(tail_forever): Don't exit-nonzero when an attempt

to put a regular file in O_NONBLOCK mode fails with EPERM.
That happens on Linux when using tail -f on a file with the
append-only attribute.  Reported by Dean Gaudet.  For details,
see http://savannah.gnu.org/bugs/?func=detailitem&item_id=15473.

diff --git a/src/tail.c b/src/tail.c
index ee18f31..1bfe4bb 100644 (file)
--- a/src/tail.c
+++ b/src/tail.c
@@ -1015,12 +1015,22 @@ tail_forever (struct File_spec *f, int nfiles, double sleep_interval)
              if (old_flags < 0
                  || (new_flags != old_flags
                      && fcntl (fd, F_SETFL, new_flags) == -1))
-               error (EXIT_FAILURE, errno,
-                      _("%s: cannot change nonblocking mode"), name);
-             f[i].blocking = blocking;
+               {
+                 /* Don't update f[i].blocking if fcntl fails.  */
+                 if (S_ISREG (f[i].mode) && errno == EPERM)
+                   {
+                     /* This happens when using tail -f on a file with
+                        the append-only attribute.  */
+                   }
+                 else
+                   error (EXIT_FAILURE, errno,
+                          _("%s: cannot change nonblocking mode"), name);
+               }
+             else
+               f[i].blocking = blocking;
            }
 
-         if (!blocking)
+         if (!f[i].blocking)
            {
              if (fstat (fd, &stats) != 0)
                {
@@ -1038,7 +1048,7 @@ tail_forever (struct File_spec *f, int nfiles, double sleep_interval)
                       <= f[i].n_unchanged_stats++)
                      && follow_mode == Follow_name)
                    {
-                     recheck (&f[i], blocking);
+                     recheck (&f[i], f[i].blocking);
                      f[i].n_unchanged_stats = 0;
                    }
                  continue;
@@ -1071,7 +1081,8 @@ tail_forever (struct File_spec *f, int nfiles, double sleep_interval)
            }
 
          bytes_read = dump_remainder (name, fd,
-                                      blocking ? COPY_A_BUFFER : COPY_TO_EOF);
+                                      (f[i].blocking
+                                       ? COPY_A_BUFFER : COPY_TO_EOF));
          any_input |= (bytes_read != 0);
          f[i].size += bytes_read;
        }