1 files changed, 100 insertions, 0 deletions

diff --git a/tools/lib/subcmd/pager.c b/tools/lib/subcmd/pager.c
new file mode 100644
index 000000000000..d50f3b58606b
--- /dev/null
+++ b/tools/lib/subcmd/pager.c
@@ -0,0 +1,100 @@
+#include <sys/select.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <signal.h>
+#include "pager.h"
+#include "run-command.h"
+#include "sigchain.h"
+#include "subcmd-config.h"
+
+/*
+ * This is split up from the rest of git so that we can do
+ * something different on Windows.
+ */
+
+static int spawned_pager;
+
+void pager_init(const char *pager_env)
+{
+        subcmd_config.pager_env = pager_env;
+}
+
+static void pager_preexec(void)
+{
+        /*
+         * Work around bug in "less" by not starting it until we
+         * have real input
+         */
+        fd_set in;
+
+        FD_ZERO(&in);
+        FD_SET(0, &in);
+        select(1, &in, NULL, &in, NULL);
+
+        setenv("LESS", "FRSX", 0);
+}
+
+static const char *pager_argv[] = { "sh", "-c", NULL, NULL };
+static struct child_process pager_process;
+
+static void wait_for_pager(void)
+{
+        fflush(stdout);
+        fflush(stderr);
+        /* signal EOF to pager */
+        close(1);
+        close(2);
+        finish_command(&pager_process);
+}
+
+static void wait_for_pager_signal(int signo)
+{
+        wait_for_pager();
+        sigchain_pop(signo);
+        raise(signo);
+}
+
+void setup_pager(void)
+{
+        const char *pager = getenv(subcmd_config.pager_env);
+
+        if (!isatty(1))
+                return;
+        if (!pager)
+                pager = getenv("PAGER");
+        if (!(pager || access("/usr/bin/pager", X_OK)))
+                pager = "/usr/bin/pager";
+        if (!(pager || access("/usr/bin/less", X_OK)))
+                pager = "/usr/bin/less";
+        if (!pager)
+                pager = "cat";
+        if (!*pager || !strcmp(pager, "cat"))
+                return;
+
+        spawned_pager = 1; /* means we are emitting to terminal */
+
+        /* spawn the pager */
+        pager_argv[2] = pager;
+        pager_process.argv = pager_argv;
+        pager_process.in = -1;
+        pager_process.preexec_cb = pager_preexec;
+
+        if (start_command(&pager_process))
+                return;
+
+        /* original process continues, but writes to the pipe */
+        dup2(pager_process.in, 1);
+        if (isatty(2))
+                dup2(pager_process.in, 2);
+        close(pager_process.in);
+
+        /* this makes sure that the parent terminates after the pager */
+        sigchain_push_common(wait_for_pager_signal);
+        atexit(wait_for_pager);
+}
+
+int pager_in_use(void)
+{
+        return spawned_pager;
+}