[PATCH v4 08/11] odb/transaction: add transaction env interface

[Justin Tobler <jltobler@gmail.com>]

The ODB transaction backend is responsible for creating/managing its own
staging area for writing objects. Other child processes spawned by Git
may need access to uncommitted objects or write new objects in the
staging area though.

Introduce `odb_transaction_env()` which is expected to provide the set
of environment variables needed by a child process to access the
transaction's staging area.

Signed-off-by: Justin Tobler <jltobler@gmail.com>
---
 object-file.c     | 16 ++++++++++++++++
 odb/transaction.c |  8 ++++++++
 odb/transaction.h | 17 +++++++++++++++++
 3 files changed, 41 insertions(+)

diff --git a/object-file.c b/object-file.c
index 358684beae..39b92e275c 100644
--- a/object-file.c
+++ b/object-file.c
@@ -27,6 +27,7 @@
 #include "path.h"
 #include "read-cache-ll.h"
 #include "setup.h"
+#include "strvec.h"
 #include "tempfile.h"
 #include "tmp-objdir.h"
 
@@ -1687,6 +1688,20 @@ static int odb_transaction_files_commit(struct odb_transaction *base)
 	return 0;
 }
 
+static int odb_transaction_files_env(struct odb_transaction *base,
+				     struct strvec *env)
+{
+	struct odb_transaction_files *transaction =
+		container_of(base, struct odb_transaction_files, base);
+	int ret;
+
+	ret = odb_transaction_files_prepare(&transaction->base);
+	if (!ret)
+		strvec_pushv(env, tmp_objdir_env(transaction->objdir));
+
+	return ret;
+}
+
 int odb_transaction_files_begin(struct odb_source *source,
 				struct odb_transaction **out)
 {
@@ -1696,6 +1711,7 @@ int odb_transaction_files_begin(struct odb_source *source,
 	transaction->base.source = source;
 	transaction->base.commit = odb_transaction_files_commit;
 	transaction->base.write_object_stream = odb_transaction_files_write_object_stream;
+	transaction->base.env = odb_transaction_files_env;
 	*out = &transaction->base;
 
 	return 0;
diff --git a/odb/transaction.c b/odb/transaction.c
index 249ef4d9b7..92ec8786a1 100644
--- a/odb/transaction.c
+++ b/odb/transaction.c
@@ -43,3 +43,11 @@ int odb_transaction_write_object_stream(struct odb_transaction *transaction,
 {
 	return transaction->write_object_stream(transaction, stream, len, oid);
 }
+
+int odb_transaction_env(struct odb_transaction *transaction, struct strvec *env)
+{
+	if (!transaction)
+		return 0;
+
+	return transaction->env(transaction, env);
+}
diff --git a/odb/transaction.h b/odb/transaction.h
index 3b0a5a78e5..5e51ce5ca4 100644
--- a/odb/transaction.h
+++ b/odb/transaction.h
@@ -34,6 +34,14 @@ struct odb_transaction {
 	int (*write_object_stream)(struct odb_transaction *transaction,
 				   struct odb_write_stream *stream, size_t len,
 				   struct object_id *oid);
+
+	/*
+	 * This callback is expected to populate the provided strvec with the
+	 * environment variables that a child process should inherit so that its
+	 * object writes participate in the transaction. Returns 0 on success, a
+	 * negative error code otherwise.
+	 */
+	int (*env)(struct odb_transaction *transaction, struct strvec *env);
 };
 
 /*
@@ -69,4 +77,13 @@ int odb_transaction_write_object_stream(struct odb_transaction *transaction,
 					struct odb_write_stream *stream,
 					size_t len, struct object_id *oid);
 
+/*
+ * Populates the provided strvec with the environment variables that a child
+ * process should inherit so that its object writes participate in the
+ * transaction, suitable for using via child_process.env. Returns 0 on success,
+ * a negative error code otherwise. Note that, if the specified transaction is
+ * NULL, the function is a no-op and no error is returned.
+ */
+int odb_transaction_env(struct odb_transaction *transaction, struct strvec *env);
+
 #endif
-- 
2.55.0.122.gf85a7e6620