linux-kernel - Re: [PATCH 1/3] fs: remove FS_COW

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Date:	Tue, 03 May 2011 17:11:44 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	"linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>
CC:	Chris Mason <chris.mason@...cle.com>,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] fs: remove FS_COW_FL

Any comments? If this patch is acceptable, it should be queued for .39?
since fs.h is exported to userspace.

Li Zefan wrote:
> FS_COW_FL and FS_NOCOW_FL were newly introduced to control per file
> COW in btrfs, but FS_NOCOW_FL is sufficient.
> 
> The fact is we don't have corresponding BTRFS_INODE_COW flag.
> 
> COW is default, and FS_NOCOW_FL can be used to switch off COW for
> a single file.
> 
> If we mount btrfs with nodatacow, a newly created file will be set with
> the FS_NOCOW_FL flag. So to turn on COW for it, we can just clear the
> FS_NOCOW_FL flag.
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> ---
>  fs/btrfs/ioctl.c   |   15 ++++++---------
>  include/linux/fs.h |    1 -
>  2 files changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index f580a3a..3240dd9 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -144,16 +144,13 @@ static int check_flags(unsigned int flags)
>  	if (flags & ~(FS_IMMUTABLE_FL | FS_APPEND_FL | \
>  		      FS_NOATIME_FL | FS_NODUMP_FL | \
>  		      FS_SYNC_FL | FS_DIRSYNC_FL | \
> -		      FS_NOCOMP_FL | FS_COMPR_FL | \
> -		      FS_NOCOW_FL | FS_COW_FL))
> +		      FS_NOCOMP_FL | FS_COMPR_FL |
> +		      FS_NOCOW_FL))
>  		return -EOPNOTSUPP;
>  
>  	if ((flags & FS_NOCOMP_FL) && (flags & FS_COMPR_FL))
>  		return -EINVAL;
>  
> -	if ((flags & FS_NOCOW_FL) && (flags & FS_COW_FL))
> -		return -EINVAL;
> -
>  	return 0;
>  }
>  
> @@ -218,6 +215,10 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
>  		ip->flags |= BTRFS_INODE_DIRSYNC;
>  	else
>  		ip->flags &= ~BTRFS_INODE_DIRSYNC;
> +	if (flags & FS_NOCOW_FL)
> +		ip->flags |= BTRFS_INODE_NODATACOW;
> +	else
> +		ip->flags &= ~BTRFS_INODE_NODATACOW;
>  
>  	/*
>  	 * The COMPRESS flag can only be changed by users, while the NOCOMPRESS
> @@ -231,10 +232,6 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
>  		ip->flags |= BTRFS_INODE_COMPRESS;
>  		ip->flags &= ~BTRFS_INODE_NOCOMPRESS;
>  	}
> -	if (flags & FS_NOCOW_FL)
> -		ip->flags |= BTRFS_INODE_NODATACOW;
> -	else if (flags & FS_COW_FL)
> -		ip->flags &= ~BTRFS_INODE_NODATACOW;
>  
>  	trans = btrfs_join_transaction(root, 1);
>  	BUG_ON(IS_ERR(trans));
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index de9dd81..56a4141 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -365,7 +365,6 @@ struct inodes_stat_t {
>  #define FS_EXTENT_FL			0x00080000 /* Extents */
>  #define FS_DIRECTIO_FL			0x00100000 /* Use direct i/o */
>  #define FS_NOCOW_FL			0x00800000 /* Do not cow file */
> -#define FS_COW_FL			0x02000000 /* Cow file */
>  #define FS_RESERVED_FL			0x80000000 /* reserved for ext2 lib */
>  
>  #define FS_FL_USER_VISIBLE		0x0003DFFF /* User visible flags */
--
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