Adding upstream version 3.5.24.upstream/3.5.24

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 546 insertions, 0 deletions

diff --git a/src/qmgr/qmgr.h b/src/qmgr/qmgr.h
new file mode 100644
index 0000000..4a205b4
--- /dev/null
+++ b/src/qmgr/qmgr.h
@@ -0,0 +1,546 @@
+/*++
+/* NAME
+/*	qmgr 3h
+/* SUMMARY
+/*	queue manager data structures
+/* SYNOPSIS
+/*	#include "qmgr.h"
+/* DESCRIPTION
+/* .nf
+
+ /*
+  * System library.
+  */
+#include <sys/time.h>
+#include <time.h>
+
+ /*
+  * Utility library.
+  */
+#include <vstream.h>
+#include <scan_dir.h>
+
+ /*
+  * Global library.
+  */
+#include <recipient_list.h>
+#include <dsn.h>
+
+ /*
+  * The queue manager is built around lots of mutually-referring structures.
+  * These typedefs save some typing.
+  */
+typedef struct QMGR_TRANSPORT QMGR_TRANSPORT;
+typedef struct QMGR_QUEUE QMGR_QUEUE;
+typedef struct QMGR_ENTRY QMGR_ENTRY;
+typedef struct QMGR_MESSAGE QMGR_MESSAGE;
+typedef struct QMGR_JOB QMGR_JOB;
+typedef struct QMGR_PEER QMGR_PEER;
+typedef struct QMGR_TRANSPORT_LIST QMGR_TRANSPORT_LIST;
+typedef struct QMGR_QUEUE_LIST QMGR_QUEUE_LIST;
+typedef struct QMGR_ENTRY_LIST QMGR_ENTRY_LIST;
+typedef struct QMGR_JOB_LIST QMGR_JOB_LIST;
+typedef struct QMGR_PEER_LIST QMGR_PEER_LIST;
+typedef struct QMGR_SCAN QMGR_SCAN;
+typedef struct QMGR_FEEDBACK QMGR_FEEDBACK;
+
+ /*
+  * Hairy macros to update doubly-linked lists.
+  */
+#define QMGR_LIST_ROTATE(head, object, peers) { \
+    head.next->peers.prev = head.prev; \
+    head.prev->peers.next = head.next; \
+    head.next = object->peers.next; \
+    head.next->peers.prev = 0; \
+    head.prev = object; \
+    object->peers.next = 0; \
+}
+
+#define QMGR_LIST_UNLINK(head, type, object, peers) { \
+    type   _next = object->peers.next; \
+    type   _prev = object->peers.prev; \
+    if (_prev) _prev->peers.next = _next; \
+	else head.next = _next; \
+    if (_next) _next->peers.prev = _prev; \
+	else head.prev = _prev; \
+    object->peers.next = object->peers.prev = 0; \
+}
+
+#define QMGR_LIST_LINK(head, pred, object, succ, peers) { \
+    object->peers.prev = pred; \
+    object->peers.next = succ; \
+    if (pred) pred->peers.next = object; \
+    else head.next = object; \
+    if (succ) succ->peers.prev = object; \
+    else head.prev = object; \
+}
+
+#define QMGR_LIST_PREPEND(head, object, peers) { \
+    object->peers.next = head.next; \
+    object->peers.prev = 0; \
+    if (head.next) { \
+	head.next->peers.prev = object; \
+    } else { \
+	head.prev = object; \
+    } \
+    head.next = object; \
+}
+
+#define QMGR_LIST_APPEND(head, object, peers) { \
+    object->peers.prev = head.prev; \
+    object->peers.next = 0; \
+    if (head.prev) { \
+	head.prev->peers.next = object; \
+    } else { \
+	head.next = object; \
+    } \
+    head.prev = object; \
+}
+
+#define QMGR_LIST_INIT(head) { \
+    head.prev = 0; \
+    head.next = 0; \
+}
+
+ /*
+  * Transports are looked up by name (when we have resolved a message), or
+  * round-robin wise (when we want to distribute resources fairly).
