setting_cmp() compares by option tag and then by name.  Empty names
will always match, which gives us a false positive.

Fix by explicitly checking for empty names.

Modified-by: Michael Brown <mcb30@etherboot.org>
Signed-off-by: Michael Brown <mcb30@etherboot.org>

This provides a mechanism for using arbitrarily-named variables within
gPXE, using the existing syntax for settings.

Add FILE_LICENCE declarations to almost all files that make up the
various standard builds of gPXE.

Reported-by: Stefan Hajnoczi <stefanha@gmail.com>

Intel's C compiler (icc) chokes on the zero-length arrays that we
currently use as part of the mechanism for accessing linker table
entries.  Abstract away the zero-length arrays, to make a port to icc
easier.

Introduce macros such as for_each_table_entry() to simplify the common
case of iterating over all entries in a linker table.

Represent table names as #defined string constants rather than
unquoted literals; this avoids visual confusion between table names
and C variable or type names, and also allows us to force a
compilation error in the event of incorrect table names.

Allow for settings blocks to be created on demand.  This allows for
constructions such as

  set defaults/filename http://bootserver/bootfile
  set defaults/priority 0xff
  dhcp net0
  chain ${filename}

which will boot from the DHCP-provided filename, or from
"http://bootserver/bootfile" if the DHCP server does not provide a
filename.

(Note that "priority" gets interpreted as a signed integer, so setting
"defaults/priority" to 0xff will cause the "defaults" settings block
to have an effective priority of -1.)

fetchf_uristring() was failing to handle error values from
fetch_setting(), resulting in its attempting to allocate extremely
large temporary buffers on the stack (and so overrunning the stack and
locking up the machine).

Problem reported by Shao Miller <Shao.Miller@yrdsb.edu.on.ca>.

Automatically unregister any settings with the same name (and position
within the settings tree) as a newly registered settings block.

This functionality is generalised out from dhcp.c.

This fixes a regression introduced in commit 612f4e7:

  [settings] Avoid returning uninitialised data on error in fetch_xxx_setting()

in which the memset() was moved from fetch_string_setting() to
fetch_setting(), in order that it would be useful for non-string
setting types.  However, this neglects to take into account the fact
that fetch_string_setting() shrinks its buffer by one byte (to allow
for the NUL) before calling fetch_setting().

Restore the memset() in fetch_string_setting(), so that the
terminating NUL is guaranteed to actually be a NUL.

Settings can be constructed using a dotted-decimal notation, to allow
for access to unnamed settings.  The default interpretation is as a
DHCP option number (with encapsulated options represented as
"<encapsulating option>.<encapsulated option>".

In several contexts (e.g. SMBIOS, Phantom CLP), it is useful to
interpret the dotted-decimal notation as referring to non-DHCP
options.  In this case, it becomes necessary for these contexts to
ignore standard DHCP options, otherwise we end up trying to, for
example, retrieve the boot filename from SMBIOS.

Allow settings blocks to specify a "tag magic".  When dotted-decimal
notation is used to construct a setting, the tag magic value of the
originating settings block will be ORed in to the tag number.
Store/fetch methods can then check for the magic number before
interpreting arbitrarily-numbered settings.

Callers (e.g. usr/autoboot.c) may not check the return values from
fetch_xxx_setting(), assuming that in error cases the returned setting
value will be "empty" (for some sensible value of "empty").

In particular, if the DHCP server did not specify a next-server
address, this would result in gPXE using uninitialised data for the
TFTP server IP address.

This allows settings to be expanded in a way that is safe to include
within a URI string, such as

  kernel http://10.0.0.1/boot.php?mf=${manufacturer:uristring}

where the ${manufacturer} setting may contain characters that are not
permitted (or have reserved purposes) within a URI.

Since whitespace characters will be URI-encoded (e.g. "%20" for a
space character), this also works around the problem that spaces
within an expanded setting would cause the shell to split command-line
arguments incorrectly.

fetch_string_setting() was subtracting one from the length of the
to-be-NUL-terminated buffer in order to obtain the length of the
unterminated buffer to be passed to fetch_setting().  This works
extremely well unless the length of the to-be-NUL-terminated buffer is
zero, at which point we end up giving fetch_setting() a buffer of
length -1UL, thereby inviting it to overwrite as much memory as it
wants...

In particular, expose the system UUID as a setting ("smbios/uuid").

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.

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.

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

Kill off DHCP option applicators.

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.

Allow setting names such as "ip:hex".

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.

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.

that we *can* place arrays in tables, which means we can force the
order within a table without having to resort to explicitly numbered
sections on everything.

names.

Add "dev" pointer in struct net_device to tie network interfaces back to a
hardware device.

Force natural alignment of data types in __table() macros.  This seems to
prevent gcc from taking the unilateral decision to occasionally increase
their alignment (which screws up the table packing).

the option config UI.

Introduce new {show,set,clear}_setting() that take a struct setting *
rather than a const char *.

set_setting() handles calling clear_setting() when appropriate, so that
individual setting types don't have to check for empty strings.

memory" and "no space left for DHCP options"

completely forgot I'd written ages ago.