[PATCH 4/5] btrfs: add nowait parameter to btrfs_encoded_read

[Mark Harmstone <maharmstone@fb.com>]

Adds a nowait parameter to btrfs_encoded_read, which if it is true
causes the function to return -EAGAIN rather than sleeping.

Signed-off-by: Mark Harmstone <maharmstone@fb.com>
---
 fs/btrfs/btrfs_inode.h |  2 +-
 fs/btrfs/inode.c       | 59 ++++++++++++++++++++++++++++++++----------
 fs/btrfs/ioctl.c       |  2 +-
 3 files changed, 47 insertions(+), 16 deletions(-)

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 3a0b519c51ca..2334961e71ed 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -618,7 +618,7 @@ int btrfs_encoded_read_regular_fill_pages(struct btrfs_inode *inode,
 					  void *cb_ctx);
 ssize_t btrfs_encoded_read(struct kiocb *iocb, struct iov_iter *iter,
 			   struct btrfs_ioctl_encoded_io_args *encoded,
-			   struct extent_state **cached_state,
+			   bool nowait, struct extent_state **cached_state,
 			   u64 *disk_bytenr, u64 *disk_io_size);
 ssize_t btrfs_encoded_read_regular(struct kiocb *iocb, struct iov_iter *iter,
 				   u64 start, u64 lockend,
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index e58284d33b35..c536e37cb6b6 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8999,7 +8999,7 @@ static ssize_t btrfs_encoded_read_inline(
 				struct extent_state **cached_state,
 				u64 extent_start, size_t count,
 				struct btrfs_ioctl_encoded_io_args *encoded,
-				bool *unlocked)
+				bool *unlocked, bool nowait)
 {
 	struct btrfs_inode *inode = BTRFS_I(file_inode(iocb->ki_filp));
 	struct btrfs_root *root = inode->root;
@@ -9018,6 +9018,9 @@ static ssize_t btrfs_encoded_read_inline(
 		ret = -ENOMEM;
 		goto out;
 	}
+
+	path->nowait = !!nowait;
+
 	ret = btrfs_lookup_file_extent(NULL, root, path, btrfs_ino(inode),
 				       extent_start, 0);
 	if (ret) {
@@ -9254,7 +9257,7 @@ ssize_t btrfs_encoded_read_regular(struct kiocb *iocb, struct iov_iter *iter,
 
 ssize_t btrfs_encoded_read(struct kiocb *iocb, struct iov_iter *iter,
 			   struct btrfs_ioctl_encoded_io_args *encoded,
-			   struct extent_state **cached_state,
+			   bool nowait, struct extent_state **cached_state,
 			   u64 *disk_bytenr, u64 *disk_io_size)
 {
 	struct btrfs_inode *inode = BTRFS_I(file_inode(iocb->ki_filp));
@@ -9268,7 +9271,10 @@ ssize_t btrfs_encoded_read(struct kiocb *iocb, struct iov_iter *iter,
 
 	file_accessed(iocb->ki_filp);
 
-	btrfs_inode_lock(inode, BTRFS_ILOCK_SHARED);
+	ret = btrfs_inode_lock(inode,
+			       BTRFS_ILOCK_SHARED | (nowait ? BTRFS_ILOCK_TRY : 0));
+	if (ret)
+		return ret;
 
 	if (iocb->ki_pos >= inode->vfs_inode.i_size) {
 		btrfs_inode_unlock(inode, BTRFS_ILOCK_SHARED);
@@ -9281,21 +9287,45 @@ ssize_t btrfs_encoded_read(struct kiocb *iocb, struct iov_iter *iter,
 	 */
 	lockend = start + BTRFS_MAX_UNCOMPRESSED - 1;
 
-	for (;;) {
+	if (nowait) {
 		struct btrfs_ordered_extent *ordered;
 
-		ret = btrfs_wait_ordered_range(inode, start,
-					       lockend - start + 1);
-		if (ret)
+		if (filemap_range_needs_writeback(inode->vfs_inode.i_mapping,
+						  start, lockend)) {
+			ret = -EAGAIN;
 			goto out_unlock_inode;
-		lock_extent(io_tree, start, lockend, cached_state);
+		}
+
+		if (!try_lock_extent(io_tree, start, lockend, cached_state)) {
+			ret = -EAGAIN;
+			goto out_unlock_inode;
+		}
+
 		ordered = btrfs_lookup_ordered_range(inode, start,
 						     lockend - start + 1);
-		if (!ordered)
-			break;
-		btrfs_put_ordered_extent(ordered);
-		unlock_extent(io_tree, start, lockend, cached_state);
-		cond_resched();
+		if (ordered) {
+			btrfs_put_ordered_extent(ordered);
+			unlock_extent(io_tree, start, lockend, cached_state);
+			ret = -EAGAIN;
+			goto out_unlock_inode;
+		}
+	} else {
+		for (;;) {
+			struct btrfs_ordered_extent *ordered;
+
+			ret = btrfs_wait_ordered_range(inode, start,
+						lockend - start + 1);
+			if (ret)
+				goto out_unlock_inode;
+			lock_extent(io_tree, start, lockend, cached_state);
+			ordered = btrfs_lookup_ordered_range(inode, start,
+							lockend - start + 1);
+			if (!ordered)
+				break;
+			btrfs_put_ordered_extent(ordered);
+			unlock_extent(io_tree, start, lockend, cached_state);
+			cond_resched();
+		}
 	}
 
 	em = btrfs_get_extent(inode, NULL, start, lockend - start + 1);
@@ -9315,7 +9345,8 @@ ssize_t btrfs_encoded_read(struct kiocb *iocb, struct iov_iter *iter,
 		em = NULL;
 		ret = btrfs_encoded_read_inline(iocb, iter, start, lockend,
 						cached_state, extent_start,
-						count, encoded, &unlocked);
+						count, encoded, &unlocked,
+						nowait);
 		goto out_em;
 	}
 
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index e2ecf0bcda24..8c9ff4898ab0 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -4579,7 +4579,7 @@ static int btrfs_ioctl_encoded_read(struct file *file, void __user *argp,
 	init_sync_kiocb(&kiocb, file);
 	kiocb.ki_pos = pos;
 
-	ret = btrfs_encoded_read(&kiocb, &iter, &args, &cached_state,
+	ret = btrfs_encoded_read(&kiocb, &iter, &args, false, &cached_state,
 				 &disk_bytenr, &disk_io_size);
 
 	if (ret == -EIOCBQUEUED) {
-- 
2.44.2