directories.
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A PXE-booted Azure Linux 4.0 image stopped at an empty grub menu, because AZL4 uses BLS (Boot Loader Specification) boot entries that grub cannot enumerate over TFTP. This change expands those BLS Type #1 entries into explicit grub
menuentryblocks when the PXE artifacts are built, so netboot works without grub readingboot/loader/entriesover TFTP. It is wired per distro through a newDistroHandler.UpdateLiveOSGrubCfgForPxehook plus a shared BLS renderer, so other BLS distros benefit too.Tests (in support of the above) —
test_pxe.pyadds bootstrap and full-OS PXE boot tests for AZL3 and AZL4 over a transient libvirt NAT network (dnsmasq DHCP and TFTP) plus an HTTP server over the extracted artifacts (pxe_server.py). They are skipped on Azure Linux hosts, whoseedk2-ovmflacks the UEFI network stack (EDK II NetworkPkg) and cannot netboot a VM, and run on Ubuntu hosts.