Adding upstream version 1:9.16.44.upstream/1%9.16.44

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

1 files changed, 1896 insertions, 0 deletions

diff --git a/lib/isc/log.c b/lib/isc/log.c
new file mode 100644
index 0000000..b15d66a
--- /dev/null
+++ b/lib/isc/log.c
@@ -0,0 +1,1896 @@
+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, you can obtain one at https://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+/*! \file */
+
+#include <errno.h>
+#include <inttypes.h>
+#include <limits.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <sys/types.h> /* dev_t FreeBSD 2.1 */
+#include <time.h>
+
+#include <isc/atomic.h>
+#include <isc/dir.h>
+#include <isc/file.h>
+#include <isc/log.h>
+#include <isc/magic.h>
+#include <isc/mem.h>
+#include <isc/platform.h>
+#include <isc/print.h>
+#include <isc/rwlock.h>
+#include <isc/stat.h>
+#include <isc/stdio.h>
+#include <isc/string.h>
+#include <isc/time.h>
+#include <isc/util.h>
+
+#define LCTX_MAGIC	    ISC_MAGIC('L', 'c', 't', 'x')
+#define VALID_CONTEXT(lctx) ISC_MAGIC_VALID(lctx, LCTX_MAGIC)
+
+#define LCFG_MAGIC	   ISC_MAGIC('L', 'c', 'f', 'g')
+#define VALID_CONFIG(lcfg) ISC_MAGIC_VALID(lcfg, LCFG_MAGIC)
+
+#define RDLOCK(lp)   RWLOCK(lp, isc_rwlocktype_read);
+#define WRLOCK(lp)   RWLOCK(lp, isc_rwlocktype_write);
+#define RDUNLOCK(lp) RWUNLOCK(lp, isc_rwlocktype_read);
+#define WRUNLOCK(lp) RWUNLOCK(lp, isc_rwlocktype_write);
+
+/*
+ * XXXDCL make dynamic?
+ */
+#define LOG_BUFFER_SIZE (8 * 1024)
+
+/*!
+ * This is the structure that holds each named channel.  A simple linked
+ * list chains all of the channels together, so an individual channel is
+ * found by doing strcmp()s with the names down the list.  Their should
+ * be no performance penalty from this as it is expected that the number
+ * of named channels will be no more than a dozen or so, and name lookups
+ * from the head of the list are only done when isc_log_usechannel() is
+ * called, which should also be very infrequent.
+ */
+typedef struct isc_logchannel isc_logchannel_t;
+
+struct isc_logchannel {
+	char *name;
+	unsigned int type;
+	int level;
+	unsigned int flags;
+	isc_logdestination_t destination;
+	ISC_LINK(isc_logchannel_t) link;
+};
+
+/*!
+ * The logchannellist structure associates categories and modules with
+ * channels.  First the appropriate channellist is found based on the
+ * category, and then each structure in the linked list is checked for
+ * a matching module.  It is expected that the number of channels
+ * associated with any given category will be very short, no more than
+ * three or four in the more unusual cases.
+ */
+typedef struct isc_logchannellist isc_logchannellist_t;
+
+struct isc_logchannellist {
+	const isc_logmodule_t *module;
+	isc_logchannel_t *channel;
+	ISC_LINK(isc_logchannellist_t) link;
+};
+
+/*!
+ * This structure is used to remember messages for pruning via
+ * isc_log_[v]write1().
+ */
+typedef struct isc_logmessage isc_logmessage_t;
+
+struct isc_logmessage {
+	char *text;
+	isc_time_t time;
+	ISC_LINK(isc_logmessage_t) link;
+};
+
+/*!
+ * The isc_logconfig structure is used to store the configurable information
+ * about where messages are actually supposed to be sent -- the information
+ * that could changed based on some configuration file, as opposed to the
+ * the category/module specification of isc_log_[v]write[1] that is compiled
+ * into a program, or the debug_level which is dynamic state information.
+ */
+struct isc_logconfig {
+	unsigned int magic;
+	isc_log_t *lctx;
+	ISC_LIST(isc_logchannel_t) channels;
+	ISC_LIST(isc_logchannellist_t) * channellists;
+	unsigned int channellist_count;
+	unsigned int duplicate_interval;
+	int_fast32_t highest_level;
+	char *tag;
+	bool dynamic;
+};
+
+/*!
+ * This isc_log structure provides the context for the isc_log functions.
+ * The log context locks itself in isc_log_doit, the internal backend to
+ * isc_log_write.  The locking is necessary both to provide exclusive access
+ * to the buffer into which the message is formatted and to guard against
+ * competing threads trying to write to the same syslog resource.  (On
+ * some systems, such as BSD/OS, stdio is thread safe but syslog is not.)
+ * Unfortunately, the lock cannot guard against a _different_ logging
+ * context in the same program competing for syslog's attention.  Thus
+ * There Can Be Only One, but this is not enforced.
+ * XXXDCL enforce it?
+ *
+ * Note that the category and module information is not locked.
+ * This is because in the usual case, only one isc_log_t is ever created
+ * in a program, and the category/module registration happens only once.
+ * XXXDCL it might be wise to add more locking overall.
+ */
+struct isc_log {
+	/* Not locked. */
+	unsigned int magic;
+	isc_mem_t *mctx;
+	isc_logcategory_t *categories;
+	unsigned int category_count;
+	isc_logmodule_t *modules;
+	unsigned int module_count;
+	atomic_int_fast32_t debug_level;
+	isc_rwlock_t lcfg_rwl;
+	/* Locked by isc_log lcfg_rwl */
+	isc_logconfig_t *logconfig;
+	isc_mutex_t lock;
+	/* Locked by isc_log lock. */
+	char buffer[LOG_BUFFER_SIZE];
+	ISC_LIST(isc_logmessage_t) messages;
+	atomic_bool dynamic;
+	atomic_int_fast32_t highest_level;
+};
+
+/*!
+ * Used when ISC_LOG_PRINTLEVEL is enabled for a channel.
+ */
+static const char *log_level_strings[] = { "debug",   "info",  "notice",
+					   "warning", "error", "critical" };
+
+/*!
+ * Used to convert ISC_LOG_* priorities into syslog priorities.
+ * XXXDCL This will need modification for NT.
+ */
+static const int syslog_map[] = { LOG_DEBUG,   LOG_INFO, LOG_NOTICE,
+				  LOG_WARNING, LOG_ERR,	 LOG_CRIT };
+
+/*!
+ * When adding new categories, a corresponding ISC_LOGCATEGORY_foo
+ * definition needs to be added to <isc/log.h>.
+ *
+ * The default category is provided so that the internal default can
+ * be overridden.  Since the default is always looked up as the first
+ * channellist in the log context, it must come first in isc_categories[].
+ */
+LIBISC_EXTERNAL_DATA isc_logcategory_t isc_categories[] = { { "default",
+							      0 }, /* "default
+								      must come
+								      first. */
+							    { "general", 0 },
+							    { NULL, 0 } };
+
+/*!
+ * See above comment for categories on LIBISC_EXTERNAL_DATA, and apply it to
+ * modules.
+ */
+LIBISC_EXTERNAL_DATA isc_logmodule_t isc_modules[] = {
+	{ "socket", 0 }, { "time", 0 },	  { "interface", 0 }, { "timer", 0 },
+	{ "file", 0 },	 { "netmgr", 0 }, { "other", 0 },     { NULL, 0 }
+};
+
+/*!
+ * This essentially constant structure must be filled in at run time,
+ * because its channel member is pointed to a channel that is created
+ * dynamically with isc_log_createchannel.
+ */
+static isc_logchannellist_t default_channel;
+
+/*!
+ * libisc logs to this context.
+ */
+LIBISC_EXTERNAL_DATA isc_log_t *isc_lctx = NULL;
+
+/*!
+ * Forward declarations.
