linux-ext4 - Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)

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Date:	Mon, 18 Apr 2011 22:05:15 -0500
From:	Eric Sandeen <sandeen@...deen.net>
To:	Ted Ts'o <tytso@....edu>
CC:	Yongqiang Yang <xiaoqiangnk@...il.com>,
	Andreas Dilger <adilger@...ger.ca>,
	Dave Chinner <david@...morbit.com>, xfs-oss <xfs@....sgi.com>,
	"coreutils@....org" <coreutils@....org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	Pádraig Brady <P@...igbrady.com>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>
Subject: Re: Files full of zeros with coreutils-8.11 and xfs (FIEMAP related?)

On 4/18/11 9:59 PM, Ted Ts'o wrote:

...

> Maybe coreutils will need to use FIEMAP_FLAG_SYNC initially, since
> it's the only way to guarantee correct behaviour for XFS.  But I would
> really rather that be the long-term way we leave things!

XFS ... or ext4:

# xfs_io -Ff -c "falloc 0 1m" -c "pwrite 0 512k" testfile; /root/fiemap-test testfile
wrote 524288/524288 bytes at offset 0
512 KiB, 128 ops; 0.0000 sec (161.342 MiB/sec and 41303.6463 ops/sec)
start 0 length -1 flags 0x0 count 32
ext:   0 logical: [       0..     255] phys:    34048..   34303 flags: 0x801 tot: 256

# uname -r
2.6.39-0.rc3.git2.0.fc16.x86_64

Above is on ext4.  It behaves exactly like XFS in my testing; data in the page cache does not cause fiemap to return anything other than "unwritten" for preallocated extents.

-Eric
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