X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=chiark-tcl.git;a=blobdiff_plain;f=cdb%2Fwriteable.c;h=9cdd0095bd615fd1a1359e2ee145a81e12487513;hp=140c1ffeaea4ed583b89997cb3c85998ffe7f94f;hb=5dca360f2da544c9b6baf9d18ad8cd0b0e073e60;hpb=7795b9e72903475e48adbc986a945ef3a7fb0309

diff --git a/cdb/writeable.c b/cdb/writeable.c
index 140c1ff..9cdd009 100644
--- a/cdb/writeable.c
+++ b/cdb/writeable.c
@@ -1,9 +1,943 @@
-/**/
+/*
+ * cdb, cdb-wr - Tcl bindings for tinycdb and a journalling write extension
+ * Copyright 2006 Ian Jackson
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
 
 #include "chiark_tcl_cdb.h"
 
-static void destroy_cdbrw_idtabcb(Tcl_Interp *ip, void *val) { abort(); }
+#define ftello ftell
+#define fseeko fseek
 
+/*---------- Forward declarations ----------*/
+
+struct ht_forall_ctx;
+
+/*---------- Useful routines ----------*/
+
+static void maybe_close(int fd) {
+  if (fd>=0) close(fd);
+}
+
+/*==================== Subsystems and subtypes ====================*/
+
+/*---------- Pathbuf ----------*/
+
+typedef struct Pathbuf {
+  char *buf, *sfx;
+} Pathbuf;
+
+#define MAX_SUFFIX 5
+
+static void pathbuf_init(Pathbuf *pb, const char *pathb) {
+  int l= strlen(pathb);
+  pb->buf= TALLOC(l + MAX_SUFFIX + 1);
+  memcpy(pb->buf, pathb, l);
+  pb->sfx= pb->buf + l;
+}
+static const char *pathbuf_sfx(Pathbuf *pb, const char *suffix) {
+  assert(strlen(suffix) <= MAX_SUFFIX);
+  strcpy(pb->sfx, suffix);
+  return pb->buf;
+}
+static void pathbuf_free(Pathbuf *pb) {
+  TFREE(pb->buf);
+  pb->buf= 0;
+}
+
+/*---------- Our hash table ----------*/
+
+typedef struct HashTable {
+  Tcl_HashTable t;
+  Byte padding[128]; /* allow for expansion by Tcl, urgh */
+  Byte confound[16];
+} HashTable;
+
+typedef struct HashValue {
+  int len;
+  Byte data[1];
+} HashValue;
+
+static HashValue *htv_prep(int len) {
+  HashValue *hd;
+  hd= TALLOC((hd->data - (Byte*)hd) + len);
+  hd->len= len;
+  return hd;
+}  
+static Byte *htv_fillptr(HashValue *hd) {
+  return hd->data;
+}
+
+static void ht_setup(HashTable *ht) {
+  Tcl_InitHashTable(&ht->t, TCL_STRING_KEYS);
+}
+static void ht_update(HashTable *ht, const char *key, HashValue *val_eat) {
+  Tcl_HashEntry *he;
+  int new;
+
+  he= Tcl_CreateHashEntry(&ht->t, (char*)key, &new);
+  if (!new) TFREE(Tcl_GetHashValue(he));
+  Tcl_SetHashValue(he, val_eat);
+    /* eats the value since the data structure owns the memory */
+}
+static void ht_maybeupdate(HashTable *ht, const char *key,
+			   HashValue *val_eat) {
+  /* like ht_update except does not overwrite existing values */
+  Tcl_HashEntry *he;
+  int new;
+
+  he= Tcl_CreateHashEntry(&ht->t, (char*)key, &new);
+  if (!new) { TFREE(val_eat); return; }
+  Tcl_SetHashValue(he, val_eat);
+}
+
+static const HashValue *ht_lookup(HashTable *ht, const char *key) {
+  Tcl_HashEntry *he;
+  
+  he= Tcl_FindHashEntry(&ht->t, key);
+  if (!he) return 0;
+  
+  return Tcl_GetHashValue(he);
+}
+
+static int ht_forall(HashTable *ht,
+		     int (*fn)(const char *key, HashValue *val,
+			       struct ht_forall_ctx *ctx),
+		     struct ht_forall_ctx *ctx) {
+  /* Returns first positive value returned by any call to fn, or 0. */
+  Tcl_HashSearch sp;
+  Tcl_HashEntry *he;
+  const char *key;
+  HashValue *val;
+  int r;
+  
+  for (he= Tcl_FirstHashEntry(&ht->t, &sp);
+       he;
+       he= Tcl_NextHashEntry(&sp)) {
+    val= Tcl_GetHashValue(he);
+    if (!val->len) continue;
+
+    key= Tcl_GetHashKey(&ht->t, he);
