Re: Is there a "make hole" (truncate in middle) syscall?

[Vladimir Saveliev]

On Fri, 2003-12-12 at 16:53, Rob Landley wrote:
> On Friday 12 December 2003 07:28, Vladimir Saveliev wrote:
> > Hi
> >
> > On Fri, 2003-12-12 at 15:55, Jörn Engel wrote:
> > > On Thu, 11 December 2003 14:32:12 -0600, Rob Landley wrote:
> > > > On Thursday 11 December 2003 13:48, Jörn Engel wrote:
> > > > > If you really do it, please don't add a syscall for it.  Simply check
> > > > > each written page if it is completely filled with zero.  (This will
> > > > > be a very quick check for most pages, as they will contain something
> > > > > nonzero in the first couple of words)
> > > >
> > > > Cache poisoning, streaming writes to large RAID arrays...  There are
> > > > about 8 zllion reasons not to do this.  Really.  (It defeats the whole
> > > > purpose of DMA, doesn't it?)
> >
> > Sorry,
> > but doesn't truncate do almost exactly what "make hole" is supposed to
> > do?
> 
> I have a 2 gigabyte file.  I want to punch a hole from 257 megabytes to 364 
> megabytes, saving over 100 megs of disk space.  I do NOT want to have to copy 
> off and rewrite 1.6 gigabytes of data from the end of the file.  (There may 
> not even be enough room on the disk, and it would take a long time anyway.)
> 
ok.
But I asked why would "make hole" have problems you list (8 zillions)
and truncate would not have them?

> No, it doesn't do the same thing.  Truncate is always to end of file.  Punch 
> hole is like a write, it takes a length.  lseek(pos), punch(length).
> 
> Rob
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