+ */
+static void
+assignchannel(isc_logconfig_t *lcfg, unsigned int category_id,
+	      const isc_logmodule_t *module, isc_logchannel_t *channel);
+
+static void
+sync_channellist(isc_logconfig_t *lcfg);
+
+static void
+sync_highest_level(isc_log_t *lctx, isc_logconfig_t *lcfg);
+
+static isc_result_t
+greatest_version(isc_logfile_t *file, int versions, int *greatest);
+
+static void
+isc_log_doit(isc_log_t *lctx, isc_logcategory_t *category,
+	     isc_logmodule_t *module, int level, bool write_once,
+	     const char *format, va_list args) ISC_FORMAT_PRINTF(6, 0);
+
+/*@{*/
+/*!
+ * Convenience macros.
+ */
+
+#define FACILITY(channel)	 (channel->destination.facility)
+#define FILE_NAME(channel)	 (channel->destination.file.name)
+#define FILE_STREAM(channel)	 (channel->destination.file.stream)
+#define FILE_VERSIONS(channel)	 (channel->destination.file.versions)
+#define FILE_SUFFIX(channel)	 (channel->destination.file.suffix)
+#define FILE_MAXSIZE(channel)	 (channel->destination.file.maximum_size)
+#define FILE_MAXREACHED(channel) (channel->destination.file.maximum_reached)
+
+/*@}*/
+/****
+**** Public interfaces.
+****/
+
+/*
+ * Establish a new logging context, with default channels.
+ */
+void
+isc_log_create(isc_mem_t *mctx, isc_log_t **lctxp, isc_logconfig_t **lcfgp) {
+	isc_log_t *lctx;
+	isc_logconfig_t *lcfg = NULL;
+
+	REQUIRE(mctx != NULL);
+	REQUIRE(lctxp != NULL && *lctxp == NULL);
+	REQUIRE(lcfgp == NULL || *lcfgp == NULL);
+
+	lctx = isc_mem_get(mctx, sizeof(*lctx));
+	lctx->mctx = NULL;
+	isc_mem_attach(mctx, &lctx->mctx);
+	lctx->categories = NULL;
+	lctx->category_count = 0;
+	lctx->modules = NULL;
+	lctx->module_count = 0;
+	atomic_init(&lctx->debug_level, 0);
+
+	ISC_LIST_INIT(lctx->messages);
+
+	isc_mutex_init(&lctx->lock);
+	isc_rwlock_init(&lctx->lcfg_rwl, 0, 0);
+
+	/*
+	 * Normally setting the magic number is the last step done
+	 * in a creation function, but a valid log context is needed
+	 * by isc_log_registercategories and isc_logconfig_create.
+	 * If either fails, the lctx is destroyed and not returned
+	 * to the caller.
+	 */
+	lctx->magic = LCTX_MAGIC;
+
+	isc_log_registercategories(lctx, isc_categories);
+	isc_log_registermodules(lctx, isc_modules);
+	isc_logconfig_create(lctx, &lcfg);
+
+	sync_channellist(lcfg);
+
+	lctx->logconfig = lcfg;
+
+	atomic_init(&lctx->highest_level, lcfg->highest_level);
+	atomic_init(&lctx->dynamic, lcfg->dynamic);
+
+	*lctxp = lctx;
+	if (lcfgp != NULL) {
+		*lcfgp = lcfg;
+	}
+}
+
+void
+isc_logconfig_create(isc_log_t *lctx, isc_logconfig_t **lcfgp) {
+	isc_logconfig_t *lcfg;
+	isc_logdestination_t destination;
+	int level = ISC_LOG_INFO;
+
+	REQUIRE(lcfgp != NULL && *lcfgp == NULL);
+	REQUIRE(VALID_CONTEXT(lctx));
+
+	lcfg = isc_mem_get(lctx->mctx, sizeof(*lcfg));
+
+	lcfg->lctx = lctx;
+	lcfg->channellists = NULL;
+	lcfg->channellist_count = 0;
+	lcfg->duplicate_interval = 0;
+	lcfg->highest_level = level;
+	lcfg->tag = NULL;
+	lcfg->dynamic = false;
+	ISC_LIST_INIT(lcfg->channels);
+	lcfg->magic = LCFG_MAGIC;
+
+	/*
+	 * Create the default channels:
+	 *      default_syslog, default_stderr, default_debug and null.
+	 */
+	destination.facility = LOG_DAEMON;
+	isc_log_createchannel(lcfg, "default_syslog", ISC_LOG_TOSYSLOG, level,
+			      &destination, 0);
+
+	destination.file.stream = stderr;
+	destination.file.name = NULL;
+	destination.file.versions = ISC_LOG_ROLLNEVER;
+	destination.file.suffix = isc_log_rollsuffix_increment;
+	destination.file.maximum_size = 0;
+	isc_log_createchannel(lcfg, "default_stderr", ISC_LOG_TOFILEDESC, level,
+			      &destination, ISC_LOG_PRINTTIME);
+
+	/*
+	 * Set the default category's channel to default_stderr,
+	 * which is at the head of the channels list because it was
+	 * just created.
+	 */
+	default_channel.channel = ISC_LIST_HEAD(lcfg->channels);
+
+	destination.file.stream = stderr;
+	destination.file.name = NULL;
+	destination.file.versions = ISC_LOG_ROLLNEVER;
+	destination.file.suffix = isc_log_rollsuffix_increment;
+	destination.file.maximum_size = 0;
+	isc_log_createchannel(lcfg, "default_debug", ISC_LOG_TOFILEDESC,
+			      ISC_LOG_DYNAMIC, &destination, ISC_LOG_PRINTTIME);
+
+	isc_log_createchannel(lcfg, "null", ISC_LOG_TONULL, ISC_LOG_DYNAMIC,
+			      NULL, 0);
+
+	*lcfgp = lcfg;
+}
+
+void
+isc_logconfig_use(isc_log_t *lctx, isc_logconfig_t *lcfg) {
+	isc_logconfig_t *old_cfg;
+
+	REQUIRE(VALID_CONTEXT(lctx));
+	REQUIRE(VALID_CONFIG(lcfg));
+	REQUIRE(lcfg->lctx == lctx);
+
+	/*
+	 * Ensure that lcfg->channellist_count == lctx->category_count.
+	 * They won't be equal if isc_log_usechannel has not been called
+	 * since any call to isc_log_registercategories.
+	 */
+	sync_channellist(lcfg);
+
+	WRLOCK(&lctx->lcfg_rwl);
+	old_cfg = lctx->logconfig;
+	lctx->logconfig = lcfg;
+	sync_highest_level(lctx, lcfg);
+	WRUNLOCK(&lctx->lcfg_rwl);
+
+	isc_logconfig_destroy(&old_cfg);
+}
+
+void
+isc_log_destroy(isc_log_t **lctxp) {
+	isc_log_t *lctx;
+	isc_logconfig_t *lcfg;
+	isc_mem_t *mctx;
+	isc_logmessage_t *message;
+
+	REQUIRE(lctxp != NULL && VALID_CONTEXT(*lctxp));
+
+	lctx = *lctxp;
+	*lctxp = NULL;
+	mctx = lctx->mctx;
+
+	/* Stop the logging as a first thing */
+	atomic_store_release(&lctx->debug_level, 0);
+	atomic_store_release(&lctx->highest_level, 0);
+	atomic_store_release(&lctx->dynamic, false);
+
+	WRLOCK(&lctx->lcfg_rwl);
+	lcfg = lctx->logconfig;
+	lctx->logconfig = NULL;
+	WRUNLOCK(&lctx->lcfg_rwl);
+
+	if (lcfg != NULL) {
+		isc_logconfig_destroy(&lcfg);
+	}
+
+	isc_rwlock_destroy(&lctx->lcfg_rwl);
+	isc_mutex_destroy(&lctx->lock);
+
+	while ((message = ISC_LIST_HEAD(lctx->messages)) != NULL) {
+		ISC_LIST_UNLINK(lctx->messages, message, link);
+
+		isc_mem_put(mctx, message,
+			    sizeof(*message) + strlen(message->text) + 1);
+	}
+
+	lctx->buffer[0] = '\0';
+	lctx->categories = NULL;
+	lctx->category_count = 0;
+	lctx->modules = NULL;
+	lctx->module_count = 0;
+	lctx->mctx = NULL;
+	lctx->magic = 0;
+
+	isc_mem_putanddetach(&mctx, lctx, sizeof(*lctx));
+}
+
+void
+isc_logconfig_destroy(isc_logconfig_t **lcfgp) {
+	isc_logconfig_t *lcfg;
+	isc_mem_t *mctx;
+	isc_logchannel_t *channel;
+	char *filename;
+	unsigned int i;
+
+	REQUIRE(lcfgp != NULL && VALID_CONFIG(*lcfgp));
+
+	lcfg = *lcfgp;
+	*lcfgp = NULL;
+
+	/*
+	 * This function cannot be called with a logconfig that is in
+	 * use by a log context.