+    
+    r= fn(key, val, ctx);
+    if (r) return r;
+  }
+  return 0;
+}
+
+static void ht_destroy(HashTable *ht) {
+  Tcl_HashSearch sp;
+  Tcl_HashEntry *he;
+  
+  for (he= Tcl_FirstHashEntry(&ht->t, &sp);
+       he;
+       he= Tcl_NextHashEntry(&sp)) {
+    /* ht_forall skips empty (deleted) entries so is no good for this */
+    TFREE(Tcl_GetHashValue(he));
+  }
+  Tcl_DeleteHashTable(&ht->t);
+}
+
+/*==================== Existential ====================*/
+
+/*---------- Rw data structure ----------*/
+
+typedef struct Rw {
+  int ix, autocompact;
+  int cdb_fd, lock_fd;
+  struct cdb cdb; /* valid iff cdb_fd >= 0 */
+  FILE *logfile;
+  HashTable logincore;
+  Pathbuf pbsome, pbother;
+  off_t mainsz;
+  ScriptToInvoke on_info, on_lexminval;
+} Rw;
+
+static int rw_close(Tcl_Interp *ip, Rw *rw) {
+  int rc, r;
+
+  rc= TCL_OK;
+  ht_destroy(&rw->logincore);
+  if (rw->cdb_fd >= 0) cdb_free(&rw->cdb);
+  maybe_close(rw->cdb_fd);
+  maybe_close(rw->lock_fd);
+
+  if (rw->logfile) {
+    r= fclose(rw->logfile);
+    if (r && ip) { rc= cht_posixerr(ip, errno, "probable data loss! failed to"
+				    " fclose logfile during untidy close"); }
+  }
+
+  pathbuf_free(&rw->pbsome); pathbuf_free(&rw->pbother);
+  return rc;
+}
+
+static void destroy_cdbrw_idtabcb(Tcl_Interp *ip, void *rw_v) {
+  rw_close(0,rw_v);
+  TFREE(rw_v);
+}
 const IdDataSpec cdbtcl_rwdatabases= {
   "cdb-rwdb", "cdb-openrwdatabases-table", destroy_cdbrw_idtabcb
 };
+
+/*---------- File handling ----------*/
+
+static int acquire_lock(Tcl_Interp *ip, Pathbuf *pb, int *lockfd_r) {
+  /* *lockfd_r must be -1 on entry.  If may be set to >=0 even
+   * on error, and must be closed by the caller. */
+  mode_t um, lockmode;
+  struct flock fl;
+  int r;
+
+  um= umask(~(mode_t)0);
+  umask(um);
+
+  lockmode= 0666 & ~((um & 0444)>>1);
+  /* Remove r where umask would remove w;
+   * eg umask intending 0664 here gives 0660 */
+  
+  *lockfd_r= open(pathbuf_sfx(pb,".lock"), O_RDWR|O_CREAT, lockmode);
+  if (*lockfd_r < 0)
+    return cht_posixerr(ip, errno, "could not open/create lockfile");
+
+  fl.l_type= F_WRLCK;
+  fl.l_whence= SEEK_SET;
+  fl.l_start= 0;
+  fl.l_len= 0;
+  fl.l_pid= getpid();
+
+  r= fcntl(*lockfd_r, F_SETLK, &fl);
+  if (r == -1) {
+    if (errno == EACCES || errno == EAGAIN)
+      return cht_staticerr(ip, "lock held by another process", "CDB LOCKED");
+    else return cht_posixerr(ip, errno, "unexpected error from fcntl while"
+			     " acquiring lock");
+  }
+
+  return TCL_OK;
+}
+
+/*---------- Log reading and writing ----------*/
+
+static int readlognum(FILE *f, int delim, int *num_r) {
+  int c;
+  char numbuf[20], *p, *ep;
+  unsigned long ul;
+
+  p= numbuf;
+  for (;;) {
+    c= getc(f);  if (c==EOF) return -2;
+    if (c == delim) break;
+    if (!isdigit((unsigned char)c)) return -2;
+    *p++= c;
+    if (p == numbuf+sizeof(numbuf)) return -2;
+  }
+  if (p == numbuf) return -2;
+  *p= 0;
+
+  errno=0; ul= strtoul(numbuf, &ep, 10);
+  if (*ep || errno || ul >= INT_MAX/2) return -2;
+  *num_r= ul;
+  return 0;
+}
+
+static int readstorelogrecord(FILE *f, HashTable *ht,
+			      int (*omitfn)(const HashValue*,
+					    struct ht_forall_ctx *ctx),
+			      struct ht_forall_ctx *ctx,
+			      void (*updatefn)(HashTable*, const char*,
+					       HashValue*)) {
+  /* returns:
+   *      0     for OK
+   *     -1     eof
+   *     -2     corrupt or error
