Adding upstream version 3.4.23.upstream/3.4.23upstream

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

1 files changed, 895 insertions, 0 deletions

diff --git a/src/util/slmdb.c b/src/util/slmdb.c
new file mode 100644
index 0000000..823d940
--- /dev/null
+++ b/src/util/slmdb.c
@@ -0,0 +1,895 @@
+/*++
+/* NAME
+/*	slmdb 3
+/* SUMMARY
+/*	Simplified LMDB API
+/* SYNOPSIS
+/*	#include <slmdb.h>
+/*
+/*	int	slmdb_init(slmdb, curr_limit, size_incr, hard_limit)
+/*	SLMDB	*slmdb;
+/*	size_t	curr_limit;
+/*	int	size_incr;
+/*	size_t	hard_limit;
+/*
+/*	int	slmdb_open(slmdb, path, open_flags, lmdb_flags, slmdb_flags)
+/*	SLMDB	*slmdb;
+/*	const char *path;
+/*	int	open_flags;
+/*	int	lmdb_flags;
+/*	int	slmdb_flags;
+/*
+/*	int	slmdb_close(slmdb)
+/*	SLMDB	*slmdb;
+/*
+/*	int	slmdb_get(slmdb, mdb_key, mdb_value)
+/*	SLMDB	*slmdb;
+/*	MDB_val	*mdb_key;
+/*	MDB_val	*mdb_value;
+/*
+/*	int	slmdb_put(slmdb, mdb_key, mdb_value, flags)
+/*	SLMDB	*slmdb;
+/*	MDB_val	*mdb_key;
+/*	MDB_val	*mdb_value;
+/*	int	flags;
+/*
+/*	int	slmdb_del(slmdb, mdb_key)
+/*	SLMDB	*slmdb;
+/*	MDB_val	*mdb_key;
+/*
+/*	int	slmdb_cursor_get(slmdb, mdb_key, mdb_value, op)
+/*	SLMDB	*slmdb;
+/*	MDB_val	*mdb_key;
+/*	MDB_val	*mdb_value;
+/*	MDB_cursor_op op;
+/* AUXILIARY FUNCTIONS
+/*	int	slmdb_fd(slmdb)
+/*	SLMDB	*slmdb;
+/*
+/*	size_t	slmdb_curr_limit(slmdb)
+/*	SLMDB	*slmdb;
+/*
+/*	int	slmdb_control(slmdb, request, ...)
+/*	SLMDB	*slmdb;
+/*	int	request;
+/* DESCRIPTION
+/*	This module simplifies the LMDB API by hiding recoverable
+/*	errors from the application.  Details are given in the
+/*	section "ERROR RECOVERY".
+/*
+/*	slmdb_init() performs mandatory initialization before opening
+/*	an LMDB database. The result value is an LMDB status code
+/*	(zero in case of success).
+/*
+/*	slmdb_open() opens an LMDB database.  The result value is
+/*	an LMDB status code (zero in case of success).
+/*
+/*	slmdb_close() finalizes an optional bulk-mode transaction
+/*	and closes a successfully-opened LMDB database.  The result
+/*	value is an LMDB status code (zero in case of success).
+/*
+/*	slmdb_get() is an mdb_get() wrapper with automatic error
+/*	recovery.  The result value is an LMDB status code (zero
+/*	in case of success).
+/*
+/*	slmdb_put() is an mdb_put() wrapper with automatic error
+/*	recovery.  The result value is an LMDB status code (zero
+/*	in case of success).
+/*
+/*	slmdb_del() is an mdb_del() wrapper with automatic error
+/*	recovery.  The result value is an LMDB status code (zero
+/*	in case of success).
+/*
+/*	slmdb_cursor_get() is an mdb_cursor_get() wrapper with
+/*	automatic error recovery.  The result value is an LMDB
+/*	status code (zero in case of success). This wrapper supports
+/*	only one cursor per database.
+/*
+/*	slmdb_fd() returns the file descriptor for the specified
+/*	database.  This may be used for file status queries or
+/*	application-controlled locking.
+/*
+/*	slmdb_curr_limit() returns the current database size limit
+/*	for the specified database.
+/*
+/*	slmdb_control() specifies optional features. The result is
+/*	an LMDB status code (zero in case of success).
+/*
+/*	Arguments:
+/* .IP slmdb
+/*	Pointer to caller-provided storage.
+/* .IP curr_limit
+/*	The initial memory mapping size limit. This limit is
+/*	automatically increased when the database becomes full.
