[PATCH v5 1/2] Return bytes transferred for partial direct I/O

[Goldwyn Rodrigues]

From: Goldwyn Rodrigues <rgold...@suse.com>

In case direct I/O encounters an error midway, it returns the error.
Instead it should be returning the number of bytes transferred so far.

Test case for filesystems (with ENOSPC):
1. Create an almost full filesystem
2. Create a file, say /mnt/lastfile, until the filesystem is full.
3. Direct write() with count > sizeof /mnt/lastfile.

Result: write() returns -ENOSPC. However, file content has data written
in step 3.

This fixes fstest generic/472.

Reviewed-by: Christoph Hellwig <h...@lst.de>
Signed-off-by: Goldwyn Rodrigues <rgold...@suse.com>
---
 fs/block_dev.c |  2 +-
 fs/direct-io.c |  4 +---
 fs/iomap.c     | 20 ++++++++++----------
 3 files changed, 12 insertions(+), 14 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 4a181fcb5175..49d94360bb51 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -409,7 +409,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter 
*iter, int nr_pages)
 
        if (!ret)
                ret = blk_status_to_errno(dio->bio.bi_status);
-       if (likely(!ret))
+       if (likely(dio->size))
                ret = dio->size;
 
        bio_put(&dio->bio);
diff --git a/fs/direct-io.c b/fs/direct-io.c
index 3aafb3343a65..0c98b6e65d7c 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -262,8 +262,6 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, 
unsigned int flags)
                ret = dio->page_errors;
        if (ret == 0)
                ret = dio->io_error;
-       if (ret == 0)
-               ret = transferred;
 
        if (dio->end_io) {
                // XXX: ki_pos??
@@ -310,7 +308,7 @@ static ssize_t dio_complete(struct dio *dio, ssize_t ret, 
unsigned int flags)
        }
 
        kmem_cache_free(dio_cache, dio);
-       return ret;
+       return transferred ? transferred : ret;
 }
 
 static void dio_aio_complete_work(struct work_struct *work)
diff --git a/fs/iomap.c b/fs/iomap.c
index 47d29ccffaef..cab57d85404e 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -716,23 +716,23 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
        struct kiocb *iocb = dio->iocb;
        struct inode *inode = file_inode(iocb->ki_filp);
        loff_t offset = iocb->ki_pos;
-       ssize_t ret;
+       ssize_t err;
+       ssize_t transferred = dio->size;
 
        if (dio->end_io) {
-               ret = dio->end_io(iocb,
-                               dio->error ? dio->error : dio->size,
+               err = dio->end_io(iocb,
+                               transferred ? transferred : dio->error,
                                dio->flags);
        } else {
-               ret = dio->error;
+               err = dio->error;
        }
 
-       if (likely(!ret)) {
-               ret = dio->size;
+       if (likely(transferred)) {
                /* check for short read */
-               if (offset + ret > dio->i_size &&
+               if (offset + transferred > dio->i_size &&
                    !(dio->flags & IOMAP_DIO_WRITE))
-                       ret = dio->i_size - offset;
-               iocb->ki_pos += ret;
+                       transferred = dio->i_size - offset;
+               iocb->ki_pos += transferred;
        }
 
        /*
@@ -759,7 +759,7 @@ static ssize_t iomap_dio_complete(struct iomap_dio *dio)
        inode_dio_end(file_inode(iocb->ki_filp));
        kfree(dio);
 
-       return ret;
+       return transferred ? transferred : err;
 }
 
 static void iomap_dio_complete_work(struct work_struct *work)
-- 
2.15.1