re: kern/50430: syscall_disestablish() can remove active syscalls

[Paul Goyette <paul%vps1.whooppee.com@localhost>]

The following reply was made to PR kern/50430; it has been noted by GNATS.

From: Paul Goyette <paul%vps1.whooppee.com@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: re: kern/50430: syscall_disestablish() can remove active syscalls
Date: Mon, 16 Nov 2015 09:36:53 +0800 (PHT)

 On Mon, 16 Nov 2015, Paul Goyette wrote:
 
 > 1. Seems to me we would need to keep a 32- or 64-bit mask for each
 >   syscall.  When a new request to sc_establish() comes in, we could
 >   calculate the logical-OR of all current bits, complement the
 >   result, and find-least-significant-bit-set.
 
 Calculating the logical-OR of all current bits requires us to know how
 many entries there are in the emul->e_sysent table.  Many ports have
 __HAVE_MINIMAL_EMUL defined, which prevents creation of the sy_nsysent
 member.
 
 For now, I am making the sy_nsysent member unconditional;  this affects
 a number of compat_* and rump/* files, but it appears that they were
 all prepared for this.
 
 > 2. What do we do if we run out of bits?  Perhaps not too likely,
 >   but we would need to handle it.  What would be an appropriate
 >   value for sc_establish() to return if no bit is available?
 
 For now, I've selected ENOFILE; simple to change if a better value is
 agreed upon.