LXR busybox/coreutils/tail.c

   1/* vi: set sw=4 ts=4: */
   2/*
   3 * Mini tail implementation for busybox
   4 *
   5 * Copyright (C) 2001 by Matt Kraai <kraai@alumni.carnegiemellon.edu>
   6 *
   7 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   8 */
   9/* Mar 16, 2003      Manuel Novoa III   (mjn3@codepoet.org)
  10 *
  11 * Pretty much rewritten to fix numerous bugs and reduce realloc() calls.
  12 * Bugs fixed (although I may have forgotten one or two... it was pretty bad)
  13 * 1) mixing printf/write without fflush()ing stdout
  14 * 2) no check that any open files are present
  15 * 3) optstring had -q taking an arg
  16 * 4) no error checking on write in some cases, and a warning even then
  17 * 5) q and s interaction bug
  18 * 6) no check for lseek error
  19 * 7) lseek attempted when count==0 even if arg was +0 (from top)
  20 */
  21//config:config TAIL
  22//config:       bool "tail (7.1 kb)"
  23//config:       default y
  24//config:       help
  25//config:       tail is used to print the last specified number of lines
  26//config:       from files.
  27//config:
  28//config:config FEATURE_FANCY_TAIL
  29//config:       bool "Enable -q, -s, -v, and -F options"
  30//config:       default y
  31//config:       depends on TAIL
  32//config:       help
  33//config:       These options are provided by GNU tail, but
  34//config:       are not specified in the SUSv3 standard:
  35//config:               -q      Never output headers giving file names
  36//config:               -s SEC  Wait SEC seconds between reads with -f
  37//config:               -v      Always output headers giving file names
  38//config:               -F      Same as -f, but keep retrying
  39
  40//applet:IF_TAIL(APPLET(tail, BB_DIR_USR_BIN, BB_SUID_DROP))
  41
  42//kbuild:lib-$(CONFIG_TAIL) += tail.o
  43
  44/* BB_AUDIT SUSv3 compliant (need fancy for -c) */
  45/* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
  46/* http://www.opengroup.org/onlinepubs/007904975/utilities/tail.html */
  47
  48//usage:#define tail_trivial_usage
  49//usage:       "[OPTIONS] [FILE]..."
  50//usage:#define tail_full_usage "\n\n"
  51//usage:       "Print last 10 lines of each FILE (or stdin) to stdout.\n"
  52//usage:       "With more than one FILE, precede each with a filename header.\n"
  53//usage:     "\n        -f              Print data as file grows"
  54//usage:     "\n        -c [+]N[kbm]    Print last N bytes"
  55//usage:     "\n        -n N[kbm]       Print last N lines"
  56//usage:     "\n        -n +N[kbm]      Start on Nth line and print the rest"
  57//usage:        IF_FEATURE_FANCY_TAIL(
  58//usage:     "\n        -q              Never print headers"
  59//usage:     "\n        -s SECONDS      Wait SECONDS between reads with -f"
  60//usage:     "\n        -v              Always print headers"
  61//usage:     "\n        -F              Same as -f, but keep retrying"
  62//usage:     "\n"
  63//usage:     "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
  64//usage:        )
  65//usage:
  66//usage:#define tail_example_usage
  67//usage:       "$ tail -n 1 /etc/resolv.conf\n"
  68//usage:       "nameserver 10.0.0.1\n"
  69
  70#include "libbb.h"
  71#include "common_bufsiz.h"
  72
  73struct globals {
  74        bool from_top;
  75        bool exitcode;
  76} FIX_ALIASING;
  77#define G (*(struct globals*)bb_common_bufsiz1)
  78#define INIT_G() do { setup_common_bufsiz(); } while (0)
  79
  80static void tail_xprint_header(const char *fmt, const char *filename)
  81{
  82        if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
  83                bb_perror_nomsg_and_die();
  84}
  85
  86static ssize_t tail_read(int fd, char *buf, size_t count)
  87{
  88        ssize_t r;
  89
  90        r = full_read(fd, buf, count);
  91        if (r < 0) {
  92                bb_perror_msg(bb_msg_read_error);
  93                G.exitcode = EXIT_FAILURE;
  94        }
  95
  96        return r;
  97}
  98
  99#define header_fmt_str "\n==> %s <==\n"
 100
 101static unsigned eat_num(const char *p)
 102{
 103        if (*p == '-')
 104                p++;
 105        else if (*p == '+') {
 106                p++;
 107                G.from_top = 1;
 108        }
 109        return xatou_sfx(p, bkm_suffixes);
 110}
 111
 112int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 113int tail_main(int argc, char **argv)
 114{
 115        unsigned count = 10;
 116        unsigned sleep_period = 1;
 117        const char *str_c, *str_n;
 118
 119        char *tailbuf;
 120        size_t tailbufsize;
 121        unsigned header_threshhold = 1;
 122        unsigned nfiles;
 123        int i, opt;
 124
 125        int *fds;
 126        const char *fmt;
 127        int prev_fd;
 128
 129        INIT_G();
 130
 131#if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 132        /* Allow legacy syntax of an initial numeric option without -n. */
 133        if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
 134         && isdigit(argv[1][1])
 135        ) {
 136                count = eat_num(argv[1]);
 137                argv++;
 138                argc--;
 139        }
 140#endif
 141
 142        /* -s NUM, -F imlies -f */
