ADDFILE should never make first block sparse

When checking if a file block can be sparse (i.e. not actually
allocated on disk), ensure the test always fails for the first
block of the file, as this would violate the ProDOS file system
specification, and makes ProDOS-8 unhappy.

Additionally, when loading a volume, log if files are encountered
that have sparse first blocks.

mach-kernel#42

Src/Dc_Prodos.c

@@ -1090,6 +1090,9 @@ static int GetFileDataResourceSize(struct prodos_image *current_image, struct fi
             if(tab_block[i] == 0)
               file_entry->nb_sparse++;
 
+          if(tab_block[0] == 0)
+            logf_error("  Warning : Block 0 is sparse in file: '%s'.\n", file_entry->file_path);
+
           /* Table des blocs utilisés */
           file_entry->tab_used_block = BuildUsedBlockTable(nb_block,tab_block,nb_index_block,tab_index_block,&file_entry->nb_used_block);
           if(file_entry->tab_used_block == NULL)
@@ -1180,6 +1183,9 @@ static int GetFileDataResourceSize(struct prodos_image *current_image, struct fi
             if(tab_block[i] == 0)
               file_entry->nb_sparse++;
 
+          if(tab_block[0] == 0)
+            logf_error("  Warning : Block 0 is sparse in data fork of file: '%s'.\n", file_entry->file_path);
+
           /* Table des blocs utilisés (Data) */
           tab_used_block_data = BuildUsedBlockTable(nb_block,tab_block,nb_index_block,tab_index_block,&nb_used_block_data);
           if(tab_used_block_data == NULL)
@@ -1250,6 +1256,9 @@ static int GetFileDataResourceSize(struct prodos_image *current_image, struct fi
             if(tab_block[i] == 0)
               file_entry->nb_sparse++;
 
+          if(tab_block[0] == 0)
+            logf_error("  Warning : Block 0 is sparse in resource fork of file: '%s'.\n", file_entry->file_path);
+
           /* Table des blocs utilisés (Resource) */
           tab_used_block_resource = BuildUsedBlockTable(nb_block,tab_block,nb_index_block,tab_index_block,&nb_used_block_resource);
           if(tab_used_block_resource == NULL)

Src/Prodos_Add.c

@@ -565,7 +565,9 @@ static void ComputeFileBlockUsage(struct prodos_file *current_file)
   for(i=0; i<current_file->data_length; i+=BLOCK_SIZE)
     {
       /* Recherche les plages de 0 */
-      if(i+BLOCK_SIZE <= current_file->data_length)
+      if(i == 0)
+        result = 1; /* Block 0 ne doit pas être Sparse */
+      else if(i+BLOCK_SIZE <= current_file->data_length)
         result = memcmp(&current_file->data[i],empty_block,BLOCK_SIZE);
       else
         result = memcmp(&current_file->data[i],empty_block,current_file->data_length-i);
@@ -586,7 +588,9 @@ static void ComputeFileBlockUsage(struct prodos_file *current_file)
       for(i=0; i<current_file->resource_length; i+=BLOCK_SIZE)
         {
           /* Recherche les plages de 0 */
-          if(i+BLOCK_SIZE <= current_file->resource_length)
+          if(i == 0)
+            result = 1; /* Block 0 ne doit pas être Sparse */
+          else if(i+BLOCK_SIZE <= current_file->resource_length)
             result = memcmp(&current_file->resource[i],empty_block,BLOCK_SIZE);
           else
             result = memcmp(&current_file->resource[i],empty_block,current_file->resource_length-i);
@@ -883,7 +887,9 @@ static WORD CreateSaplingContent(struct prodos_image *current_image, struct prod
   for(i=0,j=1,k=0; i<data_length; i+=BLOCK_SIZE,k++)
     {
       /* Recherche les plages de 0 */
-      if(i+BLOCK_SIZE <= data_length)
+      if(i == 0)
+        is_empty = 0; /* Block 0 ne doit pas être Sparse */
+      else if(i+BLOCK_SIZE <= data_length)
         is_empty = !memcmp(&data[i],empty_block,BLOCK_SIZE);
       else
         is_empty = !memcmp(&data[i],empty_block,data_length-i);
@@ -1006,7 +1012,9 @@ static WORD CreateTreeContent(struct prodos_image *current_image, struct prodos_
   for(i=0,j=index_data,k=0,l=0; i<data_length; i+=BLOCK_SIZE,k++)
     {
       /* Recherche les plages de 0 */
-      if(i+BLOCK_SIZE <= data_length)
+      if(i == 0)
+        is_empty = 0; /* Block 0 ne doit pas être Sparse */
+      else if(i+BLOCK_SIZE <= data_length)
         is_empty = !memcmp(&data[i],empty_block,BLOCK_SIZE);
       else
         is_empty = !memcmp(&data[i],empty_block,data_length-i);