busybox/coreutils/tail.c
Denys Vlasenko 79b021d738 tail: read only a portion of a file if it's huge. closes bug 551
function                                             old     new   delta
tail_main                                           1494    1526     +32
tail_read                                            125     129      +4

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2009-08-10 03:16:18 +02:00

351 lines
8.4 KiB
C

/* 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 tarball for details.
*/
/* 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 },
{ }
};
struct globals {
bool status;
};
#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;
}
static const char header_fmt[] ALIGN1 = "\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 + 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;
}
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);
}
}
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;
}
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);
}
return G.status;
}