sbin/jscan/jfile.c

   1 /*
   2  * Copyright (c) 2004,2005 The DragonFly Project.  All rights reserved.
   3  *
   4  * This code is derived from software contributed to The DragonFly Project
   5  * by Matthew Dillon <dillon@backplane.com>
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  *
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in
  15  *    the documentation and/or other materials provided with the
  16  *    distribution.
  17  * 3. Neither the name of The DragonFly Project nor the names of its
  18  *    contributors may be used to endorse or promote products derived
  19  *    from this software without specific, prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  22  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  23  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  24  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  25  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  26  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
  27  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  28  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  29  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  30  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  31  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  *
  34  * $DragonFly: src/sbin/jscan/jfile.c,v 1.10 2005/09/07 07:20:23 dillon Exp $
  35  */
  36
  37 #include "jscan.h"
  38 #include <dirent.h>
  39
  40 static void jalign(struct jfile *jf, enum jdirection direction);
  41 static int jreadbuf(struct jfile *jf, enum jdirection direction,
  42                     void *buf, int bytes);
  43
  44 /*
  45  * Open a file descriptor for journal record access.
  46  *
  47  * NOTE: only seekable descriptors are supported for backwards scans.
  48  */
  49 struct jfile *
  50 jopen_fd(int fd)
  51 {
  52     struct jfile *jf;
  53
  54     jf = malloc(sizeof(struct jfile));
  55     bzero(jf, sizeof(struct jfile));
  56     jf->jf_fd = fd;
  57     jf->jf_write_fd = -1;
  58     jf->jf_open_flags = O_RDONLY;
  59     jf->jf_pos = 0;
  60     return(jf);
  61 }
  62
  63 /*
  64  * Open a prefix set.  <prefix>.nnnnnnnnn files or a <prefix>.transid file
  65  * must exist to succeed.  No file descriptor is actually opened but
  66  * the sequence number is initialized to the beginning or end of the set.
  67  */
  68 struct jfile *
  69 jopen_prefix(const char *prefix, int rw)
  70 {
  71     struct jfile *jf;
  72     struct jdata *jd;
  73     unsigned int seq_beg = -1;
  74     unsigned int seq_end = -1;
  75     unsigned int seq;
  76     struct stat st;
  77     const char *dirname;
  78     struct dirent *den;
  79     DIR *dir;
  80     char *basename;
  81     char *data;
  82     char *ptr;
  83     int hastransid;
  84     int baselen;
  85     int fd;
  86
  87     dirname = data = strdup(prefix);
  88     if ((basename = strrchr(dirname, '/')) != NULL) {
  89         *basename++ = 0;
  90     } else {
  91         basename = data;
  92         dirname = "./";
  93     }
  94     baselen = strlen(basename);
  95     if ((dir = opendir(dirname)) != NULL) {
  96         while ((den = readdir(dir)) != NULL) {
  97             if (strncmp(den->d_name, basename, baselen) == 0 &&
  98                 den->d_name[baselen] == '.'
  99             ) {
 100                 seq = strtoul(den->d_name + baselen + 1, &ptr, 16);
 101                 if (*ptr == 0 && seq != UINT_MAX) {
 102                     if (seq_beg == (unsigned int)-1 || seq_beg > seq)
 103                         seq_beg = seq;
 104                     if (seq_end == (unsigned int)-1 || seq_end < seq)
 105                         seq_end = seq;
 106                 }
 107             }
 108         }
 109         closedir(dir);
 110     }
 111     free(data);
 112
 113     hastransid = 0;
 114     asprintf(&data, "%s.transid", prefix);
 115     if (stat(data, &st) == 0)
 116         hastransid = 1;
 117     free(data);
 118
 119     if (seq_beg != (unsigned int)-1 || hastransid) {
 120         if (seq_beg == (unsigned int)-1) {
 121             seq_beg = 0;
 122             seq_end = 0;
 123             if (rw) {
 124                 asprintf(&data, "%s.%08x", prefix, 0);
 125                 if ((fd = open(data, O_RDWR|O_CREAT, 0666)) >= 0)
 126                     close(fd);
 127                 free(data);
 128             }
 129         }
 130         jf = malloc(sizeof(struct jfile));
 131         bzero(jf, sizeof(struct jfile));
 132         jf->jf_fd = -1;
 133         jf->jf_write_fd = -1;
 134         jf->jf_prefix = strdup(prefix);
 135         jf->jf_seq = seq_beg;
 136         jf->jf_seq_beg = seq_beg;
 137         jf->jf_seq_end = seq_end;
 138         jf->jf_open_flags = rw ? (O_RDWR|O_CREAT) : O_RDONLY;
 139         if (verbose_opt)
 140             fprintf(stderr, "Open prefix set %08x-%08x\n", seq_beg, seq_end);
 141         if ((jd = jread(jf, NULL, JD_BACKWARDS)) != NULL) {
 142             jf->jf_last_transid = jd->jd_transid;
 143             jfree(jf, jd);
 144         }
 145     } else {
 146         jf = NULL;
 147     }
 148     return(jf);
 149 }
 150
 151 /*
 152  * Get a prefix set ready for append.
