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Re: ext4 testing in the F10 release cycle



Richard W.M. Jones wrote:
> On Wed, Sep 03, 2008 at 12:36:55PM -0500, Eric Sandeen wrote:
>> Hm, I probably need to get the fallocate.h header file included if it's
>> not so that sys_fallocate can be used directly, but it is also exposed
>> via posix_fallocate in glibc - tested here on xfs just because xfs_bmap
>> is a handy way to show that it actually works via glibc:
> 
> Uh, stupid me - I was looking for the wrong call.  Rawhide _does_ have
> it.
> 
>>> (c) Does ext4 preallocate in the background?  A synchronous
>>> preallocate call isn't much use to virt-manager.
>> It does not, but what is the concern?  It doesn't take much time:
> 
>> (on ext4 this time):
>>
>> [root inode test]# time test_posix_fallocate testfile 0 10737418240
>>
>> real    0m0.009s
>> user    0m0.000s
>> sys     0m0.009s
> 
> OK ... I'm assuming though that the zeroes aren't all written to disk
> in this time, so that is exactly what I wanted.

No, zeros are never written to disk if the ->fallocate call is
supported.  They are allocated, but flagged on-disk as
unwritten/uninitialized, so any read (before a write, of course) will
return zeros without the need for all that pesky writing business....

-Eric


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