[9front] Re: [PATCH] devproc: use the correct limit when warning that conf.nproc is too high

[Anthony Martin <ality@pbrane.org>]

james palmer <james@biobuf.link> once said:
> -	if(conf.nproc >= (1<<(16-QSHIFT))-1)
> +	if(conf.nproc >= (1<<23)-1)

This change could be better. Skip to the end for the patch or
continue reading for a stroll down memory lane.

The number of qid types in the proc(3) file system has slowly
increased over time. The first edition originally had nine:

	Qdir, Qctl, Qmem, Qnote, Qnotepg, Qproc, Qsegment, Qstatus,
	and Qtext.

The second edition added two:

	Qnoteid, and Qwait.

The third edition added six:

	Qfd, Qfpregs, Qkregs, Qns, Qregs, and Qprofile.

The fourth edition added three:

	Qargs in 2002, Qtrace in 2003, and Qsyscall in 2010.

And 9front has added two more:

	Qppid in 2011, and Qwatchpt in 2017.

The number surpassed 16 in 3ed so QSHIFT was incremented and the
constants were adjusted but, unfortunately, the comment was not
updated at that time.

In May 2011, quanstro pointed this out on 9fans and it was corrected.
The QID and SLOT macros were also changed to calculate the mask based
on QSHIFT. The guard testing for too many procs in procinit was also
fixed.

This change happened shortly after the 9front fork happened so it was
easily missed.

Cheers,
  Anthony

% cd /n/dump/2011
% diff -c (0526 0527)^/sys/src/9/port/devproc.c
0526/sys/src/9/port/devproc.c:132,139 - 0527/sys/src/9/port/devproc.c:132,139

  /*
   * Qids are, in path:
-  *	 4 bits of file type (qids above)
-  *	23 bits of process slot number + 1
+  *	 5 bits of file type (qids above)
+  *	26 bits of process slot number + 1
   *	     in vers,
   *	32 bits of pid, for consistency checking
   * If notepg, c->pgrpid.path is pgrp slot, .vers is noteid.
0526/sys/src/9/port/devproc.c:140,147 - 0527/sys/src/9/port/devproc.c:140,147
   */
  #define	QSHIFT	5	/* location in qid of proc slot # */

- #define	QID(q)		((((ulong)(q).path)&0x0000001F)>>0)
- #define	SLOT(q)		(((((ulong)(q).path)&0x07FFFFFE0)>>QSHIFT)-1)
+ #define	QID(q)		((((ulong)(q).path) & ((1<<QSHIFT)-1)) >> 0)
+ #define	SLOT(q)		(((((ulong)(q).path) & ~(1UL<<31)) >> QSHIFT) - 1)
  #define	PID(q)		((q).vers)
  #define	NOTEID(q)	((q).vers)

0526/sys/src/9/port/devproc.c:288,294 - 0527/sys/src/9/port/devproc.c:288,294
  static void
  procinit(void)
  {
- 	if(conf.nproc >= (1<<(16-QSHIFT))-1)
+ 	if(conf.nproc >= (1<<(31-QSHIFT))-1)
  		print("warning: too many procs for devproc\n");
  	addclock0link((void (*)(void))profclock, 113);	/* Relative prime to HZ */
  }
%