 153  */
 154 int
 155 jrecord_init(const char *prefix)
 156 {
 157     struct jfile *jf;
 158     struct stat st;
 159     char *data;
 160     int hasseqspace;
 161     int fd;
 162
 163     /*
 164      * Determine whether we already have a prefix set or whether we need
 165      * to create one.
 166      */
 167     jf = jopen_prefix(prefix, 0);
 168     hasseqspace = 0;
 169     if (jf) {
 170         if (jf->jf_seq_beg != (unsigned int)-1)
 171             hasseqspace = 1;
 172         jclose(jf);
 173     }
 174     asprintf(&data, "%s.transid", prefix);
 175
 176     /*
 177      * If the sequence exists the transid file must ALREADY exist for us
 178      * to be able to safely 'append' to the space.  Locked-down sequence
 179      * spaces do not have a transid file.
 180      */
 181     if (hasseqspace) {
 182         fd = open(data, O_RDWR, 0666);
 183     } else {
 184         fd = open(data, O_RDWR|O_CREAT, 0666);
 185     }
 186     free(data);
 187     if (fd < 0)
 188         return(-1);
 189     if (fstat(fd, &st) == 0 && st.st_size == 0)
 190         write(fd, "0000000000000000\n", 17);    /* starting transid in hex */
 191     close(fd);
 192     return(0);
 193 }
 194
 195 /*
 196  * Close a previously opened journal, clean up any side allocations.
 197  */
 198 void
 199 jclose(struct jfile *jf)
 200 {
 201     if (jf->jf_fd >= 0) {
 202         close(jf->jf_fd);
 203         jf->jf_fd = -1;
 204     }
 205     if (jf->jf_write_fd >= 0) {
 206         close(jf->jf_write_fd);
 207         jf->jf_write_fd = -1;
 208     }
 209     free(jf);
 210 }
 211
 212 /*
 213  * Locate the next (or previous) raw record given a jfile, current record,
 214  * and direction.  If the current record is NULL then the first or last
 215  * record for the current sequence number is returned.
 216  *
 217  * PAD RECORD SPECIAL CASE.  Pad records can be 16 bytes long, which means
 218  * that that rawrecend overlaps the transid field of the rawrecbeg.  Because
 219  * the transid is garbage, we must skip and cannot return pad records.
 220  */
 221 struct jdata *
 222 jread(struct jfile *jf, struct jdata *jd, enum jdirection direction)
 223 {
 224     struct journal_rawrecbeg head;
 225     struct journal_rawrecbeg *headp;
 226     struct journal_rawrecend tail;
 227     struct journal_rawrecend *tailp;
 228     struct stat st;
 229     char *filename;
 230     int allocsize;
 231     int recsize;
 232     int search;
 233     int error;
 234     int n;
 235
 236     if (jd) {
 237         /*
 238          * Handle the next/previous record case.  If running in the forwards
 239          * direction we position the file just after jd.  If running in the
 240          * backwards direction we position the file at the base of jd so
 241          * the backwards read gets the previous record.
 242          *
 243          * In prefix mode we have to get the right descriptor open and
 244          * position the file, since the fall through code resets to the
 245          * beginning or end if it has to open a descriptor.
