Improve explanation for pipable WIM pre-write checksumming

diff --git a/src/write.c b/src/write.c
index 4edf64e3350bebfc0a80f28612290a6bcef43fdd..4805913de376fab95c1982eae45f0253a6dd13ec 100644 (file)
--- a/src/write.c
+++ b/src/write.c
@@ -2590,14 +2590,15 @@ write_pipable_wim(WIMStruct *wim, int image, int write_flags,
        /* At this point, the header at the beginning of the file has already
         * been written.  */
 
-       /* For efficiency, when wimlib adds an image to the WIM with
-        * wimlib_add_image(), the SHA-1 message digests of files are not
-        * calculated; instead, they are calculated while the files are being
-        * written.  However, this does not work when writing a pipable WIM,
-        * since when writing a blob to a pipable WIM, its SHA-1 message digest
-        * needs to be known before the blob data is written.  Therefore, before
-        * getting much farther, we need to pre-calculate the SHA-1 message
-        * digests of all blobs that will be written.  */
+       /*
+        * For efficiency, wimlib normally delays calculating each newly added
+        * stream's hash until while that stream being written, or just before
+        * it is written.  However, when writing a pipable WIM (potentially to a
+        * pipe), we first have to write the metadata resources, which contain
+        * all the hashes.  Moreover each blob is prefixed with its hash (struct
+        * pwm_blob_hdr).  Thus, we have to calculate all the hashes before
+        * writing anything.
+        */
        ret = wim_checksum_unhashed_blobs(wim);
        if (ret)
                return ret;