Re: [PATCH 2/6][TAKE7] fallocate() implementation in i386, x86_64 and powerpc

Amit K. Arora
2007-07-13T14:19:06Z

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