+	 */
+	REQUIRE(lcfg->lctx != NULL);
+
+	RDLOCK(&lcfg->lctx->lcfg_rwl);
+	REQUIRE(lcfg->lctx->logconfig != lcfg);
+	RDUNLOCK(&lcfg->lctx->lcfg_rwl);
+
+	mctx = lcfg->lctx->mctx;
+
+	while ((channel = ISC_LIST_HEAD(lcfg->channels)) != NULL) {
+		ISC_LIST_UNLINK(lcfg->channels, channel, link);
+
+		if (channel->type == ISC_LOG_TOFILE) {
+			/*
+			 * The filename for the channel may have ultimately
+			 * started its life in user-land as a const string,
+			 * but in isc_log_createchannel it gets copied
+			 * into writable memory and is not longer truly const.
+			 */
+			DE_CONST(FILE_NAME(channel), filename);
+			isc_mem_free(mctx, filename);
+
+			if (FILE_STREAM(channel) != NULL) {
+				(void)fclose(FILE_STREAM(channel));
+			}
+		}
+
+		isc_mem_free(mctx, channel->name);
+		isc_mem_put(mctx, channel, sizeof(*channel));
+	}
+
+	for (i = 0; i < lcfg->channellist_count; i++) {
+		isc_logchannellist_t *item;
+		while ((item = ISC_LIST_HEAD(lcfg->channellists[i])) != NULL) {
+			ISC_LIST_UNLINK(lcfg->channellists[i], item, link);
+			isc_mem_put(mctx, item, sizeof(*item));
+		}
+	}
+
+	if (lcfg->channellist_count > 0) {
+		isc_mem_put(mctx, lcfg->channellists,
+			    lcfg->channellist_count *
+				    sizeof(ISC_LIST(isc_logchannellist_t)));
+	}
+
+	lcfg->dynamic = false;
+	if (lcfg->tag != NULL) {
+		isc_mem_free(lcfg->lctx->mctx, lcfg->tag);
+	}
+	lcfg->tag = NULL;
+	lcfg->highest_level = 0;
+	lcfg->duplicate_interval = 0;
+	lcfg->magic = 0;
+
+	isc_mem_put(mctx, lcfg, sizeof(*lcfg));
+}
+
+void
+isc_log_registercategories(isc_log_t *lctx, isc_logcategory_t categories[]) {
+	isc_logcategory_t *catp;
+
+	REQUIRE(VALID_CONTEXT(lctx));
+	REQUIRE(categories != NULL && categories[0].name != NULL);
+
+	/*
+	 * XXXDCL This somewhat sleazy situation of using the last pointer
+	 * in one category array to point to the next array exists because
+	 * this registration function returns void and I didn't want to have
+	 * change everything that used it by making it return an isc_result_t.
+	 * It would need to do that if it had to allocate memory to store
+	 * pointers to each array passed in.
+	 */
+	if (lctx->categories == NULL) {
+		lctx->categories = categories;
+	} else {
+		/*
+		 * Adjust the last (NULL) pointer of the already registered
+		 * categories to point to the incoming array.
+		 */
+		for (catp = lctx->categories; catp->name != NULL;) {
+			if (catp->id == UINT_MAX) {
+				/*
+				 * The name pointer points to the next array.
+				 * Ick.
+				 */
+				DE_CONST(catp->name, catp);
+			} else {
+				catp++;
+			}
+		}
+
+		catp->name = (void *)categories;
+		catp->id = UINT_MAX;
+	}
+
+	/*
+	 * Update the id number of the category with its new global id.
+	 */
+	for (catp = categories; catp->name != NULL; catp++) {
+		catp->id = lctx->category_count++;
+	}
+}
+
+isc_logcategory_t *
+isc_log_categorybyname(isc_log_t *lctx, const char *name) {
+	isc_logcategory_t *catp;
+
+	REQUIRE(VALID_CONTEXT(lctx));
+	REQUIRE(name != NULL);
+
+	for (catp = lctx->categories; catp->name != NULL;) {
+		if (catp->id == UINT_MAX) {
+			/*
+			 * catp is neither modified nor returned to the
+			 * caller, so removing its const qualifier is ok.
+			 */
+			DE_CONST(catp->name, catp);
+		} else {
+			if (strcmp(catp->name, name) == 0) {
+				return (catp);
+			}
+			catp++;
+		}
+	}
+
+	return (NULL);
+}
+
+void
+isc_log_registermodules(isc_log_t *lctx, isc_logmodule_t modules[]) {
+	isc_logmodule_t *modp;
+
+	REQUIRE(VALID_CONTEXT(lctx));
+	REQUIRE(modules != NULL && modules[0].name != NULL);
+
+	/*
+	 * XXXDCL This somewhat sleazy situation of using the last pointer
+	 * in one category array to point to the next array exists because
+	 * this registration function returns void and I didn't want to have
+	 * change everything that used it by making it return an isc_result_t.
+	 * It would need to do that if it had to allocate memory to store
+	 * pointers to each array passed in.
+	 */
+	if (lctx->modules == NULL) {
+		lctx->modules = modules;
+	} else {
+		/*
+		 * Adjust the last (NULL) pointer of the already registered
+		 * modules to point to the incoming array.
+		 */
+		for (modp = lctx->modules; modp->name != NULL;) {
+			if (modp->id == UINT_MAX) {
+				/*
+				 * The name pointer points to the next array.
+				 * Ick.
+				 */
+				DE_CONST(modp->name, modp);
+			} else {
+				modp++;
+			}
+		}
+
+		modp->name = (void *)modules;
+		modp->id = UINT_MAX;
+	}
+
+	/*
+	 * Update the id number of the module with its new global id.
+	 */
+	for (modp = modules; modp->name != NULL; modp++) {
+		modp->id = lctx->module_count++;
+	}
+}
+
+isc_logmodule_t *
+isc_log_modulebyname(isc_log_t *lctx, const char *name) {
+	isc_logmodule_t *modp;
+
+	REQUIRE(VALID_CONTEXT(lctx));
+	REQUIRE(name != NULL);
+
+	for (modp = lctx->modules; modp->name != NULL;) {
+		if (modp->id == UINT_MAX) {
+			/*
+			 * modp is neither modified nor returned to the
+			 * caller, so removing its const qualifier is ok.
+			 */
+			DE_CONST(modp->name, modp);
+		} else {
+			if (strcmp(modp->name, name) == 0) {
+				return (modp);
+			}
+			modp++;
+		}
+	}
+
+	return (NULL);
+}
+
+void
+isc_log_createchannel(isc_logconfig_t *lcfg, const char *name,
+		      unsigned int type, int level,
+		      const isc_logdestination_t *destination,
+		      unsigned int flags) {
+	isc_logchannel_t *channel;
+	isc_mem_t *mctx;
+	unsigned int permitted = ISC_LOG_PRINTALL | ISC_LOG_DEBUGONLY |
+				 ISC_LOG_BUFFERED | ISC_LOG_ISO8601 |
+				 ISC_LOG_UTC;
+
+	REQUIRE(VALID_CONFIG(lcfg));
+	REQUIRE(name != NULL);
+	REQUIRE(type == ISC_LOG_TOSYSLOG || type == ISC_LOG_TOFILE ||
+		type == ISC_LOG_TOFILEDESC || type == ISC_LOG_TONULL);
+	REQUIRE(destination != NULL || type == ISC_LOG_TONULL);
+	REQUIRE(level >= ISC_LOG_CRITICAL);
+	REQUIRE((flags & ~permitted) == 0);
+
+	/* XXXDCL find duplicate names? */
+
+	mctx = lcfg->lctx->mctx;
+
+	channel = isc_mem_get(mctx, sizeof(*channel));
+
+	channel->name = isc_mem_strdup(mctx, name);
+
+	channel->type = type;
+	channel->level = level;
+	channel->flags = flags;
+	ISC_LINK_INIT(channel, link);
+
+	switch (type) {
+	case ISC_LOG_TOSYSLOG:
+		FACILITY(channel) = destination->facility;
+		break;
+
+	case ISC_LOG_TOFILE:
+		/*
+		 * The file name is copied because greatest_version wants
+		 * to scribble on it, so it needs to be definitely in
+		 * writable memory.
