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From:   Bjorn Andersson <bjorn.andersson@linaro.org>
To:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Benjamin LaHaise <bcrl@kvack.org>
Cc:     linux-fsdevel@vger.kernel.org, linux-aio@kvack.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] aio: Support read/write with non-iter file-ops
Date:   Thu, 18 Jul 2019 16:10:54 -0700
Message-Id: <20190718231054.8175-1-bjorn.andersson@linaro.org>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Implement a wrapper for aio_read()/write() to allow async IO on files
not implementing the iter version of read/write, such as sysfs. This
mimics how readv/writev uses non-iter ops in do_loop_readv_writev().

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
---
 fs/aio.c | 52 +++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 45 insertions(+), 7 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index f9f441b59966..0137a1a9bef1 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1514,12 +1514,44 @@ static inline void aio_rw_done(struct kiocb *req, ssize_t ret)
 	}
 }
 
+static ssize_t aio_iter_readv_writev(struct file *file, struct kiocb *req,
+				     struct iov_iter *iter, int type)
+{
+	ssize_t ret = 0;
+	ssize_t nr;
+
+	while (iov_iter_count(iter)) {
+		struct iovec iovec = iov_iter_iovec(iter);
+
+		if (type == READ) {
+			nr = file->f_op->read(file, iovec.iov_base,
+					      iovec.iov_len, &req->ki_pos);
+		} else {
+			nr = file->f_op->write(file, iovec.iov_base,
+					       iovec.iov_len, &req->ki_pos);
+		}
+
+		if (nr < 0) {
+			ret = nr;
+			break;
+		}
+
+		ret += nr;
+		if (nr != iovec.iov_len)
+			break;
+		iov_iter_advance(iter, nr);
+	}
+
+	return ret;
+}
+
 static int aio_read(struct kiocb *req, const struct iocb *iocb,
 			bool vectored, bool compat)
 {
 	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
 	struct iov_iter iter;
 	struct file *file;
+	ssize_t count;
 	int ret;
 
 	ret = aio_prep_rw(req, iocb);
@@ -1529,15 +1561,18 @@ static int aio_read(struct kiocb *req, const struct iocb *iocb,
 	if (unlikely(!(file->f_mode & FMODE_READ)))
 		return -EBADF;
 	ret = -EINVAL;
-	if (unlikely(!file->f_op->read_iter))
-		return -EINVAL;
 
 	ret = aio_setup_rw(READ, iocb, &iovec, vectored, compat, &iter);
 	if (ret < 0)
 		return ret;
 	ret = rw_verify_area(READ, file, &req->ki_pos, iov_iter_count(&iter));
-	if (!ret)
-		aio_rw_done(req, call_read_iter(file, req, &iter));
+	if (!ret) {
+		if (likely(file->f_op->read_iter))
+			count = call_read_iter(file, req, &iter);
+		else
+			count = aio_iter_readv_writev(file, req, &iter, READ);
+		aio_rw_done(req, count);
+	}
 	kfree(iovec);
 	return ret;
 }
@@ -1548,6 +1583,7 @@ static int aio_write(struct kiocb *req, const struct iocb *iocb,
 	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
 	struct iov_iter iter;
 	struct file *file;
+	ssize_t count;
 	int ret;
 
 	ret = aio_prep_rw(req, iocb);
@@ -1557,8 +1593,6 @@ static int aio_write(struct kiocb *req, const struct iocb *iocb,
 
 	if (unlikely(!(file->f_mode & FMODE_WRITE)))
 		return -EBADF;
-	if (unlikely(!file->f_op->write_iter))
-		return -EINVAL;
 
 	ret = aio_setup_rw(WRITE, iocb, &iovec, vectored, compat, &iter);
 	if (ret < 0)
@@ -1577,7 +1611,11 @@ static int aio_write(struct kiocb *req, const struct iocb *iocb,
 			__sb_writers_release(file_inode(file)->i_sb, SB_FREEZE_WRITE);
 		}
 		req->ki_flags |= IOCB_WRITE;
-		aio_rw_done(req, call_write_iter(file, req, &iter));
+		if (likely(file->f_op->write_iter))
+			count = call_write_iter(file, req, &iter);
+		else
+			count = aio_iter_readv_writev(file, req, &iter, WRITE);
+		aio_rw_done(req, count);
 	}
 	kfree(iovec);
 	return ret;
-- 
2.18.0