linux-ext4 - Re: [RFC PATCH] ext4: Return unwritten buffer head when trying to read from prealloc space.

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Date:	Mon, 24 Mar 2008 13:41:41 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Mingming Cao <cmm@...ibm.com>
Cc:	tytso@....edu, sandeen@...hat.com, Solofo.Ramangalahy@...l.net,
	dmonakhov@...nvz.org, linux-ext4@...r.kernel.org
Subject: Re: [RFC PATCH] ext4: Return unwritten buffer head when trying to
	read from prealloc space.

On Fri, Mar 21, 2008 at 03:13:58PM -0700, Mingming Cao wrote:
> On Fri, 2008-03-21 at 11:48 +0530, Aneesh Kumar K.V wrote:
> > ext4_ext_get_blocks  returns number of blocks allocated with buffer head
> > unmapped for a read from prealloc space. This is needed so that delayed
> > allocation doesn't do block reservation for prealloc space since the blocks
> > are already resevred on disk. Fix ext4_ext_get_blocks to not return greater
> > than max_blocks and also mark the buffer head unwritten. Some code path tries
> > to read the block if buffer_head is not new and no uptodate. Marking the buffer
> > head unwritten avoid this reading.
> > 
> 
> Seems this patch fixes two bugs together, it would be nice to split to
> two as they cause two different problems.

Split patches here.

http://www.radian.org/~kvaneesh/ext4/patches-to-patchqueue/

> 
> To fix the bh->b_size warning solof founds for delayed allocation, I
> would say we need to fix it in ext4_get_blocks_handle() (for indirect
> files) and ext4_ext_get_blocks()(for extent files) both, not allowing
> returning b_size greater than what the caller asking for. Also, the
> patch below seems only address the preallocation map case, we need to
> fix in in general block lookup case.
> 

ext4_ext_get_blocks already make sure we doesn't return > max_blocks.
for normal allocation.

2694 out:
2695         if (allocated > max_blocks)
2696                 allocated = max_blocks;


-aneesh
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