+  */
+struct QMGR_TRANSPORT_LIST {
+    QMGR_TRANSPORT *next;
+    QMGR_TRANSPORT *prev;
+};
+
+extern struct HTABLE *qmgr_transport_byname;	/* transport by name */
+extern QMGR_TRANSPORT_LIST qmgr_transport_list;	/* transports, round robin */
+
+ /*
+  * Delivery agents provide feedback, as hints that Postfix should expend
+  * more or fewer resources on a specific destination domain. The main.cf
+  * file specifies how feedback affects delivery concurrency: add/subtract a
+  * constant, a ratio of constants, or a constant divided by the delivery
+  * concurrency; and it specifies how much feedback must accumulate between
+  * concurrency updates.
+  */
+struct QMGR_FEEDBACK {
+    int     hysteresis;			/* to pass, need to be this tall */
+    double  base;			/* pre-computed from main.cf */
+    int     index;			/* none, window, sqrt(window) */
+};
+
+#define QMGR_FEEDBACK_IDX_NONE		0	/* no window dependence */
+#define QMGR_FEEDBACK_IDX_WIN		1	/* 1/window dependence */
+#if 0
+#define QMGR_FEEDBACK_IDX_SQRT_WIN	2	/* 1/sqrt(window) dependence */
+#endif
+
+#ifdef QMGR_FEEDBACK_IDX_SQRT_WIN
+#include <math.h>
+#endif
+
+extern void qmgr_feedback_init(QMGR_FEEDBACK *, const char *, const char *, const char *, const char *);
+
+#ifndef QMGR_FEEDBACK_IDX_SQRT_WIN
+#define QMGR_FEEDBACK_VAL(fb, win) \
+    ((fb).index == QMGR_FEEDBACK_IDX_NONE ? (fb).base : (fb).base / (win))
+#else
+#define QMGR_FEEDBACK_VAL(fb, win) \
+    ((fb).index == QMGR_FEEDBACK_IDX_NONE ? (fb).base : \
+    (fb).index == QMGR_FEEDBACK_IDX_WIN ? (fb).base / (win) : \
+    (fb).base / sqrt(win))
+#endif
+
+ /*
+  * Each transport (local, smtp-out, bounce) can have one queue per next hop
+  * name. Queues are looked up by next hop name (when we have resolved a
+  * message destination), or round-robin wise (when we want to deliver
+  * messages fairly).
+  */
+struct QMGR_QUEUE_LIST {
+    QMGR_QUEUE *next;
+    QMGR_QUEUE *prev;
+};
+
+struct QMGR_JOB_LIST {
+    QMGR_JOB *next;
+    QMGR_JOB *prev;
+};
+
+struct QMGR_TRANSPORT {
+    int     flags;			/* blocked, etc. */
+    int     pending;			/* incomplete DA connections */
+    char   *name;			/* transport name */
+    int     dest_concurrency_limit;	/* concurrency per domain */
+    int     init_dest_concurrency;	/* init. per-domain concurrency */
+    int     recipient_limit;		/* recipients per transaction */
+    int     rcpt_per_stack;		/* extra slots reserved for jobs put
+					 * on the job stack */
+    int     rcpt_unused;		/* available in-core recipient slots */
+    int     refill_limit;		/* recipient batch size for message
+					 * refill */
+    int     refill_delay;		/* delay before message refill */
+    int     slot_cost;			/* cost of new preemption slot (# of
+					 * selected entries) */
+    int     slot_loan;			/* preemption boost offset and */
+    int     slot_loan_factor;		/* factor, see qmgr_job_preempt() */
+    int     min_slots;			/* when preemption can take effect at
+					 * all */
+    struct HTABLE *queue_byname;	/* queues indexed by domain */
+    QMGR_QUEUE_LIST queue_list;		/* queues, round robin order */
+    struct HTABLE *job_byname;		/* jobs indexed by queue id */
+    QMGR_JOB_LIST job_list;		/* list of message jobs (1 per
+					 * message) ordered by scheduler */
+    QMGR_JOB_LIST job_bytime;		/* jobs ordered by time since queued */
+    QMGR_JOB *job_current;		/* keeps track of the current job */
+    QMGR_JOB *job_next_unread;		/* next job with unread recipients */
+    QMGR_JOB *candidate_cache;		/* cached result from
+					 * qmgr_job_candidate() */
+    QMGR_JOB *candidate_cache_current;	/* current job tied to the candidate */
