cgls: add pager support to systemd-cgls

1 files changed, 122 insertions, 0 deletions

diff --git a/src/pager.c b/src/pager.c
new file mode 100644
index 0000000000..6ea25ada65
--- /dev/null
+++ b/src/pager.c
@@ -0,0 +1,122 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2010 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 2 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <sys/types.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <sys/prctl.h>
+
+#include "pager.h"
+#include "util.h"
+#include "macro.h"
+
+static pid_t pager_pid = 0;
+
+void pager_open(void) {
+        int fd[2];
+        const char *pager;
+        pid_t parent_pid;
+
+        if (pager_pid > 0)
+                return;
+
+        if (isatty(STDOUT_FILENO) <= 0)
+                return;
+
+        if ((pager = getenv("SYSTEMD_PAGER")) || (pager = getenv("PAGER")))
+                if (!*pager || streq(pager, "cat"))
+                        return;
+
+        /* Determine and cache number of columns before we spawn the
+         * pager so that we get the value from the actual tty */
+        columns();
+
+        if (pipe(fd) < 0) {
+                log_error("Failed to create pager pipe: %m");
+                return;
+        }
+
+        parent_pid = getpid();
+
+        pager_pid = fork();
+        if (pager_pid < 0) {
+                log_error("Failed to fork pager: %m");
+                close_pipe(fd);
+                return;
+        }
+
+        /* In the child start the pager */
+        if (pager_pid == 0) {
+
+                dup2(fd[0], STDIN_FILENO);
+                close_pipe(fd);
+
+                setenv("LESS", "FRSX", 0);
+
+                /* Make sure the pager goes away when the parent dies */
+                if (prctl(PR_SET_PDEATHSIG, SIGTERM) < 0)
+                        _exit(EXIT_FAILURE);
+
+                /* Check whether our parent died before we were able
+                 * to set the death signal */
+                if (getppid() != parent_pid)
+                        _exit(EXIT_SUCCESS);
+
+                if (pager) {
+                        execlp(pager, pager, NULL);
+                        execl("/bin/sh", "sh", "-c", pager, NULL);
+                }
+
+                /* Debian's alternatives command for pagers is
+                 * called 'pager'. Note that we do not call
+                 * sensible-pagers here, since that is just a
+                 * shell script that implements a logic that
+                 * is similar to this one anyway, but is
+                 * Debian-specific. */
+                execlp("pager", "pager", NULL);
+
+                execlp("less", "less", NULL);
+                execlp("more", "more", NULL);
+                execlp("cat", "cat", NULL);
+
+                log_error("Unable to execute pager: %m");
+                _exit(EXIT_FAILURE);
+        }
+
+        /* Return in the parent */
+        if (dup2(fd[1], STDOUT_FILENO) < 0)
+                log_error("Failed to duplicate pager pipe: %m");
+
+        close_pipe(fd);
+}
+
+void pager_close(void) {
+
+        if (pager_pid <= 0)
+                return;
+
+        /* Inform pager that we are done */
+        fclose(stdout);
+        kill(pager_pid, SIGCONT);
+        wait_for_terminate(pager_pid, NULL);
+        pager_pid = 0;
+}