 246          */
 247         assert(direction != JD_SEQFIRST && direction != JD_SEQLAST);
 248         if (jf->jf_prefix) {
 249             if (jf->jf_fd >= 0 && jf->jf_seq != jd->jd_seq) {
 250                 close(jf->jf_fd);
 251                 jf->jf_fd = -1;
 252             }
 253             jf->jf_seq = jd->jd_seq;
 254             if (jf->jf_fd < 0) {
 255                 asprintf(&filename, "%s.%08x", jf->jf_prefix, jf->jf_seq);
 256                 jf->jf_fd = open(filename, O_RDONLY);
 257                 if (verbose_opt > 1)
 258                     fprintf(stderr, "Open %s fd %d\n", filename, jf->jf_fd);
 259                 free(filename);
 260             }
 261         }
 262         if ((jmodes & JMODEF_INPUT_PIPE) == 0) {
 263             if (direction == JD_FORWARDS) {
 264                 jf->jf_pos = jd->jd_pos + jd->jd_size;
 265                 lseek(jf->jf_fd, jf->jf_pos, 0);
 266             } else {
 267                 jf->jf_pos = jd->jd_pos;
 268                 /* lseek(jf->jf_fd, jf->jf_pos, 0); not needed */
 269             }
 270         } else {
 271             assert(direction == JD_FORWARDS && jf->jf_prefix == NULL);
 272             assert(jf->jf_pos == jd->jd_pos + jd->jd_size);
 273         }
 274         jfree(jf, jd);
 275     } else {
 276         /*
 277          * Handle the first/last record case.  In the prefix case we only
 278          * need to set jf_seq and close the file handle and fall through.
 279          * The SEQ modes maintain the current jf_seq (kinda a hack).
 280          */
 281         if (jf->jf_prefix) {
 282             if (jf->jf_fd >= 0) {
 283                 close(jf->jf_fd);
 284                 jf->jf_fd = -1;
 285             }
 286             switch(direction) {
 287             case JD_FORWARDS:
 288                 jf->jf_seq = jf->jf_seq_beg;
 289                 break;
 290             case JD_BACKWARDS:
 291                 jf->jf_seq = jf->jf_seq_end;
 292                 break;
 293             case JD_SEQFIRST:
 294                 direction = JD_FORWARDS;
 295                 break;
 296             case JD_SEQLAST:
 297                 direction = JD_BACKWARDS;
 298                 break;
 299             }
 300         } else if ((jmodes & JMODEF_INPUT_PIPE) == 0) {
 301             switch(direction) {
 302             case JD_SEQFIRST:
 303                 direction = JD_FORWARDS;
 304                 /* fall through */
 305             case JD_FORWARDS:
 306                 jf->jf_pos = lseek(jf->jf_fd, 0L, SEEK_SET);
 307                 break;
 308             case JD_SEQLAST:
 309                 direction = JD_BACKWARDS;
 310                 /* fall through */
 311             case JD_BACKWARDS:
 312                 jf->jf_pos = lseek(jf->jf_fd, 0L, SEEK_END);
 313                 break;
 314             }
 315         } else {
 316             if (direction == JD_SEQFIRST)
 317                 direction = JD_FORWARDS;
 318             assert(jf->jf_pos == 0 && direction == JD_FORWARDS);
 319         }
 320     }
 321
 322 top:
 323     /*
 324      * If we are doing a prefix scan and the descriptor is not open,
 325      * open the file based on jf_seq and position it to the beginning
 326      * or end based on the direction.  This is how we iterate through
 327      * the prefix set.
 328      */
 329     if (jf->jf_fd < 0) {
 330         asprintf(&filename, "%s.%08x", jf->jf_prefix, jf->jf_seq);
 331         jf->jf_fd = open(filename, O_RDONLY);
 332         if (verbose_opt > 1)
 333             fprintf(stderr, "Open %s fd %d\n", filename, jf->jf_fd);
 334         free(filename);
 335         if (direction == JD_FORWARDS)
 336             jf->jf_pos = lseek(jf->jf_fd, 0L, SEEK_SET);
 337         else
 338             jf->jf_pos = lseek(jf->jf_fd, 0L, SEEK_END);
 339     }
 340
 341     /*
 342      * Get the current offset and make sure it is 16-byte aligned.  If it
 343      * isn't, align it and enter search mode.