+    time_t  candidate_cache_time;	/* when candidate_cache was last
+					 * updated */
+    int     blocker_tag;		/* for marking blocker jobs */
+    QMGR_TRANSPORT_LIST peers;		/* linkage */
+    DSN    *dsn;			/* why unavailable */
+    QMGR_FEEDBACK pos_feedback;		/* positive feedback control */
+    QMGR_FEEDBACK neg_feedback;		/* negative feedback control */
+    int     fail_cohort_limit;		/* flow shutdown control */
+    int     xport_rate_delay;		/* suspend per delivery */
+    int     rate_delay;			/* suspend per delivery */
+};
+
+#define QMGR_TRANSPORT_STAT_DEAD	(1<<1)
+#define QMGR_TRANSPORT_STAT_RATE_LOCK	(1<<2)
+
+typedef void (*QMGR_TRANSPORT_ALLOC_NOTIFY) (QMGR_TRANSPORT *, VSTREAM *);
+extern QMGR_TRANSPORT *qmgr_transport_select(void);
+extern void qmgr_transport_alloc(QMGR_TRANSPORT *, QMGR_TRANSPORT_ALLOC_NOTIFY);
+extern void qmgr_transport_throttle(QMGR_TRANSPORT *, DSN *);
+extern void qmgr_transport_unthrottle(QMGR_TRANSPORT *);
+extern QMGR_TRANSPORT *qmgr_transport_create(const char *);
+extern QMGR_TRANSPORT *qmgr_transport_find(const char *);
+
+#define QMGR_TRANSPORT_THROTTLED(t)	((t)->flags & QMGR_TRANSPORT_STAT_DEAD)
+
+ /*
+  * Each next hop (e.g., a domain name) has its own queue of pending message
+  * transactions. The "todo" queue contains messages that are to be delivered
+  * to this next hop. When a message is elected for transmission, it is moved
+  * from the "todo" queue to the "busy" queue. Messages are taken from the
+  * "todo" queue in round-robin order.
+  */
+struct QMGR_ENTRY_LIST {
+    QMGR_ENTRY *next;
+    QMGR_ENTRY *prev;
+};
+
+struct QMGR_QUEUE {
+    int     dflags;			/* delivery request options */
+    time_t  last_done;			/* last delivery completion */
+    char   *name;			/* domain name or address */
+    char   *nexthop;			/* domain name */
+    int     todo_refcount;		/* queue entries (todo list) */
+    int     busy_refcount;		/* queue entries (busy list) */
+    int     window;			/* slow open algorithm */
+    double  success;			/* accumulated positive feedback */
+    double  failure;			/* accumulated negative feedback */
+    double  fail_cohorts;		/* pseudo-cohort failure count */
+    QMGR_TRANSPORT *transport;		/* transport linkage */
+    QMGR_ENTRY_LIST todo;		/* todo queue entries */
+    QMGR_ENTRY_LIST busy;		/* messages on the wire */
+    QMGR_QUEUE_LIST peers;		/* neighbor queues */
+    DSN    *dsn;			/* why unavailable */
+    time_t  clog_time_to_warn;		/* time of last warning */
+    int     blocker_tag;		/* tagged if blocks job list */
+};
+
+#define	QMGR_QUEUE_TODO	1		/* waiting for service */
+#define QMGR_QUEUE_BUSY	2		/* recipients on the wire */
+
+extern int qmgr_queue_count;
+
+extern QMGR_QUEUE *qmgr_queue_create(QMGR_TRANSPORT *, const char *, const char *);
+extern void qmgr_queue_done(QMGR_QUEUE *);
+extern void qmgr_queue_throttle(QMGR_QUEUE *, DSN *);
+extern void qmgr_queue_unthrottle(QMGR_QUEUE *);
+extern QMGR_QUEUE *qmgr_queue_find(QMGR_TRANSPORT *, const char *);
+extern void qmgr_queue_suspend(QMGR_QUEUE *, int);
+
+ /*
+  * Exclusive queue states. Originally there were only two: "throttled" and
+  * "not throttled". It was natural to encode these in the queue window size.
+  * After 10 years it's not practical to rip out all the working code and
+  * change representations, so we just clean up the names a little.
+  * 
+  * Note: only the "ready" state can reach every state (including itself);
+  * non-ready states can reach only the "ready" state. Other transitions are
+  * forbidden, because they would result in dangling event handlers.
