linux-ext4 - Re: [PATCH 04/22] ext4: Only call out to crc32c if necessary

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Message-ID: <20111205155226.GA32031@thunk.org>
Date:	Mon, 5 Dec 2011 10:52:26 -0500
From:	Ted Ts'o <tytso@....edu>
To:	"Darrick J. Wong" <djwong@...ibm.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 04/22] ext4: Only call out to crc32c if necessary

On Mon, Nov 28, 2011 at 03:26:43PM -0800, Darrick J. Wong wrote:
> +	/* Load the checksum driver */
> +	if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
> +				       EXT4_FEATURE_RO_COMPAT_METADATA_CSUM)) {
> +		sbi->s_chksum_driver = crypto_alloc_shash("crc32c", 0, 0);
> +		if (IS_ERR(sbi->s_chksum_driver)) {
> +			ret = PTR_ERR(sbi->s_chksum_driver);
> +			sbi->s_chksum_driver = NULL;
> +			goto failed_mount;
> +		}
> +	}

Unless the crypto engine printk's a message if the crc32c algorithm is
not available (perhaps even if it does), it's probably going to be a
good idea to issue an ext4_msg() saying that we're failing because we
couldn't load the crc32c crypto module.  Otherwise the user will get a
mysterious failure (including a message from mount to check 'dmesg |
tail'), and then when they look at the kernel messages, they won't see
what might have gone wrong, and then they'll send a complaint to
ext3-users or linux-ext4....

						- Ted
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