TODO - fp2-dev/platform/external/busybox - Gitiles

 Busybox TODO

 Stuff that needs to be done.  This is organized by who plans to get around to
 doing it eventually, but that doesn't mean they "own" the item.  If you want to
 do one of these bounce an email off the person it's listed under to see if they
 have any suggestions how they plan to go about it, and to minimize conflicts
 between your work and theirs.  But otherwise, all of these are fair game.

 Rob Landley <rob@landley.net>:
   Add BB_NOMMU to platform.h and migrate __uClinux__ tests to that.
     #if defined __UCLIBC__ && !defined __ARCH_USE_MMU__
   Add a libbb/platform.c
     Implement fdprintf() for platforms that haven't got one.
     Implement bb_realpath() that can handle NULL on non-glibc.
     Cleanup bb_asprintf()

   Migrate calloc() and bb_calloc() occurrences to bb_xzalloc().
   Remove obsolete _() wrapper crud for internationalization we don't do.
   Figure out where we need utf8 support, and add it.

   sh
     The command shell situation is a big mess.  We have three or four different
     shells that don't really share any code, and the "standalone shell" doesn't
     work all that well (especially not in a chroot environment), due to apps not
     being reentrant.  I'm writing a new shell (bbsh) to unify the various
     shells and configurably add the minimal set of bash features people
     actually use.  The hardest part is it has to configure down as small as
     lash while providing lash's features.  The rest is easy in comparison.
   bzip2
     Compression-side support.
   init
     General cleanup (should use ENABLE_FEATURE_INIT_SYSLOG and ENABLE_FEATURE_INIT_DEBUG).
   depmod
     busybox lacks a way to update module deps when running from firmware without the
     use of the depmod.pl (perl is to bloated for most embedded setups) and or orig
     modutils. The orig depmod is rather pointless to have to add to a firmware image
     in when we already have a insmod/rmmod and friends.
   Unify base64 handling.
     There's base64 encoding and decoding going on in:
       networking/wget.c:base64enc()
       coreutils/uudecode.c:read_base64()
       coreutils/uuencode.c:tbl_base64[]
       networking/httpd.c:decodeBase64()
     And probably elsewhere.  That needs to be unified into libbb functions.
   Do a SUSv3 audit
     Look at the full Single Unix Specification version 3 (available online at
     "http://www.opengroup.org/onlinepubs/009695399/nfindex.html") and
     figure out which of our apps are compliant, and what we're missing that
     we might actually care about.

     Even better would be some kind of automated compliance test harness that
     exercises each command line option and the various corner cases.
   Internationalization
     How much internationalization should we do?

     The low hanging fruit is UTF-8 character set support.  We should do this.
     (Vodz pointed out the shell's cmdedit as needing work here.  What else?)

     We also have lots of hardwired english text messages.  Consolidating this
     into some kind of message table not only makes translation easier, but
     also allows us to consolidate redundant (or close) strings.

     We probably don't want to be bloated with locale support.  (Not unless we
     can cleanly export it from our underlying C library without having to
     concern ourselves with it directly.  Perhaps a few specific things like a
     config option for "date" are low hanging fruit here?)

     What level should things happen at?  How much do we care about
     internationalizing the text console when X11 and xterms are so much better
     at it?  (There's some infrastructure here we don't implement: The
     "unicode_start" and "unicode_stop" shell scripts need "vt-is-UTF8" and a
     --unicode option to loadkeys.  That implies a real loadkeys/dumpkeys
     implementation to replace loadkmap/dumpkmap.  Plus messing with console font
     loading.  Is it worth it, or do we just say "use X"?)

   Individual compilation of applets.
     It would be nice if busybox had the option to compile to individual applets,
     for people who want an alternate implementation less bloated than the gnu
     utils (or simply with less political baggage), but without it being one big
     executable.

