Re: posix_fallocate

[Matti Aarnio]

On Fri, Apr 14, 2000 at 12:23:06AM -0700, Ulrich Drepper wrote:
> One of the recent POSIX standards defines a function with the prototype
> 	int posix_fallocate (int fd, off_t offset, size_t len)
> 
> The purpose of the function is to allocate enough storage so that
> future writes to the file in the range [offset,offset+len] cannot fail
> because the storage device has no room.
> 
> I'm currently emulating this function in a ugly way in glibc: I write
> to every single block on the file.  But this is by far not the best
> way.  This function belongs into the kernel.

	Ack.   Without adding any new syscalls, I think this, and
	fadvice should be implemented as FCNTL things.

	fallocate() will need support at per inode (inode_operations),
	fadvice() propably per file (file_operations).

	The mechanisms shall use 64-bit file sizes and offsets, naturally.

> The background for this function is that, for databases or multimedia
> files etc, you can preallocate the amount of storage you need and then
> don't have to fear running out of memory and as a sideeffect also
> probably have a faster running application since the kernel does not
> have to hunt for empty blocks while writing.
> 
> Maybe somebody can take a shot at it.  I can provide more information.
> 
> -- 
> ---------------.      drepper at gnu.org  ,-.   1325 Chesapeake Terrace
> Ulrich Drepper  \    ,-------------------'   \  Sunnyvale, CA 94089 USA
> Red Hat          `--' drepper at redhat.com   `------------------------

/Matti Aarnio <[e-mail]>