+   *     -3     got newline indicating end
+   *     >0     value from omitfn
+   */
+  int keylen, vallen;
+  char *key;
+  HashValue *val;
+  int c, rc, r;
+
+  c= getc(f);
+  if (c==EOF) { return feof(f) ? -1 : -2; }
+  if (c=='\n') return -3;
+  if (c!='+') return -2;
+
+  rc= readlognum(f, ',', &keylen);  if (rc) return rc;
+  rc= readlognum(f, ':', &vallen);  if (rc) return rc;
+
+  key= TALLOC(keylen+1);
+  val= htv_prep(vallen);
+
+  r= fread(key, 1,keylen, f);
+  if (r!=keylen) goto x2_free_keyval;
+  if (memchr(key,0,keylen)) goto x2_free_keyval;
+  key[keylen]= 0;
+
+  c= getc(f);  if (c!='-') goto x2_free_keyval;
+  c= getc(f);  if (c!='>') goto x2_free_keyval;
+  
+  r= fread(htv_fillptr(val), 1,vallen, f);
+  if (r!=vallen) goto x2_free_keyval;
+
+  c= getc(f);  if (c!='\n') goto x2_free_keyval;
+
+  rc= omitfn ? omitfn(val, ctx) : TCL_OK;
+  if (rc) { assert(rc>0); TFREE(val); }
+  else updatefn(ht, key, val);
+  
+  TFREE(key);
+  return rc;
+
+ x2_free_keyval:
+  TFREE(val);
+  TFREE(key);
+  return -2;
+}
+
+static int writerecord(FILE *f, const char *key, const HashValue *val) {
+  int r;
+
+  r= fprintf(f, "+%d,%d:%s->", strlen(key), val->len, key);
+  if (r<0) return -1;
+  
+  r= fwrite(val->data, 1, val->len, f);
+  if (r != val->len) return -1;
+
+  r= putc('\n', f);
+  if (r==EOF) return -1;
+
+  return 0;
+}
+
+/*---------- Creating ----------*/
+
+int cht_do_cdbwr_create_empty(ClientData cd, Tcl_Interp *ip,
+			      const char *pathb) {
+  static const char *const toremoves[]= { ".cdb", ".jrn", ".tmp", 0 };
+
+  Pathbuf pb, pbmain;
+  int lock_fd=-1, rc, r;
+  FILE *f= 0;
+  const char *const *toremove;
+  struct stat stab;
+
+  pathbuf_init(&pb, pathb);
+  pathbuf_init(&pbmain, pathb);
+
+  rc= acquire_lock(ip, &pb, &lock_fd);  if (rc) goto x_rc;
+
+  r= lstat(pathbuf_sfx(&pbmain, ".main"), &stab);
+  if (!r) { rc= cht_staticerr(ip, "database already exists during creation",
+			      "CDB ALREADY-EXISTS");  goto x_rc; }
+  if (errno != ENOENT) PE("check for existing database .main during creation");
+
+  for (toremove=toremoves; *toremove; toremove++) {
+    r= remove(pathbuf_sfx(&pb, *toremove));
+    if (r && errno != ENOENT)
+      PE("delete possible spurious file during creation");
+  }
+  
+  f= fopen(pathbuf_sfx(&pb, ".tmp"), "w");
+  if (!f) PE("create new database .tmp");  
+  r= putc('\n', f);  if (r==EOF) PE("write sentinel to new database .tmp");
+  r= fclose(f);  f=0;  if (r) PE("close new database .tmp during creation");
+
+  r= rename(pb.buf, pbmain.buf);
+  if (r) PE("install new database .tmp as .main (finalising creation)");
+  
+  rc= TCL_OK;
+
+ x_rc:
+  if (f) fclose(f);
+  maybe_close(lock_fd);
+  pathbuf_free(&pb);
+  pathbuf_free(&pbmain);
+  return rc;
+}
+
+/*---------- Info callbacks ----------*/
+
+static int infocbv3(Tcl_Interp *ip, Rw *rw, const char *arg1,
+		    const char *arg2fmt, const char *arg3, va_list al) {
+  Tcl_Obj *aa[3];
+  int na;
+  char buf[200];
+  vsnprintf(buf, sizeof(buf), arg2fmt, al);
+
+  na= 0;
+  aa[na++]= cht_ret_string(ip, arg1);
+  aa[na++]= cht_ret_string(ip, buf);
+  if (arg3) aa[na++]= cht_ret_string(ip, arg3);
+  
+  return cht_scriptinv_invoke_fg(&rw->on_info, na, aa);
+}
+  
+static int infocb3(Tcl_Interp *ip, Rw *rw, const char *arg1,
+		   const char *arg2fmt, const char *arg3, ...) {
+  int rc;
+  va_list al;
+  va_start(al, arg3);
+  rc= infocbv3(ip,rw,arg1,arg2fmt,arg3,al);
+  va_end(al);
+  return rc;
+}
