refs/reftable: allow configuring block size

Add a new option `reftable.blockSize` that allows the user to control
the block size used by the reftable library.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 30 insertions, 1 deletions

diff --git a/refs/reftable-backend.c b/refs/reftable-backend.c
index f8f930380d..8d0ae9e285 100644
--- a/refs/reftable-backend.c
+++ b/refs/reftable-backend.c
@@ -1,6 +1,7 @@
 #include "../git-compat-util.h"
 #include "../abspath.h"
 #include "../chdir-notify.h"
+#include "../config.h"
 #include "../environment.h"
 #include "../gettext.h"
 #include "../hash.h"
@@ -228,6 +229,22 @@ done:
 	return ret;
 }
 
+static int reftable_be_config(const char *var, const char *value,
+			      const struct config_context *ctx,
+			      void *_opts)
+{
+	struct reftable_write_options *opts = _opts;
+
+	if (!strcmp(var, "reftable.blocksize")) {
+		unsigned long block_size = git_config_ulong(var, value, ctx->kvi);
+		if (block_size > 16777215)
+			die("reftable block size cannot exceed 16MB");
+		opts->block_size = block_size;
+	}
+
+	return 0;
+}
+
 static struct ref_store *reftable_be_init(struct repository *repo,
 					  const char *gitdir,
 					  unsigned int store_flags)
@@ -243,12 +260,24 @@ static struct ref_store *reftable_be_init(struct repository *repo,
 	base_ref_store_init(&refs->base, repo, gitdir, &refs_be_reftable);
 	strmap_init(&refs->worktree_stacks);
 	refs->store_flags = store_flags;
-	refs->write_options.block_size = 4096;
+
 	refs->write_options.hash_id = repo->hash_algo->format_id;
 	refs->write_options.default_permissions = calc_shared_perm(0666 & ~mask);
 	refs->write_options.disable_auto_compact =
 		!git_env_bool("GIT_TEST_REFTABLE_AUTOCOMPACTION", 1);
 
+	git_config(reftable_be_config, &refs->write_options);
+
+	/*
+	 * It is somewhat unfortunate that we have to mirror the default block
+	 * size of the reftable library here. But given that the write options
+	 * wouldn't be updated by the library here, and given that we require
+	 * the proper block size to trim reflog message so that they fit, we
+	 * must set up a proper value here.
+	 */
+	if (!refs->write_options.block_size)
+		refs->write_options.block_size = 4096;
+
 	/*
 	 * Set up the main reftable stack that is hosted in GIT_COMMON_DIR.
 	 * This stack contains both the shared and the main worktree refs.