Sys V fork IS broken!

[Jim Rosenberg]

In <1990Jul30.002642.18244 at dg-rtp.dg.com> rice at dg-rtp.dg.com (Brian Rice) writes:
>And, of course, the kernel tells you why your fork failed: you get EAGAIN or 
>ENOMEM in errno.

Not clear!  In the V.3.2 man page for fork(2) it sez:

EAGAIN		Total amount of system memory available when reading via
		raw IO is temporarily insufficient.

ENOMEM		The process requires more space than the system is able to
		supply.

The scenario causing all the ruckus is memory temporarily unavailable while
doing a fork.  Apparently ENOMEM is what you get when you run out of swap
space.  (The BSD man page mentions swap space explicitly for ENOMEM.)

I agree with those posters who argue that out of swap space is a pretty grave
condition; I would want my applications to shut down as gracefully as possible
and bail the hell out.  If we're out of swap space, it's just as likely to get
worse as to get better.  I would certainly *not* want to retry in this
circumstance.  But I think retrying when you're out of process table slots is
pretty dubious too.  That and the no-kernel-memory problem seem *both* to be
covered by the same errno.  I would say this is a flat out and out defect in
which values of errno are returned by which circumstance.  And the man page
should say something more clear than that weird "raw IO" language.  Raw IO???

If the system call doesn't distinguish between problems that *are likely* go
away in a few seconds versus those that are of unpredictable duration, then
yessiree folks, the kernel *IS DICTATING POLICY* -- and a most unfortunate
one.  If it won't let my application judge the severity of the error then the
kernel is dictating the policy of making the application plan for the worst
case -- when it may not have to.
-- 
Jim Rosenberg             #include <disclaimer.h>      --cgh!amanue!oglvee!jr
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