source: MondoRescue/branches/2.2.9/mindi-busybox/coreutils/tail.c@ 2725

/* vi: set sw=4 ts=4: */
/*
 * Mini tail implementation for busybox
 *
 * Copyright (C) 2001 by Matt Kraai <kraai@alumni.carnegiemellon.edu>
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */

/* BB_AUDIT SUSv3 compliant (need fancy for -c) */
/* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
/* http://www.opengroup.org/onlinepubs/007904975/utilities/tail.html */

/* Mar 16, 2003      Manuel Novoa III   (mjn3@codepoet.org)
 *
 * Pretty much rewritten to fix numerous bugs and reduce realloc() calls.
 * Bugs fixed (although I may have forgotten one or two... it was pretty bad)
 * 1) mixing printf/write without fflush()ing stdout
 * 2) no check that any open files are present
 * 3) optstring had -q taking an arg
 * 4) no error checking on write in some cases, and a warning even then
 * 5) q and s interaction bug
 * 6) no check for lseek error
 * 7) lseek attempted when count==0 even if arg was +0 (from top)
 */

#include "libbb.h"

static const struct suffix_mult tail_suffixes[] = {
    { "b", 512 },
    { "k", 1024 },
    { "m", 1024*1024 },
    { "", 0 }
};

struct globals {
    bool status;
} FIX_ALIASING;
#define G (*(struct globals*)&bb_common_bufsiz1)

static void tail_xprint_header(const char *fmt, const char *filename)
{
    if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
        bb_perror_nomsg_and_die();
}

static ssize_t tail_read(int fd, char *buf, size_t count)
{
    ssize_t r;
    off_t current;
    struct stat sbuf;

    /* /proc files report zero st_size, don't lseek them. */
    if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
        current = lseek(fd, 0, SEEK_CUR);
        if (sbuf.st_size < current)
            xlseek(fd, 0, SEEK_SET);
    }

    r = full_read(fd, buf, count);
    if (r < 0) {
        bb_perror_msg(bb_msg_read_error);
        G.status = EXIT_FAILURE;
    }

    return r;
}

#define header_fmt_str "\n==> %s <==\n"

static unsigned eat_num(const char *p)
{
    if (*p == '-')
        p++;
    else if (*p == '+') {
        p++;
        G.status = 1; /* mark that we saw "+" */
    }
    return xatou_sfx(p, tail_suffixes);
}

int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int tail_main(int argc, char **argv)
{
    unsigned count = 10;
    unsigned sleep_period = 1;
    bool from_top;
    const char *str_c, *str_n;

    char *tailbuf;
    size_t tailbufsize;
    unsigned header_threshhold = 1;
    unsigned nfiles;
    int i, opt;

    int *fds;
    const char *fmt;

#if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
    /* Allow legacy syntax of an initial numeric option without -n. */
    if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
     && isdigit(argv[1][1])
    ) {
        count = eat_num(argv[1]);
        argv++;
        argc--;
    }
#endif

    /* -s NUM, -F imlies -f */
    IF_FEATURE_FANCY_TAIL(opt_complementary = "s+:Ff";)
    opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:vF"),
            &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
#define FOLLOW (opt & 0x1)
#define COUNT_BYTES (opt & 0x2)
    //if (opt & 0x1) // -f
    if (opt & 0x2) count = eat_num(str_c); // -c
    if (opt & 0x4) count = eat_num(str_n); // -n
#if ENABLE_FEATURE_FANCY_TAIL
    /* q: make it impossible for nfiles to be > header_threshhold */
    if (opt & 0x8) header_threshhold = UINT_MAX; // -q
    //if (opt & 0x10) // -s
    if (opt & 0x20) header_threshhold = 0; // -v
# define FOLLOW_RETRY (opt & 0x40)
#else
# define FOLLOW_RETRY 0
#endif
    argc -= optind;
    argv += optind;
    from_top = G.status; /* 1 if there was "-c +N" or "-n +N" */
    G.status = EXIT_SUCCESS;

    /* open all the files */
    fds = xmalloc(sizeof(fds[0]) * (argc + 1));
    if (!argv[0]) {
        struct stat statbuf;

        if (fstat(STDIN_FILENO, &statbuf) == 0
         && S_ISFIFO(statbuf.st_mode)
        ) {
            opt &= ~1; /* clear FOLLOW */
        }
        argv[0] = (char *) bb_msg_standard_input;
    }
    nfiles = i = 0;
    do {
        int fd = open_or_warn_stdin(argv[i]);
        if (fd < 0 && !FOLLOW_RETRY) {
            G.status = EXIT_FAILURE;
            continue;
        }
        fds[nfiles] = fd;
        argv[nfiles++] = argv[i];
    } while (++i < argc);

    if (!nfiles)
        bb_error_msg_and_die("no files");

    /* prepare the buffer */
    tailbufsize = BUFSIZ;
    if (!from_top && COUNT_BYTES) {
        if (tailbufsize < count + BUFSIZ) {
            tailbufsize = count + BUFSIZ;
        }
    }
    tailbuf = xmalloc(tailbufsize);

