lib/pager: fix output truncation from buffered stdout

Commit 518a0ad dropped fflush(stdout) and fflush(stderr) from
wait_for_pager() before STDOUT_FILENO and STDERR_FILENO are closed
because it is called from a signal handler and they are async-unsafe.

However, failure to flush output leads to unwanted truncation when
stdout is fully buffered, which it is by default when we are linked
against musl.

Ensure stdout and stderr are line-buffered before redirecting them to
the pager subprocess to avoid this.

Addresses: https://github.com/util-linux/util-linux/issues/2218
Signed-off-by: Chris Webb <chris@arachsys.com>

diff --git a/lib/pager.c b/lib/pager.c
index 2421703669b32a829c28ced8d37067bf16c17b7c..9429032b3aef6e4a6c97f4683443235650b531b1 100644 (file)
--- a/lib/pager.c
+++ b/lib/pager.c
@@ -237,8 +237,11 @@ static void __setup_pager(void)
 
        /* original process continues, but writes to the pipe */
        dup2(pager_process.in, STDOUT_FILENO);
-       if (isatty(STDERR_FILENO))
+       setvbuf(stdout, NULL, _IOLBF, 0);
+       if (isatty(STDERR_FILENO)) {
                dup2(pager_process.in, STDERR_FILENO);
+               setvbuf(stderr, NULL, _IOLBF, 0);
+       }
        close(pager_process.in);
 
        memset(&sa, 0, sizeof(sa));