2-0001-osdep_get_cwd-linux-recurse-parents-until-one-yields.patch

From 7730ac0407ec2cb70f461ae4929e8a6ec20a3b0b Mon Sep 17 00:00:00 2001
From: "Chris West (Faux)" <git@goeswhere.com>
Date: Fri, 21 Mar 2014 23:38:23 +0000
Subject: [PATCH] osdep_get_cwd: linux: recurse parents until one yields

This helps when a command is running as a different user, it is common
to be able to see its parents, but not its cwd.  It may make sense, in
this situation, to present the parent's path.  e.g. if a user runs a set
of commands like:

$ cd /foo/bar
$ sudo hang-for-a-bit

.. it could be expected that get_cwd returns "/foo/bar", not NULL, as
previously.  sudo's cwd is not available, as the process itself is
running as root, but its parent process is, and its parent (the shell)'s
cwd is available to us.
---
 osdep-linux.c | 46 +++++++++++++++++++++++++++++++++++-----------
 1 file changed, 35 insertions(+), 11 deletions(-)

diff --git a/osdep-linux.c b/osdep-linux.c
index 46aea68..4627059 100644
--- a/osdep-linux.c
+++ b/osdep-linux.c
@@ -60,6 +60,26 @@ osdep_get_name(int fd, unused char *tty)
 	return (buf);
 }
 
+// 0 on failure
+pid_t
+parent_pid_of(pid_t pid) {
+	char		*path;
+	FILE		*f;
+	pid_t		ret = 0;
+
+	xasprintf(&path, "/proc/%lld/stat", (long long) pid);
+	f = fopen(path, "r");
+	if (!f)
+		return 0;
+
+	if (1 != fscanf(f, "%*d %*s %*c %d", &ret)) {
+		ret = 0;
+	}
+
+	fclose(f);
+	return ret;
+}
+
 char *
 osdep_get_cwd(int fd)
 {
@@ -71,20 +91,24 @@ osdep_get_cwd(int fd)
 	if ((pgrp = tcgetpgrp(fd)) == -1)
 		return (NULL);
 
-	xasprintf(&path, "/proc/%lld/cwd", (long long) pgrp);
-	n = readlink(path, target, MAXPATHLEN);
-	free(path);
-
-	if (n == -1 && ioctl(fd, TIOCGSID, &sid) != -1) {
-		xasprintf(&path, "/proc/%lld/cwd", (long long) sid);
+	do {
+		xasprintf(&path, "/proc/%lld/cwd", (long long) pgrp);
 		n = readlink(path, target, MAXPATHLEN);
 		free(path);
-	}
 
-	if (n > 0) {
-		target[n] = '\0';
-		return (target);
-	}
+		if (n == -1 && ioctl(fd, TIOCGSID, &sid) != -1) {
+			xasprintf(&path, "/proc/%lld/cwd", (long long) sid);
+			n = readlink(path, target, MAXPATHLEN);
+			free(path);
+		}
+
+		if (n > 0) {
+			target[n] = '\0';
+			return (target);
+		}
+		pgrp = parent_pid_of(pgrp);
+	} while (pgrp);
+
 	return (NULL);
 }
 
-- 
1.9.1