+  */
+#define QMGR_QUEUE_STAT_THROTTLED	0	/* back-off timer */
+#define QMGR_QUEUE_STAT_SUSPENDED	-1	/* voluntary delay timer */
+#define QMGR_QUEUE_STAT_SAVED		-2	/* delayed cleanup timer */
+#define QMGR_QUEUE_STAT_BAD		-3	/* can't happen */
+
+#define QMGR_QUEUE_READY(q)	((q)->window > 0)
+#define QMGR_QUEUE_THROTTLED(q)	((q)->window == QMGR_QUEUE_STAT_THROTTLED)
+#define QMGR_QUEUE_SUSPENDED(q)	((q)->window == QMGR_QUEUE_STAT_SUSPENDED)
+#define QMGR_QUEUE_SAVED(q)	((q)->window == QMGR_QUEUE_STAT_SAVED)
+#define QMGR_QUEUE_BAD(q)	((q)->window <= QMGR_QUEUE_STAT_BAD)
+
+#define QMGR_QUEUE_STATUS(q) ( \
+	    QMGR_QUEUE_READY(q) ? "ready" : \
+	    QMGR_QUEUE_THROTTLED(q) ? "throttled" : \
+	    QMGR_QUEUE_SUSPENDED(q) ? "suspended" : \
+	    QMGR_QUEUE_SAVED(q) ? "saved" : \
+	    "invalid queue status" \
+	)
+
+ /*
+  * Structure of one next-hop queue entry. In order to save some copying
+  * effort we allow multiple recipients per transaction.
+  */
+struct QMGR_ENTRY {
+    VSTREAM *stream;			/* delivery process */
+    QMGR_MESSAGE *message;		/* message info */
+    RECIPIENT_LIST rcpt_list;		/* as many as it takes */
+    QMGR_QUEUE *queue;			/* parent linkage */
+    QMGR_PEER *peer;			/* parent linkage */
+    QMGR_ENTRY_LIST queue_peers;	/* per queue neighbor entries */
+    QMGR_ENTRY_LIST peer_peers;		/* per peer neighbor entries */
+};
+
+extern QMGR_ENTRY *qmgr_entry_select(QMGR_PEER *);
+extern void qmgr_entry_unselect(QMGR_ENTRY *);
+extern void qmgr_entry_move_todo(QMGR_QUEUE *, QMGR_ENTRY *);
+extern void qmgr_entry_done(QMGR_ENTRY *, int);
+extern QMGR_ENTRY *qmgr_entry_create(QMGR_PEER *, QMGR_MESSAGE *);
+
+ /*
+  * All common in-core information about a message is kept here. When all
+  * recipients have been tried the message file is linked to the "deferred"
+  * queue (some hosts not reachable), to the "bounce" queue (some recipients
+  * were rejected), and is then removed from the "active" queue.
+  */
+struct QMGR_MESSAGE {
+    int     flags;			/* delivery problems */
+    int     qflags;			/* queuing flags */
+    int     tflags;			/* tracing flags */
+    long    tflags_offset;		/* offset for killing */
+    int     rflags;			/* queue file read flags */
+    VSTREAM *fp;			/* open queue file or null */
+    int     refcount;			/* queue entries */
+    int     single_rcpt;		/* send one rcpt at a time */
+    struct timeval arrival_time;	/* start of receive transaction */
+    time_t  create_time;		/* queue file create time */
+    struct timeval active_time;		/* time of entry into active queue */
+    time_t  queued_time;		/* sanitized time when moved to the
+					 * active queue */
+    time_t  refill_time;		/* sanitized time of last message
+					 * refill */
+    long    warn_offset;		/* warning bounce flag offset */
+    time_t  warn_time;			/* time next warning to be sent */
+    long    data_offset;		/* data seek offset */
+    char   *queue_name;			/* queue name */
+    char   *queue_id;			/* queue file */
+    char   *encoding;			/* content encoding */
+    char   *sender;			/* complete address */
+    char   *dsn_envid;			/* DSN envelope ID */
+    int     dsn_ret;			/* DSN headers/full */
+    int     smtputf8;			/* requires unicode */
+    char   *verp_delims;		/* VERP delimiters */
+    char   *filter_xport;		/* filtering transport */
+    char   *inspect_xport;		/* inspecting transport */
+    char   *redirect_addr;		/* info@spammer.tld */
+    long    data_size;			/* data segment size */
+    long    cont_length;		/* message content length */
+    long    rcpt_offset;		/* more recipients here */
+    char   *client_name;		/* client hostname */
+    char   *client_addr;		/* client address */
+    char   *client_port;		/* client port */
+    char   *client_proto;		/* client protocol */
+    char   *client_helo;		/* helo parameter */
+    char   *sasl_method;		/* SASL method */
+    char   *sasl_username;		/* SASL user name */
+    char   *sasl_sender;		/* SASL sender */
+    char   *log_ident;			/* up-stream queue ID */
+    char   *rewrite_context;		/* address qualification */
+    RECIPIENT_LIST rcpt_list;		/* complete addresses */
+    int     rcpt_count;			/* used recipient slots */
+    int     rcpt_limit;			/* maximum read in-core */
+    int     rcpt_unread;		/* # of recipients left in queue file */
+    QMGR_JOB_LIST job_list;		/* jobs delivering this message (1
+					 * per transport) */
+};
+
+ /*
+  * Flags 0-15 are reserved for qmgr_user.h.
