netfs: Implement unbuffered/DIO read support

Implement support for unbuffered and DIO reads in the netfs library,
utilising the existing read helper code to do block splitting and
individual queuing.  The code also handles extraction of the destination
buffer from the supplied iterator, allowing async unbuffered reads to take
place.

The read will be split up according to the rsize setting and, if supplied,
the ->clamp_length() method.  Note that the next subrequest will be issued
as soon as issue_op returns, without waiting for previous ones to finish.
The network filesystem needs to pause or handle queuing them if it doesn't
want to fire them all at the server simultaneously.

Once all the subrequests have finished, the state will be assessed and the
amount of data to be indicated as having being obtained will be
determined.  As the subrequests may finish in any order, if an intermediate
subrequest is short, any further subrequests may be copied into the buffer
and then abandoned.

In the future, this will also take care of doing an unbuffered read from
encrypted content, with the decryption being done by the library.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org

1 files changed, 9 insertions, 0 deletions

diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 70f578cf3715..7c1309568459 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -226,6 +226,7 @@ enum netfs_io_origin {
 	NETFS_READPAGE,			/* This read is a synchronous read */
 	NETFS_READ_FOR_WRITE,		/* This read is to prepare a write */
 	NETFS_WRITEBACK,		/* This write was triggered by writepages */
+	NETFS_DIO_READ,			/* This is a direct I/O read */
 	nr__netfs_io_origin
 } __mode(byte);
 
@@ -240,6 +241,7 @@ struct netfs_io_request {
 	};
 	struct inode		*inode;		/* The file being accessed */
 	struct address_space	*mapping;	/* The mapping being accessed */
+	struct kiocb		*iocb;		/* AIO completion vector */
 	struct netfs_cache_resources cache_resources;
 	struct list_head	proc_link;	/* Link in netfs_iorequests */
 	struct list_head	subrequests;	/* Contributory I/O operations */
@@ -249,12 +251,14 @@ struct netfs_io_request {
 	struct bio_vec		*direct_bv;	/* DIO buffer list (when handling iovec-iter) */
 	unsigned int		direct_bv_count; /* Number of elements in direct_bv[] */
 	unsigned int		debug_id;
+	unsigned int		rsize;		/* Maximum read size (0 for none) */
 	unsigned int		wsize;		/* Maximum write size (0 for none) */
 	unsigned int		subreq_counter;	/* Next subreq->debug_index */
 	atomic_t		nr_outstanding;	/* Number of ops in progress */
 	atomic_t		nr_copy_ops;	/* Number of copy-to-cache ops in progress */
 	size_t			submitted;	/* Amount submitted for I/O so far */
 	size_t			len;		/* Length of the request */
+	size_t			transferred;	/* Amount to be indicated as transferred */
 	short			error;		/* 0 or error that occurred */
 	enum netfs_io_origin	origin;		/* Origin of the request */
 	bool			direct_bv_unpin; /* T if direct_bv[] must be unpinned */
@@ -271,6 +275,8 @@ struct netfs_io_request {
 #define NETFS_RREQ_IN_PROGRESS		5	/* Unlocked when the request completes */
 #define NETFS_RREQ_WRITE_TO_CACHE	7	/* Need to write to the cache */
 #define NETFS_RREQ_UPLOAD_TO_SERVER	8	/* Need to write to the server */
+#define NETFS_RREQ_NONBLOCK		9	/* Don't block if possible (O_NONBLOCK) */
+#define NETFS_RREQ_BLOCKED		10	/* We blocked */
 	const struct netfs_request_ops *netfs_ops;
 	void (*cleanup)(struct netfs_io_request *req);
 };
@@ -367,6 +373,9 @@ struct netfs_cache_ops {
 			       loff_t *_data_start, size_t *_data_len);
 };
 
+/* High-level read API. */
+ssize_t netfs_unbuffered_read_iter(struct kiocb *iocb, struct iov_iter *iter);
+
 /* High-level write API */
 ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 			    struct netfs_group *netfs_group);