+/* .IP size_incr
+/*	An integer factor by which the memory mapping size limit
+/*	is increased when the database becomes full.
+/* .IP hard_limit
+/*	The upper bound for the memory mapping size limit.
+/* .IP path
+/*	LMDB database pathname.
+/* .IP open_flags
+/*	Flags that control file open operations. Do not specify
+/*	locking flags here.
+/* .IP lmdb_flags
+/*	Flags that control the LMDB environment. If MDB_NOLOCK is
+/*	specified, then each slmdb_get() or slmdb_cursor_get() call
+/*	must be protected with a shared (or exclusive) external lock,
+/*	and each slmdb_put() or slmdb_del() call must be protected
+/*	with an exclusive external lock. A lock may be released
+/*	after the call returns. A writer may atomically downgrade
+/*	an exclusive lock to shared, but it must obtain an exclusive
+/*	lock before making another slmdb(3) write request.
+/* .sp
+/*	Note: when a database is opened with MDB_NOLOCK, external
+/*	locks such as fcntl() do not protect slmdb(3) requests
+/*	within the same process against each other.  If a program
+/*	cannot avoid making simultaneous slmdb(3) requests, then
+/*	it must synchronize these requests with in-process locks,
+/*	in addition to the per-process fcntl(2) locks.
+/* .IP slmdb_flags
+/*	Bit-wise OR of zero or more of the following:
+/* .RS
+/* .IP SLMDB_FLAG_BULK
+/*	Open the database and create a "bulk" transaction that is
+/*	committed when the database is closed. If MDB_NOLOCK is
+/*	specified, then the entire transaction must be protected
+/*	with a persistent external lock.  All slmdb_get(), slmdb_put()
+/*	and slmdb_del() requests will be directed to the "bulk"
+/*	transaction.
+/* .RE
+/* .IP mdb_key
+/*	Pointer to caller-provided lookup key storage.
+/* .IP mdb_value
+/*	Pointer to caller-provided value storage.
+/* .IP op
+/*	LMDB cursor operation.
+/* .IP request
+/*	The start of a list of (name, value) pairs, terminated with
+/*	CA_SLMDB_CTL_END.  The following text enumerates the symbolic
+/*	request names and the corresponding argument types.
+/* .RS
+/* .IP "CA_SLMDB_CTL_LONGJMP_FN(void (*)(void *, int))"
+/*	Call-back function pointer. The function is called to repeat
+/*	a failed bulk-mode transaction from the start. The arguments
+/*	are the application context and the setjmp() or sigsetjmp()
+/*	result value.
+/* .IP "CA_SLMDB_CTL_NOTIFY_FN(void (*)(void *, int, ...))"
+/*	Call-back function pointer. The function is called to report
+/*	successful error recovery. The arguments are the application
+/*	context, the MDB error code, and additional arguments that
+/*	depend on the error code.  Details are given in the section
+/*	"ERROR RECOVERY".
+/* .IP "CA_SLMDB_CTL_ASSERT_FN(void (*)(void *, const char *))"
+/*	Call-back function pointer.  The function is called to
+/*	report an LMDB internal assertion failure. The arguments
+/*	are the application context, and text that describes the
+/*	problem.
+/* .IP "CA_SLMDB_CTL_CB_CONTEXT(void *)"
+/*	Application context that is passed in call-back function
+/*	calls.
+/* .IP "CA_SLMDB_CTL_API_RETRY_LIMIT(int)"
+/*	How many times to recover from LMDB errors within the
+/*	execution of a single slmdb(3) API call before giving up.
+/* .IP "CA_SLMDB_CTL_BULK_RETRY_LIMIT(int)"
+/*	How many times to recover from a bulk-mode transaction
+/*	before giving up.
+/* .RE
+/* ERROR RECOVERY
+/* .ad
+/* .fi
+/*	This module automatically repeats failed requests after
+/*	recoverable errors, up to the limits specified with
+/*	slmdb_control().
+/*
+/*	Recoverable errors are reported through an optional
+/*	notification function specified with slmdb_control().  With
+/*	recoverable MDB_MAP_FULL and MDB_MAP_RESIZED errors, the
+/*	additional argument is a size_t value with the updated
+/*	current database size limit; with recoverable MDB_READERS_FULL
+/*	errors there is no additional argument.
+/* BUGS
+/*	Recovery from MDB_MAP_FULL involves resizing the database
+/*	memory mapping.  According to LMDB documentation this
+/*	requires that there is no concurrent activity in the same
+/*	database by other threads in the same memory address space.
+/* SEE ALSO
+/*	lmdb(3) API manpage (currently, non-existent).
