[PATCH] prevent deadlocks on an corrupt udev database

Here is the patch, that should prevent all of the known deadlocks with
corrupt tdb databases we discovered.
Thanks to Frank Steiner <fsteiner-mail@bio.ifi.lmu.de>, who tested all this
endlessly with a NFS mounted /dev. The conclusion is, that udev will not work
on filesystems without proper record locking, but we should prevent the
endless loops anyway. This patch implements:

o recovery from a corrupted udev database. udev will continue
  without database support now, instead of doing nothing. So the node should
  be generated in any case, remove will obviously not work for custom names.

o added iteration limits to the tdb-code at the places we discovered endless
  loops. In the case tdb tries to find more than 100.000 entries with the
  same hash, we better give up :)

o prevent a {all_partitions} loop caused by corrupt db data

o log all tdb errors to syslog

o switch sleep() to usleep() cause we want to use alarm()

1 files changed, 15 insertions, 1 deletions

diff --git a/udevdb.c b/udevdb.c
index c4dc4f005c..a218b66179 100644
--- a/udevdb.c
+++ b/udevdb.c
@@ -42,13 +42,16 @@
 #include "tdb/tdb.h"
 
 static TDB_CONTEXT *udevdb;
-
+sig_atomic_t gotalarm;
 
 int udevdb_add_dev(const char *path, const struct udevice *dev)
 {
 	TDB_DATA key, data;
 	char keystr[SYSFS_PATH_MAX];
 
+	if (udevdb == NULL)
+		return -1;
+
 	if ((path == NULL) || (dev == NULL))
 		return -ENODEV;
 
@@ -68,6 +71,9 @@ int udevdb_get_dev(const char *path, struct udevice *dev)
 {
 	TDB_DATA key, data;
 
+	if (udevdb == NULL)
+		return -1;
+
 	if (path == NULL)
 		return -ENODEV;
 
@@ -88,6 +94,9 @@ int udevdb_delete_dev(const char *path)
 	TDB_DATA key;
 	char keystr[SYSFS_PATH_MAX];
 
+	if (udevdb == NULL)
+		return -1;
+
 	if (path == NULL)
 		return -EINVAL;
 
@@ -121,6 +130,8 @@ int udevdb_init(int init_flag)
 	if (init_flag != UDEVDB_DEFAULT && init_flag != UDEVDB_INTERNAL)
 		return -EINVAL;
 
+	tdb_set_lock_alarm(&gotalarm);
+
 	udevdb = tdb_open(udev_db_filename, 0, init_flag, O_RDWR | O_CREAT, 0644);
 	if (udevdb == NULL) {
 		if (init_flag == UDEVDB_INTERNAL)
@@ -160,6 +171,9 @@ int udevdb_call_foreach(int (*user_record_handler) (char *path, struct udevice *
 {
 	int retval = 0;
 
+	if (udevdb == NULL)
+		return -1;
+
 	if (user_record_handler == NULL) {
 		dbg("invalid user record handling function");
 		return -EINVAL;