     Turning libbb into a real dll is another possibility, especially if libbb
     could export some of the other library interfaces we've already more or less
     got the code for (like zlib).
   buildroot - Make a "dogfood" option
     Busybox 1.1 will be capable of replacing most gnu packages for real world
     use, such as developing software or in a live CD.  It needs wider testing.

     Busybox should now be able to replace bzip2, coreutils, e2fsprogs, file,
     findutils, gawk, grep, inetutils, less, modutils, net-tools, patch, procps,
     sed, shadow, sysklogd, sysvinit, tar, util-linux, and vim.  The resulting
     system should be self-hosting (I.E. able to rebuild itself from source
     code).  This means it would need (at least) binutils, gcc, and make, or
     equivalents.

     It would be a good "eating our own dogfood" test if buildroot had the option
     of using a "make allyesconfig" busybox instead of the all of the above
     packages.  Anything that's wrong with the resulting system, we can fix.  (It
     would be nice to be able to upgrade busybox to be able to replace bash and
     diffutils as well, but we're not there yet.)

     One example of an existing system that does this already is Firmware Linux:
       http://www.landley.net/code/firmware
   initramfs
     Busybox should have a sample initramfs build script.  This depends on
     bbsh, mdev, and switch_root.
   mkdep
     Write a mkdep that doesn't segfault if there's a directory it doesn't
     have permission to read, isn't based on manually editing the output of
     lexx and yacc, doesn't make such a mess under include/config, etc.
   Group globals into unions of structures.
     Go through and turn all the global and static variables into structures,
     and have all those structures be in a big union shared between processes,
     so busybox uses less bss.  (This is a big win on nommu machines.)  See
     sed.c and mdev.c for examples.
   Go through bugs.busybox.net and close out all of that somehow.
     This one's open to everybody, but I'll wind up doing it...


 Bernhard Fischer <busybox@busybox.net> suggests to look at these:
   New debug options:
     -Wlarger-than-127
     Cleanup any big users
     -Wunused-parameter
     Facilitate applet PROTOTYPES to provide means for having applets that
     do a) not take any arguments b) need only one of argc or argv c) need
     both argc and argv. All of these three options should go for the most
     feature complete denominator.
   Collate BUFSIZ IOBUF_SIZE MY_BUF_SIZE PIPE_PROGRESS_SIZE BUFSIZE PIPESIZE
     make bb_common_bufsiz1 configurable, size wise.
     make pipesize configurable, size wise.
     Use bb_common_bufsiz1 throughout applets!
   Add chrt applet. Please CC Bernhard if you suggest a patch.

 As yet unclaimed:

 ----
 find
   doesn't understand (), lots of susv3 stuff.
 ----
 diff
   Make sure we handle empty files properly:
     From the patch man page:

     you can remove a file by sending out a context diff that compares
     the file to be deleted with an empty file dated the Epoch.  The
     file will be removed unless patch is conforming to POSIX and the
     -E or --remove-empty-files option is not given.
 ---
 patch
   Should have simple fuzz factor support to apply patches at an offset which
   shouldn't take up too much space.

   And while we're at it, a new patch filename quoting format is apparently
   coming soon:  http://marc.theaimsgroup.com/?l=git&m=112927316408690&w=2
 ---
 ps / top
   Add support for both RSS and VSIZE rather than just one or the other.
   Or make it a build option.
 ---
 man
   It would be nice to have a man command.  Not one that handles troff or
   anything, just one that can handle preformatted ascii man pages, possibly
   compressed.  This could probably be a script in the extras directory that
   calls cat/zcat/bzcat | less

   (How doclifter might work into this is anybody's guess.)
 ---
 ar
   Write support?
 ----
 stty / catv
   stty's visible() function and catv's guts are identical. Merge them into
   an appropriate libbb function.
 ----
 struct suffix_mult
   Several duplicate users of: grep -r "1024\*1024" * -B2 -A1
   Merge to a single size_suffixes[] in libbb.
   Users: head tail od_bloaty hexdump and (partially as it wouldn't hurt) svlogd

 Architectural issues:

 bb_close() with fsync()
   We should have a bb_close() in place of normal close, with a CONFIG_ option
   to not just check the return value of close() for an error, but fsync().
   Close can't reliably report anything useful because if write() accepted the
   data then it either went out to the network or it's in cache or a pipe
   buffer.  Either way, there's no guarantee it'll make it to its final
   destination before close() gets called, so there's no guarantee that any
   error will be reported.

