[PATCH 0/2] first stab at NOFORK applet support

[Denis Vlasenko]

Hi Rob,

I looked at implementing NOFORK as discussed a while ago.

Two following patches are a RFC. They add a bss_size field
to struct BB_applet and global bss_buffer, which is
	memset(bss_buffer, 0 applet->bss_size);
just before applet invocation. This allows for repeated calls
of an applet from e.g. shell with correctly zeroed-out bss.

Also patches convert one applet (sed) so that it has neither
initialized data section nor bss section. #defines in quickshell.h
are provided to make it easier.

Conversion goes like this:

1) Remove 'static' keyword, bracket all bss variables in
   BEGIN_BSS/END_BSS (this places them in struct BSS_DATA).
   check with "make objsizes" that you didn't miss anything.

2) Either globally s/var/B.var/g or add line
       #define var B.var
   for each variable

3) edit line
	APPLET_DATA_SIZE(sed, <bss_size>, <data_size>)
   in quickshell.h. Set bss_size to something greater
   or equal [*] to total size of sed's bss.

4) add line
       CHECK_BSS_SIZE(sed);
   at the beginning of sed_main()
   (its's a compile check, no code generated)

This will make sed use bss_buffer for all bss variables.

Initialized data is not yet handled. To be done
after this RFC will be discussed.

[*] Why? Because it is impractical to move struct BSS_DATA
    definition out of sed.c into something.h and just use
    sizeof(struct BSS_DATA_sed). Too many applets have
    local structs and local vars with names which will
    pollute namespace. This will wreak havoc.
    Just entering bss size by hand in quickshell.h
    is a bit awkward, but at least I make compiler
    check that entered value is not less than sizeof(BSS_SIZE_sed),
    preventing a "bss is not entirely cleared" bug.
    CHECK_BSS_SIZE(sed) does that check. Spesifying
    too big a value is harmless (will memset a few extra bytes)

Please comment...
--
vda