tail compat: fix header printing for tail -f

Makes tail -f for multiple files display the header only if another (ie. not
currently displayed) file changed.

Signed-off-by: Bartosz Golaszewski <bartekgola@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 4 insertions, 6 deletions

diff --git a/TODO b/TODO
index d2a085ede..dcf48c2c2 100644
--- a/TODO
+++ b/TODO
@@ -127,11 +127,6 @@ patch
 
   And while we're at it, a new patch filename quoting format is apparently
   coming soon:  http://marc.theaimsgroup.com/?l=git&m=112927316408690&w=2
----
-tail
-  ./busybox tail -f foo.c~ TODO
-  should not print fmt=header_fmt for subsequent date >> TODO; i.e. only
-  fmt+ if another (not the current) file did change
 
 Architectural issues:
 
diff --git a/coreutils/tail.c b/coreutils/tail.c
index 07c71ca4b..eab502beb 100644
--- a/coreutils/tail.c
+++ b/coreutils/tail.c
@@ -105,6 +105,7 @@ int tail_main(int argc, char **argv)
 
         int *fds;
         const char *fmt;
+        int prev_fd;
 
         INIT_G();
 
@@ -309,6 +310,7 @@ int tail_main(int argc, char **argv)
                         xwrite(STDOUT_FILENO, tailbuf, taillen);
                 }
         } while (++i < nfiles);
+        prev_fd = fds[i-1];
 
         tailbuf = xrealloc(tailbuf, BUFSIZ);
 
@@ -365,9 +367,10 @@ int tail_main(int argc, char **argv)
                                 nread = tail_read(fd, tailbuf, BUFSIZ);
                                 if (nread <= 0)
                                         break;
-                                if (fmt) {
+                                if (fmt && (fd != prev_fd)) {
                                         tail_xprint_header(fmt, filename);
                                         fmt = NULL;
+                                        prev_fd = fd;
                                 }
                                 xwrite(STDOUT_FILENO, tailbuf, nread);
                         }