+/* AUTHOR(S)
+/*	Howard Chu
+/*	Symas Corporation
+/*
+/*	Wietse Venema
+/*	IBM T.J. Watson Research
+/*	P.O. Box 704
+/*	Yorktown Heights, NY 10598, USA
+/*--*/
+
+ /*
+  * DO NOT include other Postfix-specific header files. This LMDB wrapper
+  * must be usable outside Postfix.
+  */
+
+#ifdef HAS_LMDB
+
+/* System library. */
+
+#include <sys/stat.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+#include <limits.h>
+#include <stdarg.h>
+#include <string.h>
+#include <stdlib.h>
+
+/* Application-specific. */
+
+#include <slmdb.h>
+
+ /*
+  * Minimum LMDB patchlevel.
+  * 
+  * LMDB 0.9.11 allows Postfix daemons to log an LMDB error message instead of
+  * falling out of the sky without any explanation. Without such logging,
+  * Postfix with LMDB would be too hard to support.
+  * 
+  * LMDB 0.9.10 fixes an information leak where LMDB wrote chunks of up to 4096
+  * bytes of uninitialized heap memory to a database. This was a security
+  * violation because it made information persistent that was not meant to be
+  * persisted, or it was sharing information that was not meant to be shared.
+  * 
+  * LMDB 0.9.9 allows Postfix to use external (fcntl()-based) locks, instead of
+  * having to use world-writable LMDB lock files.
+  * 
+  * LMDB 0.9.8 allows Postfix to update the database size limit on-the-fly, so
+  * that it can recover from an MDB_MAP_FULL error without having to close
+  * the database. It also allows an application to "pick up" a new database
+  * size limit on-the-fly, so that it can recover from an MDB_MAP_RESIZED
+  * error without having to close the database.
+  * 
+  * The database size limit that remains is imposed by the hardware memory
+  * address space (31 or 47 bits, typically) or file system. The LMDB
+  * implementation is supposed to handle databases larger than physical
+  * memory. However, this is not necessarily guaranteed for (bulk)
+  * transactions larger than physical memory.
+  */
+#if MDB_VERSION_FULL < MDB_VERINT(0, 9, 11)
+#error "This Postfix version requires LMDB version 0.9.11 or later"
+#endif
+
+ /*
+  * Error recovery.
+  * 
+  * The purpose of the slmdb(3) API is to hide LMDB quirks (recoverable
+  * MAP_FULL, MAP_RESIZED, or MDB_READERS_FULL errors). With these out of the
+  * way, applications can pretend that those quirks don't exist, and focus on
+  * their own job.
+  * 
+  * - To recover from a single-transaction LMDB error, each wrapper function
+  * uses tail recursion instead of goto. Since LMDB errors are rare, code
+  * clarity is more important than speed.
+  * 
+  * - To recover from a bulk-transaction LMDB error, the error-recovery code
+  * triggers a long jump back into the caller to some pre-arranged point (the
+  * closest thing that C has to exception handling). The application is then
+  * expected to repeat the bulk transaction from scratch.
+  */
+
+ /*
+  * Our default retry attempt limits. We allow a few retries per slmdb(3) API
+  * call for non-bulk transactions. We allow a number of bulk-transaction
+  * retries that is proportional to the memory address space.
+  */
+#define SLMDB_DEF_API_RETRY_LIMIT 30	/* Retries per slmdb(3) API call */
+#define SLMDB_DEF_BULK_RETRY_LIMIT \
+        (2 * sizeof(size_t) * CHAR_BIT)	/* Retries per bulk-mode transaction */
+
+ /*
+  * We increment the recursion counter each time we try to recover from
+  * error, and reset the recursion counter when returning to the application
+  * from the slmdb(3) API.
+  */
+#define SLMDB_API_RETURN(slmdb, status) do { \
+	(slmdb)->api_retry_count = 0; \
+	return (status); \
+    } while (0)
+
+ /*
+  * With MDB_NOLOCK, the application uses an external lock for inter-process
+  * synchronization. Because the caller may release the external lock after
+  * an SLMDB API call, each SLMDB API function must use a short-lived
+  * transaction unless the transaction is a bulk-mode transaction.
+  */
+
+/* slmdb_cursor_close - close cursor and its read transaction */
+
+static void slmdb_cursor_close(SLMDB *slmdb)
+{
+    MDB_txn *txn;
+
+    /*
+     * Close the cursor and its read transaction. We can restore it later
+     * from the saved key information.
