在 git 中的应⽤用 diff_populate_filespec While doing rename detection and pickaxe operation, we may need to grab the data for the blob (or file) for our own in-core comparison.
在 libgit2 中的应⽤用 pack_index_check When doing Packed Object lookup query, Mmap the index file and do a quick run through the header to guess the index version, and to verify that the size of the index makes sense.