Re: suggestion for improvement to vfork() man page

At 12:04 PM 2/8/2012 +1300, Michael Kerrisk wrote:

Hi,

On Wed, Feb 8, 2012 at 10:50 AM,  [off-list ref] wrote:

quoted

+(However, on such systems,
+the preferred standard way of accomplishing the same result is to use
+.BR posix_spawn (3).)

I'm not sure I agree on this.  Linux posix_spawn()
calls fork()

I think isn't quite correct. I believe glibc's posix_spawn uses
vfork() where it can. See sysdeps/posix/spawni.c::spawni().

Looked at glibc-2.9 and posix_spawn() uses
fork() in only when no process attibutes are
modified (i.e. it respects the AIX and Solaris
semantics of vfork though this is a bit irrelevent
since AIX and Solaris have kernel-native support
for posix_spawn) or when a non-standard
POSIX_SPAWN_USEVFORK flag is present.  It's
rather muddy so I stick with #ifdef vfork()
for Linux and #ifdef posix_spawn() for the
*nixes.

So, I'll change that last sentence to

[[
(POSIX.1-2008 removed vfork() from the standard; the POSIX rationale
for  the posix_spawn(3) function notes that that function, which
provides functionality equivalent to fork(2)+exec(3) is designed 
to be implementable on systems that lack an MMU.)
]]

What do you think?

That's fair.  Perhaps the posix_spawn() page should
have some text regarding the conditional use of vfork()
under the covers.  I seen no mention of vfork() on
the die.net page, and can't find it on kernel.org.

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