+     */
+    txn = mdb_cursor_txn(slmdb->cursor);
+    mdb_cursor_close(slmdb->cursor);
+    slmdb->cursor = 0;
+    mdb_txn_abort(txn);
+}
+
+/* slmdb_saved_key_init - initialize saved key info */
+
+static void slmdb_saved_key_init(SLMDB *slmdb)
+{
+    slmdb->saved_key.mv_data = 0;
+    slmdb->saved_key.mv_size = 0;
+    slmdb->saved_key_size = 0;
+}
+
+/* slmdb_saved_key_free - destroy saved key info */
+
+static void slmdb_saved_key_free(SLMDB *slmdb)
+{
+    free(slmdb->saved_key.mv_data);
+    slmdb_saved_key_init(slmdb);
+}
+
+#define HAVE_SLMDB_SAVED_KEY(s) ((s)->saved_key.mv_data != 0)
+
+/* slmdb_saved_key_assign - copy the saved key */
+
+static int slmdb_saved_key_assign(SLMDB *slmdb, MDB_val *key_val)
+{
+
+    /*
+     * Extend the buffer to fit the key, so that we can avoid malloc()
+     * overhead most of the time.
+     */
+    if (slmdb->saved_key_size < key_val->mv_size) {
+	if (slmdb->saved_key.mv_data == 0)
+	    slmdb->saved_key.mv_data = malloc(key_val->mv_size);
+	else
+	    slmdb->saved_key.mv_data =
+		realloc(slmdb->saved_key.mv_data, key_val->mv_size);
+	if (slmdb->saved_key.mv_data == 0) {
+	    slmdb_saved_key_init(slmdb);
+	    return (ENOMEM);
+	} else {
+	    slmdb->saved_key_size = key_val->mv_size;
+	}
+    }
+
+    /*
+     * Copy the key under the cursor.
+     */
+    memcpy(slmdb->saved_key.mv_data, key_val->mv_data, key_val->mv_size);
+    slmdb->saved_key.mv_size = key_val->mv_size;
+    return (0);
+}
+
+/* slmdb_prepare - LMDB-specific (re)initialization before actual access */
+
+static int slmdb_prepare(SLMDB *slmdb)
+{
+    int     status = 0;
+
+    /*
+     * This is called before accessing the database, or after recovery from
+     * an LMDB error. Note: this code cannot recover from errors itself.
+     * slmdb->txn is either the database open() transaction or a
+     * freshly-created bulk-mode transaction.
+     * 
+     * - With O_TRUNC we make a "drop" request before updating the database.
+     * 
+     * - With a bulk-mode transaction we commit when the database is closed.
+     */
+    if (slmdb->open_flags & O_TRUNC) {
+	if ((status = mdb_drop(slmdb->txn, slmdb->dbi, 0)) != 0) {
+	    mdb_txn_abort(slmdb->txn);
+	    slmdb->txn = 0;
+	    return (status);
+	}
+	if ((slmdb->slmdb_flags & SLMDB_FLAG_BULK) == 0) {
+	    status = mdb_txn_commit(slmdb->txn);
+	    slmdb->txn = 0;
+	    if (status != 0)
+		return (status);
+	}
+    } else if ((slmdb->lmdb_flags & MDB_RDONLY) != 0
+	       || (slmdb->slmdb_flags & SLMDB_FLAG_BULK) == 0) {
+	mdb_txn_abort(slmdb->txn);
+	slmdb->txn = 0;
+    }
+    slmdb->api_retry_count = 0;
+    return (status);
+}
+
+/* slmdb_recover - recover from LMDB errors */
+
+static int slmdb_recover(SLMDB *slmdb, int status)
+{
+    MDB_envinfo info;
+
+    /*
+     * This may be needed in non-MDB_NOLOCK mode. Recovery is rare enough
+     * that we don't care about a few wasted cycles.
+     */
+    if (slmdb->cursor != 0)
+	slmdb_cursor_close(slmdb);
+
+    /*
+     * Recover bulk transactions only if they can be restarted. Limit the
+     * number of recovery attempts per slmdb(3) API request.
+     */
+    if ((slmdb->txn != 0 && slmdb->longjmp_fn == 0)
+	|| ((slmdb->api_retry_count += 1) >= slmdb->api_retry_limit))
+	return (status);
+
+    /*
+     * If we can recover from the error, we clear the error condition and the
+     * caller should retry the failed operation immediately. Otherwise, the
+     * caller should terminate with a fatal run-time error and the program
+     * should be re-run later.
+     * 
+     * slmdb->txn must be either null (non-bulk transaction error), or an
+     * aborted bulk-mode transaction.
