linux-kernel - Re: [PATCH 4/5] ext4: fallocate support in ext4

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Date:	Mon, 07 May 2007 10:24:37 -0500
From:	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>
To:	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org,
	xfs@....sgi.com, suparna@...ibm.com, cmm@...ibm.com
Subject: Re: [PATCH 4/5] ext4: fallocate support in ext4

On Mon, 2007-05-07 at 17:37 +0530, Amit K. Arora wrote:
> On Thu, May 03, 2007 at 09:31:33PM -0700, Andrew Morton wrote:
> > On Thu, 26 Apr 2007 23:43:32 +0530 "Amit K. Arora" <aarora@...ux.vnet.ibm.com> wrote:

> > > +int ext4_fallocate(struct inode *inode, int mode, loff_t offset, loff_t len)
> > > +{
> > > +	handle_t *handle;
> > > +	ext4_fsblk_t block, max_blocks;
> > > +	int ret, ret2, nblocks = 0, retries = 0;
> > > +	struct buffer_head map_bh;
> > > +	unsigned int credits, blkbits = inode->i_blkbits;
> > > +
> > > +	/* Currently supporting (pre)allocate mode _only_ */
> > > +	if (mode != FA_ALLOCATE)
> > > +		return -EOPNOTSUPP;
> > > +
> > > +	if (!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL))
> > > +		return -ENOTTY;
> > 
> > So we don't implement fallocate on bitmap-based files!  Well that's huge
> > news.  The changelog would be an appropriate place to communicate this,
> > along with reasons why, or a description of the plan to fix it.
> 
> Ok. Will add this in the function description as well.
> 
> > Also, posix says nothing about fallocate() returning ENOTTY.
> 
> Right. I don't seem to find any suitable error from posix description.
> Can you please suggest an error code which might make more sense here ?
> Will -ENOTSUPP be ok ? Since we want to say here that we don't support
> non-extent files.

Isn't the idea that libc will interpret -ENOTTY, or whatever is returned
here, and fall back to the current library code to do preallocation?
This way, the caller of fallocate() will never see this return code, so
it won't violate posix.

-- 
David Kleikamp
IBM Linux Technology Center

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