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Tidy up pxe flow

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Audiobuzz
2026-06-20 09:19:01 +00:00
parent fb69068980
commit 33583bb4d8
2 changed files with 36 additions and 41 deletions
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serving/tftp/README.md
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@@ -11,10 +11,16 @@ Flow for a PXE-only host:
```
firmware PXE (PXEClient) --TFTP--> snponly.efi (iPXE)
iPXE re-DHCPs (user-class "iPXE") --> handed boot.ipxe (TFTP)
iPXE autoboot DHCP (user-class "iPXE") --> handed boot.ipxe (TFTP)
boot.ipxe: imgfetch UKI over HTTP -> imgargs <real cmdline> -> boot
```
> **Requires PortFast/edge on the switch port** (see the gotchas below). iPXE's
> autoboot opens the NIC, which bounces the PHY; without PortFast the switch's STP
> forwarding delay (~30 s) drops iPXE's DHCP and the boot fails. PortFast removes
> the delay. (The earlier `autoexec.ipxe` + `ifopen` + DHCP-retry workaround was
> removed once PortFast was identified as the real fix.)
`boot.ipxe` is **rendered at container start** by the dnsmasq entrypoint; only the
iPXE binary (`snponly.efi`) is supplied here. The script exists because of a sharp
edge:
@@ -107,10 +113,16 @@ Hard-won findings from bringing up the first PXE-only physical host:
~30 s to every boot — PortFast removes the delay entirely.
- **iPXE aborts the script on any unguarded command failure** (→ iPXE exits → the
firmware restarts the whole PXE process, looking like "it doesn't retry"). Every
fallible step in `boot.ipxe`/`autoexec.ipxe` is therefore `||`-guarded.
- **`autoexec.ipxe`** (rendered by the dnsmasq entrypoint) is fetched + run at
iPXE startup, *replacing* the default autoboot; that's where the `ifopen` +
DHCP-retry + `imgargs <real cmdline>` chain lives.
fallible step in `boot.ipxe` is therefore `||`-guarded.
- **`boot.ipxe`** (rendered by the dnsmasq entrypoint, served as the `tag:ipxe`
DHCP bootfile) does `dhcp` + `imgfetch` UKI + `imgargs <real cmdline>` + `boot`.
The cmdline injection is needed only because **Secure Boot is OFF** (the stub
takes the loader's cmdline); under Secure Boot it's a no-op and `boot.ipxe`
could collapse to a plain `chain` of the UKI.
- **Removed STP-era workaround:** an `autoexec.ipxe` that ran `ifopen net0` + a
DHCP-retry loop before autoboot was used to wait out STP. It's gone now that
**PortFast is the fix** — if you ever run on a switch you can't set PortFast on,
that ifopen+retry approach (in git history) is the fallback.
## Note