 143        opt = getopt32(argv, IF_FEATURE_FANCY_TAIL("^")
 144                        "fc:n:"IF_FEATURE_FANCY_TAIL("qs:+vF")
 145                        IF_FEATURE_FANCY_TAIL("\0" "Ff"),
 146                        &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period)
 147        );
 148#define FOLLOW (opt & 0x1)
 149#define COUNT_BYTES (opt & 0x2)
 150        //if (opt & 0x1) // -f
 151        if (opt & 0x2) count = eat_num(str_c); // -c
 152        if (opt & 0x4) count = eat_num(str_n); // -n
 153#if ENABLE_FEATURE_FANCY_TAIL
 154        /* q: make it impossible for nfiles to be > header_threshhold */
 155        if (opt & 0x8) header_threshhold = UINT_MAX; // -q
 156        //if (opt & 0x10) // -s
 157        if (opt & 0x20) header_threshhold = 0; // -v
 158# define FOLLOW_RETRY (opt & 0x40)
 159#else
 160# define FOLLOW_RETRY 0
 161#endif
 162        argc -= optind;
 163        argv += optind;
 164
 165        /* open all the files */
 166        fds = xmalloc(sizeof(fds[0]) * (argc + 1));
 167        if (!argv[0]) {
 168                struct stat statbuf;
 169
 170                if (fstat(STDIN_FILENO, &statbuf) == 0
 171                 && S_ISFIFO(statbuf.st_mode)
 172                ) {
 173                        opt &= ~1; /* clear FOLLOW */
 174                }
 175                argv[0] = (char *) bb_msg_standard_input;
 176        }
 177        nfiles = i = 0;
 178        do {
 179                int fd = open_or_warn_stdin(argv[i]);
 180                if (fd < 0 && !FOLLOW_RETRY) {
 181                        G.exitcode = EXIT_FAILURE;
 182                        continue;
 183                }
 184                fds[nfiles] = fd;
 185                argv[nfiles++] = argv[i];
 186        } while (++i < argc);
 187
 188        if (!nfiles)
 189                bb_error_msg_and_die("no files");
 190
 191        /* prepare the buffer */
 192        tailbufsize = BUFSIZ;
 193        if (!G.from_top && COUNT_BYTES) {
 194                if (tailbufsize < count + BUFSIZ) {
 195                        tailbufsize = count + BUFSIZ;
 196                }
 197        }
 198        /* tail -c1024m REGULAR_FILE doesn't really need 1G mem block.
 199         * (In fact, it doesn't need ANY memory). So delay allocation.
 200         */
 201        tailbuf = NULL;
 202
 203        /* tail the files */
 204
 205        fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */
 206        i = 0;
 207        do {
 208                char *buf;
 209                int taillen;
 210                int newlines_seen;
 211                unsigned seen;
 212                int nread;
 213                int fd = fds[i];
 214
 215                if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 216                        continue; /* may happen with -F */
 217
 218                if (nfiles > header_threshhold) {
 219                        tail_xprint_header(fmt, argv[i]);
 220                        fmt = header_fmt_str;
 221                }
 222
 223                if (!G.from_top) {
 224                        off_t current = lseek(fd, 0, SEEK_END);
 225                        if (current > 0) {
 226                                unsigned off;
 227                                if (COUNT_BYTES) {
 228                                /* Optimizing count-bytes case if the file is seekable.
 229                                 * Beware of backing up too far.
 230                                 * Also we exclude files with size 0 (because of /proc/xxx) */
 231                                        if (count == 0)
 232                                                continue; /* showing zero bytes is easy :) */
 233                                        current -= count;
 234                                        if (current < 0)
 235                                                current = 0;
 236                                        xlseek(fd, current, SEEK_SET);
 237                                        bb_copyfd_size(fd, STDOUT_FILENO, count);
 238                                        continue;
 239                                }
 240#if 1 /* This is technically incorrect for *LONG* strings, but very useful */
 241                                /* Optimizing count-lines case if the file is seekable.
 242                                 * We assume the lines are <64k.
 243                                 * (Users complain that tail takes too long
 244                                 * on multi-gigabyte files) */
 245                                off = (count | 0xf); /* for small counts, be more paranoid */
 246                                if (off > (INT_MAX / (64*1024)))
 247                                        off = (INT_MAX / (64*1024));
 248                                current -= off * (64*1024);
 249                                if (current < 0)
 250                                        current = 0;
 251                                xlseek(fd, current, SEEK_SET);
 252#endif
 253                        }
 254                }
 255
 256                if (!tailbuf)
 257                        tailbuf = xmalloc(tailbufsize);
 258
 259                buf = tailbuf;
 260                taillen = 0;
 261                /* "We saw 1st line/byte".
