linux-ext4 - Re: [PATCH 2/6][TAKE7] fallocate() implementation in i386, x86

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Message-ID: <20070713132118.GA23256@infradead.org>
Date:	Fri, 13 Jul 2007 14:21:19 +0100
From:	Christoph Hellwig <hch@...radead.org>
To:	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>
Cc:	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 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.

> + * <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.

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.

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