+     */
+    switch (status) {
+
+	/*
+	 * As of LMDB 0.9.8 when a non-bulk update runs into a "map full"
+	 * error, we can resize the environment's memory map and clear the
+	 * error condition. The caller should retry immediately.
+	 */
+    case MDB_MAP_FULL:
+	/* Can we increase the memory map? Give up if we can't. */
+	if (slmdb->curr_limit < slmdb->hard_limit / slmdb->size_incr) {
+	    slmdb->curr_limit = slmdb->curr_limit * slmdb->size_incr;
+	} else if (slmdb->curr_limit < slmdb->hard_limit) {
+	    slmdb->curr_limit = slmdb->hard_limit;
+	} else {
+	    /* Sorry, we are already maxed out. */
+	    break;
+	}
+	if (slmdb->notify_fn)
+	    slmdb->notify_fn(slmdb->cb_context, MDB_MAP_FULL,
+			     slmdb->curr_limit);
+	status = mdb_env_set_mapsize(slmdb->env, slmdb->curr_limit);
+	break;
+
+	/*
+	 * When a writer resizes the database, read-only applications must
+	 * increase their LMDB memory map size limit, too. Otherwise, they
+	 * won't be able to read a table after it grows.
+	 * 
+	 * As of LMDB 0.9.8 we can import the new memory map size limit into the
+	 * database environment by calling mdb_env_set_mapsize() with a zero
+	 * size argument. Then we extract the map size limit for later use.
+	 * The caller should retry immediately.
+	 */
+    case MDB_MAP_RESIZED:
+	if ((status = mdb_env_set_mapsize(slmdb->env, 0)) == 0) {
+	    /* Do not panic. Maps may shrink after bulk update. */
+	    mdb_env_info(slmdb->env, &info);
+	    slmdb->curr_limit = info.me_mapsize;
+	    if (slmdb->notify_fn)
+		slmdb->notify_fn(slmdb->cb_context, MDB_MAP_RESIZED,
+				 slmdb->curr_limit);
+	}
+	break;
+
+	/*
+	 * What is it with these built-in hard limits that cause systems to
+	 * stop when demand is at its highest? When the system is under
+	 * stress it should slow down and keep making progress.
+	 */
+    case MDB_READERS_FULL:
+	if (slmdb->notify_fn)
+	    slmdb->notify_fn(slmdb->cb_context, MDB_READERS_FULL);
+	sleep(1);
+	status = 0;
+	break;
+
+	/*
+	 * We can't solve this problem. The application should terminate with
+	 * a fatal run-time error and the program should be re-run later.
+	 */
+    default:
+	break;
+    }
+
+    /*
+     * If a bulk-transaction error is recoverable, build a new bulk
+     * transaction from scratch, by making a long jump back into the caller
+     * at some pre-arranged point. In MDB_NOLOCK mode, there is no need to
+     * upgrade the lock to "exclusive", because the failed write transaction
+     * has no side effects.
+     */
+    if (slmdb->txn != 0 && status == 0 && slmdb->longjmp_fn != 0
+	&& (slmdb->bulk_retry_count += 1) <= slmdb->bulk_retry_limit) {
+	if ((status = mdb_txn_begin(slmdb->env, (MDB_txn *) 0,
+				    slmdb->lmdb_flags & MDB_RDONLY,
+				    &slmdb->txn)) == 0
+	    && (status = slmdb_prepare(slmdb)) == 0)
+	    slmdb->longjmp_fn(slmdb->cb_context, 1);
+    }
+    return (status);
+}
+
+/* slmdb_txn_begin - mdb_txn_begin() wrapper with LMDB error recovery */
+
+static int slmdb_txn_begin(SLMDB *slmdb, int rdonly, MDB_txn **txn)
+{
+    int     status;
+
+    if ((status = mdb_txn_begin(slmdb->env, (MDB_txn *) 0, rdonly, txn)) != 0
+	&& (status = slmdb_recover(slmdb, status)) == 0)
+	status = slmdb_txn_begin(slmdb, rdonly, txn);
+
+    return (status);
+}
+
+/* slmdb_get - mdb_get() wrapper with LMDB error recovery */
+
+int     slmdb_get(SLMDB *slmdb, MDB_val *mdb_key, MDB_val *mdb_value)
+{
+    MDB_txn *txn;
+    int     status;
+
+    /*
+     * Start a read transaction if there's no bulk-mode txn.
