Re: [PATCH v4] fuse: O_DIRECT support for files

[Josef Bacik <josef-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Fri, Feb 17, 2012 at 08:49:58AM -0500, Anand Avati wrote:
> Implement ->direct_IO() method in aops. The ->direct_IO() method combines
> the existing fuse_direct_read/fuse_direct_write methods to implement
> O_DIRECT functionality.
> 
> Reaching ->direct_IO() in the read path via generic_file_aio_read ensures
> proper synchronization with page cache with its existing framework.
> 
> Reaching ->direct_IO() in the write path via fuse_file_aio_write is made
> to come via generic_file_direct_write() which makes it play nice with
> the page cache w.r.t other mmap pages etc.
> 
> On files marked 'direct_io' by the filesystem server, IO always follows
> the fuse_direct_read/write path. There is no effect of fcntl(O_DIRECT)
> and it always succeeds.
> 
> On files not marked with 'direct_io' by the filesystem server, the IO
> path depends on O_DIRECT flag by the application. This can be passed
> at the time of open() as well as via fcntl().
> 
> Note that asynchronous O_DIRECT iocb jobs are completed synchronously
> always (this has been the case with FUSE even before this patch)
> 
> Signed-off-by: Anand Avati <avati-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
> 
> Test case:
> 
> - concurrent read and write DDs with oflag=direct and iflag=direct set
>   in a few writes and a few reads
> 
> - artificially decrease 6th parameter to generic_file_direct_write to
>   simulate a partial write of the direct IO request and verify proper
>   buffered I/O for remaining offset and size with printk's and verify
>   write completion at backend
> 
>  fs/fuse/dir.c  |    3 -
>  fs/fuse/file.c |  124 ++++++++++++++++++++++++++++++++++++++++++++++++--------
>  2 files changed, 107 insertions(+), 20 deletions(-)
> 

All in all it looks good, just one little nit

> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> index 2066328..7e5dbd0 100644
> --- a/fs/fuse/dir.c
> +++ b/fs/fuse/dir.c
> @@ -387,9 +387,6 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
>  	if (fc->no_create)
>  		return -ENOSYS;
>  
> -	if (flags & O_DIRECT)
> -		return -EINVAL;
> -
>  	forget = fuse_alloc_forget();
>  	if (!forget)
>  		return -ENOMEM;
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 4a199fd..9dd611b 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -194,10 +194,6 @@ int fuse_open_common(struct inode *inode, struct file *file, bool isdir)
>  	struct fuse_conn *fc = get_fuse_conn(inode);
>  	int err;
>  
> -	/* VFS checks this, but only _after_ ->open() */
> -	if (file->f_flags & O_DIRECT)
> -		return -EINVAL;
> -
>  	err = generic_file_open(inode, file);
>  	if (err)
>  		return err;
> @@ -932,17 +928,23 @@ static ssize_t fuse_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
>  	struct file *file = iocb->ki_filp;
>  	struct address_space *mapping = file->f_mapping;
>  	size_t count = 0;
> +	size_t ocount = 0;
>  	ssize_t written = 0;
> +	ssize_t written_buffered = 0;
>  	struct inode *inode = mapping->host;
>  	ssize_t err;
>  	struct iov_iter i;
> +	loff_t endbyte = 0;
>  
>  	WARN_ON(iocb->ki_pos != pos);
>  
> -	err = generic_segment_checks(iov, &nr_segs, &count, VERIFY_READ);
> +	ocount = 0;
> +	err = generic_segment_checks(iov, &nr_segs, &ocount, VERIFY_READ);
>  	if (err)
>  		return err;
>  
> +	count = ocount;
> +
>  	mutex_lock(&inode->i_mutex);
>  	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
>  
> @@ -962,11 +964,36 @@ static ssize_t fuse_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
>  
>  	file_update_time(file);
>  
> -	iov_iter_init(&i, iov, nr_segs, count, 0);
> -	written = fuse_perform_write(file, mapping, &i, pos);
> -	if (written >= 0)
> -		iocb->ki_pos = pos + written;
> +	if (file->f_flags & O_DIRECT) {
> +		written = generic_file_direct_write(iocb, iov, &nr_segs,
> +						    pos, &iocb->ki_pos,
> +						    count, ocount);
> +		if (written < 0 || written == count)
> +			goto out;
> +
> +		pos += written;
> +		count -= written;
> +
> +		iov_iter_init(&i, iov, nr_segs, count, written);
> +		written_buffered = fuse_perform_write(file, mapping, &i, pos);
> +		if (written_buffered < 0) {
> +			err = written_buffered;
> +			goto out;
> +		}
> +		endbyte = pos + written_buffered - 1;
>  
> +		err = filemap_write_and_wait_range(file->f_mapping, pos,
> +						   endbyte);
> +		if (err)
> +			goto out;
> +		written += written_buffered;
> +		iocb->ki_pos = pos + written_buffered;

You need to call invalidate_mapping_pages here to evict the pages from
pagecache, basically copy what __generic_file_aio_write does and you are good to
go.  Thanks,

Josef

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