RFC: API change for sema_timedwait

[Scott Long]

John Polstra wrote:
> Before 5.x becomes -stable, I'd like to change the API of
> sema_timedwait(9).  This function is used in only 3 places in the
> kernel, all in "dev/ips/ips_commands.c".
> 
> Currently, sema_timedwait returns 0 if the operation fails due to a
> timeout.  On success, it returns a non-zero value.  This is precisely
> the opposite of the standard convention in the kernel, where 0 means
> success and a non-zero value (taken from <sys/errno.h>) means failure.
> The convention exists because most functions can succeed in only one
> way but can fail in several different ways.
> 
> The reason I care about this is because I'd like to add new functions
> sema_wait_sig() and sema_timedwait_sig() which can be interrupted
> by a signal.  Then sema_timedwait_sig could fail in two different
> ways: as a result of a timeout or as a result of a signal.  If these
> functions returned proper errno values on failure, it would be easy to
> distinguish between the two failure cases.
> 
> This change would also make the return values of sema_timedwait,
> sema_wait_sig, and sema_timedwait_sig consistent with the analogous
> condition variable operations cv_timedwait, cv_wait_sig, and
> cv_timedwait_sig and with tsleep and msleep.
> 
> Does this change sound OK to you folks?
> 
> John

Being the ips maintainer, I have no objection to this change.

Scott