 262                 * Used only by +N code ("start from Nth", 1-based): */
 263                seen = 1;
 264                newlines_seen = 0;
 265                while ((nread = tail_read(fd, buf, tailbufsize - taillen)) > 0) {
 266                        if (G.from_top) {
 267                                int nwrite = nread;
 268                                if (seen < count) {
 269                                        /* We need to skip a few more bytes/lines */
 270                                        if (COUNT_BYTES) {
 271                                                nwrite -= (count - seen);
 272                                                seen += nread;
 273                                        } else {
 274                                                char *s = buf;
 275                                                do {
 276                                                        --nwrite;
 277                                                        if (*s++ == '\n' && ++seen == count) {
 278                                                                break;
 279                                                        }
 280                                                } while (nwrite);
 281                                        }
 282                                }
 283                                if (nwrite > 0)
 284                                        xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
 285                        } else if (count) {
 286                                if (COUNT_BYTES) {
 287                                        taillen += nread;
 288                                        if (taillen > (int)count) {
 289                                                memmove(tailbuf, tailbuf + taillen - count, count);
 290                                                taillen = count;
 291                                        }
 292                                } else {
 293                                        int k = nread;
 294                                        int newlines_in_buf = 0;
 295
 296                                        do { /* count '\n' in last read */
 297                                                k--;
 298                                                if (buf[k] == '\n') {
 299                                                        newlines_in_buf++;
 300                                                }
 301                                        } while (k);
 302
 303                                        if (newlines_seen + newlines_in_buf < (int)count) {
 304                                                newlines_seen += newlines_in_buf;
 305                                                taillen += nread;
 306                                        } else {
 307                                                int extra = (buf[nread-1] != '\n');
 308                                                char *s;
 309
 310                                                k = newlines_seen + newlines_in_buf + extra - count;
 311                                                s = tailbuf;
 312                                                while (k) {
 313                                                        if (*s == '\n') {
 314                                                                k--;
 315                                                        }
 316                                                        s++;
 317                                                }
 318                                                taillen += nread - (s - tailbuf);
 319                                                memmove(tailbuf, s, taillen);
 320                                                newlines_seen = count - extra;
 321                                        }
 322                                        if (tailbufsize < (size_t)taillen + BUFSIZ) {
 323                                                tailbufsize = taillen + BUFSIZ;
 324                                                tailbuf = xrealloc(tailbuf, tailbufsize);
 325                                        }
 326                                }
 327                                buf = tailbuf + taillen;
 328                        }
 329                } /* while (tail_read() > 0) */
 330                if (!G.from_top) {
 331                        xwrite(STDOUT_FILENO, tailbuf, taillen);
 332                }
 333        } while (++i < nfiles);
 334        prev_fd = fds[i-1];
 335
 336        tailbuf = xrealloc(tailbuf, BUFSIZ);
 337
 338        fmt = NULL;
 339
 340        if (FOLLOW) while (1) {
 341                sleep(sleep_period);
 342
 343                i = 0;
 344                do {
 345                        int nread;
 346                        const char *filename = argv[i];
 347                        int fd = fds[i];
 348
 349                        if (FOLLOW_RETRY) {
 350                                struct stat sbuf, fsbuf;
 351
 352                                if (fd < 0
 353                                 || fstat(fd, &fsbuf) < 0
 354                                 || stat(filename, &sbuf) < 0
 355                                 || fsbuf.st_dev != sbuf.st_dev
 356                                 || fsbuf.st_ino != sbuf.st_ino
 357                                ) {
 358                                        int new_fd;
 359
 360                                        if (fd >= 0)
 361                                                close(fd);
 362                                        new_fd = open(filename, O_RDONLY);
 363                                        if (new_fd >= 0) {
 364                                                bb_error_msg("%s has %s; following end of new file",
 365                                                        filename, (fd < 0) ? "appeared" : "been replaced"
 366                                                );
 367                                        } else if (fd >= 0) {
 368                                                bb_perror_msg("%s has become inaccessible", filename);
 369                                        }
 370                                        fds[i] = fd = new_fd;
 371                                }
 372                        }
 373                        if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 374                                continue;
 375                        if (nfiles > header_threshhold) {
 376                                fmt = header_fmt_str;
 377                        }
 378                        for (;;) {
 379                                /* tail -f keeps following files even if they are truncated */
 380                                struct stat sbuf;
 381                                /* /proc files report zero st_size, don't lseek them */
 382                                if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
 383                                        off_t current = lseek(fd, 0, SEEK_CUR);
 384                                        if (sbuf.st_size < current)
 385                                                xlseek(fd, 0, SEEK_SET);
 386                                }
 387
 388                                nread = tail_read(fd, tailbuf, BUFSIZ);
 389                                if (nread <= 0)
 390                                        break;
 391                                if (fmt && (fd != prev_fd)) {
 392                                        tail_xprint_header(fmt, filename);
 393                                        fmt = NULL;
 394                                        prev_fd = fd;
 395                                }
 396                                xwrite(STDOUT_FILENO, tailbuf, nread);
 397                        }
 398                } while (++i < nfiles);
 399        } /* while (1) */
 400
 401        if (ENABLE_FEATURE_CLEAN_UP) {
 402                free(fds);
 403                free(tailbuf);
 404        }
 405        return G.exitcode;
 406}
 407