[PATCH 1/6] block: Add blk_completion

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

This new data structure allows a task to wait for N things to complete.
Usually the submitting task will handle cleanup, but if it is killed,
the last completer will take care of it.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 block/blk-core.c    | 61 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/bio.h | 11 ++++++++
 2 files changed, 72 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index 10c08ac50697..2892246f2176 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1900,6 +1900,67 @@ void blk_io_schedule(void)
 }
 EXPORT_SYMBOL_GPL(blk_io_schedule);
 
+void blk_completion_init(struct blk_completion *cmpl, int n)
+{
+	spin_lock_init(&cmpl->cmpl_lock);
+	cmpl->cmpl_count = n;
+	cmpl->cmpl_task = current;
+	cmpl->cmpl_status = BLK_STS_OK;
+}
+
+int blk_completion_sub(struct blk_completion *cmpl, blk_status_t status, int n)
+{
+	int ret = 0;
+
+	spin_lock_bh(&cmpl->cmpl_lock);
+	if (cmpl->cmpl_status == BLK_STS_OK && status != BLK_STS_OK)
+		cmpl->cmpl_status = status;
+	cmpl->cmpl_count -= n;
+	BUG_ON(cmpl->cmpl_count < 0);
+	if (cmpl->cmpl_count == 0) {
+		if (cmpl->cmpl_task)
+			wake_up_process(cmpl->cmpl_task);
+		else
+			ret = -EINTR;
+	}
+	spin_unlock_bh(&cmpl->cmpl_lock);
+	if (ret < 0)
+		kfree(cmpl);
+	return ret;
+}
+
+int blk_completion_wait_killable(struct blk_completion *cmpl)
+{
+	int err = 0;
+
+	for (;;) {
+		set_current_state(TASK_KILLABLE);
+		spin_lock_bh(&cmpl->cmpl_lock);
+		if (cmpl->cmpl_count == 0)
+			break;
+		spin_unlock_bh(&cmpl->cmpl_lock);
+		blk_io_schedule();
+		if (fatal_signal_pending(current)) {
+			spin_lock_bh(&cmpl->cmpl_lock);
+			cmpl->cmpl_task = NULL;
+			if (cmpl->cmpl_count != 0) {
+				spin_unlock_bh(&cmpl->cmpl_lock);
+				cmpl = NULL;
+			}
+			err = -ERESTARTSYS;
+			break;
+		}
+	}
+	set_current_state(TASK_RUNNING);
+	if (cmpl) {
+		spin_unlock_bh(&cmpl->cmpl_lock);
+		err = blk_status_to_errno(cmpl->cmpl_status);
+		kfree(cmpl);
+	}
+
+	return err;
+}
+
 int __init blk_dev_init(void)
 {
 	BUILD_BUG_ON(REQ_OP_LAST >= (1 << REQ_OP_BITS));
diff --git a/include/linux/bio.h b/include/linux/bio.h
index f254bc79bb3a..0bde05f5548c 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -814,4 +814,15 @@ static inline void bio_set_polled(struct bio *bio, struct kiocb *kiocb)
 		bio->bi_opf |= REQ_NOWAIT;
 }
 
+struct blk_completion {
+	struct task_struct *cmpl_task;
+	spinlock_t cmpl_lock;
+	int cmpl_count;
+	blk_status_t cmpl_status;
+};
+
+void blk_completion_init(struct blk_completion *, int n);
+int blk_completion_sub(struct blk_completion *, blk_status_t status, int n);
+int blk_completion_wait_killable(struct blk_completion *);
+
 #endif /* __LINUX_BIO_H */
-- 
2.28.0