linux-kernel - Re: [RFC] Heads up on sys

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Date:	Mon, 5 Mar 2007 13:27:42 +0100
From:	Jan Kara <jack@...e.cz>
To:	Mingming Cao <cmm@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, nscott@...nex.com,
	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org, suparna@...ibm.com, alex@...sterfs.com,
	suzuki@...ibm.com, Ulrich Drepper <drepper@...hat.com>
Subject: Re: [RFC] Heads up on sys_fallocate()

> >On Fri, 02 Mar 2007 09:40:54 +1100
> >Nathan Scott <nscott@...nex.com> wrote:
> >
> >
> >>On Thu, 2007-03-01 at 14:25 -0800, Andrew Morton wrote:
> >>
> >>>On Fri, 2 Mar 2007 00:04:45 +0530
> >>>"Amit K. Arora" <aarora@...ux.vnet.ibm.com> wrote:
> >>>
> >>>
> >>>>This is to give a heads up on few patches that we will be soon coming up
> >>>>with. These patches implement a new system call sys_fallocate() and a
> >>>>new inode operation "fallocate", for persistent preallocation. The new
> >>>>system call, as Andrew suggested, will look like:
> >>>>
> >>>> asmlinkage long sys_fallocate(int fd, loff_t offset, loff_t len);
> >>>
> >>>...
> >>>
> >>>I'd agree with Eric on the "command" flag extension.
> >>
> >>Seems like a separate syscall would be better, "command" sounds
> >>a bit ioctl like, especially if that command is passed into the
> >>filesystems..
> >>
> >
> >
> >madvise, fadvise, lseek, etc seem to work OK.
> >
> >I get repeatedly traumatised by patch rejects whenever a new syscall gets
> >added, so I'm biased.
> >
> >The advantage of a command flag is that we can add new modes in the future
> >without causing lots of churn, waiting for arch maintainers to catch up,
> >potentially adding new compat code, etc.
> >
> >Rename it to "mode"? ;)
> >
> I am wondering if it is useful to add another mode to advise block 
> allocation policy? Something like indicating which physical block/block 
> group to allocate from (goal), and whether ask for strict contigous 
> blocks. This will help preallocation or reservation to choose the right 
> blocks for the file.
  Yes, I also think this would be useful so you can "guide"
preallocation for things like defragmentation (e.g. preallocate space
for the file being defragmented and move the file to it).

									Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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