snapscan-mutex.c: Use hash instead of parsing the device string.

ChangeLog

@@ -1,3 +1,8 @@
+2010-01-28  Oliver Schwartz <oliverschwartz at users.sourceforge.net>
+	* backend/snapscan-usb.c: Use hash of device string instead of parsing
+	it to create a semaphore id. The new code is less platform dependent
+	and should also work on FreeBSD 8.0.
+
 2010-01-27  Stéphane Voltz <stef.dev at free.fr>
 	* backend/genesys.c backend/genesys.h backend/genesys_conv.c
 	backend/genesys_low.h backend/genesys_gl841.c: add dynamic lineart

backend/snapscan-mutex.c

@@ -97,6 +97,8 @@ static void snapscani_mutex_unlock(snapscan_mutex_t* sem_id)
 
 #include <sys/ipc.h>
 #include <sys/sem.h>
+#include <sys/types.h>
+#include <unistd.h>
 
 #define snapscan_mutex_t int
 
@@ -116,32 +118,29 @@ union semun {
 static struct sembuf sem_wait = { 0, -1, 0 };
 static struct sembuf sem_signal = { 0, 1, 0 };
 
+static unsigned int snapscani_bernstein(const unsigned char* str)
+{
+    unsigned int hash = 5381; /* some arbitrary number */
+    int c;
+    
+    while (*str)
+    {
+        c = *str++;    
+        hash = ((hash << 5) + hash) + c;
+    }
+    return hash;
+} 
+
 static int snapscani_mutex_open(snapscan_mutex_t* sem_id, const char* dev)
 {
     static const char *me = "snapscani_mutex_open";
-    key_t ipc_key;
-    int pid, devnum, busnum;
+    key_t ipc_key = -1;
 
     if (strstr(dev, "libusb:") == dev)
     {
-        if (sanei_usb_get_vendor_product_byname(dev, NULL, &pid) != SANE_STATUS_GOOD)
-	{
-	    DBG (DL_MAJOR_ERROR, "%s: could not obtain USB product ID for device %s\n", me, dev);
-	    return 0;
-	}
-
-	if (sscanf(dev, "libusb:%d:%d", &busnum, &devnum) != 2)
-	{
-	    DBG (DL_MAJOR_ERROR, "%s: could not parse device string: %s\n", me, strerror(errno));
-	    return 0;
-	}
-
-	ipc_key = pid << 16;
-	ipc_key |= (busnum & 0xff) << 8;
-	ipc_key |= (devnum & 0xff);
-
-	DBG (DL_INFO, "%s: using IPC key 0x%08x for device %s (pid 0x%04x, bus 0x%02x, dev 0x%02x)\n",
-	     me, ipc_key, dev, pid, busnum, devnum);
+        key_t ipc_key = (key_t) snapscani_bernstein((const unsigned char*) dev+7);
+	DBG (DL_INFO, "%s: using IPC key 0x%08x for device %s\n",
+	     me, ipc_key, dev);
     }
     else
     {