chain.c32: explicitly verify after writing MBR

If we write the MBR, do verify by reading it back and comparing.
Right now all we do is print an error, though.

diff --git a/com32/modules/chain.c b/com32/modules/chain.c
index 9fda1c9..e6409b4 100644 (file)
--- a/com32/modules/chain.c
+++ b/com32/modules/chain.c
@@ -244,7 +244,7 @@ static int write_sector(unsigned int lba, const void *buf)
     inreg.esi.w[0] = OFFS(dapa);
     inreg.ds       = SEG(dapa);
     inreg.edx.b[0] = disk_info.disk;
-    inreg.eax.b[1] = 0x43;     /* Extended write */
+    inreg.eax.w[0] = 0x4300;   /* Extended write */
   } else {
     unsigned int c, h, s, t;
 
@@ -280,6 +280,22 @@ static int write_sector(unsigned int lba, const void *buf)
   return 0;                    /* ok */
 }
 
+static int write_verify_sector(unsigned int lba, const void *buf)
+{
+  char *rb;
+  int rv;
+
+  rv = write_sector(lba, buf);
+  if (rv)
+    return rv;         /* Write failure */
+  rb = read_sector(lba);
+  if (!rb)
+    return -1;         /* Readback failure */
+  rv = memcmp(buf, rb, SECTOR);
+  free(rb);
+  return rv ? -1 : 0;
+}
+
 /* Search for a specific drive, based on the MBR signature; bytes
    440-443. */
 static int find_disk(uint32_t mbr_sig)
@@ -621,9 +637,9 @@ static int hide_unhide(char *mbr, int part)
   }
 
   if (write_back)
-    return write_sector(0, mbr);
-  else
-    return 0;                  /* Nothing to do, return OK */
+    return write_verify_sector(0, mbr);
+
+  return 0;                    /* ok */
 }
 
 int main(int argc, char *argv[])