 344      */
 345     if (jf->jf_pos & 15) {
 346         jf_warn(jf, "realigning bad offset and entering search mode");
 347         jalign(jf, direction);
 348         search = 1;
 349     } else {
 350         search = 0;
 351     }
 352
 353     error = 0;
 354     if (direction == JD_FORWARDS) {
 355         /*
 356          * Scan the journal forwards.  Note that the file pointer might not
 357          * be seekable.
 358          */
 359         while ((error = jreadbuf(jf, direction, &head, sizeof(head))) == sizeof(head)) {
 360             if (head.begmagic != JREC_BEGMAGIC) {
 361                 if (search == 0)
 362                     jf_warn(jf, "bad beginmagic, searching for new record");
 363                 search = 1;
 364                 jalign(jf, direction);
 365                 continue;
 366             }
 367
 368             /*
 369              * The actual record is 16-byte aligned.  head.recsize contains
 370              * the unaligned record size.
 371              */
 372             recsize = (head.recsize + 15) & ~15;
 373             if (recsize < JREC_MINRECSIZE || recsize > JREC_MAXRECSIZE) {
 374                 if (search == 0)
 375                     jf_warn(jf, "bad recordsize: %d\n", recsize);
 376                 search = 1;
 377                 jalign(jf, direction);
 378                 continue;
 379             }
 380             allocsize = offsetof(struct jdata, jd_data[recsize]);
 381             allocsize = (allocsize + 255) & ~255;
 382             jd = malloc(allocsize);
 383             bzero(jd, offsetof(struct jdata, jd_data[0]));
 384             bcopy(&head, jd->jd_data, sizeof(head));
 385             n = jreadbuf(jf, direction, jd->jd_data + sizeof(head),
 386                          recsize - sizeof(head));
 387             if (n != (int)(recsize - sizeof(head))) {
 388                 if (search == 0)
 389                     jf_warn(jf, "Incomplete stream record\n");
 390                 search = 1;
 391                 jalign(jf, direction);
 392                 free(jd);
 393                 continue;
 394             }
 395
 396             tailp = (void *)(jd->jd_data + recsize - sizeof(*tailp));
 397             if (tailp->endmagic != JREC_ENDMAGIC) {
 398                 if (search == 0)
 399                     jf_warn(jf, "bad endmagic, searching for new record");
 400                 search = 1;
 401                 jalign(jf, direction);
 402                 free(jd);
 403                 continue;
 404             }
 405
 406             /*
 407              * Skip pad records.
 408              */
 409             if (head.streamid == JREC_STREAMID_PAD) {
 410                 free(jd);
 411                 continue;
 412             }
 413
 414             /*
 415              * note: recsize is aligned (the actual record size),
 416              * head.recsize is unaligned (the actual payload size).
 417              */
 418             jd->jd_transid = head.transid;
 419             jd->jd_alloc = allocsize;
 420             jd->jd_size = recsize;
 421             jd->jd_seq = jf->jf_seq;
 422             jd->jd_pos = jf->jf_pos - recsize;
 423             jd->jd_refs = 1;
 424             return(jd);
 425         }
 426     } else {
 427         /*
 428          * Scan the journal backwards.  Note that jread()'s reverse-seek and
 429          * read.  The data read will be forward ordered, however.
 430          */
 431         while ((error = jreadbuf(jf, direction, &tail, sizeof(tail))) == sizeof(tail)) {
 432             if (tail.endmagic != JREC_ENDMAGIC) {
 433                 if (search == 0)
 434                     jf_warn(jf, "bad endmagic, searching for new record");
 435                 search = 1;
 436                 jalign(jf, direction);
 437                 continue;
 438             }
 439
 440             /*
 441              * The actual record is 16-byte aligned.  head.recsize contains
 442              * the unaligned record size.