+		 */
+		FILE_NAME(channel) = isc_mem_strdup(mctx,
+						    destination->file.name);
+		FILE_STREAM(channel) = NULL;
+		FILE_VERSIONS(channel) = destination->file.versions;
+		FILE_SUFFIX(channel) = destination->file.suffix;
+		FILE_MAXSIZE(channel) = destination->file.maximum_size;
+		FILE_MAXREACHED(channel) = false;
+		break;
+
+	case ISC_LOG_TOFILEDESC:
+		FILE_NAME(channel) = NULL;
+		FILE_STREAM(channel) = destination->file.stream;
+		FILE_MAXSIZE(channel) = 0;
+		FILE_VERSIONS(channel) = ISC_LOG_ROLLNEVER;
+		FILE_SUFFIX(channel) = isc_log_rollsuffix_increment;
+		break;
+
+	case ISC_LOG_TONULL:
+		/* Nothing. */
+		break;
+
+	default:
+		UNREACHABLE();
+	}
+
+	ISC_LIST_PREPEND(lcfg->channels, channel, link);
+
+	/*
+	 * If default_stderr was redefined, make the default category
+	 * point to the new default_stderr.
+	 */
+	if (strcmp(name, "default_stderr") == 0) {
+		default_channel.channel = channel;
+	}
+}
+
+isc_result_t
+isc_log_usechannel(isc_logconfig_t *lcfg, const char *name,
+		   const isc_logcategory_t *category,
+		   const isc_logmodule_t *module) {
+	isc_log_t *lctx;
+	isc_logchannel_t *channel;
+
+	REQUIRE(VALID_CONFIG(lcfg));
+	REQUIRE(name != NULL);
+
+	lctx = lcfg->lctx;
+
+	REQUIRE(category == NULL || category->id < lctx->category_count);
+	REQUIRE(module == NULL || module->id < lctx->module_count);
+
+	for (channel = ISC_LIST_HEAD(lcfg->channels); channel != NULL;
+	     channel = ISC_LIST_NEXT(channel, link))
+	{
+		if (strcmp(name, channel->name) == 0) {
+			break;
+		}
+	}
+
+	if (channel == NULL) {
+		return (ISC_R_NOTFOUND);
+	}
+
+	if (category != NULL) {
+		assignchannel(lcfg, category->id, module, channel);
+	} else {
+		/*
+		 * Assign to all categories.  Note that this includes
+		 * the default channel.
+		 */
+		for (size_t i = 0; i < lctx->category_count; i++) {
+			assignchannel(lcfg, i, module, channel);
+		}
+	}
+
+	/*
+	 * Update the highest logging level, if the current lcfg is in use.
+	 */
+	if (lcfg->lctx->logconfig == lcfg) {
+		sync_highest_level(lctx, lcfg);
+	}
+
+	return (ISC_R_SUCCESS);
+}
+
+void
+isc_log_write(isc_log_t *lctx, isc_logcategory_t *category,
+	      isc_logmodule_t *module, int level, const char *format, ...) {
+	va_list args;
+
+	/*
+	 * Contract checking is done in isc_log_doit().
+	 */
+
+	va_start(args, format);
+	isc_log_doit(lctx, category, module, level, false, format, args);
+	va_end(args);
+}
+
+void
+isc_log_vwrite(isc_log_t *lctx, isc_logcategory_t *category,
+	       isc_logmodule_t *module, int level, const char *format,
+	       va_list args) {
+	/*
+	 * Contract checking is done in isc_log_doit().
+	 */
+	isc_log_doit(lctx, category, module, level, false, format, args);
+}
+
+void
+isc_log_write1(isc_log_t *lctx, isc_logcategory_t *category,
+	       isc_logmodule_t *module, int level, const char *format, ...) {
+	va_list args;
+
+	/*
+	 * Contract checking is done in isc_log_doit().
+	 */
+
+	va_start(args, format);
+	isc_log_doit(lctx, category, module, level, true, format, args);
+	va_end(args);
+}
+
+void
+isc_log_vwrite1(isc_log_t *lctx, isc_logcategory_t *category,
+		isc_logmodule_t *module, int level, const char *format,
+		va_list args) {
+	/*
+	 * Contract checking is done in isc_log_doit().
+	 */
+	isc_log_doit(lctx, category, module, level, true, format, args);
+}
+
+void
+isc_log_setcontext(isc_log_t *lctx) {
+	isc_lctx = lctx;
+}
+
+void
+isc_log_setdebuglevel(isc_log_t *lctx, unsigned int level) {
+	REQUIRE(VALID_CONTEXT(lctx));
+
+	atomic_store_release(&lctx->debug_level, level);
+	/*
+	 * Close ISC_LOG_DEBUGONLY channels if level is zero.
+	 */
+	if (level == 0) {
+		RDLOCK(&lctx->lcfg_rwl);
+		isc_logconfig_t *lcfg = lctx->logconfig;
+		if (lcfg != NULL) {
+			LOCK(&lctx->lock);
+			for (isc_logchannel_t *channel =
+				     ISC_LIST_HEAD(lcfg->channels);
+			     channel != NULL;
+			     channel = ISC_LIST_NEXT(channel, link))
+			{
+				if (channel->type == ISC_LOG_TOFILE &&
+				    (channel->flags & ISC_LOG_DEBUGONLY) != 0 &&
+				    FILE_STREAM(channel) != NULL)
+				{
+					(void)fclose(FILE_STREAM(channel));
+					FILE_STREAM(channel) = NULL;
+				}
+			}
+			UNLOCK(&lctx->lock);
+		}
+		RDUNLOCK(&lctx->lcfg_rwl);
+	}
+}
+
+unsigned int
+isc_log_getdebuglevel(isc_log_t *lctx) {
+	REQUIRE(VALID_CONTEXT(lctx));
+
+	return (atomic_load_acquire(&lctx->debug_level));
+}
+
+void
+isc_log_setduplicateinterval(isc_logconfig_t *lcfg, unsigned int interval) {
+	REQUIRE(VALID_CONFIG(lcfg));
+
+	lcfg->duplicate_interval = interval;
+}
+
+unsigned int
+isc_log_getduplicateinterval(isc_logconfig_t *lcfg) {
+	REQUIRE(VALID_CONTEXT(lcfg));
+
+	return (lcfg->duplicate_interval);
+}
+
+void
+isc_log_settag(isc_logconfig_t *lcfg, const char *tag) {
+	REQUIRE(VALID_CONFIG(lcfg));
+
+	if (tag != NULL && *tag != '\0') {
+		if (lcfg->tag != NULL) {
+			isc_mem_free(lcfg->lctx->mctx, lcfg->tag);
+		}
+		lcfg->tag = isc_mem_strdup(lcfg->lctx->mctx, tag);
+	} else {
+		if (lcfg->tag != NULL) {
+			isc_mem_free(lcfg->lctx->mctx, lcfg->tag);
+		}
+		lcfg->tag = NULL;
+	}
+}
+
+char *
+isc_log_gettag(isc_logconfig_t *lcfg) {
+	REQUIRE(VALID_CONFIG(lcfg));
+
+	return (lcfg->tag);
+}
+
+/* XXXDCL NT  -- This interface will assuredly be changing. */
+void
+isc_log_opensyslog(const char *tag, int options, int facility) {
+	(void)openlog(tag, options, facility);
+}
+
+void
+isc_log_closefilelogs(isc_log_t *lctx) {
+	REQUIRE(VALID_CONTEXT(lctx));
+
+	RDLOCK(&lctx->lcfg_rwl);
+	isc_logconfig_t *lcfg = lctx->logconfig;
+	if (lcfg != NULL) {
+		LOCK(&lctx->lock);
+		for (isc_logchannel_t *channel = ISC_LIST_HEAD(lcfg->channels);
+		     channel != NULL; channel = ISC_LIST_NEXT(channel, link))
+		{
+			if (channel->type == ISC_LOG_TOFILE &&
+			    FILE_STREAM(channel) != NULL)
+			{
+				(void)fclose(FILE_STREAM(channel));
+				FILE_STREAM(channel) = NULL;
+			}
+		}
+		UNLOCK(&lctx->lock);
+	}
+	RDUNLOCK(&lctx->lcfg_rwl);
+}
+
+/****
+**** Internal functions
+****/
+
+static void
+assignchannel(isc_logconfig_t *lcfg, unsigned int category_id,
+	      const isc_logmodule_t *module, isc_logchannel_t *channel) {
+	isc_logchannellist_t *new_item;
+	isc_log_t *lctx;
+
+	REQUIRE(VALID_CONFIG(lcfg));
+
+	lctx = lcfg->lctx;
+
+	REQUIRE(category_id < lctx->category_count);
+	REQUIRE(module == NULL || module->id < lctx->module_count);
+	REQUIRE(channel != NULL);
+
+	/*
+	 * Ensure lcfg->channellist_count == lctx->category_count.
