maint: refactor tail.c to use iopoll

* src/tail.c (check_output_alive): Reuse iopoll()
rather than directly calling poll() or select().
* src/iopoll.c (iopoll): Refactor to support non blocking operation,
or ignoring descriptors by passing a negative value.
* src/iopoll.h (iopoll): Adjust to support a BLOCK parameter.
* src/tee.c (tee_files): Adjust iopoll() call to explicitly block.
* src/local.mk: Have tail depend on iopoll.c.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/tee.c b/src/tee.c
index e328e6f04..dcf773e16 100644
--- a/src/tee.c
+++ b/src/tee.c
@@ -290,7 +290,8 @@ tee_files (int nfiles, char **files)
       if (pipe_check && out_pollable[first_out])
         {
           /* Monitor for input, or errors on first valid output.  */
-          int err = iopoll (STDIN_FILENO, fileno (descriptors[first_out]));
+          int err = iopoll (STDIN_FILENO, fileno (descriptors[first_out]),
+                            true);
 
           /* Close the output if it became a broken pipe.  */
           if (err == IOPOLL_BROKEN_OUTPUT)