Signed-off-by: Wolfgang Denk <wd@denx.de>

This patch adds a new config parameter for adjusting the calculation of
hash table size when importing a buffer.

When importing a extremely small buffer (e.g. the default_environment)
the old calculation generated a hash table which could hold at most the
buffer content but no more entires.

The new calculation add a fixed number of entries to the result to fit
better for small import buffers. This amount may be configured by the
user in board file to adjust the behaviour.

Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>

Motivation:

* Old environment code used a pessimizing implementation:
  - variable lookup used linear search => slow
  - changed/added variables were added at the end, i. e. most
    frequently used variables had the slowest access times => slow
  - each setenv() would calculate the CRC32 checksum over the whole
    environment block => slow
* "redundant" envrionment was locked down to two copies
* No easy way to implement features like "reset to factory defaults",
  or to select one out of several pre-defined (previously saved) sets
  of environment settings ("profiles")
* No easy way to import or export environment settings

======================================================================

API Changes:

- Variable names starting with '#' are no longer allowed

  I didn't find any such variable names being used; it is highly
  recommended to follow standard conventions and start variable names
  with an alphanumeric character

- "printenv" will now print a backslash at the end of all but the last
  lines of a multi-line variable value.

  Multi-line variables have never been formally defined, allthough
  there is no reason not to use them. Now we define rules how to deal
  with them, allowing for import and export.

- Function forceenv() and the related code in saveenv() was removed.
  At the moment this is causing build problems for the only user of
  this code (schmoogie - which has no entry in MAINTAINERS); may be
  fixed later by implementing the "env set -f" feature.

Inconsistencies:

- "printenv" will '\\'-escape the '\n' in multi-line variables, while
  "printenv var" will not do that.

======================================================================

Advantages:

- "printenv" output much better readable (sorted)
- faster!
- extendable (additional variable properties can be added)
- new, powerful features like "factory reset" or easy switching
  between several different environment settings ("profiles")

Disadvantages:

- Image size grows by typically 5...7 KiB (might shrink a bit again on
  systems with redundant environment with a following patch series)

======================================================================

Implemented:

- env command with subcommands:

  - env print [arg ...]

    same as "printenv": print environment

  - env set [-f] name [arg ...]

    same as "setenv": set (and delete) environment variables

    ["-f" - force setting even for read-only variables - not
    implemented yet.]

  - end delete [-f] name

    not implemented yet

    ["-f" - force delete even for read-only variables]

  - env save

    same as "saveenv": save environment

  - env export [-t | -b | -c] addr [size]

    export internal representation (hash table) in formats usable for
    persistent storage or processing:

	-t:	export as text format; if size is given, data will be
		padded with '\0' bytes; if not, one terminating '\0'
		will be added (which is included in the "filesize"
		setting so you can for exmple copy this to flash and
		keep the termination).
	-b:	export as binary format (name=value pairs separated by
		'\0', list end marked by double "\0\0")
	-c:	export as checksum protected environment format as
		used for example by "saveenv" command
	addr:	memory address where environment gets stored
	size:	size of output buffer

	With "-c" and size is NOT given, then the export command will
	format the data as currently used for the persistent storage,
	i. e. it will use CONFIG_ENV_SECT_SIZE as output block size and
	prepend a valid CRC32 checksum and, in case of resundant
	environment, a "current" redundancy flag. If size is given, this
	value will be used instead of CONFIG_ENV_SECT_SIZE; again, CRC32
	checksum and redundancy flag will be inserted.

	With "-b" and "-t", always only the real data (including a
	terminating '\0' byte) will be written; here the optional size
	argument will be used to make sure not to overflow the user
	provided buffer; the command will abort if the size is not
	sufficient. Any remainign space will be '\0' padded.

        On successful return, the variable "filesize" will be set.
        Note that filesize includes the trailing/terminating '\0'
        byte(s).