+     */
+    if (slmdb->txn)
+	txn = slmdb->txn;
+    else if ((status = slmdb_txn_begin(slmdb, MDB_RDONLY, &txn)) != 0)
+	SLMDB_API_RETURN(slmdb, status);
+
+    /*
+     * Do the lookup.
+     */
+    if ((status = mdb_get(txn, slmdb->dbi, mdb_key, mdb_value)) != 0
+	&& status != MDB_NOTFOUND) {
+	mdb_txn_abort(txn);
+	if ((status = slmdb_recover(slmdb, status)) == 0)
+	    status = slmdb_get(slmdb, mdb_key, mdb_value);
+	SLMDB_API_RETURN(slmdb, status);
+    }
+
+    /*
+     * Close the read txn if it's not the bulk-mode txn.
+     */
+    if (slmdb->txn == 0)
+	mdb_txn_abort(txn);
+
+    SLMDB_API_RETURN(slmdb, status);
+}
+
+/* slmdb_put - mdb_put() wrapper with LMDB error recovery */
+
+int     slmdb_put(SLMDB *slmdb, MDB_val *mdb_key,
+		          MDB_val *mdb_value, int flags)
+{
+    MDB_txn *txn;
+    int     status;
+
+    /*
+     * Start a write transaction if there's no bulk-mode txn.
+     */
+    if (slmdb->txn)
+	txn = slmdb->txn;
+    else if ((status = slmdb_txn_begin(slmdb, 0, &txn)) != 0)
+	SLMDB_API_RETURN(slmdb, status);
+
+    /*
+     * Do the update.
+     */
+    if ((status = mdb_put(txn, slmdb->dbi, mdb_key, mdb_value, flags)) != 0) {
+	if (status != MDB_KEYEXIST) {
+	    mdb_txn_abort(txn);
+	    if ((status = slmdb_recover(slmdb, status)) == 0)
+		status = slmdb_put(slmdb, mdb_key, mdb_value, flags);
+	    SLMDB_API_RETURN(slmdb, status);
+	} else {
+	    /* Abort non-bulk transaction only. */
+	    if (slmdb->txn == 0)
+		mdb_txn_abort(txn);
+	}
+    }
+
+    /*
+     * Commit the transaction if it's not the bulk-mode txn.
+     */
+    if (status == 0 && slmdb->txn == 0 && (status = mdb_txn_commit(txn)) != 0
+	&& (status = slmdb_recover(slmdb, status)) == 0)
+	status = slmdb_put(slmdb, mdb_key, mdb_value, flags);
+
+    SLMDB_API_RETURN(slmdb, status);
+}
+
+/* slmdb_del - mdb_del() wrapper with LMDB error recovery */
+
+int     slmdb_del(SLMDB *slmdb, MDB_val *mdb_key)
+{
+    MDB_txn *txn;
+    int     status;
+
+    /*
+     * Start a write transaction if there's no bulk-mode txn.
+     */
+    if (slmdb->txn)
+	txn = slmdb->txn;
+    else if ((status = slmdb_txn_begin(slmdb, 0, &txn)) != 0)
+	SLMDB_API_RETURN(slmdb, status);
+
+    /*
+     * Do the update.
+     */
+    if ((status = mdb_del(txn, slmdb->dbi, mdb_key, (MDB_val *) 0)) != 0) {
+	mdb_txn_abort(txn);
+	if (status != MDB_NOTFOUND) {
+	    if ((status = slmdb_recover(slmdb, status)) == 0)
+		status = slmdb_del(slmdb, mdb_key);
+	    SLMDB_API_RETURN(slmdb, status);
+	}
+    }
+
+    /*
+     * Commit the transaction if it's not the bulk-mode txn.
+     */
+    if (status == 0 && slmdb->txn == 0 && (status = mdb_txn_commit(txn)) != 0
+	&& (status = slmdb_recover(slmdb, status)) == 0)
+	status = slmdb_del(slmdb, mdb_key);
+
+    SLMDB_API_RETURN(slmdb, status);
+}
+
+/* slmdb_cursor_get - mdb_cursor_get() wrapper with LMDB error recovery */
+
+int     slmdb_cursor_get(SLMDB *slmdb, MDB_val *mdb_key,
+			         MDB_val *mdb_value, MDB_cursor_op op)
+{
+    MDB_txn *txn;
+    int     status = 0;
+
+    /*
+     * Open a read transaction and cursor if needed.
