Rewrite all file IO for more performance

The new `git_filebuf` structure provides atomic high-performance writes
to disk by using a write cache, and optionally a double-buffered scheme
through a worker thread (not enabled yet).

Writes can be done 3-layered, like in git.git (user code -> write cache
-> disk), or 2-layered, by writing directly on the cache. This makes
index writing considerably faster.

The `git_filebuf` structure contains all the old functionality of
`git_filelock` for atomic file writes and reads. The `git_filelock`
structure has been removed.

Additionally, the `git_filebuf` API allows to automatically hash (SHA1)
all the data as it is written to disk (hashing is done smartly on big
chunks to improve performance).

Signed-off-by: Vicent Marti <tanoku@gmail.com>

1 files changed, 40 insertions, 0 deletions

diff --git a/src/filebuf.h b/src/filebuf.h
new file mode 100644
index 000000000..f2e4dba51
--- /dev/null
+++ b/src/filebuf.h
@@ -0,0 +1,40 @@
+#ifndef INCLUDE_filebuf_h__
+#define INCLUDE_filebuf_h__
+
+#include "fileops.h"
+#include "hash.h"
+
+#ifdef GIT_THREADS
+#	define GIT_FILEBUF_THREADS
+#endif
+
+#define GIT_FILEBUF_HASH_CONTENTS 0x1
+#define GIT_FILEBUF_APPEND 0x2
+#define GIT_FILEBUF_FORCE 0x4
+
+struct git_filebuf {
+	char *path_original;
+	char *path_lock;
+
+	git_hash_ctx *digest;
+
+	unsigned char *buffer;
+#ifdef GIT_FILEBUF_THREADS
+	unsigned char *buffer_back;
+#endif
+
+	size_t buf_size, buf_pos;
+	git_file fd;
+};
+
+typedef struct git_filebuf git_filebuf;
+
+int git_filebuf_write(git_filebuf *lock, void *buff, size_t len);
+int git_filebuf_reserve(git_filebuf *file, void **buff, size_t len);
+
+int git_filebuf_open(git_filebuf *lock, const char *path, int flags);
+int git_filebuf_commit(git_filebuf *lock);
+void git_filebuf_cleanup(git_filebuf *lock);
+int git_filebuf_hash(git_oid *oid, git_filebuf *file);
+
+#endif