+	 */
+	sync_channellist(lcfg);
+
+	new_item = isc_mem_get(lctx->mctx, sizeof(*new_item));
+
+	new_item->channel = channel;
+	new_item->module = module;
+	ISC_LIST_INITANDPREPEND(lcfg->channellists[category_id], new_item,
+				link);
+
+	/*
+	 * Remember the highest logging level set by any channel in the
+	 * logging config, so isc_log_doit() can quickly return if the
+	 * message is too high to be logged by any channel.
+	 */
+	if (channel->type != ISC_LOG_TONULL) {
+		if (lcfg->highest_level < channel->level) {
+			lcfg->highest_level = channel->level;
+		}
+		if (channel->level == ISC_LOG_DYNAMIC) {
+			lcfg->dynamic = true;
+		}
+	}
+}
+
+/*
+ * This would ideally be part of isc_log_registercategories(), except then
+ * that function would have to return isc_result_t instead of void.
+ */
+static void
+sync_channellist(isc_logconfig_t *lcfg) {
+	unsigned int bytes;
+	isc_log_t *lctx;
+	void *lists;
+
+	REQUIRE(VALID_CONFIG(lcfg));
+
+	lctx = lcfg->lctx;
+
+	REQUIRE(lctx->category_count != 0);
+
+	if (lctx->category_count == lcfg->channellist_count) {
+		return;
+	}
+
+	bytes = lctx->category_count * sizeof(ISC_LIST(isc_logchannellist_t));
+
+	lists = isc_mem_get(lctx->mctx, bytes);
+
+	memset(lists, 0, bytes);
+
+	if (lcfg->channellist_count != 0) {
+		bytes = lcfg->channellist_count *
+			sizeof(ISC_LIST(isc_logchannellist_t));
+		memmove(lists, lcfg->channellists, bytes);
+		isc_mem_put(lctx->mctx, lcfg->channellists, bytes);
+	}
+
+	lcfg->channellists = lists;
+	lcfg->channellist_count = lctx->category_count;
+}
+
+static void
+sync_highest_level(isc_log_t *lctx, isc_logconfig_t *lcfg) {
+	atomic_store(&lctx->highest_level, lcfg->highest_level);
+	atomic_store(&lctx->dynamic, lcfg->dynamic);
+}
+
+static isc_result_t
+greatest_version(isc_logfile_t *file, int versions, int *greatestp) {
+	char *bname, *digit_end;
+	const char *dirname;
+	int version, greatest = -1;
+	size_t bnamelen;
+	isc_dir_t dir;
+	isc_result_t result;
+	char sep = '/';
+#ifdef _WIN32
+	char *bname2;
+#endif /* ifdef _WIN32 */
+
+	/*
+	 * It is safe to DE_CONST the file.name because it was copied
+	 * with isc_mem_strdup().
+	 */
+	bname = strrchr(file->name, sep);
+#ifdef _WIN32
+	bname2 = strrchr(file->name, '\\');
+	if ((bname != NULL && bname2 != NULL && bname2 > bname) ||
+	    (bname == NULL && bname2 != NULL))
+	{
+		bname = bname2;
+		sep = '\\';
+	}
+#endif /* ifdef _WIN32 */
+	if (bname != NULL) {
+		*bname++ = '\0';
+		dirname = file->name;
+	} else {
+		DE_CONST(file->name, bname);
+		dirname = ".";
+	}
+	bnamelen = strlen(bname);
+
+	isc_dir_init(&dir);
+	result = isc_dir_open(&dir, dirname);
+
+	/*
+	 * Replace the file separator if it was taken out.
+	 */
+	if (bname != file->name) {
+		*(bname - 1) = sep;
+	}
+
+	/*
+	 * Return if the directory open failed.
+	 */
+	if (result != ISC_R_SUCCESS) {
+		return (result);
+	}
+
+	while (isc_dir_read(&dir) == ISC_R_SUCCESS) {
+		if (dir.entry.length > bnamelen &&
+		    strncmp(dir.entry.name, bname, bnamelen) == 0 &&
+		    dir.entry.name[bnamelen] == '.')
+		{
+			version = strtol(&dir.entry.name[bnamelen + 1],
+					 &digit_end, 10);
+			/*
+			 * Remove any backup files that exceed versions.
+			 */
+			if (*digit_end == '\0' && version >= versions) {
+				result = isc_file_remove(dir.entry.name);
+				if (result != ISC_R_SUCCESS &&
+				    result != ISC_R_FILENOTFOUND)
+				{
+					syslog(LOG_ERR,
+					       "unable to remove "
+					       "log file '%s': %s",
+					       dir.entry.name,
+					       isc_result_totext(result));
+				}
+			} else if (*digit_end == '\0' && version > greatest) {
+				greatest = version;
+			}
+		}
+	}
+	isc_dir_close(&dir);
+
+	*greatestp = greatest;
+
+	return (ISC_R_SUCCESS);
+}
+
+static void
+insert_sort(int64_t to_keep[], int64_t versions, int64_t version) {
+	int i = 0;
+	while (i < versions && version < to_keep[i]) {
+		i++;
+	}
+	if (i == versions) {
+		return;
+	}
+	if (i < versions - 1) {
+		memmove(&to_keep[i + 1], &to_keep[i],
+			sizeof(to_keep[0]) * (versions - i - 1));
+	}
+	to_keep[i] = version;
+}
+
+static int64_t
+last_to_keep(int64_t versions, isc_dir_t *dirp, char *bname, size_t bnamelen) {
+	int64_t to_keep[ISC_LOG_MAX_VERSIONS] = { 0 };
+	int64_t version = 0;
+
+	if (versions <= 0) {
+		return (INT64_MAX);
+	}
+
+	if (versions > ISC_LOG_MAX_VERSIONS) {
+		versions = ISC_LOG_MAX_VERSIONS;
+	}
+	/*
+	 * First we fill 'to_keep' structure using insertion sort
+	 */
+	memset(to_keep, 0, sizeof(to_keep));
+	while (isc_dir_read(dirp) == ISC_R_SUCCESS) {
+		char *digit_end = NULL;
+		char *ename = NULL;
+
+		if (dirp->entry.length <= bnamelen ||
+		    strncmp(dirp->entry.name, bname, bnamelen) != 0 ||
+		    dirp->entry.name[bnamelen] != '.')
