qmgr_feedback.c

[詳解]

/*++
/* NAME
/*  qmgr_feedback 3
/* SUMMARY
/*  delivery agent feedback management
/* SYNOPSIS
/*  #include "qmgr.h"
/*
/*  void    qmgr_feedback_init(fbck_ctl, name_prefix, name_tail,
/*                  def_name, def_value)
/*  QMGR_FEEDBACK *fbck_ctl;
/*  const char *name_prefix;
/*  const char *name_tail;
/*  const char *def_name;
/*  const char *def_value;
/*
/*  double  QMGR_FEEDBACK_VAL(fbck_ctl, concurrency)
/*  QMGR_FEEDBACK *fbck_ctl;
/*  const int concurrency;
/* DESCRIPTION
/*  Upon completion of a delivery request, a delivery agent
/*  provides a hint that the scheduler should dedicate fewer or
/*  more resources to a specific destination.
/*
/*  qmgr_feedback_init() looks up transport-dependent positive
/*  or negative concurrency feedback control information from
/*  main.cf, and converts it to internal form.
/*
/*  QMGR_FEEDBACK_VAL() computes a concurrency adjustment based
/*  on a preprocessed feedback control information and the
/*  current concurrency window. This is an "unsafe" macro that
/*  evaluates some arguments multiple times.
/*
/*  Arguments:
/* .IP fbck_ctl
/*  Pointer to QMGR_FEEDBACK structure where the result will
/*  be stored.
/* .IP name_prefix
/*  Mail delivery transport name, used as the initial portion
/*  of a transport-dependent concurrency feedback parameter
/*  name.
/* .IP name_tail
/*  The second, and fixed, portion of a transport-dependent
/*  concurrency feedback parameter.
/* .IP def_name
/*  The name of a default feedback parameter.
/* .IP def_val
/*  The value of the default feedback parameter.
/* .IP concurrency
/*  Delivery concurrency for concurrency-dependent feedback calculation.
/* DIAGNOSTICS
/*  Warning: configuration error or unreasonable input. The program
/*  uses name_tail feedback instead.
/*  Panic: consistency check failure.
/* LICENSE
/* .ad
/* .fi
/*  The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*--*/

/* System library. */

#include <sys_defs.h>
#include <stdlib.h>
#include <limits.h>         /* INT_MAX */
#include <stdio.h>          /* sscanf() */
#include <string.h>

/* Utility library. */

#include <msg.h>
#include <name_code.h>
#include <stringops.h>
#include <mymalloc.h>

/* Global library. */

#include <mail_params.h>
#include <mail_conf.h>

/* Application-specific. */

#include "qmgr.h"

 /*
  * Lookup tables for main.cf feedback method names.
  */
const NAME_CODE qmgr_feedback_map[] = {
    CONC_FDBACK_NAME_WIN, QMGR_FEEDBACK_IDX_WIN,
#ifdef QMGR_FEEDBACK_IDX_SQRT_WIN
    CONC_FDBACK_NAME_SQRT_WIN, QMGR_FEEDBACK_IDX_SQRT_WIN,
#endif
    0, QMGR_FEEDBACK_IDX_NONE,
};

/* qmgr_feedback_init - initialize feedback control */

void    qmgr_feedback_init(QMGR_FEEDBACK *fb,
                       const char *name_prefix,
                       const char *name_tail,
                       const char *def_name,
                       const char *def_val)
{
    double  enum_val;
    char    denom_str[30 + 1];
    double  denom_val;
    char    slash;
    char    junk;
    char   *fbck_name;
    char   *fbck_val;

    /*
     * Look up the transport-dependent feedback value.
     */
    fbck_name = concatenate(name_prefix, name_tail, (char *) 0);
    fbck_val = get_mail_conf_str(fbck_name, def_val, 1, 0);

    /*
     * We allow users to express feedback as 1/8, as a more user-friendly
     * alternative to 0.125 (or worse, having users specify the number of
     * events in a feedback hysteresis cycle).
     * 
     * We use some sscanf() fu to parse the value into numerator and optional
     * "/" followed by denominator. We're doing this only a few times during
     * the process life time, so we strive for convenience instead of speed.
     */
#define INCLUSIVE_BOUNDS(val, low, high) ((val) >= (low) && (val) <= (high))

    fb->hysteresis = 1;             /* legacy */
    fb->base = -1;              /* assume error */

    switch (sscanf(fbck_val, "%lf %1[/] %30s%c",
           &enum_val, &slash, denom_str, &junk)) {
    case 1:
    fb->index = QMGR_FEEDBACK_IDX_NONE;
    fb->base = enum_val;
    break;
    case 3:
    if ((fb->index = name_code(qmgr_feedback_map, NAME_CODE_FLAG_NONE,
                   denom_str)) != QMGR_FEEDBACK_IDX_NONE) {
        fb->base = enum_val;
    } else if (INCLUSIVE_BOUNDS(enum_val, 0, INT_MAX)
           && sscanf(denom_str, "%lf%c", &denom_val, &junk) == 1
           && INCLUSIVE_BOUNDS(denom_val, 1.0 / INT_MAX, INT_MAX)) {
        fb->base = enum_val / denom_val;
    }
    break;
    }

    /*
     * Sanity check. If input is bad, we just warn and use a reasonable
     * default.
     */
    if (!INCLUSIVE_BOUNDS(fb->base, 0, 1)) {
    msg_warn("%s: ignoring malformed or unreasonable feedback: %s",
         strcmp(fbck_val, def_val) ? fbck_name : def_name, fbck_val);
    fb->index = QMGR_FEEDBACK_IDX_NONE;
    fb->base = 1;
    }

    /*
     * Performance debugging/analysis.
     */
    if (var_conc_feedback_debug)
    msg_info("%s: %s feedback type %d value at %d: %g",
         name_prefix, strcmp(fbck_val, def_val) ?
         fbck_name : def_name, fb->index, var_init_dest_concurrency,
         QMGR_FEEDBACK_VAL(*fb, var_init_dest_concurrency));

    myfree(fbck_name);
    myfree(fbck_val);
}