linux-kernel - Re: Re: [PATCH V2 0/2] Auto stop async-write on block device when device removed.

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Date:	Tue, 24 Sep 2013 11:07:34 +0800
From:	majianpeng <majianpeng@...il.com>
To:	"Jeff Moyer" <jmoyer@...hat.com>
Cc:	axboe <axboe@...nel.dk>, viro <viro@...iv.linux.org.uk>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: Re: [PATCH V2 0/2] Auto stop async-write on block device when device removed.

>majianpeng <majianpeng@...il.com> writes:
>
>> For async-write on block device,if device removed,but the vfs don't know it.
>> It will continue to do.
>> Patch1 set size of inode of block device to zero when removed disk.By this,vfs know 
>> disk changed.
>> Path2 add size-check on blk_aio_write.If pos of write larger than size of inode,it will
>> return zero.So the user can check disk state.
>
>OK, so the basic problem is that __generic_file_aio_write will always
>return 0 after device removal, yes?  I'm not sure why that's a real
>issue, can you explain exactly why you're trying to change this?
>
At prenset, the __generic_file_aio_write don't return zero rather that the wanted size.
So the user can't know the disk removed. 
For example:
dd if=/dev/zero of=usb-disk bs=64k
When removed usb-disk, dd stoped until reached the endof usb-disk.

Using this patch, after removed disk, the aio-write will return zero.I think the upper user will check.
(or if the size of block is zero, we return -ENOSPC).

>As for your patches, I don't think that putting the i_size_write into
>invalidate_partitions is a good idea.  Consider the case of rescanning
>partitions: you will always detect a size change now, which is not good.
>
Yes.But in func rescan_partitions, after invalidate_partitions it will call check_disk_size_change to set size of block_device.

Thanks!
Jianpeng Ma
>Cheers,
>Jeff