+  
+static int infocb(Tcl_Interp *ip, Rw *rw, const char *arg1,
+		  const char *arg2fmt, ...) {
+  int rc;
+  va_list al;
+  va_start(al, arg2fmt);
+  rc= infocbv3(ip,rw,arg1,arg2fmt,0,al);
+  va_end(al);
+  return rc;
+}
+  
+/*---------- Opening ----------*/
+
+static int cdbinit(Tcl_Interp *ip, Rw *rw) {
+  /* On entry, cdb_fd >=0 but cdb is _undefined_/
+   * On exit, either cdb_fd<0 or cdb is initialised */
+  int r, rc;
+  
+  r= cdb_init(&rw->cdb, rw->cdb_fd);
+  if (r) {
+    rc= cht_posixerr(ip, errno, "failed to initialise cdb reader");
+    close(rw->cdb_fd);  rw->cdb_fd= -1;  return rc;
+  }
+  return TCL_OK;
+}
+
+int cht_do_cdbwr_open(ClientData cd, Tcl_Interp *ip, const char *pathb,
+		      Tcl_Obj *on_info, Tcl_Obj *on_lexminval,
+		      void **result) {
+  const Cdbwr_SubCommand *subcmd= cd;
+  int r, rc, mainfd=-1;
+  Rw *rw;
+  struct stat stab;
+  off_t logrecstart, logjunkpos;
+
+  rw= TALLOC(sizeof(*rw));
+  rw->ix= -1;
+  ht_setup(&rw->logincore);
+  cht_scriptinv_init(&rw->on_info);
+  cht_scriptinv_init(&rw->on_lexminval);
+  rw->cdb_fd= rw->lock_fd= -1;  rw->logfile= 0;
+  pathbuf_init(&rw->pbsome, pathb);
+  pathbuf_init(&rw->pbother, pathb);
+  rw->autocompact= 1;
+
+  rc= cht_scriptinv_set(&rw->on_info, ip, on_info, 0);
+  if (rc) goto x_rc;
+
+  rc= cht_scriptinv_set(&rw->on_lexminval, ip, on_lexminval, 0);
+  if (rc) goto x_rc;
+
+  mainfd= open(pathbuf_sfx(&rw->pbsome,".main"), O_RDONLY);
+  if (mainfd<0) PE("open existing database file .main");
+  rc= acquire_lock(ip, &rw->pbsome, &rw->lock_fd);  if (rc) goto x_rc;
+
+  r= fstat(mainfd, &stab);  if (r) PE("fstat .main");
+  rw->mainsz= stab.st_size;
+
+  rw->cdb_fd= open(pathbuf_sfx(&rw->pbsome,".cdb"), O_RDONLY);
+  if (rw->cdb_fd >=0) {
+    rc= cdbinit(ip, rw);  if (rc) goto x_rc;
+  } else if (errno == ENOENT) {
+    if (rw->mainsz > 1) {
+      rc= cht_staticerr(ip, ".cdb does not exist but .main is >1byte -"
+			" .cdb must have been accidentally deleted!",
+			"CDB CDBMISSING");
+      goto x_rc;
+    }
+    /* fine */
+  } else {
+    PE("open .cdb");
+  }
+
+  rw->logfile= fopen(pathbuf_sfx(&rw->pbsome,".jrn"), "r+");
+  if (!rw->logfile) {
+    if (errno != ENOENT) PE("failed to open .jrn during open");
+    rw->logfile= fopen(rw->pbsome.buf, "w");
+    if (!rw->logfile) PE("create .jrn during (clean) open");
+  } else { /* rw->logfile */
+    r= fstat(fileno(rw->logfile), &stab);
+    if (r==-1) PE("fstat .jrn during open");
+    rc= infocb(ip, rw, "open-dirty-start", "log=%luby",
+	       (unsigned long)stab.st_size);
+    if (rc) goto x_rc;
+
+    for (;;) {
+      logrecstart= ftello(rw->logfile);
+      if (logrecstart < 0) PE("ftello .jrn during (dirty) open");
+      r= readstorelogrecord(rw->logfile, &rw->logincore, 0,0, ht_update);
+      if (ferror(rw->logfile)) {
+	rc= cht_posixerr(ip, errno, "error reading .jrn during (dirty) open");
+	goto x_rc;
+      }
+      if (r==-1) {
+	break;
+      } else if (r==-2 || r==-3) {
+	char buf[100];
+	logjunkpos= ftello(rw->logfile);
+	if(logjunkpos<0) PE("ftello .jrn during report of junk in dirty open");
+
+	snprintf(buf,sizeof(buf), "CDB SYNTAX LOG %lu %lu",
+		 (unsigned long)logjunkpos, (unsigned long)logrecstart);
+
+	if (!(subcmd->flags & RWSCF_OKJUNK)) {
+	  Tcl_SetObjErrorCode(ip, Tcl_NewStringObj(buf,-1));
+	  snprintf(buf,sizeof(buf),"%lu",(unsigned long)logjunkpos);
+	  Tcl_ResetResult(ip);
+	  Tcl_AppendResult(ip, "syntax error (junk) in .jrn during"
