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Subject: [PATCH 08/10] afs: Add O_DIRECT read support
From:   David Howells <dhowells@redhat.com>
To:     viro@zeniv.linux.org.uk
Cc:     dhowells@redhat.com, linux-fsdevel@vger.kernel.org,
        linux-afs@lists.infradead.org, linux-kernel@vger.kernel.org
Date:   Thu, 13 Sep 2018 16:52:39 +0100
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Add synchronous O_DIRECT read support to AFS (no AIO yet).  It can
theoretically handle reads up to the maximum size describable by loff_t -
and given an iterator with sufficiently capacity to handle that and given
support on the server.

Signed-off-by: David Howells <dhowells@redhat.com>
---

 fs/afs/file.c     |   61 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/afs/internal.h |    1 +
 fs/afs/write.c    |    8 +++++++
 3 files changed, 70 insertions(+)

diff --git a/fs/afs/file.c b/fs/afs/file.c
index 36ba263db749..60f9896e1426 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -27,6 +27,7 @@ static int afs_releasepage(struct page *page, gfp_t gfp_flags);
 
 static int afs_readpages(struct file *filp, struct address_space *mapping,
 			 struct list_head *pages, unsigned nr_pages);
+static ssize_t afs_direct_IO(struct kiocb *iocb, struct iov_iter *iter);
 
 const struct file_operations afs_file_operations = {
 	.open		= afs_open,
@@ -55,6 +56,7 @@ const struct address_space_operations afs_fs_aops = {
 	.launder_page	= afs_launder_page,
 	.releasepage	= afs_releasepage,
 	.invalidatepage	= afs_invalidatepage,
+	.direct_IO	= afs_direct_IO,
 	.write_begin	= afs_write_begin,
 	.write_end	= afs_write_end,
 	.writepage	= afs_writepage,
@@ -731,3 +733,62 @@ static int afs_file_mmap(struct file *file, struct vm_area_struct *vma)
 		vma->vm_ops = &afs_vm_ops;
 	return ret;
 }
+
+/*
+ * Direct file read operation for an AFS file.
+ */
+static ssize_t afs_file_direct_read(struct kiocb *iocb, struct iov_iter *iter)
+{
+	struct file *file = iocb->ki_filp;
+	struct address_space *mapping = file->f_mapping;
+	struct afs_vnode *vnode = AFS_FS_I(mapping->host);
+	struct afs_read *req;
+	struct key *key = afs_file_key(file);
+	ssize_t ret;
+	size_t count = iov_iter_count(iter), transferred = 0;
+
+	if (!count)
+		return 0;
+	if (!is_sync_kiocb(iocb))
+		return -EOPNOTSUPP;
+
+	req = kzalloc(sizeof(struct afs_read), GFP_KERNEL);
+	if (!req)
+		return -ENOMEM;
+
+	refcount_set(&req->usage, 1);
+	req->pos = iocb->ki_pos;
+	req->len = count;
+	req->iter = *iter;
+
+	task_io_account_read(count);
+
+
+	// TODO afs_start_io_direct(inode);
+	ret = afs_fetch_data(vnode, key, req);
+	if (ret == 0)
+		transferred = req->actual_len;
+	*iter = req->iter;
+	afs_put_read(req);
+
+	// TODO afs_end_io_direct(inode);
+
+	BUG_ON(ret == -EIOCBQUEUED); // TODO
+
+	if (ret == 0)
+		ret = transferred;
+
+	return ret;
+}
+
+/*
+ * Do direct I/O.
+ */
+static ssize_t afs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
+{
+	VM_BUG_ON(iov_iter_count(iter) != PAGE_SIZE);
+
+	if (iov_iter_rw(iter) == READ)
+		return afs_file_direct_read(iocb, iter);
+	return afs_file_direct_write(iocb, iter);
+}
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 7c7598856b96..38b48382db52 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -1111,6 +1111,7 @@ extern int afs_fsync(struct file *, loff_t, loff_t, int);
 extern vm_fault_t afs_page_mkwrite(struct vm_fault *vmf);
 extern void afs_prune_wb_keys(struct afs_vnode *);
 extern int afs_launder_page(struct page *);
+extern ssize_t afs_file_direct_write(struct kiocb *, struct iov_iter *);
 
 /*
  * xattr.c
diff --git a/fs/afs/write.c b/fs/afs/write.c
index 9f035386b9c7..46a3a911c682 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -874,3 +874,11 @@ int afs_launder_page(struct page *page)
 #endif
 	return ret;
 }
+
+/*
+ * Direct file write operation for an AFS file.
+ */
+ssize_t afs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter)
+{
+	return -EOPNOTSUPP;
+}