linux-kernel - Re: [RFC PATCH] ide-floppy partitions

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Message-ID: <20081101201419.GA29462@gollum.tnic>
Date:	Sat, 1 Nov 2008 21:14:20 +0100
From:	Borislav Petkov <petkovbb@...glemail.com>
To:	Tejun Heo <tj@...nel.org>, axboe@...nel.dk
Cc:	bzolnier@...il.com, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] ide-floppy partitions

On Wed, Oct 29, 2008 at 08:13:19AM +0100, Borislav Petkov wrote:
> Hi Tejun,
> 
> recent changes at 0762b8bde9729f10f8e6249809660ff2ec3ad735 and around
> break ide-floppy. Since it is a removable media drive and the partition
> scan during boot returns empty (no media in the drive), when you later
> put in a disk and try to mount it, mount returns saying
> 
> /dev/hdc4 is not a valid block device.
> 
> Which brings me to the other possible issue: Since having a hdc4
> partition as a single FAT16 partition on a ZIP drive is the "factory
> default" you could fabricate a case where you have a partition number> 1
> as the only partition on a hard drive too, i.e. no continuous
> partition numbering and the mount would theoretically fail there too
> since, for example, there's a check in disk_get_part() which does:
> 
> if (likely(partno < ptbl->len)) {
> 
> and in this case the check will fail if partno >= 1 while you have only
> one partition on the disk with a number higher than the partition table
> length and the above described failure will happen too. Anyways, this is
> just a hypothesis, but it happens with the ZIP drive here so other block
> devices should behave similarly.
> 
> Here's a patch that fixes the ide-floppy case a bit clumsily, I admit.
> 
> ---
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 88a776f..b798ea0 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1011,6 +1011,23 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
>  	disk = get_gendisk(bdev->bd_dev, &partno);
>  	if (!disk)
>  		goto out_unlock_kernel;
> +
> +	part = disk_get_part(disk, partno);
> +	if (!part) {
> +		struct block_device *whole;
> +
> +		mutex_lock_nested(&bdev->bd_mutex, for_part);
> +		whole = bdget_disk(disk, 0);
> +		ret = -ENOMEM;
> +		if (!whole)
> +			goto out_clear;
> +		ret = __blkdev_get(whole, mode, 1);
> +		if (ret)
> +			goto out_clear;
> +		bdev->bd_contains = whole;
> +		mutex_unlock(&bdev->bd_mutex);
> +	}
> +
>  	part = disk_get_part(disk, partno);
>  	if (!part)
>  		goto out_unlock_kernel;

Tejun, Jens,

can you guys please ACK/NACK this so that we can have an agreed upon solution
and so that I can stop applying it ontop of current git before testing any
further.

Thanks.

-- 
Regards/Gruss,
    Boris.
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