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tail: read only a portion of a file if it's huge. closes bug 551

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function                                             old     new   delta
tail_main                                           1494    1526     +32
tail_read                                            125     129      +4

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2009-08-10 03:16:18 +02:00
parent e531759ef1
commit 79b021d738
1 changed files with 33 additions and 16 deletions
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49
coreutils/tail.c
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@ -51,10 +51,10 @@ static ssize_t tail_read(int fd, char *buf, size_t count)
struct stat sbuf; struct stat sbuf;
/* /proc files report zero st_size, don't lseek them. */ /* /proc files report zero st_size, don't lseek them. */
if (fstat(fd, &sbuf) == 0 && sbuf.st_size) { if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
current = lseek(fd, 0, SEEK_CUR); current = lseek(fd, 0, SEEK_CUR);
if (sbuf.st_size < current) if (sbuf.st_size < current)
lseek(fd, 0, SEEK_SET); xlseek(fd, 0, SEEK_SET);
} }
r = full_read(fd, buf, count); r = full_read(fd, buf, count);
@ -174,8 +174,9 @@ int tail_main(int argc, char **argv)
int newlines_seen; int newlines_seen;
unsigned seen; unsigned seen;
int nread; int nread;
int fd = fds[i];
if (ENABLE_FEATURE_FANCY_TAIL && fds[i] < 0) if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
continue; /* may happen with -E */ continue; /* may happen with -E */
if (nfiles > header_threshhold) { if (nfiles > header_threshhold) {
@ -183,30 +184,46 @@ int tail_main(int argc, char **argv)
fmt = header_fmt; fmt = header_fmt;
} }
/* Optimizing count-bytes case if the file is seekable. if (!from_top) {
* Beware of backing up too far. off_t current = lseek(fd, 0, SEEK_END);
* Also we exclude files with size 0 (because of /proc/xxx) */
if (COUNT_BYTES && !from_top) {
off_t current = lseek(fds[i], 0, SEEK_END);
if (current > 0) { if (current > 0) {
if (count == 0) unsigned off;
continue; /* showing zero bytes is easy :) */ if (COUNT_BYTES) {
current -= count; /* 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) if (current < 0)
current = 0; current = 0;
xlseek(fds[i], current, SEEK_SET); xlseek(fd, current, SEEK_SET);
bb_copyfd_size(fds[i], STDOUT_FILENO, count); #endif
continue;
} }
} }
buf = tailbuf; buf = tailbuf;
taillen = 0; taillen = 0;
/* "We saw 1st line/byte". /* "We saw 1st line/byte".
* Used only by +N code ("start from Nth", 1-based) */ * Used only by +N code ("start from Nth", 1-based): */
seen = 1; seen = 1;
newlines_seen = 0; newlines_seen = 0;
while ((nread = tail_read(fds[i], buf, tailbufsize-taillen)) > 0) { while ((nread = tail_read(fd, buf, tailbufsize-taillen)) > 0) {
if (from_top) { if (from_top) {
int nwrite = nread; int nwrite = nread;
if (seen < count) { if (seen < count) {