diff options
Diffstat (limited to 'libblkid/pager.c')
| -rw-r--r-- | libblkid/pager.c | 220 |
1 files changed, 220 insertions, 0 deletions
diff --git a/libblkid/pager.c b/libblkid/pager.c new file mode 100644 index 000000000..5cf8c03b5 --- /dev/null +++ b/libblkid/pager.c @@ -0,0 +1,220 @@ +/* + * 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 "c.h" +#include "xalloc.h" +#include "nls.h" + +#define NULL_DEVICE "/dev/null" + +void setup_pager(void); + +static const char *pager_argv[] = { "sh", "-c", NULL, NULL }; + +struct child_process { + const char **argv; + pid_t pid; + int in; + int out; + int err; + 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 inline void dup_devnull(int to) +{ + int fd = open(NULL_DEVICE, O_RDWR); + + if (fd < 0) + err(EXIT_FAILURE, _("cannot open %s"), NULL_DEVICE); + dup2(fd, to); + close(fd); +} + +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], 0); + close_pair(fdin); + } else if (cmd->in > 0) { + dup2(cmd->in, 0); + close(cmd->in); + } + + cmd->preexec_cb(); + execvp(cmd->argv[0], (char *const*) cmd->argv); + exit(127); /* cmd not found */ + } + + if (cmd->pid < 0) { + if (need_in) + close_pair(fdin); + else if (cmd->in) + close(cmd->in); + return -1; + } + + if (need_in) + close(fdin[0]); + else if (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; + err(EXIT_FAILURE, _("waitpid failed (%s)"), strerror(errno)); + } + 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; + + FD_ZERO(&in); + FD_SET(0, &in); + select(1, &in, NULL, &in, NULL); + + setenv("LESS", "FRSX", 0); +} + +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(); + raise(signo); +} + +void setup_pager(void) +{ + const char *pager = getenv("PAGER"); + + if (!isatty(1)) + return; + + if (!pager) + pager = "less"; + else if (!*pager || !strcmp(pager, "cat")) + 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, 1); + if (isatty(2)) + dup2(pager_process.in, 2); + close(pager_process.in); + + /* this makes sure that the parent terminates after the pager */ + signal(SIGINT, wait_for_pager_signal); + signal(SIGHUP, wait_for_pager_signal); + signal(SIGTERM, wait_for_pager_signal); + signal(SIGQUIT, wait_for_pager_signal); + signal(SIGPIPE, wait_for_pager_signal); + + atexit(wait_for_pager); +} + +#ifdef TEST_PROGRAM + +#define MAX 255 + +int main(int argc __attribute__ ((__unused__)), + char *argv[] __attribute__ ((__unused__))) +{ + int i; + + setup_pager(); + for (i = 0; i < MAX; i++) + printf("%d\n", i); + return EXIT_SUCCESS; +} +#endif /* TEST_PROGRAM */ |