 443              */
 444             recsize = (tail.recsize + 15) & ~15;
 445             if (recsize < JREC_MINRECSIZE || recsize > JREC_MAXRECSIZE) {
 446                 if (search == 0)
 447                     jf_warn(jf, "bad recordsize: %d\n", recsize);
 448                 search = 1;
 449                 jalign(jf, direction);
 450                 continue;
 451             }
 452             allocsize = offsetof(struct jdata, jd_data[recsize]);
 453             allocsize = (allocsize + 255) & ~255;
 454             jd = malloc(allocsize);
 455             bzero(jd, offsetof(struct jdata, jd_data[0]));
 456             bcopy(&tail, jd->jd_data + recsize - sizeof(tail), sizeof(tail));
 457             n = jreadbuf(jf, direction, jd->jd_data, recsize - sizeof(tail));
 458             if (n != (int)(recsize - sizeof(tail))) {
 459                 if (search == 0)
 460                     jf_warn(jf, "Incomplete stream record\n");
 461                 search = 1;
 462                 jalign(jf, direction);
 463                 free(jd);
 464                 continue;
 465             }
 466
 467             headp = (void *)jd->jd_data;
 468             if (headp->begmagic != JREC_BEGMAGIC) {
 469                 if (search == 0)
 470                     jf_warn(jf, "bad begmagic, searching for new record");
 471                 search = 1;
 472                 jalign(jf, direction);
 473                 free(jd);
 474                 continue;
 475             }
 476
 477             /*
 478              * Skip pad records.
 479              */
 480             if (head.streamid == JREC_STREAMID_PAD) {
 481                 free(jd);
 482                 continue;
 483             }
 484
 485             /*
 486              * note: recsize is aligned (the actual record size),
 487              * head.recsize is unaligned (the actual payload size).
 488              */
 489             jd->jd_transid = headp->transid;
 490             jd->jd_alloc = allocsize;
 491             jd->jd_size = recsize;
 492             jd->jd_seq = jf->jf_seq;
 493             jd->jd_pos = jf->jf_pos;
 494             jd->jd_refs = 1;
 495             return(jd);
 496         }
 497     }
 498
 499     /*
 500      * If reading in prefix mode and there is no more data, close the
 501      * current descriptor, adjust the sequence number, and loop.
 502      *
 503      * If we hit the end of the sequence space and were asked to loop,
 504      * check for the next sequence number and adjust jf_seq_end.  Leave
 505      * the current descriptor open so we do not loose track of its seek
 506      * position, and also to catch a race where another jscan may have
 507      * written more data to the current sequence number before rolling
 508      * the next sequence number.
 509      */
 510     if (error == 0 && jf->jf_prefix) {
 511         if (direction == JD_FORWARDS) {
 512             if (jf->jf_seq < jf->jf_seq_end) {
 513                 ++jf->jf_seq;
 514                 if (verbose_opt)
 515                     fprintf(stderr, "jread: roll to seq %08x\n", jf->jf_seq);
 516                 if (jf->jf_fd >= 0) {
 517                     close(jf->jf_fd);
 518                     jf->jf_fd = -1;
 519                 }
 520                 goto top;
 521             }
 522             if (jmodes & JMODEF_LOOP_FOREVER) {
 523                 asprintf(&filename, "%s.%08x", jf->jf_prefix, jf->jf_seq + 1);
 524                 if (stat(filename, &st) == 0) {
 525                     ++jf->jf_seq_end;
 526                     if (verbose_opt)
 527                         fprintf(stderr, "jread: roll seq_end to %08x\n",
 528                                          jf->jf_seq_end);
 529                 } else {
 530                     sleep(5);
 531                 }
 532                 goto top;
 533             }
 534         } else {
 535             if (jf->jf_seq > jf->jf_seq_beg) {
 536                 --jf->jf_seq;
 537                 if (verbose_opt)
 538                     fprintf(stderr, "jread: roll to seq %08x\n", jf->jf_seq);
 539                 if (jf->jf_fd >= 0) {
 540                     close(jf->jf_fd);
 541                     jf->jf_fd = -1;
 542                 }
 543                 goto top;
 544             }
 545         }
 546     }
 547
 548     /*
 549      * If we hit EOF and were asked to loop forever on the input, leave
 550      * the current descriptor open, sleep, and loop.
 551      *
 552      * We have already handled the prefix case.  This feature only works
 553      * when doing forward scans and the input is not a pipe.
 554      */
 555     if (error == 0 && jf->jf_prefix == NULL &&
 556         (jmodes & JMODEF_LOOP_FOREVER) &&
 557         !(jmodes & JMODEF_INPUT_PIPE) &&
 558         direction == JD_FORWARDS
 559     ) {
 560         sleep(5);
 561         goto top;
 562     }
 563
 564     /*
 565      * Otherwise there are no more records and we are done.
