read_user() assumes that zero-length buffers don't exist, and optimises
around this.

Allow for settings to be described by something other than a DHCP option
tag if desirable.  Currently used only for the MAC address setting.

Separate out fake DHCP packet creation code from dhcp.c to fakedhcp.c.

Remove notion of settings from dhcppkt.c.

Rationalise dhcp.c to use settings API only for final registration of the
DHCP options, rather than using {store,fetch}_setting throughout.

DHCP code was using an incorrect check for whether to construct a
DHCPDISCOVER or DHCPREQUEST packet.

It's probably easier to have a named setting for next-server, rather
than to explain to people why they need to pretend it is option 175.3.

Using -MM strips out any system header files from the dependency list,
which means that we could safely use an external stdarg.h if we wanted
to.

The home-grown versions don't work properly for static variadic
functions, when gcc can choose to use a non-standard calling convention.

Add dedicated functions create_dhcpdiscover(), create_dhcpack() and
create_proxydhcpack() for use by external code such as the PXE preboot
code.

Register ProxyDHCP options under the global scope "proxydhcp".

Unregister previously-acquired DHCP and ProxyDHCP settings when DHCP
succeeds.

IPv4 may not always be dragged into the link, so add a specific
configuration option for it.

Convert DHCP option applicators in dns.c and iscsi.c to settings
applicators.

Kill off DHCP option applicators.

Add a configuration settings block for each net device.  This will
provide the parent scope for settings applicable only to that network
device (e.g. non-volatile options stored on the NIC, options obtained via
DHCP, etc.).

Expose the MAC address as a setting.

Add the notion of the settings hierarchy, complete with
register/unregister routines.

Rename set->store and get->fetch to avoid naming conflicts with get/put
as used in reference counting.

Add the concept of an abstract configuration setting, comprising a (DHCP)
tag value and an associated byte sequence.

Add the concept of a settings namespace.

Add functions for extracting string, IPv4 address, and signed and
unsigned integer values from configuration settings (analogous to
dhcp_snprintf(), dhcp_ipv4_option(), etc.).

Update functions for parsing and formatting named/typed options to work
with new settings API.

Update NVO commands and config UI to use new settings API.

Russ Nelson sent an email requesting the license change to
GPL Version 2.

Allow setting names such as "ip:hex".

Timers are sometimes required before the call to initialise(), so we
cannot rely on initialise() to set up the timers before use.

Also fix a potential integer overflow issue in generic_currticks_udelay()

Add missing comments to timer code.

Lock system if no suitable timer source is found.

Fix initialisation order so that timers are initialised before code that
needs to use them.

Allow encapsulated options to be specified as e.g. "175.3".  As a
side-effect, change the separator character for the type field from "." to
":"; for example, the IP address pseudo-option is now "175.3:ipv4".

Add parse and display routines for 16-bit and 32-bit integer configuration
settings.

Add parse and display routines for hex-string configuration settings.

Assume hex-string as a configuration setting type if no type is explicitly
specified.

strtoul() was accepting the characters immediately above ASCII 0..9 as
valid hex digits, due to a missing comparison.

show_setting() and related functions now return an "actual length" in the
style of snprintf().  This is to allow consumers to allocate buffers large
enough to hold the formatted setting.

Minor bugfix: 4 x 2 = 8, not 16

When PMM is used, the gPXE image source will no longer be in base memory.
Decompression of .text16 and .data16 can therefore no longer be done in
real mode.

Use BBS installation check to see if we need to hook INT19 even on a PnP
BIOS.

Verify that $PnP signature is paragraph-aligned; bochs/qemu BIOS provides
a dummy $PnP signature with no valid entry point, and deliberately
unaligns the signature to indicate that it is not properly valid.

Print message if INT19 is hooked.

Attempt to use PMM even if BBS check failed.

Move the printing functions from pxeprefix.S into libprefix.S, so they
are available for debug from any prefix.

WinPE's pxeboot.n12 takes the BufferLimit returned by gPXE (indicating
the size of gPXE's internal DHCP packet buffers) and erroneously passes
it in as BufferSize (indicating the size of pxeboot.n12's DHCP packet
buffer).  If these don't match, then pxeboot.n12 ends up instructing gPXE
to overwrite parts of its data segment.

Change gPXE's internal DHCP packet buffers to be exactly
sizeof(BOOTPLAYER_t) bytes to work around this problem.

ROM initialisation vector now attempts to allocate a 2MB block using
PMM.  If successful, it copies the ROM image to this block, then
shrinks the ROM image to allow for more option ROMs.  If unsuccessful,
it leaves the ROM as-is.

ROM BEV now attempts to return to the BIOS, resorting to INT 18 only
if the BIOS stack has been corrupted.

The generate-by-PCI-device-ID rules (bin/pci_VVVV_DDDD.rom) are generally
used for building actual ROM images to be burned, and the burning
utilities generally run under some DOS variant.  Change the filename from
pci_VVVV_DDDD.rom to VVVVDDDD.rom so that it is compatible with the DOS
8.3-character filename limit.

This also fixes a bug in rdtsc_currticks when the result did not fix in %eax

Signed-off-by: Alexey Zaytsev <zaytsev.a@protei.ru>

This allows pxelinux to execute arbitrary gPXE commands.  This is
remarkably unsafe (not least because some of the commands will assume
full ownership of memory and do nasty things like edit the e820 map
underneath the calling pxelinux), but it does allow access to the
"sanboot" command.