linux-kernel - Re: [PATCH 2/6][TAKE7] fallocate() implementation in i386, x86

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Date:	Fri, 13 Jul 2007 19:48:58 +0530
From:	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>
To:	Christoph Hellwig <hch@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org, xfs@....sgi.com, tytso@....edu,
	cmm@...ibm.com, suparna@...ibm.com, adilger@...sterfs.com,
	dgc@....com
Subject: Re: [PATCH 2/6][TAKE7] fallocate() implementation in i386, x86_64 and powerpc

On Fri, Jul 13, 2007 at 02:21:19PM +0100, Christoph Hellwig wrote:
> On Fri, Jul 13, 2007 at 06:17:55PM +0530, Amit K. Arora wrote:
> >  /*
> > + * sys_fallocate - preallocate blocks or free preallocated blocks
> > + * @fd: the file descriptor
> > + * @mode: mode specifies the behavior of allocation.
> > + * @offset: The offset within file, from where allocation is being
> > + *	    requested. It should not have a negative value.
> > + * @len: The amount of space in bytes to be allocated, from the offset.
> > + *	 This can not be zero or a negative value.
> 
> kerneldoc comments are for in-kernel APIs which syscalls aren't.  I'd say
> just temove this comment, the manpage is a much better documentation anyway.

Ok. I will remove this entire comment.
 
> > + * <TBD> Generic fallocate to be added for file systems that do not
> > + *	 support fallocate.
> 
> Please remove the comment, adding a generic fallback in kernelspace is a
> very dumb idea as we already discussed long time ago.
>
> > --- linux-2.6.22.orig/include/linux/fs.h
> > +++ linux-2.6.22/include/linux/fs.h
> > @@ -266,6 +266,21 @@ extern int dir_notify_enable;
> >  #define SYNC_FILE_RANGE_WRITE		2
> >  #define SYNC_FILE_RANGE_WAIT_AFTER	4
> >  
> > +/*
> > + * sys_fallocate modes
> > + * Currently sys_fallocate supports two modes:
> > + * FALLOC_ALLOCATE :	This is the preallocate mode, using which an application
> > + *			may request reservation of space for a particular file.
> > + *			The file size will be changed if the allocation is
> > + *			beyond EOF.
> > + * FALLOC_RESV_SPACE :	This is same as the above mode, with only one difference
> > + *			that the file size will not be modified.
> > + */
> > +#define FALLOC_FL_KEEP_SIZE    0x01 /* default is extend/shrink size */
> > +
> > +#define FALLOC_ALLOCATE        0
> > +#define FALLOC_RESV_SPACE      FALLOC_FL_KEEP_SIZE
> 
> Just remove FALLOC_ALLOCATE, 0 flags should be the default.  I'm also
> not sure there is any point in having two namespace now that we have a flags-
> based ABI.

Ok. Since we have only one flag (FALLOC_FL_KEEP_SIZE) and we do not want
to declare the default mode (FALLOC_ALLOCATE), we can _just_ have this
flag and remove the other mode too (FALLOC_RESV_SPACE).
Is this what you are suggesting ?

> Also please don't add this to fs.h.  fs.h is a complete mess and the
> falloc flags are a new user ABI.  Add a linux/falloc.h instead which can
> be added to headers-y so the ABI constant can be exported to userspace.

Should we need a header file just to declare one flag - i.e.
FALLOC_FL_KEEP_SIZE (since now there is no point of declaring the two
modes) ? If "linux/fs.h" is not a good place, will "asm-generic/fcntl.h"
be a sane place for this flag ?

Thanks!
--
Regards,
Amit Arora
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