 566      */
 567     return(NULL);
 568 }
 569
 570 /*
 571  * Write a record out.  If this is a prefix set and the file would
 572  * exceed record_size, we rotate into a new sequence number.
 573  */
 574 void
 575 jwrite(struct jfile *jf, struct jdata *jd)
 576 {
 577     struct stat st;
 578     char *path;
 579     int n;
 580
 581     assert(jf->jf_prefix);
 582
 583 again:
 584     /*
 585      * Open/create a new file in the prefix set
 586      */
 587     if (jf->jf_write_fd < 0) {
 588         asprintf(&path, "%s.%08x", jf->jf_prefix, jf->jf_seq_end);
 589         jf->jf_write_fd = open(path, O_RDWR|O_CREAT, 0666);
 590         if (jf->jf_write_fd < 0 || fstat(jf->jf_write_fd, &st) != 0) {
 591             fprintf(stderr, "Unable to open/create %s\n", path);
 592             exit(1);
 593         }
 594         jf->jf_write_pos = st.st_size;
 595         lseek(jf->jf_write_fd, jf->jf_write_pos, 0);
 596         free(path);
 597     }
 598
 599     /*
 600      * Each file must contain at least one raw record, even if it exceeds
 601      * the user-requested record-size.  Apart from that, we cycle to the next
 602      * file when its size would exceed the user-specified
 603      */
 604     if (jf->jf_write_pos > 0 &&
 605         jf->jf_write_pos + jd->jd_size > prefix_file_size
 606     ) {
 607         close(jf->jf_write_fd);
 608         jf->jf_write_fd = -1;
 609         ++jf->jf_seq_end;
 610         goto again;
 611     }
 612
 613     /*
 614      * Terminate if a failure occurs (for now).
 615      */
 616     n = write(jf->jf_write_fd, jd->jd_data, jd->jd_size);
 617     if (n != jd->jd_size) {
 618         ftruncate(jf->jf_write_fd, jf->jf_write_pos);
 619         fprintf(stderr, "jwrite: failed %s\n", strerror(errno));
 620         exit(1);
 621     }
 622     jf->jf_write_pos += n;
 623     jf->jf_last_transid = jd->jd_transid;
 624 }
 625
 626 /*
 627  * Attempt to locate and return the record specified by the transid.  The
 628  * returned record may be inexact.
 629  *
 630  * If scanning forwards this function guarentees that no record prior
 631  * to the returned record is >= transid.
 632  *
 633  * If scanning backwards this function guarentees that no record after
 634  * the returned record is <= transid.
 635  */
 636 struct jdata *
 637 jseek(struct jfile *jf, int64_t transid, enum jdirection direction)
 638 {
 639     unsigned int seq;
 640     struct jdata *jd = NULL;
 641
 642     /*
 643      * If the input is a pipe we can't seek.
 644      */
 645     if (jmodes & JMODEF_INPUT_PIPE) {
 646         assert(direction == JD_FORWARDS);
 647         return (jread(jf, NULL, direction));
 648     }
 649
 650     if (jf->jf_prefix) {
 651         /*
 652          * If we have a prefix set search the sequence space backwards until
 653          * we find the file most likely to contain the transaction id.
 654          */
 655         if (verbose_opt > 2) {
 656             fprintf(stderr, "jseek prefix set %s %08x-%08x\n", jf->jf_prefix,
 657                     jf->jf_seq_beg, jf->jf_seq_end);
 658         }
 659         jd = NULL;
 660         for (seq = jf->jf_seq_end; seq != jf->jf_seq_beg - 1; --seq) {
 661             if (verbose_opt > 2)
 662                 fprintf(stderr, "try seq %08x\n", seq);
 663             jf->jf_seq = seq;
 664             if ((jd = jread(jf, NULL, JD_SEQFIRST)) != NULL) {
 665                 if (jd->jd_transid == transid)
 666                     return(jd);
 667                 if (jd->jd_transid < transid) {
 668                     jfree(jf, jd);
 669                     break;
 670                 }
 671                 jfree(jf, jd);
 672             }
 673         }
 674
 675         /*
 676          * if transid is less the first file in the sequence space we
 677          * return NULL if scanning backwards, indicating no records are
 678          * available, or the first record in the sequence space if we
 679          * are scanning forwards.
