We use p->index_map.data to check whether the struct has been set up
and all the information about the index is stored there. This variable
gets set up halfway through the setup process, however, and a thread
can come along and use fields that haven't been written to yet.
Crucially, pack_entry_find_offset() needs to read the index version
(which is written after index_map) to know the offset and stride
length to pass to sha1_entry_pos(). If these values are wrong,
assertions in it will fail, as it will be reading bogus data.
Make index_version the last field to be written and switch from using
p->index_map.data to p->index_version as "git_pack_file is ready" flag
as we can use it to know if every field has been written.
Older versions of git would only write peeled entries for
items under refs/tags/. Newer versions will write them for
all refs, and we should be prepared to handle that.
There is an occasional assertion failure in sha1_entry_pos from
pack_entry_find_index when running threaded. Holding the mutex
around the code that grabs the index_map data and processes it
makes this assertion failure go away.
There are many paths through revparse that may return an error
code without reporting an error, I believe. This fixes one of
them. Because of the backtracking in revparse, it is pretty
complicated to fix the others.
A number of places were looking up option config values and then
not clearing the error codes if the values were not found. This
moves the repeated pattern into a shared routine and adds the
extra call to giterr_clear() when needed.
There are some cases, particularly where no loaded ODB backends
support a particular operation, where we would return an error
code without having set an error. This catches those cases and
reports that no ODB backends support the operation in question.
