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Re: file preallocation without unwritten flag being set

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: file preallocation without unwritten flag being set
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Wed, 13 May 2009 19:41:22 -0500
Cc: p v <pvlogin@xxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20090514003422.GM16929@xxxxxxxxxxxxxxxx>
References: <283244.29270.qm@xxxxxxxxxxxxxxxxxxxxxxxxxxx> <4A0A0E76.6000701@xxxxxxxxxxx> <618437.93111.qm@xxxxxxxxxxxxxxxxxxxxxxxxxxx> <4A0A55E0.4010202@xxxxxxxxxxx> <705795.15734.qm@xxxxxxxxxxxxxxxxxxxxxxxxxxx> <20090513222823.GL16929@xxxxxxxxxxxxxxxx> <502709.63746.qm@xxxxxxxxxxxxxxxxxxxxxxxxxxx> <4A0B6325.8000706@xxxxxxxxxxx> <20090514003422.GM16929@xxxxxxxxxxxxxxxx>
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Dave Chinner wrote:

>> Unmounting will flush the filesytem address space, but not the block
>> device address space.
> 
> Not exactly the problem, though. XFS opens it's own device address space
> when mounting - not the address space you get by opening /dev/sdX.
> xfs_db uses the address space associated with /dev/sdX. hence
> if you do:
> 
> # xfs_db /dev/sdc
> ....
> # mount /dev/sdc
> <do some changes>
> # unmount /dev/sdc
> # xfs_db /dev/sdc
> 
> The second invocation of xfs_db will not see any of the changes that
> occured to the filesystem because it will read from the buffers
> cached on /dev/sdc during the first invocation.
> 
> This is the same problem Grub has....

We meant the same thing, even if I said it wrong ;)

-Eric

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