libs/guest: Allocate rec_pfns earlier in write_batch()

For reasons which escape me, rec_pfns are allocated separately to the rest of
the batch allocations.

Allocate them all together.  This will allow for future simplifications to be
performed in an incremental mannor.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>

tools/libs/guest/xg_sr_save.c

@@ -115,8 +115,10 @@ static int write_batch(struct xc_sr_context *ctx)
     local_pages = calloc(nr_pfns, sizeof(*local_pages));
     /* iovec[] for writev(). */
     iov = malloc((nr_pfns + 4) * sizeof(*iov));
+    /* page_data record PFNs list */
+    rec_pfns = malloc(nr_pfns * sizeof(*rec_pfns));
 
-    if ( !mfns || !types || !errors || !guest_data || !local_pages || !iov )
+    if ( !mfns || !types || !errors || !guest_data || !local_pages || !iov || !rec_pfns )
     {
         ERROR("Unable to allocate arrays for a batch of %u pages",
               nr_pfns);
@@ -207,14 +209,6 @@ static int write_batch(struct xc_sr_context *ctx)
         }
     }
 
-    rec_pfns = malloc(nr_pfns * sizeof(*rec_pfns));
-    if ( !rec_pfns )
-    {
-        ERROR("Unable to allocate %zu bytes of memory for page data pfn list",
-              nr_pfns * sizeof(*rec_pfns));
-        goto err;
-    }
-
     hdr.count = nr_pfns;
 
     rec.length = sizeof(hdr);
@@ -263,11 +257,11 @@ static int write_batch(struct xc_sr_context *ctx)
     rc = ctx->save.nr_batch_pfns = 0;
 
  err:
-    free(rec_pfns);
     if ( guest_mapping )
         xenforeignmemory_unmap(xch->fmem, guest_mapping, nr_pages_mapped);
     for ( i = 0; local_pages && i < nr_pfns; ++i )
         free(local_pages[i]);
+    free(rec_pfns);
     free(iov);
     free(local_pages);
     free(guest_data);