+  */
+#define QMGR_READ_FLAG_SEEN_ALL_NON_RCPT	(1<<16)
+
+#define QMGR_MESSAGE_LOCKED	((QMGR_MESSAGE *) 1)
+
+extern int qmgr_message_count;
+extern int qmgr_recipient_count;
+extern int qmgr_vrfy_pend_count;
+
+extern void qmgr_message_free(QMGR_MESSAGE *);
+extern void qmgr_message_update_warn(QMGR_MESSAGE *);
+extern void qmgr_message_kill_record(QMGR_MESSAGE *, long);
+extern QMGR_MESSAGE *qmgr_message_alloc(const char *, const char *, int, mode_t);
+extern QMGR_MESSAGE *qmgr_message_realloc(QMGR_MESSAGE *);
+
+#define QMGR_MSG_STATS(stats, message) \
+    MSG_STATS_INIT2(stats, \
+                    incoming_arrival, message->arrival_time, \
+                    active_arrival, message->active_time)
+
+ /*
+  * Sometimes it's required to access the transport queues and entries on per
+  * message basis. That's what the QMGR_JOB structure is for - it groups all
+  * per message information within each transport using a list of QMGR_PEER
+  * structures. These structures in turn correspond with per message
+  * QMGR_QUEUE structure and list all per message QMGR_ENTRY structures.
+  */
+struct QMGR_PEER_LIST {
+    QMGR_PEER *next;
+    QMGR_PEER *prev;
+};
+
+struct QMGR_JOB {
+    QMGR_MESSAGE *message;		/* message delivered by this job */
+    QMGR_TRANSPORT *transport;		/* transport this job belongs to */
+    QMGR_JOB_LIST message_peers;	/* per message neighbor linkage */
+    QMGR_JOB_LIST transport_peers;	/* per transport neighbor linkage */
+    QMGR_JOB_LIST time_peers;		/* by time neighbor linkage */
+    QMGR_JOB *stack_parent;		/* stack parent */
+    QMGR_JOB_LIST stack_children;	/* all stack children */
+    QMGR_JOB_LIST stack_siblings;	/* stack children linkage */
+    int     stack_level;		/* job stack nesting level (-1 means
+					 * it's not on the lists at all) */
+    int     blocker_tag;		/* tagged if blocks the job list */
+    struct HTABLE *peer_byname;		/* message job peers, indexed by
+					 * domain */
+    QMGR_PEER_LIST peer_list;		/* list of message job peers */
+    int     slots_used;			/* slots used during preemption */
+    int     slots_available;		/* slots available for preemption (in
+					 * multiples of slot_cost) */
+    int     selected_entries;		/* # of entries selected for delivery
+					 * so far */
+    int     read_entries;		/* # of entries read in-core so far */
+    int     rcpt_count;			/* used recipient slots */
+    int     rcpt_limit;			/* available recipient slots */
+};
+
+struct QMGR_PEER {
+    QMGR_JOB *job;			/* job handling this peer */
+    QMGR_QUEUE *queue;			/* queue corresponding with this peer */
+    int     refcount;			/* peer entries */
+    QMGR_ENTRY_LIST entry_list;		/* todo message entries queued for
+					 * this peer */
+    QMGR_PEER_LIST peers;		/* neighbor linkage */
+};