+     */
+    if (slmdb->cursor == 0) {
+	if ((status = slmdb_txn_begin(slmdb, MDB_RDONLY, &txn)) != 0)
+	    SLMDB_API_RETURN(slmdb, status);
+	if ((status = mdb_cursor_open(txn, slmdb->dbi, &slmdb->cursor)) != 0) {
+	    mdb_txn_abort(txn);
+	    if ((status = slmdb_recover(slmdb, status)) == 0)
+		status = slmdb_cursor_get(slmdb, mdb_key, mdb_value, op);
+	    SLMDB_API_RETURN(slmdb, status);
+	}
+
+	/*
+	 * Restore the cursor position from the saved key information.
+	 */
+	if (HAVE_SLMDB_SAVED_KEY(slmdb) && op != MDB_FIRST)
+	    status = mdb_cursor_get(slmdb->cursor, &slmdb->saved_key,
+				    (MDB_val *) 0, MDB_SET);
+    }
+
+    /*
+     * Database lookup.
+     */
+    if (status == 0)
+	status = mdb_cursor_get(slmdb->cursor, mdb_key, mdb_value, op);
+
+    /*
+     * Save the cursor position if successful. This can fail only with
+     * ENOMEM.
+     * 
+     * Close the cursor read transaction if in MDB_NOLOCK mode, because the
+     * caller may release the external lock after we return.
+     */
+    if (status == 0) {
+	status = slmdb_saved_key_assign(slmdb, mdb_key);
+	if (slmdb->lmdb_flags & MDB_NOLOCK)
+	    slmdb_cursor_close(slmdb);
+    }
+
+    /*
+     * Handle end-of-database or other error.
+     */
+    else {
+	/* Do not hand-optimize out the slmdb_cursor_close() calls below. */
+	if (status == MDB_NOTFOUND) {
+	    slmdb_cursor_close(slmdb);
+	    if (HAVE_SLMDB_SAVED_KEY(slmdb))
+		slmdb_saved_key_free(slmdb);
+	} else {
+	    slmdb_cursor_close(slmdb);
+	    if ((status = slmdb_recover(slmdb, status)) == 0)
+		status = slmdb_cursor_get(slmdb, mdb_key, mdb_value, op);
+	    SLMDB_API_RETURN(slmdb, status);
+	    /* Do not hand-optimize out the above return statement. */
+	}
+    }
+    SLMDB_API_RETURN(slmdb, status);
+}
+
+/* slmdb_assert_cb - report LMDB assertion failure */
+
+static void slmdb_assert_cb(MDB_env *env, const char *text)
+{
+    SLMDB  *slmdb = (SLMDB *) mdb_env_get_userctx(env);
+
+    if (slmdb->assert_fn)
+	slmdb->assert_fn(slmdb->cb_context, text);
+}
+
+/* slmdb_control - control optional settings */
+
+int     slmdb_control(SLMDB *slmdb, int first,...)
+{
+    va_list ap;
+    int     status = 0;
+    int     reqno;
+    int     rc;
+
+    va_start(ap, first);
+    for (reqno = first; status == 0 && reqno != SLMDB_CTL_END; reqno = va_arg(ap, int)) {
+	switch (reqno) {
+	case SLMDB_CTL_LONGJMP_FN:
+	    slmdb->longjmp_fn = va_arg(ap, SLMDB_LONGJMP_FN);
+	    break;
+	case SLMDB_CTL_NOTIFY_FN:
+	    slmdb->notify_fn = va_arg(ap, SLMDB_NOTIFY_FN);
+	    break;
+	case SLMDB_CTL_ASSERT_FN:
+	    slmdb->assert_fn = va_arg(ap, SLMDB_ASSERT_FN);
+	    if ((rc = mdb_env_set_userctx(slmdb->env, (void *) slmdb)) != 0
+	     || (rc = mdb_env_set_assert(slmdb->env, slmdb_assert_cb)) != 0)
+		status = rc;
+	    break;
+	case SLMDB_CTL_CB_CONTEXT:
+	    slmdb->cb_context = va_arg(ap, void *);
+	    break;
+	case SLMDB_CTL_API_RETRY_LIMIT:
+	    slmdb->api_retry_limit = va_arg(ap, int);
+	    break;
+	case SLMDB_CTL_BULK_RETRY_LIMIT:
+	    slmdb->bulk_retry_limit = va_arg(ap, int);
+	    break;
+	default:
+	    status = errno = EINVAL;
+	    break;
+	}
+    }
+    va_end(ap);
+    return (status);
+}
+
+/* slmdb_close - wrapper with LMDB error recovery */
+
+int     slmdb_close(SLMDB *slmdb)
+{
+    int     status = 0;
+
+    /*
+     * Finish an open bulk transaction. If slmdb_recover() returns after a
+     * bulk-transaction error, then it was unable to recover.