    /* tail the files */
    fmt = header_fmt_str + 1; /* skip header leading newline on first output */
    i = 0;
    do {
        char *buf;
        int taillen;
        int newlines_seen;
        unsigned seen;
        int nread;
        int fd = fds[i];

        if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
            continue; /* may happen with -E */

        if (nfiles > header_threshhold) {
            tail_xprint_header(fmt, argv[i]);
            fmt = header_fmt_str;
        }

        if (!from_top) {
            off_t current = lseek(fd, 0, SEEK_END);
            if (current > 0) {
                unsigned off;
                if (COUNT_BYTES) {
                /* Optimizing count-bytes case if the file is seekable.
                 * Beware of backing up too far.
                 * Also we exclude files with size 0 (because of /proc/xxx) */
                    if (count == 0)
                        continue; /* showing zero bytes is easy :) */
                    current -= count;
                    if (current < 0)
                        current = 0;
                    xlseek(fd, current, SEEK_SET);
                    bb_copyfd_size(fd, STDOUT_FILENO, count);
                    continue;
                }
#if 1 /* This is technically incorrect for *LONG* strings, but very useful */
                /* Optimizing count-lines case if the file is seekable.
                 * We assume the lines are <64k.
                 * (Users complain that tail takes too long
                 * on multi-gigabyte files) */
                off = (count | 0xf); /* for small counts, be more paranoid */
                if (off > (INT_MAX / (64*1024)))
                    off = (INT_MAX / (64*1024));
                current -= off * (64*1024);
                if (current < 0)
                    current = 0;
                xlseek(fd, current, SEEK_SET);
#endif
            }
        }

        buf = tailbuf;
        taillen = 0;
        /* "We saw 1st line/byte".
         * Used only by +N code ("start from Nth", 1-based): */
        seen = 1;
        newlines_seen = 0;
        while ((nread = tail_read(fd, buf, tailbufsize-taillen)) > 0) {
            if (from_top) {
                int nwrite = nread;
                if (seen < count) {
                    /* We need to skip a few more bytes/lines */
                    if (COUNT_BYTES) {
                        nwrite -= (count - seen);
                        seen = count;
                    } else {
                        char *s = buf;
                        do {
                            --nwrite;
                            if (*s++ == '\n' && ++seen == count) {
                                break;
                            }
                        } while (nwrite);
                    }
                }
                if (nwrite > 0)
                    xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
            } else if (count) {
                if (COUNT_BYTES) {
                    taillen += nread;
                    if (taillen > (int)count) {
                        memmove(tailbuf, tailbuf + taillen - count, count);
                        taillen = count;
                    }
                } else {
                    int k = nread;
                    int newlines_in_buf = 0;

                    do { /* count '\n' in last read */
                        k--;
                        if (buf[k] == '\n') {
                            newlines_in_buf++;
                        }
                    } while (k);

                    if (newlines_seen + newlines_in_buf < (int)count) {
                        newlines_seen += newlines_in_buf;
                        taillen += nread;
                    } else {
                        int extra = (buf[nread-1] != '\n');
                        char *s;

                        k = newlines_seen + newlines_in_buf + extra - count;
                        s = tailbuf;
                        while (k) {
                            if (*s == '\n') {
                                k--;
                            }
                            s++;
                        }
                        taillen += nread - (s - tailbuf);
                        memmove(tailbuf, s, taillen);
                        newlines_seen = count - extra;
                    }
                    if (tailbufsize < (size_t)taillen + BUFSIZ) {
                        tailbufsize = taillen + BUFSIZ;
                        tailbuf = xrealloc(tailbuf, tailbufsize);
                    }
                }
                buf = tailbuf + taillen;
            }
        } /* while (tail_read() > 0) */
        if (!from_top) {
            xwrite(STDOUT_FILENO, tailbuf, taillen);
        }
    } while (++i < nfiles);

    tailbuf = xrealloc(tailbuf, BUFSIZ);

    fmt = NULL;

    if (FOLLOW) while (1) {
        sleep(sleep_period);

        i = 0;
        do {
            int nread;
            const char *filename = argv[i];
            int fd = fds[i];

            if (FOLLOW_RETRY) {
                struct stat sbuf, fsbuf;

                if (fd < 0
                 || fstat(fd, &fsbuf) < 0
                 || stat(filename, &sbuf) < 0
                 || fsbuf.st_dev != sbuf.st_dev
                 || fsbuf.st_ino != sbuf.st_ino
                ) {
                    int new_fd;

                    if (fd >= 0)
                        close(fd);
                    new_fd = open(filename, O_RDONLY);
                    if (new_fd >= 0) {
                        bb_error_msg("%s has %s; following end of new file",
                            filename, (fd < 0) ? "appeared" : "been replaced"
                        );
                    } else if (fd >= 0) {
                        bb_perror_msg("%s has become inaccessible", filename);
                    }
                    fds[i] = fd = new_fd;
                }
            }
            if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
                continue;
            if (nfiles > header_threshhold) {
                fmt = header_fmt_str;
            }
            while ((nread = tail_read(fd, tailbuf, BUFSIZ)) > 0) {
                if (fmt) {
                    tail_xprint_header(fmt, filename);
                    fmt = NULL;
                }
                xwrite(STDOUT_FILENO, tailbuf, nread);
            }
        } while (++i < nfiles);
    }
    if (ENABLE_FEATURE_CLEAN_UP) {
        free(fds);
        free(tailbuf);
    }
    return G.status;
}