linux-ext4 - Re: [Ocfs2-devel] [PATCH 1/3] ext3/ext4: Factor out disk addressability check

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Message-ID: <20100813163006.GB4329@quack.suse.cz>
Date:	Fri, 13 Aug 2010 18:30:07 +0200
From:	Jan Kara <jack@...e.cz>
To:	Joel Becker <Joel.Becker@...cle.com>
Cc:	Andreas Dilger <adilger@...ger.ca>, Ted Ts'o <tytso@....edu>,
	Jan Kara <jack@...e.cz>, ocfs2-devel@....oracle.com,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
	"linux-kernel@...r.kernel.org Patrick J. LoPresti" 
	<lopresti@...il.com>
Subject: Re: [Ocfs2-devel] [PATCH 1/3] ext3/ext4: Factor out disk
 addressability check

On Thu 12-08-10 15:29:49, Joel Becker wrote:
> diff --git a/fs/libfs.c b/fs/libfs.c
> index dcaf972..f099566 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -955,6 +955,35 @@ int generic_file_fsync(struct file *file, int datasync)
>  }
>  EXPORT_SYMBOL(generic_file_fsync);
>  
> +/**
> + * generic_check_addressable - Check addressability of file system
> + * @blocksize_bits:	log of file system block size
> + * @num_blocks:		number of blocks in file system
> + *
> + * Determine whether a file system with @num_blocks blocks (and a
> + * block size of 2**@...cksize_bits) is addressable by the sector_t
> + * and page cache of the system.  Return 0 if so and -EFBIG otherwise.
> + */
> +int generic_check_addressable(unsigned blocksize_bits, u64 num_blocks)
> +{
> +	u64 last_fs_block = num_blocks - 1;
> +
> +	if (unlikely(num_blocks == 0))
> +		return 0;
> +
> +	if ((blocksize_bits < 9) || (blocksize_bits > PAGE_CACHE_SHIFT))
> +		return -EINVAL;
> +
> +	if ((last_fs_block >
> +	     (sector_t)(~0ULL) >> (blocksize_bits - 9)) ||
> +	    (last_fs_block >
> +	     (pgoff_t)(~0ULL) >> (PAGE_CACHE_SHIFT - blocksize_bits))) {
            ^^^ I don't get the pgoff_t check. Shouldn't it rather be
(u64)(pgoff_t)(~0ULL) << (PAGE_CACHE_SHIFT - blocksize_bits)?
Because on 32-bit arch we are able to address 16TB device, which is for 1KB
blocksize 1<<34 blocks. But your math gives 1<<30 blocks...

									Honza

-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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