+     */
+    if (slmdb->txn != 0
+	&& (status = mdb_txn_commit(slmdb->txn)) != 0)
+	status = slmdb_recover(slmdb, status);
+
+    /*
+     * Clean up after an unfinished sequence() operation.
+     */
+    if (slmdb->cursor != 0)
+	slmdb_cursor_close(slmdb);
+
+    mdb_env_close(slmdb->env);
+
+    /*
+     * Clean up the saved key information.
+     */
+    if (HAVE_SLMDB_SAVED_KEY(slmdb))
+	slmdb_saved_key_free(slmdb);
+
+    SLMDB_API_RETURN(slmdb, status);
+}
+
+/* slmdb_init - mandatory initialization */
+
+int     slmdb_init(SLMDB *slmdb, size_t curr_limit, int size_incr,
+		           size_t hard_limit)
+{
+
+    /*
+     * This is a separate operation to keep the slmdb_open() API simple.
+     * Don't allocate resources here. Just store control information,
+     */
+    slmdb->curr_limit = curr_limit;
+    slmdb->size_incr = size_incr;
+    slmdb->hard_limit = hard_limit;
+
+    return (MDB_SUCCESS);
+}
+
+/* slmdb_open - open wrapped LMDB database */
+
+int     slmdb_open(SLMDB *slmdb, const char *path, int open_flags,
+		           int lmdb_flags, int slmdb_flags)
+{
+    struct stat st;
+    MDB_env *env;
+    MDB_txn *txn;
+    MDB_dbi dbi;
+    int     db_fd;
+    int     status;
+
+    /*
+     * Create LMDB environment.
+     */
+    if ((status = mdb_env_create(&env)) != 0)
+	return (status);
+
+    /*
+     * Make sure that the memory map has room to store and commit an initial
+     * "drop" transaction as well as fixed database metadata. We have no way
+     * to recover from errors before the first application-level I/O request.
+     */
+#define SLMDB_FUDGE      10240
+
+    if (slmdb->curr_limit < SLMDB_FUDGE)
+	slmdb->curr_limit = SLMDB_FUDGE;
+    if (stat(path, &st) == 0
+	&& st.st_size > slmdb->curr_limit - SLMDB_FUDGE) {
+	if (st.st_size > slmdb->hard_limit)
+	    slmdb->hard_limit = st.st_size;
+	if (st.st_size < slmdb->hard_limit - SLMDB_FUDGE)
+	    slmdb->curr_limit = st.st_size + SLMDB_FUDGE;
+	else
+	    slmdb->curr_limit = slmdb->hard_limit;
+    }
+
+    /*
+     * mdb_open() requires a txn, but since the default DB always exists in
+     * an LMDB environment, we usually don't need to do anything else with
+     * the txn. It is currently used for truncate and for bulk transactions.
+     */
+    if ((status = mdb_env_set_mapsize(env, slmdb->curr_limit)) != 0
+	|| (status = mdb_env_open(env, path, lmdb_flags, 0644)) != 0
+	|| (status = mdb_txn_begin(env, (MDB_txn *) 0,
+				   lmdb_flags & MDB_RDONLY, &txn)) != 0
+	|| (status = mdb_open(txn, (const char *) 0, 0, &dbi)) != 0
+	|| (status = mdb_env_get_fd(env, &db_fd)) != 0) {
+	mdb_env_close(env);
+	return (status);
+    }
+
+    /*
+     * Bundle up.
+     */
+    slmdb->open_flags = open_flags;
+    slmdb->lmdb_flags = lmdb_flags;
+    slmdb->slmdb_flags = slmdb_flags;
+    slmdb->env = env;
+    slmdb->dbi = dbi;
+    slmdb->db_fd = db_fd;
+    slmdb->cursor = 0;
+    slmdb_saved_key_init(slmdb);
+    slmdb->api_retry_count = 0;
+    slmdb->bulk_retry_count = 0;
+    slmdb->api_retry_limit = SLMDB_DEF_API_RETRY_LIMIT;
+    slmdb->bulk_retry_limit = SLMDB_DEF_BULK_RETRY_LIMIT;
+    slmdb->longjmp_fn = 0;
+    slmdb->notify_fn = 0;
+    slmdb->assert_fn = 0;
+    slmdb->cb_context = 0;
+    slmdb->txn = txn;
+
+    if ((status = slmdb_prepare(slmdb)) != 0)
+	mdb_env_close(env);
+
+    return (status);
+}
+
+#endif