Fix for rewriting uncompressed resources when exporting from solid WIM

[wimlib] / src / write.c

diff --git a/src/write.c b/src/write.c
index 7da18891132f466374a1cd72766e27f7758ade82..908de9adbb17b18ca645aabe33fbfc316bdd685f 100644 (file)
--- a/src/write.c
+++ b/src/write.c
@@ -882,7 +882,15 @@ should_rewrite_stream_uncompressed(const struct write_streams_ctx *ctx,
         * Exception: if the compressed size happens to be *exactly* the same as
         * the uncompressed size, then the stream *must* be written uncompressed
         * in order to remain compatible with the Windows Overlay Filesystem
-        * Filter Driver (WOF).  */
+        * Filter Driver (WOF).
+        *
+        * TODO: we are currently assuming that the optimization for
+        * single-chunk resources in maybe_rewrite_stream_uncompressed()
+        * prevents this case from being triggered too often.  To fully prevent
+        * excessive decompressions in degenerate cases, we really should
+        * obtain the uncompressed data by decompressing the compressed data we
+        * wrote to the output file.
+        */
        if ((lte->flags & WIM_RESHDR_FLAG_PACKED_STREAMS) &&
            (lte->out_reshdr.size_in_wim != lte->out_reshdr.uncompressed_size))
                return false;
@@ -890,6 +898,28 @@ should_rewrite_stream_uncompressed(const struct write_streams_ctx *ctx,
        return true;
 }
 
+static int
+maybe_rewrite_stream_uncompressed(struct write_streams_ctx *ctx,
+                                 struct wim_lookup_table_entry *lte)
+{
+       if (!should_rewrite_stream_uncompressed(ctx, lte))
+               return 0;
+
+       /* Regular (non-solid) WIM resources with exactly one chunk and
+        * compressed size equal to uncompressed size are exactly the same as
+        * the corresponding compressed data --- since there must be 0 entries
+        * in the chunk table and the only chunk must be stored uncompressed.
+        * In this case, there's no need to rewrite anything.  */
+       if (ctx->chunk_index == 1 &&
+           lte->out_reshdr.size_in_wim == lte->out_reshdr.uncompressed_size)
+       {
+               lte->out_reshdr.flags &= ~WIM_RESHDR_FLAG_COMPRESSED;
+               return 0;
+       }
+
+       return write_stream_uncompressed(lte, ctx->out_fd);
+}
+
 /* Write the next chunk of (typically compressed) data to the output WIM,
  * handling the writing of the chunk table.  */
 static int
@@ -996,14 +1026,10 @@ write_chunk(struct write_streams_ctx *ctx, const void *cchunk,
                        if (ctx->compressor != NULL)
                                lte->out_reshdr.flags |= WIM_RESHDR_FLAG_COMPRESSED;
 
-                       if (should_rewrite_stream_uncompressed(ctx, lte)) {
-                               DEBUG("Stream of size %"PRIu64" did not compress to "
-                                     "less than original size; writing uncompressed.",
-                                     lte->size);
-                               ret = write_stream_uncompressed(lte, ctx->out_fd);
-                               if (ret)
-                                       return ret;
-                       }
+                       ret = maybe_rewrite_stream_uncompressed(ctx, lte);
+                       if (ret)
+                               return ret;
+
                        wimlib_assert(lte->out_reshdr.uncompressed_size == lte->size);
 
                        ctx->cur_write_stream_offset = 0;