+		{
+			continue;
+		}
+
+		ename = &dirp->entry.name[bnamelen + 1];
+		version = strtoull(ename, &digit_end, 10);
+		if (*digit_end == '\0') {
+			insert_sort(to_keep, versions, version);
+		}
+	}
+
+	isc_dir_reset(dirp);
+
+	/*
+	 * to_keep[versions - 1] is the last one we want to keep
+	 */
+	return (to_keep[versions - 1]);
+}
+
+static isc_result_t
+remove_old_tsversions(isc_logfile_t *file, int versions) {
+	isc_result_t result;
+	char *bname = NULL, *digit_end = NULL;
+	const char *dirname = NULL;
+	int64_t version, last = INT64_MAX;
+	size_t bnamelen;
+	isc_dir_t dir;
+	char sep = '/';
+#ifdef _WIN32
+	char *bname2;
+#endif /* ifdef _WIN32 */
+	/*
+	 * It is safe to DE_CONST the file.name because it was copied
+	 * with isc_mem_strdup().
+	 */
+	bname = strrchr(file->name, sep);
+#ifdef _WIN32
+	bname2 = strrchr(file->name, '\\');
+	if ((bname != NULL && bname2 != NULL && bname2 > bname) ||
+	    (bname == NULL && bname2 != NULL))
+	{
+		bname = bname2;
+		sep = '\\';
+	}
+#endif /* ifdef _WIN32 */
+	if (bname != NULL) {
+		*bname++ = '\0';
+		dirname = file->name;
+	} else {
+		DE_CONST(file->name, bname);
+		dirname = ".";
+	}
+	bnamelen = strlen(bname);
+
+	isc_dir_init(&dir);
+	result = isc_dir_open(&dir, dirname);
+
+	/*
+	 * Replace the file separator if it was taken out.
+	 */
+	if (bname != file->name) {
+		*(bname - 1) = sep;
+	}
+
+	/*
+	 * Return if the directory open failed.
+	 */
+	if (result != ISC_R_SUCCESS) {
+		return (result);
+	}
+
+	last = last_to_keep(versions, &dir, bname, bnamelen);
+
+	/*
+	 * Then we remove all files that we don't want to_keep
+	 */
+	while (isc_dir_read(&dir) == ISC_R_SUCCESS) {
+		if (dir.entry.length > bnamelen &&
+		    strncmp(dir.entry.name, bname, bnamelen) == 0 &&
+		    dir.entry.name[bnamelen] == '.')
+		{
+			char *ename = &dir.entry.name[bnamelen + 1];
+			version = strtoull(ename, &digit_end, 10);
+			/*
+			 * Remove any backup files that exceed versions.
+			 */
+			if (*digit_end == '\0' && version < last) {
+				result = isc_file_remove(dir.entry.name);
+				if (result != ISC_R_SUCCESS &&
+				    result != ISC_R_FILENOTFOUND)
+				{
+					syslog(LOG_ERR,
+					       "unable to remove "
+					       "log file '%s': %s",
+					       dir.entry.name,
+					       isc_result_totext(result));
+				}
+			}
+		}
+	}
+
+	isc_dir_close(&dir);
+
+	return (ISC_R_SUCCESS);
+}
+
+static isc_result_t
+roll_increment(isc_logfile_t *file) {
+	int i, n, greatest;
+	char current[PATH_MAX + 1];
+	char newpath[PATH_MAX + 1];
+	const char *path;
+	isc_result_t result = ISC_R_SUCCESS;
+
+	REQUIRE(file != NULL);
+	REQUIRE(file->versions != 0);
+
+	path = file->name;
+
+	if (file->versions == ISC_LOG_ROLLINFINITE) {
+		/*
+		 * Find the first missing entry in the log file sequence.
+		 */
+		for (greatest = 0; greatest < INT_MAX; greatest++) {
+			n = snprintf(current, sizeof(current), "%s.%u", path,
+				     (unsigned)greatest);
+			if (n >= (int)sizeof(current) || n < 0 ||
+			    !isc_file_exists(current))
+			{
+				break;
+			}
+		}
+	} else {
+		/*
+		 * Get the largest existing version and remove any
+		 * version greater than the permitted version.
+		 */
+		result = greatest_version(file, file->versions, &greatest);
+		if (result != ISC_R_SUCCESS) {
+			return (result);
+		}
+
+		/*
+		 * Increment if greatest is not the actual maximum value.
+		 */
+		if (greatest < file->versions - 1) {
+			greatest++;
+		}
+	}
+
+	for (i = greatest; i > 0; i--) {
+		result = ISC_R_SUCCESS;
+		n = snprintf(current, sizeof(current), "%s.%u", path,
+			     (unsigned)(i - 1));
+		if (n >= (int)sizeof(current) || n < 0) {
+			result = ISC_R_NOSPACE;
+		}
+		if (result == ISC_R_SUCCESS) {
+			n = snprintf(newpath, sizeof(newpath), "%s.%u", path,
+				     (unsigned)i);
+			if (n >= (int)sizeof(newpath) || n < 0) {
+				result = ISC_R_NOSPACE;
+			}
+		}
+		if (result == ISC_R_SUCCESS) {
+			result = isc_file_rename(current, newpath);
+		}
+		if (result != ISC_R_SUCCESS && result != ISC_R_FILENOTFOUND) {
+			syslog(LOG_ERR,
+			       "unable to rename log file '%s.%u' to "
+			       "'%s.%u': %s",
+			       path, i - 1, path, i, isc_result_totext(result));
+		}
+	}
+
+	n = snprintf(newpath, sizeof(newpath), "%s.0", path);
+	if (n >= (int)sizeof(newpath) || n < 0) {
+		result = ISC_R_NOSPACE;
+	} else {
+		result = isc_file_rename(path, newpath);
+	}
+	if (result != ISC_R_SUCCESS && result != ISC_R_FILENOTFOUND) {
+		syslog(LOG_ERR, "unable to rename log file '%s' to '%s.0': %s",
+		       path, path, isc_result_totext(result));
+	}
+
+	return (ISC_R_SUCCESS);
+}
+
+static isc_result_t
+roll_timestamp(isc_logfile_t *file) {
+	int n;
+	char newts[PATH_MAX + 1];
+	char newpath[PATH_MAX + 1];
+	const char *path;
+	isc_time_t now;
+	isc_result_t result = ISC_R_SUCCESS;
+
+	REQUIRE(file != NULL);
+	REQUIRE(file->versions != 0);
+
+	path = file->name;
+
+	/*
+	 * First find all the logfiles and remove the oldest ones
+	 * Save one fewer than file->versions because we'll be renaming
+	 * the existing file to a timestamped version after this.
+	 */
+	if (file->versions != ISC_LOG_ROLLINFINITE) {
+		remove_old_tsversions(file, file->versions - 1);
+	}
+
+	/* Then just rename the current logfile */
+	isc_time_now(&now);
+	isc_time_formatshorttimestamp(&now, newts, PATH_MAX + 1);
+	n = snprintf(newpath, sizeof(newpath), "%s.%s", path, newts);
+	if (n >= (int)sizeof(newpath) || n < 0) {
+		result = ISC_R_NOSPACE;
+	} else {
+		result = isc_file_rename(path, newpath);
+	}
+	if (result != ISC_R_SUCCESS && result != ISC_R_FILENOTFOUND) {
+		syslog(LOG_ERR, "unable to rename log file '%s' to '%s.0': %s",
+		       path, path, isc_result_totext(result));
+	}
+
+	return (ISC_R_SUCCESS);
+}
+
+isc_result_t
+isc_logfile_roll(isc_logfile_t *file) {
+	isc_result_t result;
+
+	REQUIRE(file != NULL);
+
+	/*
+	 * Do nothing (not even excess version trimming) if ISC_LOG_ROLLNEVER
+	 * is specified.  Apparently complete external control over the log
+	 * files is desired.