+			   " (dirty) open, at file position ", buf, (char*)0);
+	  rc= TCL_ERROR;
+	  goto x_rc;
+	}
+	rc= infocb3(ip, rw, "open-dirty-junk", "errorfpos=%luby", buf,
+		    (unsigned long)logjunkpos);
+	if (rc) goto x_rc;
+
+	r= fseeko(rw->logfile, logrecstart, SEEK_SET);
+	if (r) PE("failed to fseeko .jrn before junk during dirty open");
+
+	r= ftruncate(fileno(rw->logfile), logrecstart);
+	if (r) PE("ftruncate .jrn to chop junk during dirty open");
+      } else {
+	assert(!r);
+      }
+    }
+  }
+  /* now log is positioned for appending and everything is read */
+
+  *result= rw;
+  maybe_close(mainfd);
+  return TCL_OK;
+
+ x_rc:
+  rw_close(0,rw);
+  TFREE(rw);
+  maybe_close(mainfd);
+  return rc;
+}
+
+int cht_do_cdbwr_open_okjunk(ClientData cd, Tcl_Interp *ip, const char *pathb,
+		      Tcl_Obj *on_info, Tcl_Obj *on_lexminval,
+		      void **result) {
+  return cht_do_cdbwr_open(cd,ip,pathb,on_info,on_lexminval,result);
+}
+
+/*==================== COMPACTION ====================*/
+
+struct ht_forall_ctx {
+  struct cdb_make cdbm;
+  FILE *mainfile;
+  long *reccount;
+  int lexminvall;
+  const char *lexminval; /* may be invalid if lexminvall <= 0 */
+};
+
+/*---------- helper functions ----------*/
+
+static int expiredp(const HashValue *val, struct ht_forall_ctx *a) {
+  int r, l;
+  if (!val->len || a->lexminvall<=0) return 0;
+  l= val->len < a->lexminvall ? val->len : a->lexminvall;
+  r= memcmp(val->data, a->lexminval, l);
+  if (r>0) return 0;
+  if (r<0) return 1;
+  return val->len < a->lexminvall;
+}
+
+static int delete_ifexpired(const char *key, HashValue *val,
+			    struct ht_forall_ctx *a) {
+  if (!expiredp(val, a)) return 0;
+  val->len= 0;
+  /* we don't actually need to realloc it to free the memory because
+   * this will shortly all be deleted as part of the compaction */
+  return 0;
+}
+
+static int addto_cdb(const char *key, HashValue *val,
+		     struct ht_forall_ctx *a) {
+  return cdb_make_add(&a->cdbm, key, strlen(key), val->data, val->len);
+}
+
+static int addto_main(const char *key, HashValue *val,
+		      struct ht_forall_ctx *a) {
+  (*a->reccount)++;
+  return writerecord(a->mainfile, key, val);
+}
+
+/*---------- compact main entrypoint ----------*/
+
+static int compact_core(Tcl_Interp *ip, Rw *rw, unsigned long logsz,
+			long *reccount_r) {
+  /* creates new .cdb and .main
+   * closes logfile
+   * leaves .jrn with old data
+   * leaves cdb fd open onto old db
+   * leaves logincore full of crap
+   */
+  int r, rc;
+  int cdbfd, cdbmaking;
+  off_t errpos, newmainsz;
+  char buf[100];
+  Tcl_Obj *res;
+  struct ht_forall_ctx a;
+
+  a.mainfile= 0;
+  cdbfd= -1;
+  cdbmaking= 0;
+  *reccount_r= 0;
+  a.reccount= reccount_r;
+
+  r= fclose(rw->logfile);
+  if (r) { rc= cht_posixerr(ip, errno, "probable data loss!  failed to fclose"
+			    " logfile during compact");  goto x_rc; }
+  rw->logfile= 0;
+  
+  rc= infocb(ip, rw, "compact-start", "log=%luby main=%luby",
+	     logsz, (unsigned long)rw->mainsz);
+  if (rc) goto x_rc;
+
+  if (cht_scriptinv_interp(&rw->on_lexminval)) {
+    rc= cht_scriptinv_invoke_fg(&rw->on_lexminval, 0,0);
+    if (rc) goto x_rc;
+
+    res= Tcl_GetObjResult(ip);  assert(res);
+    a.lexminval= Tcl_GetStringFromObj(res, &a.lexminvall);
+    assert(a.lexminval);
+
+    /* we rely not calling Tcl_Eval during the actual compaction;
+     * if we did Tcl_Eval then the interp result would be trashed.
