This adds a `git_pool` object that can do simple paged memory
allocation with free for the entire pool at once. Using this,
you can replace many small allocations with large blocks that
can then cheaply be doled out in small pieces. This is best
used when you plan to free the small blocks all at once - for
example, if they represent the parsed state from a file or data
stream that are either all kept or all discarded.
There are two real patterns of usage for `git_pools`: either
for "string" allocation, where the item size is a single byte
and you end up just packing the allocations in together, or for
"fixed size" allocation where you are allocating a large object
(e.g. a `git_oid`) and you generally just allocation single
objects that can be tightly packed. Of course, you can use it
for other things, but those two cases are the easiest.
Initial implementation. The relevant code is in `blob.c`: the blob write
function has been split into smaller functions.
- Directly write a file to the ODB in streaming mode
- Directly write a symlink to the ODB in direct mode
- Apply a filter, and write a file to the ODB in direct mode
When trying to write a file, we first call `git_filter__load_for_file`,
which populates a filters array with the required filters based on the
filename.
If no filters are resolved to the filename, we can write to the ODB in
streaming mode straight from disk. Otherwise, we load the whole file in
memory and use double-buffering to apply the filter chain. We finish
by writing the file as a whole to the ODB.
