On 5 Mar 2007, at 14:37, Theodore Tso wrote:

On Sun, Mar 04, 2007 at 11:22:06PM +0000, Anton Altaparmakov wrote:

quoted

And I specifically did NOT update the initialized size in the inode
thus it will remain at its old value thus all new allocated blocks
will be considered as present but not initialized thus a read will
always return zero whilst a write will do the right thing and pad
with zeroes as necessary (if the write is smaller than the block
size, etc).

	You're describing a method of doing in-advance preallocation
where the filesystem format explicitly has support for this kind of
feature in a way that doesn't require pre-zeroing the data blocks in
question.

Indeed.

	The question which this subthread was concerned about was
whether the kernel should get involved in initializing datablocks in
the case where the filesystem format does not have this support, or
whether this functionality should continue to be done in userspace.
Given that glibc already has to support this for older kernels, I
would argue that there's no point putting in generic support for
filesystem that can't support a more advanced way of doing things.

Yes, I understood that after I had sent my post...  And yes, I would  
agree.  If glibc already does this there does not appear to be any  
value in just moving existing functionality into the kernel.  Simply  
let "dumb" file systems return ENOSYS and let glibc do it...  And any  
FS which can do it better can implement the function and then glibc  
should not go anywhere near it.

Best regards,

	Anton
-- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer, http://www.linux-ntfs.org/