   You need to call fsync() if you care about errors that occur after write(),
   but that can have a big performance impact.  So make it a config option.
 ---
 Unify archivers
   Lots of archivers have the same general infrastructure.  The directory
   traversal code should be factored out, and the guts of each archiver could
   be some setup code and a series of callbacks for "add this file",
   "add this directory", "add this symlink" and so on.

   This could clean up tar and zip, and make it cheaper to add cpio and ar
   write support, and possibly even cheaply add things like mkisofs or
   mksquashfs someday, if they become relevant.
 ---
 Text buffer support.
   Several existing applets (sort, vi, less...) read
   a whole file into memory and act on it.  There might be an opportunity
   for shared code in there that could be moved into libbb...
 ---
 Memory Allocation
   We have a CONFIG_BUFFER mechanism that lets us select whether to do memory
   allocation on the stack or the heap.  Unfortunately, we're not using it much.
   We need to audit our memory allocations and turn a lot of malloc/free calls
   into RESERVE_CONFIG_BUFFER/RELEASE_CONFIG_BUFFER.
   For a start, see e.g. make EXTRA_CFLAGS=-Wlarger-than-64

   And while we're at it, many of the CONFIG_FEATURE_CLEAN_UP #ifdefs will be
   optimized out by the compiler in the stack allocation case (since there's no
   free for an alloca()), and this means that various cleanup loops that just
   call free might also be optimized out by the compiler if written right, so
   we can yank those #ifdefs too, and generally clean up the code.
 ---
 Switch CONFIG_SYMBOLS to ENABLE_SYMBOLS

   In busybox 1.0 and earlier, configuration was done by CONFIG_SYMBOLS
   that were either defined or undefined to indicate whether the symbol was
   selected in the .config file.  They were used with #ifdefs, ala:

     #ifdef CONFIG_SYMBOL
       if (other_test) {
         do_code();
       }
     #endif

   In 1.1, we have new ENABLE_SYMBOLS which are always defined (as 0 or 1),
   meaning you can still use them for preprocessor tests by replacing
   "#ifdef CONFIG_SYMBOL" with "#if ENABLE_SYMBOL".  But more importantly, we
   can use them as a true or false test in normal C code:

     if (ENABLE_SYMBOL && other_test) {
       do_code();
     }

   (Optimizing away if() statements that resolve to a constant value
   is known as "dead code elimination", an optimization so old and simple that
   Turbo Pascal for DOS did it twenty years ago.  Even modern mini-compilers
   like the Tiny C Compiler (tcc) and the Small Device C Compiler (SDCC)
   perform dead code elimination.)

   Right now, busybox.h is #including both "config.h" (defining the
   CONFIG_SYMBOLS) and "bb_config.h" (defining the ENABLE_SYMBOLS).  At some
   point in the future, it would be nice to wean ourselves off of the
   CONFIG versions.  (Among other things, some defective build environments
   leak the Linux kernel's CONFIG_SYMBOLS into the system's standard #include
   files.  We've experienced collisions before.)
 ---
 FEATURE_CLEAN_UP
   This is more an unresolved issue than a to-do item.  More thought is needed.

   Normally we rely on exit() to free memory, close files, and unmap segments
   for us.  This makes most calls to free(), close(), and unmap() optional in
   busybox applets that don't intend to run for very long, and optional stuff
   can be omitted to save size.

   The idea was raised that we could simulate fork/exit with setjmp/longjmp
   for _really_ brainless embedded systems, or speed up the standalone shell
   by not forking.  Doing so would require a reliable FEATURE_CLEAN_UP.
   Unfortunately, this isn't as easy as it sounds.

