Bug#968202: preseed: Checks only BOOTP filename and not DHCP option 67, "bootfile-name"

[Bob Ham <rah+debianbts@settrans.net>]

Package: debian-installer
Severity: normal

The dhcp_preseed_url function in preseed.sh, part of preseed:

https://salsa.debian.org/installer-team/preseed/-/blob/399d9e8d56d64161449e9415cc8fe33ae88711f2/preseed.sh#L173

only checks for the "filename" entry in DHCP lease files.  The
"filename" entry is a holdover from the BOOTP protocol.  Some DHCP
servers don't allow setting the filename at all.  OpenWRT's odhcpd,
doesn't allow setting the filename in DHCP responses for classified
clients, such as clients with a vendor class containing "d-i", it only
allows setting DHCP options.

It would be good if dhcp_preseed_url could take advantage of the
DHCP "bootfile-name" option and not just the BOOTP filename.


-- System Information:
Debian Release: 10.4
  APT prefers stable
  APT policy: (991, 'stable'), (500, 'stable-updates'), (500, 'stable-debug'), (500, 'oldstable-updates'), (500, 'oldstable-debug'), (500, 'oldstable'), (70, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.6.0-linux-latest-32 (SMP w/16 CPU cores; PREEMPT)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: sysvinit (via /sbin/init)