+
+extern QMGR_ENTRY *qmgr_job_entry_select(QMGR_TRANSPORT *);
+extern QMGR_PEER *qmgr_peer_select(QMGR_JOB *);
+extern void qmgr_job_blocker_update(QMGR_QUEUE *);
+
+extern QMGR_JOB *qmgr_job_obtain(QMGR_MESSAGE *, QMGR_TRANSPORT *);
+extern void qmgr_job_free(QMGR_JOB *);
+extern void qmgr_job_move_limits(QMGR_JOB *);
+
+extern QMGR_PEER *qmgr_peer_create(QMGR_JOB *, QMGR_QUEUE *);
+extern QMGR_PEER *qmgr_peer_find(QMGR_JOB *, QMGR_QUEUE *);
+extern QMGR_PEER *qmgr_peer_obtain(QMGR_JOB *, QMGR_QUEUE *);
+extern void qmgr_peer_free(QMGR_PEER *);
+
+ /*
+  * qmgr_defer.c
+  */
+extern void qmgr_defer_transport(QMGR_TRANSPORT *, DSN *);
+extern void qmgr_defer_todo(QMGR_QUEUE *, DSN *);
+extern void qmgr_defer_recipient(QMGR_MESSAGE *, RECIPIENT *, DSN *);
+
+ /*
+  * qmgr_bounce.c
+  */
+extern void qmgr_bounce_recipient(QMGR_MESSAGE *, RECIPIENT *, DSN *);
+
+ /*
+  * qmgr_deliver.c
+  */
+extern int qmgr_deliver_concurrency;
+extern void qmgr_deliver(QMGR_TRANSPORT *, VSTREAM *);
+
+ /*
+  * qmgr_active.c
+  */
+extern int qmgr_active_feed(QMGR_SCAN *, const char *);
+extern void qmgr_active_drain(void);
+extern void qmgr_active_done(QMGR_MESSAGE *);
+
+ /*
+  * qmgr_move.c
+  */
+extern void qmgr_move(const char *, const char *, time_t);
+
+ /*
+  * qmgr_enable.c
+  */
+extern void qmgr_enable_all(void);
+extern void qmgr_enable_transport(QMGR_TRANSPORT *);
+extern void qmgr_enable_queue(QMGR_QUEUE *);
+
+ /*
+  * Queue scan context.
+  */
+struct QMGR_SCAN {
+    char   *queue;			/* queue name */
+    int     flags;			/* private, this run */
+    int     nflags;			/* private, next run */
+    struct SCAN_DIR *handle;		/* scan */
+};
+
+ /*
+  * Flags that control queue scans or destination selection. These are
+  * similar to the QMGR_REQ_XXX request codes.
+  */
+#define QMGR_SCAN_START	(1<<0)		/* start now/restart when done */
+#define QMGR_SCAN_ALL	(1<<1)		/* all queue file time stamps */
+#define QMGR_FLUSH_ONCE	(1<<2)		/* unthrottle once */
+#define QMGR_FLUSH_DFXP	(1<<3)		/* override defer_transports */
+#define QMGR_FLUSH_EACH	(1<<4)		/* unthrottle per message */
+#define QMGR_FORCE_EXPIRE (1<<5)	/* force-defer and force-expire */
+
+ /*
+  * qmgr_scan.c
+  */
+extern QMGR_SCAN *qmgr_scan_create(const char *);
+extern void qmgr_scan_request(QMGR_SCAN *, int);
+extern char *qmgr_scan_next(QMGR_SCAN *);
+
+ /*
+  * qmgr_error.c
+  */
+extern QMGR_TRANSPORT *qmgr_error_transport(const char *);
+extern QMGR_QUEUE *qmgr_error_queue(const char *, DSN *);
+extern char *qmgr_error_nexthop(DSN *);
+
+/* 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
+/*
+/*	Wietse Venema
+/*	Google, Inc.
+/*	111 8th Avenue
+/*	New York, NY 10011, USA
+/*
+/*	Preemptive scheduler enhancements:
+/*	Patrik Rak
+/*	Modra 6
+/*	155 00, Prague, Czech Republic
+/*--*/