   The problem is, lots of things exit(), sometimes unexpectedly (xmalloc())
   and sometimes reliably (bb_perror_msg_and_die() or show_usage()).  This
   jumps out of the normal flow control and bypasses any cleanup code we
   put at the end of our applets.

   It's possible to add hooks to libbb functions like xmalloc() and xopen()
   to add their entries to a linked list, which could be traversed and
   freed/closed automatically.  (This would need to be able to free just the
   entries after a checkpoint to be usable for a forkless standalone shell.
   You don't want to free the shell's own resources.)

   Right now, FEATURE_CLEAN_UP is more or less a debugging aid, to make things
   like valgrind happy.  It's also documentation of _what_ we're trusting
   exit() to clean up for us.  But new infrastructure to auto-free stuff would
   render the existing FEATURE_CLEAN_UP code redundant.

   For right now, exit() handles it just fine.


 Minor stuff:
   watchdog.c could autodetect the timer duration via:
     if(!ioctl (fd, WDIOC_GETTIMEOUT, &tmo)) timer_duration = 1 + (tmo / 2);
   Unfortunately, that needs linux/watchdog.h and that contains unfiltered
   kernel types on some distros, which breaks the build.
 ---
   use bb_error_msg where appropriate: See
   egrep "(printf.*\([[:space:]]*(stderr|2)|[^_]write.*\([[:space:]]*(stderr|2))"
 ---
   use bb_perror_msg where appropriate: See
   egrep "[^_]perror"
 ---
   Remove superfluous fmt occurances: e.g.
   fprintf(stderr, "%s: %s not found\n", "unalias", *argptr);
   -> fprintf(stderr, "unalias: %s not found\n", *argptr);
 ---
   possible code duplication ingroup() and is_a_group_member()
 ---
   Move __get_hz() to a better place and (re)use it in route.c, ash.c, msh.c
 ---


 Code cleanup:

 Replace deprecated functions.

 bzero() -> memset()
 ---
 sigblock(), siggetmask(), sigsetmask(), sigmask() -> sigprocmask et al
 ---
 vdprintf() -> similar sized functionality
 ---
	Busybox TODO

	Stuff that needs to be done. This is organized by who plans to get around to
	doing it eventually, but that doesn't mean they "own" the item. If you want to
	do one of these bounce an email off the person it's listed under to see if they
	have any suggestions how they plan to go about it, and to minimize conflicts
	between your work and theirs. But otherwise, all of these are fair game.

	Rob Landley <rob@landley.net>:
	Add BB_NOMMU to platform.h and migrate __uClinux__ tests to that.
	#if defined __UCLIBC__ && !defined __ARCH_USE_MMU__
	Add a libbb/platform.c
	Implement fdprintf() for platforms that haven't got one.
	Implement bb_realpath() that can handle NULL on non-glibc.
	Cleanup bb_asprintf()

	Migrate calloc() and bb_calloc() occurrences to bb_xzalloc().
	Remove obsolete _() wrapper crud for internationalization we don't do.
	Figure out where we need utf8 support, and add it.

	sh
	The command shell situation is a big mess. We have three or four different
	shells that don't really share any code, and the "standalone shell" doesn't
	work all that well (especially not in a chroot environment), due to apps not
	being reentrant. I'm writing a new shell (bbsh) to unify the various
	shells and configurably add the minimal set of bash features people
	actually use. The hardest part is it has to configure down as small as
	lash while providing lash's features. The rest is easy in comparison.
	bzip2
	Compression-side support.
	init
	General cleanup (should use ENABLE_FEATURE_INIT_SYSLOG and ENABLE_FEATURE_INIT_DEBUG).
	depmod
	busybox lacks a way to update module deps when running from firmware without the
	use of the depmod.pl (perl is to bloated for most embedded setups) and or orig
	modutils. The orig depmod is rather pointless to have to add to a firmware image
	in when we already have a insmod/rmmod and friends.
	Unify base64 handling.
	There's base64 encoding and decoding going on in:
	networking/wget.c:base64enc()
	coreutils/uudecode.c:read_base64()
	coreutils/uuencode.c:tbl_base64[]
	networking/httpd.c:decodeBase64()
	And probably elsewhere. That needs to be unified into libbb functions.
	Do a SUSv3 audit
	Look at the full Single Unix Specification version 3 (available online at
	"http://www.opengroup.org/onlinepubs/009695399/nfindex.html") and
	figure out which of our apps are compliant, and what we're missing that
	we might actually care about.

