linux-kernel - Re: [PATCH v2] fadvise: introduce POSIX_FADV_DONTNEED

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Date:	Wed, 27 Apr 2011 12:33:08 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Andrea Righi <andrea@...terlinux.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Chinner <david@...morbit.com>,
	Mike Frysinger <vapier@...too.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, linux-fsdevel@...r.kernel.org,
	linux-api@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] fadvise: introduce POSIX_FADV_DONTNEED_FS

On Wed, Apr 27, 2011 at 08:13:47PM +0200, Andrea Righi wrote:
> @@ -127,6 +128,12 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)
>  			invalidate_mapping_pages(mapping, start_index,
>  						end_index);
>  		break;
> +	case POSIX_FADV_DONTNEED_FS:
> +		if (capable(CAP_SYS_ADMIN))
> +			drop_pagecache_sb(file->f_dentry->d_sb, NULL);
> +		else
> +			ret = -EPERM;
> +		break;
>  	default:
>  		ret = -EINVAL;
>  	}

Mmm ... what if I open /dev/sdxyz and call fadvise() on it?  I think
you end up flushing /dev's page cache entries, instead of the filesystem
which is on /dev/sdxyz.

If I understand correctly, you want mapping->host->i_sb instead of
file->f_dentry->d_sb.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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