 680          */
 681         if (seq == jf->jf_seq_beg - 1) {
 682             if (direction == JD_BACKWARDS)
 683                 return(NULL);
 684             else
 685                 return(jread(jf, NULL, JD_FORWARDS));
 686         }
 687         if (verbose_opt > 1)
 688             fprintf(stderr, "jseek input prefix set to seq %08x\n", seq);
 689     }
 690
 691     /*
 692      * Position us to the end of the current record, then scan backwards
 693      * looking for the requested transid.
 694      */
 695     jd = jread(jf, NULL, JD_SEQLAST);
 696     while (jd != NULL) {
 697         if (jd->jd_transid <= transid) {
 698             if (jd->jd_transid < transid) {
 699                 if (direction == JD_FORWARDS)
 700                     jd =jread(jf, jd, JD_FORWARDS);
 701             }
 702             if (verbose_opt > 1) {
 703                 fprintf(stderr, "jseek returning seq %08x offset 0x%08jx\n",
 704                         jd->jd_seq, (uintmax_t)jd->jd_pos);
 705             }
 706             return(jd);
 707         }
 708         jd = jread(jf, jd, JD_BACKWARDS);
 709     }
 710
 711     /*
 712      * We scanned the whole file with no luck, all the transid's are
 713      * greater then the requested transid.  If the intended read
 714      * direction is backwards there are no records and we return NULL.
 715      * If it is forwards we return the first record.
 716      */
 717     if (direction == JD_BACKWARDS)
 718         return(NULL);
 719     else
 720         return(jread(jf, NULL, JD_FORWARDS));
 721 }
 722
 723 /*
 724  * Data returned by jread() is persistent until released.
 725  */
 726 struct jdata *
 727 jref(struct jdata *jd)
 728 {
 729     ++jd->jd_refs;
 730     return(jd);
 731 }
 732
 733 void
 734 jfree(struct jfile *jf __unused, struct jdata *jd)
 735 {
 736     if (--jd->jd_refs == 0)
 737         free(jd);
 738 }
 739
 740 /*
 741  * Align us to the next 16 byte boundary.  If scanning forwards we align
 742  * forwards if not already aligned.  If scanning backwards we align
 743  * backwards if not already aligned.  We only have to synchronize the
 744  * seek position with the file seek position for forward scans.
 745  */
 746 static void
 747 jalign(struct jfile *jf, enum jdirection direction)
 748 {
 749     char dummy[16];
 750     int bytes;
 751
 752     if ((int)jf->jf_pos & 15) {
 753         if (direction == JD_FORWARDS) {
 754             bytes = 16 - ((int)jf->jf_pos & 15);
 755             jreadbuf(jf, direction, dummy, bytes);
 756         } else {
 757             jf->jf_pos = jf->jf_pos & ~(off_t)15;
 758         }
 759     }
 760 }
 761
 762 /*
 763  * Read the next raw journal record forwards or backwards and return a
 764  * pointer to it.  Note that the file pointer's actual seek position does
 765  * not match jf_pos in the reverse direction case.
 766  */
 767 static int
 768 jreadbuf(struct jfile *jf, enum jdirection direction, void *buf, int bytes)
 769 {
 770     int ttl = 0;
 771     int n;
 772
 773     if (jf->jf_fd < 0)
 774         return(0);
 775
 776     if (direction == JD_FORWARDS) {
 777         while (ttl != bytes) {
 778             n = read(jf->jf_fd, (char *)buf + ttl, bytes - ttl);
 779             if (n <= 0) {
 780                 if (n < 0 && ttl == 0)
 781                     ttl = -errno;
 782                 break;
 783             }
 784             ttl += n;
 785             jf->jf_pos += n;
 786         }
 787     } else {
 788         if (jf->jf_pos >= bytes) {
 789             jf->jf_pos -= bytes;
 790             lseek(jf->jf_fd, jf->jf_pos, 0);
 791             while (ttl != bytes) {
 792                 n = read(jf->jf_fd, (char *)buf + ttl, bytes - ttl);
 793                 if (n <= 0) {
 794                     if (n < 0 && ttl == 0)
 795                         ttl = -errno;
 796                     break;
 797                 }
 798                 ttl += n;
 799             }
 800         }
 801     }
 802     return(ttl);
 803 }
 804