linux-ext4 - Re: [PATCH 0/5][TAKE2] fallocate system call

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Date:	Tue, 15 May 2007 00:31:21 -0600
From:	Andreas Dilger <adilger@...sterfs.com>
To:	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>
Cc:	torvalds@...l.org, akpm@...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 0/5][TAKE2] fallocate system call

On May 14, 2007  18:59 +0530, Amit K. Arora wrote:
>  asmlinkage long sys_fallocate(int fd, int mode, loff_t offset, loff_t len)
> 
> fd: The descriptor of the open file.
> 
> mode*: This specifies the behavior of the system call. Currently the
>   system call supports two modes - FA_ALLOCATE and FA_DEALLOCATE.
>   FA_ALLOCATE: Applications can use this mode to preallocate blocks to
>     a given file (specified by fd). This mode changes the file size if
>     the preallocation is done beyond the EOF. It also updates the
>     ctime/mtime in the inode of the corresponding file, marking a
>     successfull allocation.
>   FA_DEALLOCATE: This mode can be used by applications to deallocate the
>     previously preallocated blocks. This also may change the file size
>     and the ctime/mtime.
> * New modes might get added in future. One such new mode which is
>   already under discussion is FA_PREALLOCATE, which when used will
>   preallocate space but will not change the filesize and [cm]time.
>   Since the semantics of this new mode is not clear and agreed upon yet,
>   this patchset does not implement it currently.
> 
> offset: This is the offset in bytes, from where the preallocation should
>   start.
> 
> len: This is the number of bytes requested for preallocation (from
>   offset).

What is the return value?  I'd hope it is the number of bytes preallocated,
in case of interrupted preallocation for whatever reason (interrupt, out of
space, etc) like a regular write(2) call.  In this case the return type needs
to also be an loff_t to match @len.

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.

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