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tail: optimize "tail -c HUGENUM REGULAR_FILE". Closes 3763. 

function                                             old     new   delta
tail_main                                           1541    1547      +6

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2011-05-20 00:30:04 +02:00
parent 24b71fd894
commit 9e933d9bfc
1 changed files with 21 additions and 15 deletions
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36
coreutils/tail.c
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@ -59,7 +59,8 @@ static const struct suffix_mult tail_suffixes[] = {
};
struct globals {
bool status;
bool from_top;
bool exitcode;
} FIX_ALIASING;
#define G (*(struct globals*)&bb_common_bufsiz1)
@ -85,7 +86,7 @@ static ssize_t tail_read(int fd, char *buf, size_t count)
r = full_read(fd, buf, count);
if (r < 0) {
bb_perror_msg(bb_msg_read_error);
G.status = EXIT_FAILURE;
G.exitcode = EXIT_FAILURE;
}
return r;
@ -99,7 +100,7 @@ static unsigned eat_num(const char *p)
p++;
else if (*p == '+') {
p++;
G.status = 1; /* mark that we saw "+" */
G.from_top = 1;
}
return xatou_sfx(p, tail_suffixes);
}
@ -109,7 +110,6 @@ 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;
@ -152,8 +152,6 @@ int tail_main(int argc, char **argv)
#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));
@ -171,7 +169,7 @@ int tail_main(int argc, char **argv)
do {
int fd = open_or_warn_stdin(argv[i]);
if (fd < 0 && !FOLLOW_RETRY) {
G.status = EXIT_FAILURE;
G.exitcode = EXIT_FAILURE;
continue;
}
fds[nfiles] = fd;
@ -183,15 +181,19 @@ int tail_main(int argc, char **argv)
/* prepare the buffer */
tailbufsize = BUFSIZ;
if (!from_top && COUNT_BYTES) {
if (!G.from_top && COUNT_BYTES) {
if (tailbufsize < count + BUFSIZ) {
tailbufsize = count + BUFSIZ;
}
}
tailbuf = xmalloc(tailbufsize);
/* tail -c1024m REGULAR_FILE doesn't really need 1G mem block.
* (In fact, it doesn't need ANY memory). So delay allocation.
*/
tailbuf = NULL;
/* tail the files */
fmt = header_fmt_str + 1; /* skip header leading newline on first output */
fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */
i = 0;
do {
char *buf;
@ -209,7 +211,7 @@ int tail_main(int argc, char **argv)
fmt = header_fmt_str;
}
if (!from_top) {
if (!G.from_top) {
off_t current = lseek(fd, 0, SEEK_END);
if (current > 0) {
unsigned off;
@ -242,6 +244,9 @@ int tail_main(int argc, char **argv)
}
}
if (!tailbuf)
tailbuf = xmalloc(tailbufsize);
buf = tailbuf;
taillen = 0;
/* "We saw 1st line/byte".
@ -249,7 +254,7 @@ int tail_main(int argc, char **argv)
seen = 1;
newlines_seen = 0;
while ((nread = tail_read(fd, buf, tailbufsize-taillen)) > 0) {
if (from_top) {
if (G.from_top) {
int nwrite = nread;
if (seen < count) {
/* We need to skip a few more bytes/lines */
@ -313,7 +318,7 @@ int tail_main(int argc, char **argv)
buf = tailbuf + taillen;
}
} /* while (tail_read() > 0) */
if (!from_top) {
if (!G.from_top) {
xwrite(STDOUT_FILENO, tailbuf, taillen);
}
} while (++i < nfiles);
@ -368,10 +373,11 @@ int tail_main(int argc, char **argv)
xwrite(STDOUT_FILENO, tailbuf, nread);
}
} while (++i < nfiles);
}
} /* while (1) */
if (ENABLE_FEATURE_CLEAN_UP) {
free(fds);
free(tailbuf);
}
return G.status;
return G.exitcode;
}