linux-ext4 - Re: [RFC][Patch 1/2] Persistent preallocation in ext4

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Message-ID: <20070109090530.GA19130@amitarora.in.ibm.com>
Date:	Tue, 9 Jan 2007 14:35:30 +0530
From:	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>
To:	Mingming Cao <cmm@...ibm.com>
Cc:	linux-ext4@...r.kernel.org, suparna@...ibm.com, suzuki@...ibm.com,
	alex@...sterfs.com
Subject: Re: [RFC][Patch 1/2] Persistent preallocation in ext4

On Tue, Jan 02, 2007 at 04:34:09PM +0530, Amit K. Arora wrote:
> On Wed, Dec 27, 2006 at 03:30:44PM -0800, Mingming Cao wrote:
> > Since the API takes the number of bytes to preallocate, at return time,
> > shall we convert the blocks to bytes to the user?
> >
> > Here it returns the number of allocated blocks to the user.   Do we need
> > to worry about the case when dealing with a range with partial hole and
> > partial blocks already allocated? In that case nblocks(the new
> > preallocated blocks) will less than the maxblocks (the number of blocks
> > asked by application).  I am wondering what does other filesystem like
> > xfs do? Maybe we should do the same thing.
> 
> I think xfs just returns 0 on success, and errno on an error. Do we
> want to keep the same behavior here ? Or, should we return the number of
> bytes preallocated ?

We still need to decide on what the ioctl should return. Should it
return zero on success and errno on error, like how posix_fallocate and
xfs behave ?  If yes, then should we undo partial preallocation (if any)
in case of an error (say ENOSPC) ?

If no, then should we return the number of bytes preallocated ? In this
case we have to think about the situation Mingming mentioned above (i.e.
when the preallocation request partially spans through a hole and
partially through few already allocated blocks).

--
Regards,
Amit Arora
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