+     */
+    rc= ht_forall(&rw->logincore, delete_ifexpired, &a);
+
+  } else {
+    a.lexminvall= 0;
+  }
+
+  /* merge unsuperseded records from main into hash table */
+
+  a.mainfile= fopen(pathbuf_sfx(&rw->pbsome,".main"), "r");
+  if (!a.mainfile) PE("failed to open .main for reading during compact");
+
+  for (;;) {
+    r= readstorelogrecord(a.mainfile, &rw->logincore,
+			  expiredp, &a,
+			  ht_maybeupdate);
+    if (ferror(a.mainfile)) { rc= cht_posixerr(ip, errno, "error reading"
+                         " .main during compact"); goto x_rc; }
+    if (r==-3) {
+      break;
+    } else if (r==-1 || r==-2) {
+      errpos= ftello(a.mainfile);
+      if (errpos<0) PE("ftello .main during report of syntax error");
+      snprintf(buf,sizeof(buf), "CDB %s MAIN %lu",
+	       r==-1 ? "TRUNCATED" : "SYNTAX", (unsigned long)errpos);
+      Tcl_SetObjErrorCode(ip, Tcl_NewStringObj(buf,-1));
+      snprintf(buf,sizeof(buf), "%lu", (unsigned long)errpos);
+      Tcl_ResetResult(ip);
+      Tcl_AppendResult(ip,
+		       r==-1 ? "unexpected eof (truncated file)"
+		       " in .main during compact, at file position "
+		       : "syntax error"
+		       " in .main during compact, at file position ",
+		       buf, (char*)0);
+      rc= TCL_ERROR;
+      goto x_rc;
+    } else {
+      assert(!rc);
+    }
+  }
+  fclose(a.mainfile);
+  a.mainfile= 0;
+
+  /* create new cdb */
+
+  cdbfd= open(pathbuf_sfx(&rw->pbsome,".tmp"), O_WRONLY|O_CREAT|O_TRUNC, 0666);
+  if (cdbfd<0) PE("create .tmp for new cdb during compact");
+
+  r= cdb_make_start(&a.cdbm, cdbfd);
+  if (r) PE("cdb_make_start during compact");
+  cdbmaking= 1;
+
+  r= ht_forall(&rw->logincore, addto_cdb, &a);
+  if (r) PE("cdb_make_add during compact");
+
+  r= cdb_make_finish(&a.cdbm);
+  if(r) PE("cdb_make_finish during compact");
+  cdbmaking= 0;
+
+  r= fdatasync(cdbfd);  if (r) PE("fdatasync new cdb during compact");
+  r= close(cdbfd);  if (r) PE("close new cdb during compact");
+  cdbfd= -1;
+
+  r= rename(rw->pbsome.buf, pathbuf_sfx(&rw->pbother,".cdb"));
+  if (r) PE("install new .cdb during compact");
+
+  /* create new main */
+
+  a.mainfile= fopen(pathbuf_sfx(&rw->pbsome,".tmp"), "w");
+  if (!a.mainfile) PE("create .tmp for new main during compact");
+
+  r= ht_forall(&rw->logincore, addto_main, &a);
+  if (r) { rc= cht_posixerr(ip, r, "error writing to new .main"
+			    " during compact");  goto x_rc; }
+
+  r= putc('\n', a.mainfile);
+  if (r==EOF) PE("write trailing \n to main during compact");
+  
+  r= fflush(a.mainfile);  if (r) PE("fflush new main during compact");
+  r= fdatasync(fileno(a.mainfile));
+  if (r) PE("fdatasync new main during compact");
+
+  newmainsz= ftello(a.mainfile);
+  if (newmainsz<0) PE("ftello new main during compact");
+  
+  r= fclose(a.mainfile);  if (r) PE("fclose new main during compact");
+  a.mainfile= 0;
+
+  r= rename(rw->pbsome.buf, pathbuf_sfx(&rw->pbother,".main"));
+  if (r) PE("install new .main during compact");
+
+  rw->mainsz= newmainsz;
+
+  /* done! */
+  
+  rc= infocb(ip, rw, "compact-end", "main=%luby nrecs=%ld",
+	     (unsigned long)rw->mainsz, *a.reccount);
+  if (rc) goto x_rc;
+
+  return rc;
