From 14e7caf6b2b557d9e39f92fa5f4706dc45248d47 Mon Sep 17 00:00:00 2001
From: Luca BRUNO <luca.bruno@coreos.com>
Date: Mon, 29 Aug 2022 12:35:07 +0000
Subject: [PATCH] lib/commonio: make lock failures more detailed

This tweaks the database locking logic so that failures in the
link-checking paths are more detailed.
The rationale for this is that I've experienced a non-deterministic
bug which seems to be coming from this logic, and I'd like to get
more details about the actual failing condition.
---
 lib/commonio.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/lib/commonio.c b/lib/commonio.c
index 80288d64..f7fb1597 100644
--- a/lib/commonio.c
+++ b/lib/commonio.c
@@ -32,7 +32,7 @@
 
 /* local function prototypes */
 static int lrename (const char *, const char *);
-static int check_link_count (const char *file);
+static int check_link_count (const char *file, bool log);
 static int do_lock_file (const char *file, const char *lock, bool log);
 static /*@null@*/ /*@dependent@*/FILE *fopen_set_perms (
 	const char *name,
@@ -93,15 +93,25 @@ int lrename (const char *old, const char *new)
 	return res;
 }
 
-static int check_link_count (const char *file)
+static int check_link_count (const char *file, bool log)
 {
 	struct stat sb;
 
 	if (stat (file, &sb) != 0) {
+		if (log) {
+			(void) fprintf (shadow_logfd,
+			                "%s: %s file stat error: %s\n",
+			                shadow_progname, file, strerror (errno));
+		}
 		return 0;
 	}
 
 	if (sb.st_nlink != 2) {
+		if (log) {
+			(void) fprintf (shadow_logfd,
+			                "%s: %s: lock file already used (nlink: %u)\n",
+			                shadow_progname, file, sb.st_nlink);
+		}
 		return 0;
 	}
 
@@ -153,12 +163,7 @@ static int do_lock_file (const char *file, const char *lock, bool log)
 	close (fd);
 
 	if (link (file, lock) == 0) {
-		retval = check_link_count (file);
-		if ((0==retval) && log) {
-			(void) fprintf (shadow_logfd,
-			                "%s: %s: lock file already used\n",
-			                shadow_progname, file);
-		}
+		retval = check_link_count (file, log);
 		unlink (file);
 		return retval;
 	}
@@ -219,12 +224,7 @@ static int do_lock_file (const char *file, const char *lock, bool log)
 
 	retval = 0;
 	if (link (file, lock) == 0) {
-		retval = check_link_count (file);
-		if ((0==retval) && log) {
-			(void) fprintf (shadow_logfd,
-			                "%s: %s: lock file already used\n",
-			                shadow_progname, file);
-		}
+		retval = check_link_count (file, log);
 	} else {
 		if (log) {
 			(void) fprintf (shadow_logfd,