+	 */
+	if (file->versions == ISC_LOG_ROLLNEVER) {
+		return (ISC_R_SUCCESS);
+	} else if (file->versions == 0) {
+		result = isc_file_remove(file->name);
+		if (result != ISC_R_SUCCESS && result != ISC_R_FILENOTFOUND) {
+			syslog(LOG_ERR, "unable to remove log file '%s': %s",
+			       file->name, isc_result_totext(result));
+		}
+		return (ISC_R_SUCCESS);
+	}
+
+	switch (file->suffix) {
+	case isc_log_rollsuffix_increment:
+		return (roll_increment(file));
+	case isc_log_rollsuffix_timestamp:
+		return (roll_timestamp(file));
+	default:
+		return (ISC_R_UNEXPECTED);
+	}
+}
+
+static isc_result_t
+isc_log_open(isc_logchannel_t *channel) {
+	struct stat statbuf;
+	bool regular_file;
+	bool roll = false;
+	isc_result_t result = ISC_R_SUCCESS;
+	const char *path;
+
+	REQUIRE(channel->type == ISC_LOG_TOFILE);
+	REQUIRE(FILE_STREAM(channel) == NULL);
+
+	path = FILE_NAME(channel);
+
+	REQUIRE(path != NULL && *path != '\0');
+
+	/*
+	 * Determine type of file; only regular files will be
+	 * version renamed, and only if the base file exists
+	 * and either has no size limit or has reached its size limit.
+	 */
+	if (stat(path, &statbuf) == 0) {
+		regular_file = S_ISREG(statbuf.st_mode) ? true : false;
+		/* XXXDCL if not regular_file complain? */
+		if ((FILE_MAXSIZE(channel) == 0 &&
+		     FILE_VERSIONS(channel) != ISC_LOG_ROLLNEVER) ||
+		    (FILE_MAXSIZE(channel) > 0 &&
+		     statbuf.st_size >= FILE_MAXSIZE(channel)))
+		{
+			roll = regular_file;
+		}
+	} else if (errno == ENOENT) {
+		regular_file = true;
+		POST(regular_file);
+	} else {
+		result = ISC_R_INVALIDFILE;
+	}
+
+	/*
+	 * Version control.
+	 */
+	if (result == ISC_R_SUCCESS && roll) {
+		if (FILE_VERSIONS(channel) == ISC_LOG_ROLLNEVER) {
+			return (ISC_R_MAXSIZE);
+		}
+		result = isc_logfile_roll(&channel->destination.file);
+		if (result != ISC_R_SUCCESS) {
+			if ((channel->flags & ISC_LOG_OPENERR) == 0) {
+				syslog(LOG_ERR,
+				       "isc_log_open: isc_logfile_roll '%s' "
+				       "failed: %s",
+				       FILE_NAME(channel),
+				       isc_result_totext(result));
+				channel->flags |= ISC_LOG_OPENERR;
+			}
+			return (result);
+		}
+	}
+
+	result = isc_stdio_open(path, "a", &FILE_STREAM(channel));
+
+	return (result);
+}
+
+ISC_NO_SANITIZE_THREAD bool
+isc_log_wouldlog(isc_log_t *lctx, int level) {
+	/*
+	 * Try to avoid locking the mutex for messages which can't
+	 * possibly be logged to any channels -- primarily debugging
+	 * messages that the debug level is not high enough to print.
+	 *
+	 * If the level is (mathematically) less than or equal to the
+	 * highest_level, or if there is a dynamic channel and the level is
+	 * less than or equal to the debug level, the main loop must be
+	 * entered to see if the message should really be output.
+	 */
+	if (lctx == NULL) {
+		return (false);
+	}
+
+	int highest_level = atomic_load_acquire(&lctx->highest_level);
+	if (level <= highest_level) {
+		return (true);
+	}
+	if (atomic_load_acquire(&lctx->dynamic)) {
+		int debug_level = atomic_load_acquire(&lctx->debug_level);
+		if (level <= debug_level) {
+			return (true);
+		}
+	}
+
+	return (false);
+}
+
+static void
+isc_log_doit(isc_log_t *lctx, isc_logcategory_t *category,
+	     isc_logmodule_t *module, int level, bool write_once,
+	     const char *format, va_list args) {
+	int syslog_level;
+	const char *time_string;
+	char local_time[64];
+	char iso8601z_string[64];
+	char iso8601l_string[64];
+	char level_string[24] = { 0 };
+	struct stat statbuf;
+	bool matched = false;
+	bool printtime, iso8601, utc, printtag, printcolon;
+	bool printcategory, printmodule, printlevel, buffered;
+	isc_logchannel_t *channel;
+	isc_logchannellist_t *category_channels;
+	isc_result_t result;
+
+	REQUIRE(lctx == NULL || VALID_CONTEXT(lctx));
+	REQUIRE(category != NULL);
+	REQUIRE(module != NULL);
+	REQUIRE(level != ISC_LOG_DYNAMIC);
+	REQUIRE(format != NULL);
+
+	/*
+	 * Programs can use libraries that use this logging code without
+	 * wanting to do any logging, thus the log context is allowed to
+	 * be non-existent.
+	 */
+	if (lctx == NULL) {
+		return;
+	}
+
+	REQUIRE(category->id < lctx->category_count);
+	REQUIRE(module->id < lctx->module_count);
+
+	if (!isc_log_wouldlog(lctx, level)) {
+		return;
+	}
+
+	local_time[0] = '\0';
+	iso8601l_string[0] = '\0';
+	iso8601z_string[0] = '\0';
+
+	RDLOCK(&lctx->lcfg_rwl);
+	LOCK(&lctx->lock);
+
+	lctx->buffer[0] = '\0';
+
+	isc_logconfig_t *lcfg = lctx->logconfig;
+
+	category_channels = ISC_LIST_HEAD(lcfg->channellists[category->id]);
+
+	/*
+	 * XXXDCL add duplicate filtering? (To not write multiple times
+	 * to the same source via various channels).
+	 */
+	do {
+		/*
+		 * If the channel list end was reached and a match was
+		 * made, everything is finished.
+		 */
+		if (category_channels == NULL && matched) {
+			break;
+		}
+
+		if (category_channels == NULL && !matched &&
+		    category_channels != ISC_LIST_HEAD(lcfg->channellists[0]))
+		{
+			/*
+			 * No category/module pair was explicitly
+			 * configured. Try the category named "default".
+			 */
+			category_channels =
+				ISC_LIST_HEAD(lcfg->channellists[0]);
+		}
+
+		if (category_channels == NULL && !matched) {
+			/*
+			 * No matching module was explicitly configured
+			 * for the category named "default".  Use the
+			 * internal default channel.
+			 */
+			category_channels = &default_channel;
+		}
+
+		if (category_channels->module != NULL &&
+		    category_channels->module != module)
+		{
+			category_channels = ISC_LIST_NEXT(category_channels,
+							  link);
+			continue;
+		}
+
+		matched = true;
+
+		channel = category_channels->channel;
+		category_channels = ISC_LIST_NEXT(category_channels, link);
+
+		int_fast32_t dlevel = atomic_load_acquire(&lctx->debug_level);
+		if (((channel->flags & ISC_LOG_DEBUGONLY) != 0) && dlevel == 0)
+		{
+			continue;
+		}
+
+		if (channel->level == ISC_LOG_DYNAMIC) {
+			if (dlevel < level) {
+				continue;
+			}
+		} else if (channel->level < level) {
+			continue;
+		}
+
+		if ((channel->flags & ISC_LOG_PRINTTIME) != 0 &&
+		    local_time[0] == '\0')
+		{
+			isc_time_t isctime;
+
+			TIME_NOW(&isctime);
+
+			isc_time_formattimestamp(&isctime, local_time,
+						 sizeof(local_time));
+			isc_time_formatISO8601ms(&isctime, iso8601z_string,
+						 sizeof(iso8601z_string));
+			isc_time_formatISO8601Lms(&isctime, iso8601l_string,
+						  sizeof(iso8601l_string));
+		}
+
+		if ((channel->flags & ISC_LOG_PRINTLEVEL) != 0 &&
+		    level_string[0] == '\0')
+		{
+			if (level < ISC_LOG_CRITICAL) {
+				snprintf(level_string, sizeof(level_string),
+					 "level %d: ", level);
+			} else if (level > ISC_LOG_DYNAMIC) {
+				snprintf(level_string, sizeof(level_string),
+					 "%s %d: ", log_level_strings[0],
+					 level);
+			} else {
+				snprintf(level_string, sizeof(level_string),
+					 "%s: ", log_level_strings[-level]);
+			}
+		}
+
+		/*
+		 * Only format the message once.