+
+x_rc:
+  if (a.mainfile) fclose(a.mainfile);
+  if (cdbmaking) cdb_make_finish(&a.cdbm);
+  maybe_close(cdbfd);
+  remove(pathbuf_sfx(&rw->pbsome,".tmp")); /* for tidyness */
+  return rc;
+}
+
+/*---------- Closing ----------*/
+
+static int compact_forclose(Tcl_Interp *ip, Rw *rw, long *reccount_r) {
+  off_t logsz;
+  int r, rc;
+
+  logsz= ftello(rw->logfile);
+  if (logsz < 0) PE("ftello logfile (during tidy close)");
+
+  rc= compact_core(ip, rw, logsz, reccount_r);  if (rc) goto x_rc;
+
+  r= remove(pathbuf_sfx(&rw->pbsome,".jrn"));
+  if (r) PE("remove .jrn (during tidy close)");
+
+  return TCL_OK;
+
+x_rc: return rc;
+}
+  
+int cht_do_cdbwr_close(ClientData cd, Tcl_Interp *ip, void *rw_v) {
+  Rw *rw= rw_v;
+  int rc, rc_close;
+  long reccount= -1;
+  off_t logsz;
+
+  if (rw->autocompact) rc= compact_forclose(ip, rw, &reccount);
+  else rc= TCL_OK;
+
+  if (!rc) {
+    if (rw->logfile) {
+      logsz= ftello(rw->logfile);
+      if (logsz < 0)
+	rc= cht_posixerr(ip, errno, "ftell logfile during close info");
+      else
+	rc= infocb(ip, rw, "close", "main=%luby log=%luby",
+		   rw->mainsz, logsz);
+    } else if (reccount>=0) {
+      rc= infocb(ip, rw, "close", "main=%luby nrecs=%ld",
+		 rw->mainsz, reccount);
+    } else {
+      rc= infocb(ip, rw, "close", "main=%luby", rw->mainsz);
+    }
+  }
+  rc_close= rw_close(ip,rw);
+  if (rc_close) rc= rc_close;
+  
+  cht_tabledataid_disposing(ip, rw_v, &cdbtcl_rwdatabases);
+  TFREE(rw);
+  return rc;
+}
+
+/*---------- Other compaction-related entrypoints ----------*/
+
+static int compact_keepopen(Tcl_Interp *ip, Rw *rw, int force) {
+  off_t logsz;
+  long reccount;
+  int rc, r;
+
+  logsz= ftello(rw->logfile);
+  if (logsz < 0) return cht_posixerr(ip, errno, "ftell .jrn"
+				       " during compact check or force");
+
+  if (!force && logsz < rw->mainsz / 3 + 1000) return TCL_OK;
+  /* Test case:                    ^^^ testing best value for this
+   *   main=9690434by nrecs=122803  read all in one go
+   *  no autocompact, :    6.96user 0.68system 0:08.93elapsed
+   *  auto, mulitplier 2:  7.10user 0.79system 0:09.54elapsed
+   *  auto, unity:         7.80user 0.98system 0:11.84elapsed
+   *  auto, divisor  2:    8.23user 1.05system 0:13.30elapsed
+   *  auto, divisor  3:    8.55user 1.12system 0:12.88elapsed
+   *  auto, divisor  5:    9.95user 1.43system 0:15.72elapsed
+   */
+
+  rc= compact_core(ip, rw, logsz, &reccount);  if (rc) goto x_rc;
+
+  maybe_close(rw->cdb_fd);
+  rw->cdb_fd= -1;
+  ht_destroy(&rw->logincore);
+  ht_setup(&rw->logincore);
+
+  rw->cdb_fd= open(pathbuf_sfx(&rw->pbsome,".cdb"), O_RDONLY);
+  if (rw->cdb_fd < 0) PE("reopen .cdb after compact");
+
+  rc= cdbinit(ip, rw);  if (rc) goto x_rc;
+
+  rw->logfile= fopen(pathbuf_sfx(&rw->pbsome,".jrn"), "w");
+  if (!rw->logfile) PE("reopen .jrn after compact");
+
+  r= fsync(fileno(rw->logfile));  if (r) PE("fsync .jrn after compact reopen");
+
+  return TCL_OK;
+
+x_rc:
+  /* doom! all updates fail after this (because rw->logfile is 0), and
+   * we may be using a lot more RAM than would be ideal.  Program will
+   * have to reopen if it really wants sanity. */
+  return rc;
+}
+
