linux-kernel - Re: [PATCH] Propagate CRAMFS uncompression errors

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Date:	Mon, 09 Feb 2009 20:06:01 -0800
From:	David VomLehn <dvomlehn@...co.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Propagate CRAMFS uncompression errors


On Mon, 2009-02-09 at 19:48 -0800, Andrew Morton wrote:
...
> 
> umm...
> 
> Nope, it's still not right.  We'll treat this case:
> 
> 		if (compr_len == 0)
> 			; /* hole */
> 
> as an IO error.  grr.
> 
> --- a/fs/cramfs/inode.c~cramfs-propagate-uncompression-errors
> +++ a/fs/cramfs/inode.c
> @@ -477,7 +477,7 @@ static int cramfs_readpage(struct file *
>  		mutex_unlock(&read_mutex);
>  		pgdata = kmap(page);
>  		if (compr_len == 0)
> -			; /* hole */
> +			goto out; /* hole */
>  		else if (compr_len > (PAGE_CACHE_SIZE << 1))
>  			printk(KERN_ERR "cramfs: bad compressed blocksize %u\n", compr_len);
>  		else {
> @@ -488,12 +488,20 @@ static int cramfs_readpage(struct file *
>  				 compr_len);
>  			mutex_unlock(&read_mutex);
>  		}
> -	} else
> -		pgdata = kmap(page);
> -	memset(pgdata + bytes_filled, 0, PAGE_CACHE_SIZE - bytes_filled);
> -	kunmap(page);
> -	flush_dcache_page(page);
> -	SetPageUptodate(page);
> +
> +		if (bytes_filled == 0) {
> +			/* Decompression error */
> +			ClearPageUptodate(page);
> +			SetPageError(page);
> +		} else {
> +			memset(pgdata + bytes_filled, 0,
> +					PAGE_CACHE_SIZE - bytes_filled);
> +			flush_dcache_page(page);
> +			SetPageUptodate(page);
> +		}
> +		kunmap(page);
> +	}
> +out:
>  	unlock_page(page);
>  	return 0;
>  }

Is that actually an error. The comment in the code is, uh, a bit terse,
but I took it to mean that there was a deliberate hole, just like holes
in files that should read as all zeroes. But even if it's actually an
error, we still need to kunmap the page
-- 
David VomLehn, dvomlehn@...co.com




     - - - - -                              Cisco                            - - - - -         
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