Re: [External] [PATCH] hostmem: Add clear option to file backend

[David Hildenbrand]

On 02.03.23 12:48, Feiran Zheng wrote:
> > On 2 Mar 2023, at 11:39, David Hildenbrand <david@redhat.com> wrote:
> >
> > On 02.03.23 12:37, Feiran Zheng wrote:
> > > > On 2 Mar 2023, at 11:31, David Hildenbrand <david@redhat.com> wrote:
> > > >
> > > > On 02.03.23 12:09, Fam Zheng wrote:
> > > > > This adds a memset to clear the backing memory. This is useful in the
> > > > > case of PMEM DAX to drop dirty data, if the backing memory is handed
> > > > > over from a previous application or firmware which didn't clean up
> > > > > before exiting.
> > > >
> > > > Why can't the VM manager do that instead? If you have a file that's certainly 
> > > > easily possible.
> > > Hi David,
> > > Technically yes, but I have a simple VM manager here which wants to avoid 
> > > replicating the same mmap code, such as handling the flags depending on 
> > > share=on|off,hugepages=on|off. All in all this approach requires the least 
> > > additional code to achieve it.
> >
> > so ... we're supposed to maintain that code in QEMU instead to make your life 
> > easier ? :)
> >
> > Sorry, for this particular use case I don't see the big benefit of moving that 
> > code into QEMU.
>
> I am posting because this does not only makes my life easier, supposedly it 
> also make other developers life easier, because the file here can be a char 
> file and there is no easy way to clear it (/dev/dax1.0) from command line if 
> you want to invoke a QEMU command directly.
>
> Maybe I’m missing a convenient command to clear a DAX char file?

Can't you simply use dd and read from /dev/zero?

--
Thanks,

David / dhildenb