+int cht_do_cdbwr_compact_force(ClientData cd, Tcl_Interp *ip, void *rw_v) {
+  return compact_keepopen(ip, rw_v, 1);
+}
+int cht_do_cdbwr_compact_check(ClientData cd, Tcl_Interp *ip, void *rw_v) {
+  return compact_keepopen(ip, rw_v, 0);
+}
+
+int cht_do_cdbwr_compact_explicit(ClientData cd, Tcl_Interp *ip, void *rw_v) {
+  Rw *rw= rw_v;
+  rw->autocompact= 0;
+  return TCL_OK;
+}
+int cht_do_cdbwr_compact_auto(ClientData cd, Tcl_Interp *ip, void *rw_v) {
+  Rw *rw= rw_v;
+  rw->autocompact= 1;
+  return TCL_OK;
+}
+
+/*---------- Updateing ----------*/
+
+static int update(Tcl_Interp *ip, Rw *rw, const char *key,
+		  const Byte *data, int dlen) {
+  HashValue *val;
+  int rc, r;
+
+  if (!rw->logfile) return cht_staticerr
+    (ip, "previous compact failed; cdbwr must be closed and reopened "
+     "before any further updates", "CDB BROKEN");
+  
+  val= htv_prep(dlen);  assert(val);
+  memcpy(htv_fillptr(val), data, dlen);
+
+  r= writerecord(rw->logfile, key, val);
+  if (!r) r= fflush(rw->logfile);
+  if (r) PE("write update to logfile");
+
+  ht_update(&rw->logincore, key, val);
+
+  if (!rw->autocompact) return TCL_OK;
+  return compact_keepopen(ip, rw, 0);
+
+ x_rc:
+  TFREE(val);
+  return rc;
+}  
+
+int cht_do_cdbwr_update(ClientData cd, Tcl_Interp *ip,
+			void *rw_v, const char *key, Tcl_Obj *value) {
+  int dlen;
+  const char *data;
+  data= Tcl_GetStringFromObj(value, &dlen);  assert(data);
+  return update(ip, rw_v, key, data, dlen);
+}
+
+int cht_do_cdbwr_update_hb(ClientData cd, Tcl_Interp *ip,
+			   void *rw_v, const char *key, HBytes_Value value) {
+  return update(ip, rw_v, key, cht_hb_data(&value), cht_hb_len(&value));
+}
+
+int cht_do_cdbwr_delete(ClientData cd, Tcl_Interp *ip, void *rw_v,
+			const char *key) {
+  return update(ip, rw_v, key, 0, 0);
+}
+
+/*---------- Lookups ----------*/
+
+static int lookup_rw(Tcl_Interp *ip, void *rw_v, const char *key,
+		    const Byte **data_r, int *len_r /* -1 => notfound */) {
+  Rw *rw= rw_v;
+  const HashValue *val;
+
+  val= ht_lookup(&rw->logincore, key);
+  if (val) {
+    if (val->len) { *data_r= val->data; *len_r= val->len; return TCL_OK; }
+    else { *data_r= 0; *len_r= -1; return TCL_OK; }
+  }
+
+  return cht_cdb_lookup_cdb(ip, &rw->cdb, key, strlen(key), data_r, len_r);
+} 
+
+int cht_do_cdbwr_lookup(ClientData cd, Tcl_Interp *ip, void *rw_v,
+			const char *key, Tcl_Obj *def,
+			Tcl_Obj **result) {
+  const Byte *data;
+  int dlen, r;
+  
+  r= lookup_rw(ip, rw_v, key, &data, &dlen);  if (r) return r;
+  return cht_cdb_donesomelookup(ip, rw_v, def, result, data, dlen,
+				cht_cdb_storeanswer_string);
+}
+  
+int cht_do_cdbwr_lookup_hb(ClientData cd, Tcl_Interp *ip, void *rw_v,
+			   const char *key, Tcl_Obj *def,
+			   Tcl_Obj **result) {
+  const Byte *data;
+  int dlen, r;
+  
+  r= lookup_rw(ip, rw_v, key, &data, &dlen);  if (r) return r;
+  return cht_cdb_donesomelookup(ip, rw_v, def, result, data, dlen,
+				cht_cdb_storeanswer_hb);
+}
+
+int cht_do_cdbtoplevel_cdb_wr(ClientData cd, Tcl_Interp *ip,
+			      const Cdbwr_SubCommand* subcmd,
+			      int objc, Tcl_Obj *const *objv) {
+  return subcmd->func((void*)subcmd,ip,objc,objv);
+}