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Date: Tue, 15 Apr 2014 12:52:46 +0800
From: Qu Wenruo <quwenruo@cn.fujitsu.com>
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To: "Theodore Ts'o" <tytso@mit.edu>
CC: <util-linux@vger.kernel.org>
Subject: Re: libblkid: Idea to force given cached entry to be invalidated?
References: <534C9625.8030906@cn.fujitsu.com> <20140415042729.GC3403@thunk.org>
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-------- Original Message --------
Subject: Re: libblkid: Idea to force given cached entry to be invalidated?
From: Theodore Ts'o <tytso@mit.edu>
To: Qu Wenruo <quwenruo@cn.fujitsu.com>
Date: 2014年04月15日 12:27
> On Tue, Apr 15, 2014 at 10:15:01AM +0800, Qu Wenruo wrote:
>> Though the above patch try to avoid the whole cache, it's not good enough
>> since it break the pricible not
>> to probe the devices too frequently.
>>
>> After some searching, it seems that libblkid does not provide such API, or
>> am I missing something?
> The blkid_verify() function is designed to make sure the information
> in the cache corresponds with reality.  If it does not, it will update
> the cache to match with reality, so it will do what you want.
>
> Using blkid_verify() will involve accessing the disk involved, but
> that's still better than the alternative of scanning all of the disks
> in the system.
>
> Cheers,
>
> 					- Ted
> --
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I hope I was wrong but according to the codes, blkid_verify() seems 
still using the cache:
------
blkid_dev blkid_verify(blkid_cache cache, blkid_dev dev)
{
......
             (diff < BLKID_PROBE_MIN ||
                 (dev->bid_flags & BLKID_BID_FL_VERIFIED &&
                  diff < BLKID_PROBE_INTERVAL)))
                 return dev;
------

So it seems not working in the case.

Also in the btrfs-progs codes, it has already called blkid_verify() 
before operations.

Thanks,
Qu.