linux-kernel - Re: [RESEND PATCH] fs: add RWF

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Date:   Sat, 30 Sep 2017 19:31:58 -0500
From:   Goldwyn Rodrigues <rgoldwyn@...e.de>
To:     Jürg Billeter <j@...ron.ch>,
        Al Viro <viro@...iv.linux.org.uk>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH] fs: add RWF_APPEND



On 09/29/2017 07:07 AM, Jürg Billeter wrote:
> This is the per-I/O equivalent of O_APPEND to support atomic append
> operations on any open file.
> 
> If a file is opened with O_APPEND, pwrite() ignores the offset and
> always appends data to the end of the file. RWF_APPEND enables atomic
> append and pwrite() with offset on a single file descriptor.
> 

I think similarly we can introduce RWF_DIRECT, though I am not sure if
users would want to mix buffered writes and direct writes.

Reviewed-by: Goldwyn Rodrigues <rgoldwyn@...e.com>

> Signed-off-by: Jürg Billeter <j@...ron.ch>
> ---
>  include/linux/fs.h      | 2 ++
>  include/uapi/linux/fs.h | 6 +++++-
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 339e73742e73..fee24eae7523 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3204,6 +3204,8 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
>  		ki->ki_flags |= IOCB_DSYNC;
>  	if (flags & RWF_SYNC)
>  		ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
> +	if (flags & RWF_APPEND)
> +		ki->ki_flags |= IOCB_APPEND;
>  	return 0;
>  }
>  
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 56235dddea7d..ac145430bcd8 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -376,7 +376,11 @@ typedef int __bitwise __kernel_rwf_t;
>  /* per-IO, return -EAGAIN if operation would block */
>  #define RWF_NOWAIT	((__force __kernel_rwf_t)0x00000008)
>  
> +/* per-IO O_APPEND */
> +#define RWF_APPEND	((__force __kernel_rwf_t)0x00000010)
> +
>  /* mask of flags supported by the kernel */
> -#define RWF_SUPPORTED	(RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT)
> +#define RWF_SUPPORTED	(RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
> +			 RWF_APPEND)
>  
>  #endif /* _UAPI_LINUX_FS_H */
> 

-- 
Goldwyn