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authorDenys Vlasenko <vda.linux@googlemail.com>2013-07-02 18:09:15 (GMT)
committer Denys Vlasenko <vda.linux@googlemail.com>2013-07-02 18:09:15 (GMT)
commit6651e4260955d159e6a4f794d0a69c1b3f8e670c (patch)
treeee1417b778865b3115a12f4e1295f90cea7d50f5
parentcd8eece88ed6da58209a18a8c3edac73eab27e1c (diff)
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tail: track file size only in -f mode
This eliminates extra fstat and lseek calls on every read Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
-rw-r--r--coreutils/tail.c26
1 files changed, 15 insertions, 11 deletions
diff --git a/coreutils/tail.c b/coreutils/tail.c
index 19fd8f6..fb07ca2 100644
--- a/coreutils/tail.c
+++ b/coreutils/tail.c
@@ -66,17 +66,21 @@ static void tail_xprint_header(const char *fmt, const char *filename)
bb_perror_nomsg_and_die();
}
-static ssize_t tail_read(int fd, char *buf, size_t count)
+static ssize_t tail_read(int fd, char *buf, size_t count, int follow)
{
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);
+
+ if (follow) {
+ /* tail -f keeps following files even if they are truncated */
+ 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);
@@ -251,7 +255,7 @@ int tail_main(int argc, char **argv)
* Used only by +N code ("start from Nth", 1-based): */
seen = 1;
newlines_seen = 0;
- while ((nread = tail_read(fd, buf, tailbufsize - taillen)) > 0) {
+ while ((nread = tail_read(fd, buf, tailbufsize - taillen, /*follow:*/ 0)) > 0) {
if (G.from_top) {
int nwrite = nread;
if (seen < count) {
@@ -363,7 +367,7 @@ int tail_main(int argc, char **argv)
if (nfiles > header_threshhold) {
fmt = header_fmt_str;
}
- while ((nread = tail_read(fd, tailbuf, BUFSIZ)) > 0) {
+ while ((nread = tail_read(fd, tailbuf, BUFSIZ, /*follow:*/ 1)) > 0) {
if (fmt) {
tail_xprint_header(fmt, filename);
fmt = NULL;