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

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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 { struct globals {
bool status; bool from_top;
bool exitcode;
} FIX_ALIASING; } FIX_ALIASING;
#define G (*(struct globals*)&bb_common_bufsiz1) #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); r = full_read(fd, buf, count);
if (r < 0) { if (r < 0) {
bb_perror_msg(bb_msg_read_error); bb_perror_msg(bb_msg_read_error);
G.status = EXIT_FAILURE; G.exitcode = EXIT_FAILURE;
} }
return r; return r;
@ -99,7 +100,7 @@ static unsigned eat_num(const char *p)
p++; p++;
else if (*p == '+') { else if (*p == '+') {
p++; p++;
G.status = 1; /* mark that we saw "+" */ G.from_top = 1;
} }
return xatou_sfx(p, tail_suffixes); return xatou_sfx(p, tail_suffixes);
} }
@ -109,7 +110,6 @@ int tail_main(int argc, char **argv)
{ {
unsigned count = 10; unsigned count = 10;
unsigned sleep_period = 1; unsigned sleep_period = 1;
bool from_top;
const char *str_c, *str_n; const char *str_c, *str_n;
char *tailbuf; char *tailbuf;
@ -152,8 +152,6 @@ int tail_main(int argc, char **argv)
#endif #endif
argc -= optind; argc -= optind;
argv += optind; argv += optind;
from_top = G.status; /* 1 if there was "-c +N" or "-n +N" */
G.status = EXIT_SUCCESS;
/* open all the files */ /* open all the files */
fds = xmalloc(sizeof(fds[0]) * (argc + 1)); fds = xmalloc(sizeof(fds[0]) * (argc + 1));
@ -171,7 +169,7 @@ int tail_main(int argc, char **argv)
do { do {
int fd = open_or_warn_stdin(argv[i]); int fd = open_or_warn_stdin(argv[i]);
if (fd < 0 && !FOLLOW_RETRY) { if (fd < 0 && !FOLLOW_RETRY) {
G.status = EXIT_FAILURE; G.exitcode = EXIT_FAILURE;
continue; continue;
} }
fds[nfiles] = fd; fds[nfiles] = fd;
@ -183,15 +181,19 @@ int tail_main(int argc, char **argv)
/* prepare the buffer */ /* prepare the buffer */
tailbufsize = BUFSIZ; tailbufsize = BUFSIZ;
if (!from_top && COUNT_BYTES) { if (!G.from_top && COUNT_BYTES) {
if (tailbufsize < count + BUFSIZ) { if (tailbufsize < count + BUFSIZ) {
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 */ /* 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; i = 0;
do { do {
char *buf; char *buf;
@ -209,7 +211,7 @@ int tail_main(int argc, char **argv)
fmt = header_fmt_str; fmt = header_fmt_str;
} }
if (!from_top) { if (!G.from_top) {
off_t current = lseek(fd, 0, SEEK_END); off_t current = lseek(fd, 0, SEEK_END);
if (current > 0) { if (current > 0) {
unsigned off; unsigned off;
@ -242,6 +244,9 @@ int tail_main(int argc, char **argv)
} }
} }
if (!tailbuf)
tailbuf = xmalloc(tailbufsize);
buf = tailbuf; buf = tailbuf;
taillen = 0; taillen = 0;
/* "We saw 1st line/byte". /* "We saw 1st line/byte".
@ -249,7 +254,7 @@ int tail_main(int argc, char **argv)
seen = 1; seen = 1;
newlines_seen = 0; newlines_seen = 0;
while ((nread = tail_read(fd, buf, tailbufsize-taillen)) > 0) { while ((nread = tail_read(fd, buf, tailbufsize-taillen)) > 0) {
if (from_top) { if (G.from_top) {
int nwrite = nread; int nwrite = nread;
if (seen < count) { if (seen < count) {
/* We need to skip a few more bytes/lines */ /* We need to skip a few more bytes/lines */
@ -313,7 +318,7 @@ int tail_main(int argc, char **argv)
buf = tailbuf + taillen; buf = tailbuf + taillen;
} }
} /* while (tail_read() > 0) */ } /* while (tail_read() > 0) */
if (!from_top) { if (!G.from_top) {
xwrite(STDOUT_FILENO, tailbuf, taillen); xwrite(STDOUT_FILENO, tailbuf, taillen);
} }
} while (++i < nfiles); } while (++i < nfiles);
@ -368,10 +373,11 @@ int tail_main(int argc, char **argv)
xwrite(STDOUT_FILENO, tailbuf, nread); xwrite(STDOUT_FILENO, tailbuf, nread);
} }
} while (++i < nfiles); } while (++i < nfiles);
} } /* while (1) */
if (ENABLE_FEATURE_CLEAN_UP) { if (ENABLE_FEATURE_CLEAN_UP) {
free(fds); free(fds);
free(tailbuf); free(tailbuf);
} }
return G.status; return G.exitcode;
} }