// SPDX-License-Identifier: GPL-2.0#include <sys/select.h>#include <stdlib.h>#include <stdio.h>#include <string.h>#include <signal.h>#include <sys/ioctl.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;static int pager_columns; void pager_init(const char *pager_env){	subcmd_config.pager_env = pager_env;} static const char *forced_pager; void force_pager(const char *pager){	forced_pager = pager;} static void pager_preexec(void){	/*	 * Work around bug in "less" by not starting it until we	 * have real input	 */	fd_set in;	fd_set exception; 	FD_ZERO(&in);	FD_ZERO(&exception);	FD_SET(0, &in);	FD_SET(0, &exception);	select(1, &in, NULL, &exception, 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);	struct winsize sz; 	if (forced_pager)		pager = forced_pager;	if (!isatty(1) && !forced_pager)		return;	if (ioctl(1, TIOCGWINSZ, &sz) == 0)		pager_columns = sz.ws_col;	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;} int pager_get_columns(void){	char *s; 	s = getenv("COLUMNS");	if (s)		return atoi(s); 	return (pager_columns ? pager_columns : 80) - 2;}