SMB3 Unix extensions

[Christoph Hellwig]

On Fri, Apr 28, 2017 at 12:26:28PM -0700, Jeremy Allison via samba-technical wrote:
> Checking - Looks like it's already done ! See:
> 
> VFS_FALLOCATE_FL_PUNCH_HOLE
> 
> and this is plumbed down into source3/lib/system.c:sys_fallocate().
> 
> You get to this via SMB2 ioctl FSCTL_SET_ZERO_DATA.

Note that in Linux FALLOC_FL_PUNCH_HOLE will release space allocated
in the range as much as possible, thus creating a sparse file.

If you just want to zero the range the flag to use is
FALLOC_FL_ZERO_RANGE.

The SMB2 ioctl sounds closer to the latter at least by name, I haven't
found a definition of the semantics.