diff options
Diffstat (limited to 'lib/pager.c')
| -rw-r--r-- | lib/pager.c | 323 |
1 files changed, 323 insertions, 0 deletions
diff --git a/lib/pager.c b/lib/pager.c new file mode 100644 index 0000000..9429032 --- /dev/null +++ b/lib/pager.c @@ -0,0 +1,323 @@ +/* + * SPDX-License-Identifier: GPL-2.0-or-later + * + * This file may be redistributed under the terms of the GNU Public + * License. + * + * Based on linux-perf/git scm + * + * Some modifications and simplifications for util-linux + * by Davidlohr Bueso <dave@xxxxxxx> - March 2012. + */ + +#include <unistd.h> +#include <stdlib.h> +#include <string.h> +#include <err.h> +#include <sys/types.h> +#include <sys/stat.h> +#include <sys/wait.h> +#include <signal.h> + +#include "c.h" +#include "xalloc.h" +#include "nls.h" +#include "ttyutils.h" +#include "pager.h" + +#define NULL_DEVICE "/dev/null" + +static const char *pager_argv[] = { "sh", "-c", NULL, NULL }; + +struct child_process { + const char **argv; + pid_t pid; + int in; + int out; + int err; + + int org_err; + int org_out; + struct sigaction orig_sigint; + struct sigaction orig_sighup; + struct sigaction orig_sigterm; + struct sigaction orig_sigquit; + struct sigaction orig_sigpipe; + + unsigned no_stdin:1; + void (*preexec_cb)(void); +}; +static struct child_process pager_process; + +static inline void close_pair(int fd[2]) +{ + close(fd[0]); + close(fd[1]); +} + +static int start_command(struct child_process *cmd) +{ + int need_in; + int fdin[2]; + + /* + * In case of errors we must keep the promise to close FDs + * that have been passed in via ->in and ->out. + */ + need_in = !cmd->no_stdin && cmd->in < 0; + if (need_in) { + if (pipe(fdin) < 0) { + if (cmd->out > 0) + close(cmd->out); + return -1; + } + cmd->in = fdin[1]; + } + + fflush(NULL); + cmd->pid = fork(); + if (!cmd->pid) { + if (need_in) { + dup2(fdin[0], STDIN_FILENO); + close_pair(fdin); + } else if (cmd->in > 0) { + dup2(cmd->in, STDIN_FILENO); + close(cmd->in); + } + + cmd->preexec_cb(); + execvp(cmd->argv[0], (char *const*) cmd->argv); + errexec(cmd->argv[0]); + } + + if (cmd->pid < 0) { + if (need_in) + close_pair(fdin); + else if (0 <= cmd->in) + close(cmd->in); + return -1; + } + + if (need_in) + close(fdin[0]); + else if (0 <= cmd->in) + close(cmd->in); + return 0; +} + +static int wait_or_whine(pid_t pid) +{ + for (;;) { + int status, code; + pid_t waiting = waitpid(pid, &status, 0); + + if (waiting < 0) { + if (errno == EINTR) + continue; + ul_sig_err(EXIT_FAILURE, "waitpid failed"); + } + if (waiting != pid) + return -1; + if (WIFSIGNALED(status)) + return -1; + + if (!WIFEXITED(status)) + return -1; + code = WEXITSTATUS(status); + switch (code) { + case 127: + return -1; + case 0: + return 0; + default: + return -1; + } + } +} + +static int finish_command(struct child_process *cmd) +{ + return wait_or_whine(cmd->pid); +} + +static void pager_preexec(void) +{ + /* + * Work around bug in "less" by not starting it until we + * have real input + */ + fd_set in, ex; + + FD_ZERO(&in); + FD_SET(STDIN_FILENO, &in); + ex = in; + + select(STDIN_FILENO + 1, &in, NULL, &ex, NULL); + + if (setenv("LESS", "FRSX", 0) != 0) + warn(_("failed to set the %s environment variable"), "LESS"); +} + +static void wait_for_pager(void) +{ + if (pager_process.pid == 0) + return; + + /* signal EOF to pager */ + close(STDOUT_FILENO); + close(STDERR_FILENO); + finish_command(&pager_process); +} + +static void wait_for_pager_signal(int signo) +{ + wait_for_pager(); + raise(signo); +} + +static int has_command(const char *cmd) +{ + const char *path; + char *p, *s; + int rc = 0; + + if (!cmd) + goto done; + if (*cmd == '/') { + rc = access(cmd, X_OK) == 0; + goto done; + } + + path = getenv("PATH"); + if (!path) + goto done; + p = xstrdup(path); + if (!p) + goto done; + + for(s = strtok(p, ":"); s; s = strtok(NULL, ":")) { + int fd = open(s, O_RDONLY|O_CLOEXEC); + if (fd < 0) + continue; + rc = faccessat(fd, cmd, X_OK, 0) == 0; + close(fd); + if (rc) + break; + } + free(p); +done: + /*fprintf(stderr, "has PAGER %s rc=%d\n", cmd, rc);*/ + return rc; +} + +static void __setup_pager(void) +{ + const char *pager = getenv("PAGER"); + struct sigaction sa; + + if (!isatty(STDOUT_FILENO)) + return; + + if (!pager) + pager = "less"; + else if (!*pager || !strcmp(pager, "cat")) + return; + + if (!has_command(pager)) + return; + + /* 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, STDOUT_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)); + sa.sa_handler = wait_for_pager_signal; + + /* this makes sure that the parent terminates after the pager */ + sigaction(SIGINT, &sa, &pager_process.orig_sigint); + sigaction(SIGHUP, &sa, &pager_process.orig_sighup); + sigaction(SIGTERM, &sa, &pager_process.orig_sigterm); + sigaction(SIGQUIT, &sa, &pager_process.orig_sigquit); + sigaction(SIGPIPE, &sa, &pager_process.orig_sigpipe); +} + +/* Setup pager and redirects output to the $PAGER. The pager is closed at exit. + */ +void pager_redirect(void) +{ + if (pager_process.pid) + return; /* already running */ + + __setup_pager(); + + atexit(wait_for_pager); +} + +/* Setup pager and redirect output, the pager may be closed by pager_close(). + */ +void pager_open(void) +{ + if (pager_process.pid) + return; /* already running */ + + pager_process.org_out = dup(STDOUT_FILENO); + pager_process.org_err = dup(STDERR_FILENO); + + __setup_pager(); +} + +/* Close pager and restore original std{out,err}. + */ +void pager_close(void) +{ + if (pager_process.pid == 0) + return; + + wait_for_pager(); + + /* restore original output */ + dup2(pager_process.org_out, STDOUT_FILENO); + dup2(pager_process.org_err, STDERR_FILENO); + + close(pager_process.org_out); + close(pager_process.org_err); + + /* restore original segnals setting */ + sigaction(SIGINT, &pager_process.orig_sigint, NULL); + sigaction(SIGHUP, &pager_process.orig_sighup, NULL); + sigaction(SIGTERM, &pager_process.orig_sigterm, NULL); + sigaction(SIGQUIT, &pager_process.orig_sigquit, NULL); + sigaction(SIGPIPE, &pager_process.orig_sigpipe, NULL); + + memset(&pager_process, 0, sizeof(pager_process)); +} + +#ifdef TEST_PROGRAM_PAGER + +#define MAX 255 + +int main(int argc __attribute__ ((__unused__)), + char *argv[] __attribute__ ((__unused__))) +{ + int i; + + pager_redirect(); + for (i = 0; i < MAX; i++) + printf("%d\n", i); + return EXIT_SUCCESS; +} +#endif /* TEST_PROGRAM_PAGER */ |