implement pgetppid

pgetppid will aid in detecting which terminal emulator a process is running under

Makefile

@@ -27,7 +27,7 @@ all: tests
 .PHONY: tests
 tests: $(BIN) $(BIN)/ct_test
 
-$(BIN)/ct_test: $(BUILD) $(addprefix $(BUILD)/, ct_test.o term.o termio.o)
+$(BIN)/ct_test: $(BUILD) $(addprefix $(BUILD)/, ct_test.o term.o termio.o pgetppid.o)
 	$(LD) $(LDFLAGS) -o $@ $(filter %.o, $^)
 
 $(BUILD)/%.o: $(SRC)/%.c

src/pgetppid.c

@@ -0,0 +1,85 @@
+/* XXX: WARNING: TODO
+ * This file's implementation is Linux dependent!
+ * XXX: WARNING: TODO
+ */
+#include <stdio.h>
+#include <unistd.h>
+
+#include "pgetppid.h"
+#include "ct_shared.h"
+
+int pgetppid(const pid_t pid, pid_t *const ppid, char *const name) {
+  /* I'm making the assumption that each line in /proc/pid/status
+   * has a hard length limit of PAGE_SIZE.
+   */
+  static int CT_K_PAGE_SIZE;
+  CT_K_PAGE_SIZE = getpagesize();
+
+  FILE *stream;
+  char line[CT_K_PAGE_SIZE];
+
+  /* The maximum PID value on a 64-Bit Linux kernel is defined 4194304,
+   * not INT_MAX even through pid_t is typedef'd to signed int.
+   * Hence "/proc/4194304/status\0" is the maximum path (length 21).
+   */
+#define PROCPATH_MAX (21)
+  char procname[PROCPATH_MAX]; // Holds /proc/4294967296/status\0
+  // XXX: NOTE: should this be %d not %u since pid_t is typedef'd to signed int?
+  snprintf(procname, PROCPATH_MAX, "/proc/%u/status", pid);
+#undef PROCPATH_MAX
+  stream = fopen(procname, "r");
+  if (stream == NULL) {
+    return NERR;
+  }
+
+  /* /proc/pid/status format: ($ cat /proc/$$/status)
+         Name:   bash
+         Umask:  0022
+         State:  S (sleeping)
+         Tgid:   17248
+         Ngid:   0
+         Pid:    17248
+         PPid:   17200
+   */
+
+  /* Name Line Format: "Name:___$NAME\n\0" where _ are spaces (5+3+len(NAME)+2 =
+   * 10+len(NAME)) `man proc_pid_status` claims $NAME will be truncated to
+   * TASK_COMM_LEN (including \0 terminating byte) aka 15+1 bytes long. However,
+   * They fail to account for work-queue-threads and kernel-threads which
+   * seem to not have this restriction.
+   * ie `rcu_exp_par_gp_kthread_worker/0` clearly exceeds this.
+   * We define NAMELINE_MAX to 9 + TASK_COMM_LEN (yes 9) because TASK_COMMON =
+   * len(NAME)+1 (for \0).
+   * NOTE: TASK_COMM_LEN isn't accessible in userspace so we define CT_PROC_NAME_MAX
+   */
+#define NAMELINE_MAX (9 + CT_PROC_NAME_MAX)
+  if (fgets(line, NAMELINE_MAX, stream) == NULL)
+    goto fail;
+  /* Fail if over max length, ie this is kernel related
+   * thread and we've recursed too deep. */
+  // if (line[NAMELINE_MAX - 2] != '\n')
+  //   goto fail;
+  else if (sscanf(line, "Name: %s\n", name) == 0)
+    return 0;
+#undef NAMELINE_MAX
+
+  /* Skip over the Umask, State, Tgid, Ngid, Pid lines
+   * The compiler can unroll this loop for us. */
+  for (int i = 0; i < 5; i++) {
+    if (fgets(line, CT_K_PAGE_SIZE, stream) == NULL)
+      goto fail;
+  }
+
+  if (fgets(line, CT_K_PAGE_SIZE, stream) == NULL)
+    goto fail;
+  else if (sscanf(line, "PPid: %d\n", ppid) == 0)
+    goto fail;
+
+  fclose(stream);
+  return OK;
+
+fail:
+  fclose(stream);
+  return NERR;
+}
+

src/pgetppid.h

@@ -0,0 +1,15 @@
+#ifndef CURSETREE_PGETPPID_H
+#define CURSETREE_PGETPPID_H
+
+#include <sys/types.h>
+
+/* XXX: WARNING: TODO: Linux kernel specific
+ * TASK_COMM_LEN isn't accessible in userspace so we define CT_PROC_NAME_MAX
+ * instead, representing the maximum (in most instances) truncated length of
+ * a process' Name field in /proc/pid/status.
+ */
+#define CT_PROC_NAME_MAX 16
+
+int pgetppid(const pid_t pid, pid_t *const ppid, char *const name);
+
+#endif

src/term.c

@@ -1,5 +1,4 @@
 #include <fcntl.h>
-#include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 
@@ -51,3 +50,7 @@ void ct_resetterm(struct ct_term *const term) {
   free(term);
 }
 
+/* TODO: use pgetppid() and write a terminfo parser, otherwise default to TERM */
+// static inline int ct_detectterm() {
+//   secure_getenv("TERM");
+// }