	Even better would be some kind of automated compliance test harness that
	exercises each command line option and the various corner cases.
	Internationalization
	How much internationalization should we do?

	The low hanging fruit is UTF-8 character set support. We should do this.
	(Vodz pointed out the shell's cmdedit as needing work here. What else?)

	We also have lots of hardwired english text messages. Consolidating this
	into some kind of message table not only makes translation easier, but
	also allows us to consolidate redundant (or close) strings.

	We probably don't want to be bloated with locale support. (Not unless we
	can cleanly export it from our underlying C library without having to
	concern ourselves with it directly. Perhaps a few specific things like a
	config option for "date" are low hanging fruit here?)

	What level should things happen at? How much do we care about
	internationalizing the text console when X11 and xterms are so much better
	at it? (There's some infrastructure here we don't implement: The
	"unicode_start" and "unicode_stop" shell scripts need "vt-is-UTF8" and a
	--unicode option to loadkeys. That implies a real loadkeys/dumpkeys
	implementation to replace loadkmap/dumpkmap. Plus messing with console font
	loading. Is it worth it, or do we just say "use X"?)

	Individual compilation of applets.
	It would be nice if busybox had the option to compile to individual applets,
	for people who want an alternate implementation less bloated than the gnu
	utils (or simply with less political baggage), but without it being one big
	executable.

	Turning libbb into a real dll is another possibility, especially if libbb
	could export some of the other library interfaces we've already more or less
	got the code for (like zlib).
	buildroot - Make a "dogfood" option
	Busybox 1.1 will be capable of replacing most gnu packages for real world
	use, such as developing software or in a live CD. It needs wider testing.

	Busybox should now be able to replace bzip2, coreutils, e2fsprogs, file,
	findutils, gawk, grep, inetutils, less, modutils, net-tools, patch, procps,
	sed, shadow, sysklogd, sysvinit, tar, util-linux, and vim. The resulting
	system should be self-hosting (I.E. able to rebuild itself from source
	code). This means it would need (at least) binutils, gcc, and make, or
	equivalents.

	It would be a good "eating our own dogfood" test if buildroot had the option
	of using a "make allyesconfig" busybox instead of the all of the above
	packages. Anything that's wrong with the resulting system, we can fix. (It
	would be nice to be able to upgrade busybox to be able to replace bash and
	diffutils as well, but we're not there yet.)

	One example of an existing system that does this already is Firmware Linux:
	http://www.landley.net/code/firmware
	initramfs
	Busybox should have a sample initramfs build script. This depends on
	bbsh, mdev, and switch_root.
	mkdep
	Write a mkdep that doesn't segfault if there's a directory it doesn't
	have permission to read, isn't based on manually editing the output of
	lexx and yacc, doesn't make such a mess under include/config, etc.
	Group globals into unions of structures.
	Go through and turn all the global and static variables into structures,
	and have all those structures be in a big union shared between processes,
	so busybox uses less bss. (This is a big win on nommu machines.) See
	sed.c and mdev.c for examples.
	Go through bugs.busybox.net and close out all of that somehow.
	This one's open to everybody, but I'll wind up doing it...


