/* $NetBSD: reverse.c,v 1.24 2026/04/30 15:52:40 christos Exp $ */ /*- * Copyright (c) 1991, 1993 * The Regents of the University of California. All rights reserved. * * This code is derived from software contributed to Berkeley by * Edward Sze-Tyan Wang. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. Neither the name of the University nor the names of its contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ #include <sys/cdefs.h> #ifndef lint #if 0 static char sccsid[] = "@(#)reverse.c 8.1 (Berkeley) 6/6/93"; #endif __RCSID("$NetBSD: reverse.c,v 1.24 2026/04/30 15:52:40 christos Exp $"); #endif /* not lint */ #include <sys/param.h> #include <sys/stat.h> #include <sys/mman.h> #include <limits.h> #include <errno.h> #include <unistd.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include "extern.h" static void r_buf(FILE *); static void r_reg(FILE *, enum STYLE, off_t, struct stat *); /* * reverse -- display input in reverse order by line. * * There are six separate cases for this -- regular and non-regular * files by bytes, lines or the whole file. * * BYTES display N bytes * REG mmap the file and display the lines * NOREG cyclically read characters into a wrap-around buffer * * LINES display N lines * REG mmap the file and display the lines * NOREG cyclically read lines into a wrap-around array of buffers * * FILE display the entire file * REG mmap the file and display the lines * NOREG cyclically read input into a linked list of buffers */ void reverse(FILE *fp, enum STYLE style, off_t off, struct stat *sbp) { if (style != REVERSE && off == 0) return; if (S_ISREG(sbp->st_mode) && sbp->st_size > 0) r_reg(fp, style, off, sbp); else switch(style) { case FBYTES: case RBYTES: (void)displaybytes(fp, off); break; case FLINES: case RLINES: (void)displaylines(fp, off); break; case REVERSE: r_buf(fp); break; default: break; } } /* * r_reg -- display a regular file in reverse order by line. */ static void r_reg(FILE *fp, enum STYLE style, off_t off, struct stat *sbp) { off_t size; int llen; char *p; char *start; if (!(size = sbp->st_size)) return; if ((uint64_t)size > SIZE_T_MAX) { /* XXX: need a cleaner way to check this on amd64 */ errno = EFBIG; xerr(0, "%s", fname); return; } if ((start = mmap(NULL, (size_t)size, PROT_READ, MAP_FILE|MAP_SHARED, fileno(fp), (off_t)0)) == MAP_FAILED) { xerr(0, "%s", fname); return; } p = start + size - 1; if (style == RBYTES && off < size) size = off; /* Last char is special, ignore whether newline or not. */ for (llen = 1; --size; ++llen) if (*--p == '\n') { WR(p + 1, llen); llen = 0; if (style == RLINES && !--off) { ++p; break; } } if (llen) WR(p, llen); if (munmap(start, (size_t)sbp->st_size)) xerr(0, "%s", fname); } typedef struct bf { struct bf *next; struct bf *prev; int len; char *l; } BF; /* * r_buf -- display a non-regular file in reverse order by line. * * This is the function that saves the entire input, storing the data in a * doubly linked list of buffers and then displays them in reverse order. * It has the usual nastiness of trying to find the newlines, as there's no * guarantee that a newline occurs anywhere in the file, let alone in any * particular buffer. If we run out of memory, input is discarded (and the * user warned). */ static void r_buf(FILE *fp) { BF *mark, *tl, *tr; int ch, len, llen; char *p; off_t enomem; #define BSZ (128 * 1024) tl = NULL; for (mark = NULL, enomem = 0;;) { /* * Allocate a new block and link it into place in a doubly * linked list. If out of memory, toss the LRU block and * keep going. */ if (enomem) { if (!mark) { errno = ENOMEM; xerr(1, NULL); } tl = tl->next; enomem += tl->len; } else if ((tl = malloc(sizeof(*tl))) == NULL || (tl->l = malloc(BSZ)) == NULL) { if (tl) free(tl); if (!mark) { errno = ENOMEM; xerr(1, NULL); } tl = mark; enomem += tl->len; } else if (mark) { tl->next = mark; tl->prev = mark->prev; mark->prev->next = tl; mark->prev = tl; } else { mark = tl; mark->next = mark->prev = mark; } /* Fill the block with input data. */ ch = 0; for (p = tl->l, len = 0; len < BSZ && (ch = getc(fp)) != EOF; ++len) *p++ = ch; /* * If no input data for this block and we tossed some data, * recover it. */ if (!len) { if (enomem) enomem -= tl->len; tl = tl->prev; break; } tl->len = len; if (ch == EOF) break; } if (enomem) { xerrx(0, "Warning: %lld bytes discarded", (long long)enomem); } /* * Step through the blocks in the reverse order read. The last char * is special, ignore whether newline or not. */ for (mark = tl;;) { for (p = tl->l + (len = tl->len) - 1, llen = 0; len--; --p, ++llen) if (*p == '\n') { if (llen) { WR(p + 1, llen); llen = 0; } if (tl == mark) continue; for (tr = tl->next; tr->len; tr = tr->next) { WR(tr->l, tr->len); tr->len = 0; if (tr == mark) break; } } tl->len = llen; if ((tl = tl->prev) == mark) break; } tl = tl->next; if (tl->len) { WR(tl->l, tl->len); tl->len = 0; } while ((tl = tl->next)->len) { WR(tl->l, tl->len); tl->len = 0; } }