        Usage szenario: create a text snapshot/backup of the current
	settings:

		=> env export -t 100000
		=> era ${backup_addr} +${filesize}
		=> cp.b 100000 ${backup_addr} ${filesize}

	Re-import this snapshot, deleting all other settings:

		=> env import -d -t ${backup_addr}

  - env import [-d] [-t | -b | -c] addr [size]

    import external format (text or binary) into hash table,
    optionally deleting existing values:

	-d:	delete existing environment before importing;
		otherwise overwrite / append to existion definitions
	-t:	assume text format; either "size" must be given or the
		text data must be '\0' terminated
	-b:	assume binary format ('\0' separated, "\0\0" terminated)
	-c:	assume checksum protected environment format
	addr:	memory address to read from
	size:	length of input data; if missing, proper '\0'
		termination is mandatory

  - env default -f

    reset default environment: drop all environment settings and load
    default environment

  - env ask name [message] [size]

    same as "askenv": ask for environment variable

  - env edit name

    same as "editenv": edit environment variable

  - env run

    same as "run": run commands in an environment variable

======================================================================

TODO:

- drop default env as implemented now; provide a text file based
  initialization instead (eventually using several text files to
  incrementally build it from common blocks) and a tool to convert it
  into a binary blob / object file.

- It would be nice if we could add wildcard support for environment
  variables; this is needed for variable name auto-completion,
  but it would also be nice to be able to say "printenv ip*" or
  "printenv *addr*"

- Some boards don't link any more due to the grown code size:
  DU405, canyonlands, sequoia, socrates.

	=> cc: Matthias Fuchs <matthias.fuchs@esd-electronics.com>,
	       Stefan Roese <sr@denx.de>,
	       Heiko Schocher <hs@denx.de>

- Dropping forceenv() causes build problems on schmoogie

	=> cc: Sergey Kubushyn <ksi@koi8.net>

- Build tested on PPC and ARM only; runtime tested with NOR and NAND
  flash only => needs testing!!

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Matthias Fuchs <matthias.fuchs@esd-electronics.com>,
Cc: Stefan Roese <sr@denx.de>,
Cc: Heiko Schocher <hs@denx.de>
Cc: Sergey Kubushyn <ksi@koi8.net>

This implementation is based on code from uClibc-0.9.30.3 but was
modified and extended for use within U-Boot.

Major modifications and extensions:

* hsearch() [modified / extended]:
  - While the standard version does not make any assumptions about
    the type of the stored data objects at all, this implementation
    works with NUL terminated strings only.
  - Instead of storing just pointers to the original objects, we
    create local copies so the caller does not need to care about the
    data any more.
  - The standard implementation does not provide a way to update an
    existing entry.  This version will create a new entry or update an
    existing one when both "action == ENTER" and "item.data != NULL".
  - hsearch_r(): Instead of returning 1 on success, we return the
    index into the internal hash table, which is also guaranteed to be
    positive.  This allows us direct access to the found hash table
    slot for example for functions like hdelete().
* hdelete() [added]:
  - The standard implementation of hsearch(3) does not provide any way
    to delete any entries from the hash table.  We extend the code to
    do that.
* hexport() [added]:
  - Export the data stored in the hash table in linearized form:
    Entries are exported as "name=value" strings, separated by an
    arbitrary (non-NUL, of course) separator character. This allows to
    use this function both when formatting the U-Boot environment for
    external storage (using '\0' as separator), but also when using it
    for the "printenv" command to print all variables, simply by using
    as '\n" as separator. This can also be used for new features like
    exporting the environment data as text file, including the option
    for later re-import.
  - The entries in the result list will be sorted by ascending key
    values.
* himport() [added]:
  - Import linearized data into hash table.  This is the inverse
    function to hexport(): it takes a linear list of "name=value"
    pairs and creates hash table entries from it.
  - Entries without "value", i. e. consisting of only "name" or
    "name=", will cause this entry to be deleted from the hash table.
  - The "flag" argument can be used to control the behaviour: when
    the H_NOCLEAR bit is set, then an existing hash table will kept,
    i. e. new data will be added to an existing hash table;
    otherwise, old data will be discarded and a new hash table will
    be created.
  - The separator character for the "name=value" pairs can be
    selected, so we both support importing from externally stored
    environment data (separated by NUL characters) and from plain text
    files (entries separated by newline characters).
  - To allow for nicely formatted text input, leading white space
    (sequences of SPACE and TAB chars) is ignored, and entries
    starting (after removal of any leading white space) with a '#'
    character are considered comments and ignored.
  - NOTE: this means that a variable name cannot start with a '#'
    character.
  - When using a non-NUL separator character, backslash is used as
    escape character in the value part, allowing for example fo
    multi-line values.
  - In theory, arbitrary separator characters can be used, but only
    '\0' and '\n' have really been tested.

Signed-off-by: Wolfgang Denk <wd@denx.de>