Avoid consuming lots of space and time if the first partition is not near the start of the disk (Debian bug #619458, Ubuntu bug #691569).

ChangeLog.embed-sectors

@@ -1,7 +1,12 @@
 2011-03-14  Colin Watson  <cjwatson@ubuntu.com>
 
+	* include/grub/partition.h (grub_partition_map): Change prototype of
+	embed to take a maximum value for nsectors.
 	* grub-core/partmap/msdos.c (embed_signatures): New array.
 	(pc_partition_map_embed): Check for and avoid sectors matching any
-	of the signatures in embed_signatures.
+	of the signatures in embed_signatures, up to max_nsectors.
+	* grub-core/partmap/gpt.c (gpt_partition_map_embed): Restrict
+	returned sector map to max_nsectors.
 	* util/grub-setup.c (setup): Allow for the embedding area being
-	split into multiple blocklists.
+	split into multiple blocklists.  Tell dest_partmap->embed the
+	maximum number of sectors we care about.

grub-core/partmap/gpt.c

@@ -125,6 +125,7 @@ gpt_partition_map_iterate (grub_disk_t disk,
 #ifdef GRUB_UTIL
 static grub_err_t
 gpt_partition_map_embed (struct grub_disk *disk, unsigned int *nsectors,
+			 unsigned int max_nsectors,
 			 grub_embed_type_t embed_type,
 			 grub_disk_addr_t **sectors)
 {
@@ -174,6 +175,8 @@ gpt_partition_map_embed (struct grub_disk *disk, unsigned int *nsectors,
 		       " embedding won't be possible!");
 
   *nsectors = len;
+  if (*nsectors > max_nsectors)
+    *nsectors = max_nsectors;
   *sectors = grub_malloc (*nsectors * sizeof (**sectors));
   if (!*sectors)
     return grub_errno;

grub-core/partmap/msdos.c

@@ -185,6 +185,7 @@ grub_partition_msdos_iterate (grub_disk_t disk,
 #ifdef GRUB_UTIL
 static grub_err_t
 pc_partition_map_embed (struct grub_disk *disk, unsigned int *nsectors,
+			unsigned int max_nsectors,
 			grub_embed_type_t embed_type,
 			grub_disk_addr_t **sectors)
 {
@@ -275,10 +276,13 @@ pc_partition_map_embed (struct grub_disk *disk, unsigned int *nsectors,
     {
       unsigned i, j;
       char *embed_signature_check;
-      unsigned int orig_nsectors;
+      unsigned int orig_nsectors, avail_nsectors;
 
       orig_nsectors = *nsectors;
       *nsectors = end - 2;
+      avail_nsectors = *nsectors;
+      if (*nsectors > max_nsectors)
+	*nsectors = max_nsectors;
       *sectors = grub_malloc (*nsectors * sizeof (**sectors));
       if (!*sectors)
 	return grub_errno;
@@ -307,11 +311,20 @@ pc_partition_map_embed (struct grub_disk *disk, unsigned int *nsectors,
 			  "future.  Please ask its authors not to store data "
 			  "in the boot track",
 			  (*sectors)[i], embed_signatures[j].name);
-	  (*nsectors)--;
+	  avail_nsectors--;
+	  if (avail_nsectors < *nsectors)
+	    *nsectors = avail_nsectors;
 
 	  /* Avoid this sector.  */
 	  for (j = i; j < *nsectors; j++)
 	    (*sectors)[j]++;
+
+	  /* Have we run out of space?  */
+	  if (avail_nsectors < orig_nsectors)
+	    break;
+
+	  /* Make sure to check the next sector.  */
+	  i--;
 	}
       grub_free (embed_signature_check);
 

include/grub/partition.h

@@ -49,6 +49,7 @@ struct grub_partition_map
 #ifdef GRUB_UTIL
   /* Determine sectors available for embedding.  */
   grub_err_t (*embed) (struct grub_disk *disk, unsigned int *nsectors,
+		       unsigned int max_nsectors,
 		       grub_embed_type_t embed_type,
 		       grub_disk_addr_t **sectors);
 #endif

util/grub-setup.c

@@ -426,10 +426,8 @@ setup (const char *dir,
       }
 
     nsec = core_sectors;
-    err = dest_partmap->embed (dest_dev->disk, &nsec,
+    err = dest_partmap->embed (dest_dev->disk, &nsec, 2 * core_sectors,
 			       GRUB_EMBED_PCBIOS, &sectors);
-    if (nsec > 2 * core_sectors)
-      nsec = 2 * core_sectors;
     
     if (err)
       {