Add commands pci_{set,get}_path, add pci config files.

linux/pci.c

@@ -4,12 +4,20 @@
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <unistd.h>
+#include <limits.h>
+#include "pci.h"
+
+char pci_path[PATH_MAX] = ".";
 
 __attribute__((stdcall)) uint32_t pci_read(uint32_t bus, uint32_t dev, uint32_t fun, uint32_t offset, size_t len) {
-    char path[128];
+    char path[PATH_MAX*2];
     uint32_t value = 0;
-    sprintf(path, "/sys/bus/pci/devices/%4.4u:%2.2u:%2.2u.%u/config", 0, bus, dev, fun);
+    sprintf(path, "%s/%4.4u:%2.2u:%2.2u.%u/config", pci_path, 0, bus, dev, fun);
     int fd = open(path, O_RDONLY);
+    if (!fd) {
+        // TODO: report an error
+        return UINT32_MAX;
+    }
     lseek(fd, offset, SEEK_SET);
     read(fd, &value, len);
     close(fd);