[PATCH] Convert relative to absolute paths in printpathn

[zubin.mithra at gmail.com]

From: Zubin Mithra <zubin.mithra at gmail.com>

* util.c (print_abspath): New function that converts
  a relative to an absolute path.
* util.c (get_tracee_cwd): New function that finds
  the current working directory of the tracee.
* (printpathn): Use print_abspath to print out links
  if `-yy` flag is used.

Signed-off-by: Zubin Mithra <zubin.mithra at gmail.com>
---
 defs.h |  2 ++
 util.c | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 89 insertions(+), 3 deletions(-)

diff --git a/defs.h b/defs.h
index 5381e60..25d845d 100644
--- a/defs.h
+++ b/defs.h
@@ -631,6 +631,8 @@ extern const char *signame(int);
 extern void pathtrace_select(const char *);
 extern int pathtrace_match(struct tcb *);
 extern int getfdpath(struct tcb *, int, char *, unsigned);
+extern int get_tracee_cwd(struct tcb *, char *);
+extern bool print_abspath(struct tcb *, char *, int);
 
 extern const char *xlookup(const struct xlat *, int);
 
diff --git a/util.c b/util.c
index b1f1e90..6da6d00 100644
--- a/util.c
+++ b/util.c
@@ -593,9 +593,17 @@ printpathn(struct tcb *tcp, long addr, int n)
 		n++;
 		outstr = alloca(4 * n); /* 4*(n-1) + 3 for quotes and NUL */
 		string_quote(path, outstr, -1, n);
-		tprints(outstr);
-		if (!nul_seen)
-			tprints("...");
+		if (show_fd_path == 2) {
+			/* "..." is printed if the length of current working
+			   directory + length of outstr > 4096 */
+			if (print_abspath(tcp, outstr, nul_seen))
+				tprints("...");
+		}
+		else {
+			tprints(outstr);
+			if (!nul_seen)
+				tprints("...");
+		}
 	}
 }
 
@@ -1562,3 +1570,79 @@ returns_fd(struct tcb *tcp)
 		return 1;
 	return 0;
 }
+
+/* Return the current working directory of the tracee process,
+   with a trailing slash. */
+int
+get_tracee_cwd(struct tcb *tcp, char *cwd)
+{
+	int link_size = sizeof("/proc/%u/cwd") + sizeof(int) * 3;
+	char linkpath[link_size];
+	ssize_t n;
+
+	snprintf(linkpath, link_size, "/proc/%u/cwd", tcp->pid);
+	n = readlink(linkpath, cwd, MAXPATHLEN);
+
+	/* If readlink fails, something is abnormal(path > 4096) about
+	   the traced process and its cwd, so return an empty cwd. */
+	if (n == -1)
+		cwd[0] = '\0';
+
+	if (n >= 0) {
+		cwd[n] = '/';
+		cwd[n+1] = '\0';
+	}
+	return n;
+}
+
+bool
+print_abspath(struct tcb *tcp, char *outstr, int nulseen)
+{
+	char cwd[MAXPATHLEN + 2];
+	char quoted_path[MAXPATHLEN+2];
+	char *ptr = NULL;
+	char *abspath = NULL;
+	char *unquoted_outstr = NULL;
+
+	/* Just print it out if its an absolute path */
+	if (outstr[1] == '/') {
+		tprints(outstr);
+		return 0;
+	}
+
+	int len = get_tracee_cwd(tcp, cwd);
+	if (len == -1) {
+		/* There was a problem getting the cwd, so we print the
+		relative path we have */
+		tprints(outstr);
+		if (nulseen) return 0;
+	}
+
+	/* If the combined lengths of the absolute path and the
+	   relative paths > 4096, we just print out the cwd, followed by
+	   the relative path, without calling realpath on the combination */
+	if (strlen(outstr) + strlen(cwd) - /* 2 quotes in outstr */ 2 > MAXPATHLEN) {
+		tprintf("\"%s%s", cwd, outstr+1);
+		return 1;
+	}
+
+	/* Remove quotes at the start and end */
+	unquoted_outstr = outstr + 1;
+	unquoted_outstr[strlen(unquoted_outstr)-1] = '\0';
+
+	strncat(cwd, unquoted_outstr, MAXPATHLEN-len);
+	ptr = realpath(cwd, abspath);
+	if (ptr != NULL) {
+		snprintf(quoted_path, MAXPATHLEN, "\"%s\"", ptr);
+		tprints(quoted_path);
+		free(ptr);
+		return 0;
+	}
+	/* realpath failed for some reason, so we print the
+	   relative path that we have */
+	else {
+		tprintf("\"%s%s", cwd, outstr+1);
+		return 0;
+	}
+	return 0;
+}
-- 
1.8.4