[PATCH 2/3] reftable/stack: move list lock to `struct reftable_stack`

[Karthik Nayak <karthik.188@gmail.com>]

The struct `reftable_addition` is used to modify a given stack, as such,
it also includes a `struct reftable_flock` used to obtain the lock to
the list file. While the scope of the field lies within this struct, it
doesn't allow for optimizations to be made on `struct reftable_stack`
itself.

Move the field to `struct reftable_stack`, allowing us to make a simple
optimization around avoiding a stack reload when we have already
obtained a lock. While this is currently possible in the write path, the
write path also contains multiple branches to reads which only work
on top of `struct reftable_stack`, and we would miss the optimization in
such paths.

While here, remove an unused header file from 'reftable/stack.h'.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 reftable/stack.c | 15 ++++++++-------
 reftable/stack.h |  7 ++++++-
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/reftable/stack.c b/reftable/stack.c
index 540f5e77ac..e449af9c03 100644
--- a/reftable/stack.c
+++ b/reftable/stack.c
@@ -536,6 +536,8 @@ int reftable_new_stack(struct reftable_stack **dest, const char *dir,
 		goto out;
 	}
 
+	p->list_lock = REFTABLE_FLOCK_INIT;
+
 	err = reftable_stack_reload_maybe_reuse(p, 1);
 	if (err < 0)
 		goto out;
@@ -628,7 +630,6 @@ int reftable_stack_reload(struct reftable_stack *st)
 }
 
 struct reftable_addition {
-	struct reftable_flock tables_list_lock;
 	struct reftable_stack *stack;
 	struct reftable_write_options opts;
 
@@ -653,7 +654,7 @@ static void reftable_addition_close(struct reftable_addition *add)
 	add->new_tables_len = 0;
 	add->new_tables_cap = 0;
 
-	flock_release(&add->tables_list_lock);
+	flock_release(&add->stack->list_lock);
 	reftable_buf_release(&nm);
 }
 
@@ -669,13 +670,13 @@ static int reftable_stack_init_addition(struct reftable_addition *add,
 	if (opts)
 		add->opts = *opts;
 
-	err = flock_acquire(&add->tables_list_lock, st->list_file,
+	err = flock_acquire(&add->stack->list_lock, st->list_file,
 			    add->opts.lock_timeout_ms);
 	if (err < 0)
 		goto done;
 
 	if (add->opts.default_permissions) {
-		if (chmod(add->tables_list_lock.path,
+		if (chmod(add->stack->list_lock.path,
 			  add->opts.default_permissions) < 0) {
 			err = REFTABLE_IO_ERROR;
 			goto done;
@@ -774,7 +775,7 @@ int reftable_addition_commit(struct reftable_addition *add)
 			goto done;
 	}
 
-	err = reftable_write_data(add->tables_list_lock.fd,
+	err = reftable_write_data(add->stack->list_lock.fd,
 				  table_list.buf, table_list.len);
 	reftable_buf_release(&table_list);
 	if (err < 0) {
@@ -782,13 +783,13 @@ int reftable_addition_commit(struct reftable_addition *add)
 		goto done;
 	}
 
-	err = fsync(add->tables_list_lock.fd);
+	err = fsync(add->stack->list_lock.fd);
 	if (err < 0) {
 		err = REFTABLE_IO_ERROR;
 		goto done;
 	}
 
-	err = flock_commit(&add->tables_list_lock);
+	err = flock_commit(&add->stack->list_lock);
 	if (err < 0) {
 		err = REFTABLE_IO_ERROR;
 		goto done;
diff --git a/reftable/stack.h b/reftable/stack.h
index f7901e6c6f..52e07ad551 100644
--- a/reftable/stack.h
+++ b/reftable/stack.h
@@ -10,7 +10,6 @@
 #define STACK_H
 
 #include "system.h"
-#include "reftable-writer.h"
 #include "reftable-stack.h"
 
 struct reftable_stack {
@@ -18,6 +17,12 @@ struct reftable_stack {
 	char *list_file;
 	int list_fd;
 
+	/*
+	 * Set while an addition holds the stack locked. Used by
+	 * stack_uptodate() to skip reload checks while locked.
+	 */
+	struct reftable_flock list_lock;
+
 	char *reftable_dir;
 
 	struct reftable_stack_options opts;

-- 
2.55.GIT