Re: [RFC PATCH v3 01/18] block: Add check for async buffered writes to generic_write_checks

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

On Wed, May 18, 2022 at 04:36:52PM -0700, Stefan Roesch wrote:
> @@ -1633,7 +1633,9 @@ int generic_write_checks_count(struct kiocb *iocb, loff_t *count)
>  	if (iocb->ki_flags & IOCB_APPEND)
>  		iocb->ki_pos = i_size_read(inode);
>  
> -	if ((iocb->ki_flags & IOCB_NOWAIT) && !(iocb->ki_flags & IOCB_DIRECT))
> +	if ((iocb->ki_flags & IOCB_NOWAIT) &&
> +		!((iocb->ki_flags & IOCB_DIRECT) ||
> +		  (file->f_mode & FMODE_BUF_WASYNC)))

This is some really odd indentation.  I'd expect something like:

	if ((iocb->ki_flags & IOCB_NOWAIT) &&
	    !((iocb->ki_flags & IOCB_DIRECT) ||
	      (file->f_mode & FMODE_BUF_WASYNC)))

> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index bbde95387a23..3b479d02e210 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -177,6 +177,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
>  /* File supports async buffered reads */
>  #define FMODE_BUF_RASYNC	((__force fmode_t)0x40000000)
>  
> +/* File supports async nowait buffered writes */
> +#define FMODE_BUF_WASYNC	((__force fmode_t)0x80000000)

This is the last available flag in fmode_t.

At some point we should probably move the static capabilities to
a member of file_operations.