	Bernhard Fischer <busybox@busybox.net> suggests to look at these:
	New debug options:
	-Wlarger-than-127
	Cleanup any big users
	-Wunused-parameter
	Facilitate applet PROTOTYPES to provide means for having applets that
	do a) not take any arguments b) need only one of argc or argv c) need
	both argc and argv. All of these three options should go for the most
	feature complete denominator.
	Collate BUFSIZ IOBUF_SIZE MY_BUF_SIZE PIPE_PROGRESS_SIZE BUFSIZE PIPESIZE
	make bb_common_bufsiz1 configurable, size wise.
	make pipesize configurable, size wise.
	Use bb_common_bufsiz1 throughout applets!
	Add chrt applet. Please CC Bernhard if you suggest a patch.

	As yet unclaimed:

	----
	find
	doesn't understand (), lots of susv3 stuff.
	----
	diff
	Make sure we handle empty files properly:
	From the patch man page:

	you can remove a file by sending out a context diff that compares
	the file to be deleted with an empty file dated the Epoch. The
	file will be removed unless patch is conforming to POSIX and the
	-E or --remove-empty-files option is not given.
	---
	patch
	Should have simple fuzz factor support to apply patches at an offset which
	shouldn't take up too much space.

	And while we're at it, a new patch filename quoting format is apparently
	coming soon: http://marc.theaimsgroup.com/?l=git&m=112927316408690&w=2
	---
	ps / top
	Add support for both RSS and VSIZE rather than just one or the other.
	Or make it a build option.
	---
	man
	It would be nice to have a man command. Not one that handles troff or
	anything, just one that can handle preformatted ascii man pages, possibly
	compressed. This could probably be a script in the extras directory that
	calls cat/zcat/bzcat \| less

	(How doclifter might work into this is anybody's guess.)
	---
	ar
	Write support?
	----
	stty / catv
	stty's visible() function and catv's guts are identical. Merge them into
	an appropriate libbb function.
	----
	struct suffix_mult
	Several duplicate users of: grep -r "1024\1024" -B2 -A1
	Merge to a single size_suffixes[] in libbb.
	Users: head tail od_bloaty hexdump and (partially as it wouldn't hurt) svlogd

	Architectural issues:

	bb_close() with fsync()
	We should have a bb_close() in place of normal close, with a CONFIG_ option
	to not just check the return value of close() for an error, but fsync().
	Close can't reliably report anything useful because if write() accepted the
	data then it either went out to the network or it's in cache or a pipe
	buffer. Either way, there's no guarantee it'll make it to its final
	destination before close() gets called, so there's no guarantee that any
	error will be reported.

	You need to call fsync() if you care about errors that occur after write(),
	but that can have a big performance impact. So make it a config option.
	---
	Unify archivers
	Lots of archivers have the same general infrastructure. The directory
	traversal code should be factored out, and the guts of each archiver could
	be some setup code and a series of callbacks for "add this file",
	"add this directory", "add this symlink" and so on.

	This could clean up tar and zip, and make it cheaper to add cpio and ar
	write support, and possibly even cheaply add things like mkisofs or
	mksquashfs someday, if they become relevant.
	---
	Text buffer support.
	Several existing applets (sort, vi, less...) read
	a whole file into memory and act on it. There might be an opportunity
	for shared code in there that could be moved into libbb...
	---
	Memory Allocation
	We have a CONFIG_BUFFER mechanism that lets us select whether to do memory
	allocation on the stack or the heap. Unfortunately, we're not using it much.
	We need to audit our memory allocations and turn a lot of malloc/free calls
	into RESERVE_CONFIG_BUFFER/RELEASE_CONFIG_BUFFER.
	For a start, see e.g. make EXTRA_CFLAGS=-Wlarger-than-64

	And while we're at it, many of the CONFIG_FEATURE_CLEAN_UP #ifdefs will be
	optimized out by the compiler in the stack allocation case (since there's no
	free for an alloca()), and this means that various cleanup loops that just
	call free might also be optimized out by the compiler if written right, so
	we can yank those #ifdefs too, and generally clean up the code.
	---
	Switch CONFIG_SYMBOLS to ENABLE_SYMBOLS

	In busybox 1.0 and earlier, configuration was done by CONFIG_SYMBOLS
	that were either defined or undefined to indicate whether the symbol was
	selected in the .config file. They were used with #ifdefs, ala:

	#ifdef CONFIG_SYMBOL
	if (other_test) {
	do_code();
	}
	#endif

	In 1.1, we have new ENABLE_SYMBOLS which are always defined (as 0 or 1),
	meaning you can still use them for preprocessor tests by replacing
	"#ifdef CONFIG_SYMBOL" with "#if ENABLE_SYMBOL". But more importantly, we
	can use them as a true or false test in normal C code:

	if (ENABLE_SYMBOL && other_test) {
	do_code();
	}

	(Optimizing away if() statements that resolve to a constant value
	is known as "dead code elimination", an optimization so old and simple that
	Turbo Pascal for DOS did it twenty years ago. Even modern mini-compilers
	like the Tiny C Compiler (tcc) and the Small Device C Compiler (SDCC)
	perform dead code elimination.)

	Right now, busybox.h is #including both "config.h" (defining the
	CONFIG_SYMBOLS) and "bb_config.h" (defining the ENABLE_SYMBOLS). At some
	point in the future, it would be nice to wean ourselves off of the
	CONFIG versions. (Among other things, some defective build environments
	leak the Linux kernel's CONFIG_SYMBOLS into the system's standard #include
	files. We've experienced collisions before.)
	---
	FEATURE_CLEAN_UP
	This is more an unresolved issue than a to-do item. More thought is needed.

	Normally we rely on exit() to free memory, close files, and unmap segments
	for us. This makes most calls to free(), close(), and unmap() optional in
	busybox applets that don't intend to run for very long, and optional stuff
	can be omitted to save size.

	The idea was raised that we could simulate fork/exit with setjmp/longjmp
	for _really_ brainless embedded systems, or speed up the standalone shell
	by not forking. Doing so would require a reliable FEATURE_CLEAN_UP.
	Unfortunately, this isn't as easy as it sounds.

	The problem is, lots of things exit(), sometimes unexpectedly (xmalloc())
	and sometimes reliably (bb_perror_msg_and_die() or show_usage()). This
	jumps out of the normal flow control and bypasses any cleanup code we
	put at the end of our applets.

	It's possible to add hooks to libbb functions like xmalloc() and xopen()
	to add their entries to a linked list, which could be traversed and
	freed/closed automatically. (This would need to be able to free just the
	entries after a checkpoint to be usable for a forkless standalone shell.
	You don't want to free the shell's own resources.)

	Right now, FEATURE_CLEAN_UP is more or less a debugging aid, to make things
	like valgrind happy. It's also documentation of _what_ we're trusting
	exit() to clean up for us. But new infrastructure to auto-free stuff would
	render the existing FEATURE_CLEAN_UP code redundant.

	For right now, exit() handles it just fine.



	Minor stuff:
	watchdog.c could autodetect the timer duration via:
	if(!ioctl (fd, WDIOC_GETTIMEOUT, &tmo)) timer_duration = 1 + (tmo / 2);
	Unfortunately, that needs linux/watchdog.h and that contains unfiltered
	kernel types on some distros, which breaks the build.
	---
	use bb_error_msg where appropriate: See
	egrep "(printf.\([[:space:]](stderr\|2)\|[^_]write.\([[:space:]](stderr\|2))"
	---
	use bb_perror_msg where appropriate: See
	egrep "[^_]perror"
	---
	Remove superfluous fmt occurances: e.g.
	fprintf(stderr, "%s: %s not found\n", "unalias", *argptr);
	-> fprintf(stderr, "unalias: %s not found\n", *argptr);
	---
	possible code duplication ingroup() and is_a_group_member()
	---
	Move __get_hz() to a better place and (re)use it in route.c, ash.c, msh.c
	---


	Code cleanup:

	Replace deprecated functions.

	bzero() -> memset()
	---
	sigblock(), siggetmask(), sigsetmask(), sigmask() -> sigprocmask et al
	---
	vdprintf() -> similar sized functionality
	---