+		 */
+		if (lctx->buffer[0] == '\0') {
+			(void)vsnprintf(lctx->buffer, sizeof(lctx->buffer),
+					format, args);
+
+			/*
+			 * Check for duplicates.
+			 */
+			if (write_once) {
+				isc_logmessage_t *message, *next;
+				isc_time_t oldest;
+				isc_interval_t interval;
+				size_t size;
+
+				isc_interval_set(&interval,
+						 lcfg->duplicate_interval, 0);
+
+				/*
+				 * 'oldest' is the age of the oldest
+				 * messages which fall within the
+				 * duplicate_interval range.
+				 */
+				TIME_NOW(&oldest);
+				if (isc_time_subtract(&oldest, &interval,
+						      &oldest) != ISC_R_SUCCESS)
+				{
+					/*
+					 * Can't effectively do the
+					 * checking without having a
+					 * valid time.
+					 */
+					message = NULL;
+				} else {
+					message = ISC_LIST_HEAD(lctx->messages);
+				}
+
+				while (message != NULL) {
+					if (isc_time_compare(&message->time,
+							     &oldest) < 0)
+					{
+						/*
+						 * This message is older
+						 * than the
+						 * duplicate_interval,
+						 * so it should be
+						 * dropped from the
+						 * history.
+						 *
+						 * Setting the interval
+						 * to be to be longer
+						 * will obviously not
+						 * cause the expired
+						 * message to spring
+						 * back into existence.
+						 */
+						next = ISC_LIST_NEXT(message,
+								     link);
+
+						ISC_LIST_UNLINK(lctx->messages,
+								message, link);
+
+						isc_mem_put(
+							lctx->mctx, message,
+							sizeof(*message) + 1 +
+								strlen(message->text));
+
+						message = next;
+						continue;
+					}
+
+					/*
+					 * This message is in the
+					 * duplicate filtering interval
+					 * ...
+					 */
+					if (strcmp(lctx->buffer,
+						   message->text) == 0)
+					{
+						/*
+						 * ... and it is a
+						 * duplicate. Unlock the
+						 * mutex and get the
+						 * hell out of Dodge.
+						 */
+						goto unlock;
+					}
+
+					message = ISC_LIST_NEXT(message, link);
+				}
+
+				/*
+				 * It wasn't in the duplicate interval,
+				 * so add it to the message list.
+				 */
+				size = sizeof(isc_logmessage_t) +
+				       strlen(lctx->buffer) + 1;
+				message = isc_mem_get(lctx->mctx, size);
+				message->text = (char *)(message + 1);
+				size -= sizeof(isc_logmessage_t);
+				strlcpy(message->text, lctx->buffer, size);
+				TIME_NOW(&message->time);
+				ISC_LINK_INIT(message, link);
+				ISC_LIST_APPEND(lctx->messages, message, link);
+			}
+		}
+
+		utc = ((channel->flags & ISC_LOG_UTC) != 0);
+		iso8601 = ((channel->flags & ISC_LOG_ISO8601) != 0);
+		printtime = ((channel->flags & ISC_LOG_PRINTTIME) != 0);
+		printtag = ((channel->flags &
+			     (ISC_LOG_PRINTTAG | ISC_LOG_PRINTPREFIX)) != 0 &&
+			    lcfg->tag != NULL);
+		printcolon = ((channel->flags & ISC_LOG_PRINTTAG) != 0 &&
+			      lcfg->tag != NULL);
+		printcategory = ((channel->flags & ISC_LOG_PRINTCATEGORY) != 0);
+		printmodule = ((channel->flags & ISC_LOG_PRINTMODULE) != 0);
+		printlevel = ((channel->flags & ISC_LOG_PRINTLEVEL) != 0);
+		buffered = ((channel->flags & ISC_LOG_BUFFERED) != 0);
+
+		if (printtime) {
+			if (iso8601) {
+				if (utc) {
+					time_string = iso8601z_string;
+				} else {
+					time_string = iso8601l_string;
+				}
+			} else {
+				time_string = local_time;
+			}
+		} else {
+			time_string = "";
+		}
+
+		switch (channel->type) {
+		case ISC_LOG_TOFILE:
+			if (FILE_MAXREACHED(channel)) {
+				/*
+				 * If the file can be rolled, OR
+				 * If the file no longer exists, OR
+				 * If the file is less than the maximum
+				 * size, (such as if it had been renamed
+				 * and a new one touched, or it was
+				 * truncated in place)
+				 * ... then close it to trigger
+				 * reopening.
+				 */
+				if (FILE_VERSIONS(channel) !=
+					    ISC_LOG_ROLLNEVER ||
+				    (stat(FILE_NAME(channel), &statbuf) != 0 &&
+				     errno == ENOENT) ||
+				    statbuf.st_size < FILE_MAXSIZE(channel))
+				{
+					(void)fclose(FILE_STREAM(channel));
+					FILE_STREAM(channel) = NULL;
+					FILE_MAXREACHED(channel) = false;
+				} else {
+					/*
+					 * Eh, skip it.
+					 */
+					break;
+				}
+			}
+
+			if (FILE_STREAM(channel) == NULL) {
+				result = isc_log_open(channel);
+				if (result != ISC_R_SUCCESS &&
+				    result != ISC_R_MAXSIZE &&
+				    (channel->flags & ISC_LOG_OPENERR) == 0)
+				{
+					syslog(LOG_ERR,
+					       "isc_log_open '%s' "
+					       "failed: %s",
+					       FILE_NAME(channel),
+					       isc_result_totext(result));
+					channel->flags |= ISC_LOG_OPENERR;
+				}
+				if (result != ISC_R_SUCCESS) {
+					break;
+				}
+				channel->flags &= ~ISC_LOG_OPENERR;
+			}
+			FALLTHROUGH;
+
+		case ISC_LOG_TOFILEDESC:
+			fprintf(FILE_STREAM(channel), "%s%s%s%s%s%s%s%s%s%s\n",
+				printtime ? time_string : "",
+				printtime ? " " : "", printtag ? lcfg->tag : "",
+				printcolon ? ": " : "",
+				printcategory ? category->name : "",
+				printcategory ? ": " : "",
+				printmodule ? (module != NULL ? module->name
+							      : "no_module")
+					    : "",
+				printmodule ? ": " : "",
+				printlevel ? level_string : "", lctx->buffer);
+
+			if (!buffered) {
+				fflush(FILE_STREAM(channel));
+			}
+
+			/*
+			 * If the file now exceeds its maximum size
+			 * threshold, note it so that it will not be
+			 * logged to any more.
+			 */
+			if (FILE_MAXSIZE(channel) > 0) {
+				INSIST(channel->type == ISC_LOG_TOFILE);
+
+				/* XXXDCL NT fstat/fileno */
+				/* XXXDCL complain if fstat fails? */
+				if (fstat(fileno(FILE_STREAM(channel)),
+					  &statbuf) >= 0 &&
+				    statbuf.st_size > FILE_MAXSIZE(channel))
+				{
+					FILE_MAXREACHED(channel) = true;
+				}
+			}
+
+			break;
+
+		case ISC_LOG_TOSYSLOG:
+			if (level > 0) {
+				syslog_level = LOG_DEBUG;
+			} else if (level < ISC_LOG_CRITICAL) {
+				syslog_level = LOG_CRIT;
+			} else {
+				syslog_level = syslog_map[-level];
+			}
+
+			(void)syslog(
+				FACILITY(channel) | syslog_level,
+				"%s%s%s%s%s%s%s%s%s%s",
+				printtime ? time_string : "",
+				printtime ? " " : "", printtag ? lcfg->tag : "",
+				printcolon ? ": " : "",
+				printcategory ? category->name : "",
+				printcategory ? ": " : "",
+				printmodule ? (module != NULL ? module->name
+							      : "no_module")
+					    : "",
+				printmodule ? ": " : "",
+				printlevel ? level_string : "", lctx->buffer);
+			break;
+
+		case ISC_LOG_TONULL:
+			break;
+		}
+	} while (1);
+
+unlock:
+	UNLOCK(&lctx->lock);
+	RDUNLOCK(&lctx->lcfg_rwl);
+}