Re: [Xen-devel] [RFC 3/6] Introduce _xrealloc

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Oct 12, 2017 at 02:33:04PM +0100, Julien Grall wrote:
> Hi,
> 
> Bringing back this discussion.
> 
> On 28/08/17 22:39, Goel, Sameer wrote:
> > 
> > 
> > On 6/9/2017 3:44 AM, Wei Liu wrote:
> > > On Thu, Jun 08, 2017 at 08:49:01PM +0100, Julien Grall wrote:
> > > > CC the REST maintainers
> > > > 
> > > > On 08/06/2017 20:30, Sameer Goel wrote:
> > > > > Introduce a memory realloc function.
> > > > > 
> > > > > Signed-off-by: Sameer Goel <sgoel@xxxxxxxxxxxxxx>
> > > > > ---
> > > > >   xen/common/xmalloc_tlsf.c | 13 +++++++++++++
> > > > >   xen/include/xen/xmalloc.h |  1 +
> > > > >   2 files changed, 14 insertions(+)
> > > > > 
> > > > > diff --git a/xen/common/xmalloc_tlsf.c b/xen/common/xmalloc_tlsf.c
> > > > > index b256dc5..52385a8 100644
> > > > > --- a/xen/common/xmalloc_tlsf.c
> > > > > +++ b/xen/common/xmalloc_tlsf.c
> > > > > @@ -612,6 +612,19 @@ void *_xzalloc(unsigned long size, unsigned long 
> > > > > align)
> > > > >       return p ? memset(p, 0, size) : p;
> > > > >   }
> > > > > 
> > > > > +void *_xrealloc(void *p, unsigned long new_size, unsigned long align)
> > > > > +{
> > > > > +    void *new_p = _xmalloc(new_size, align);
> > > > > +
> > > > > +    if(new_p && p)
> > > > 
> > > > Coding style: if ( ... )
> > > > 
> > > > > +    {
> > > > > +        memcpy(new_p, p, new_size);
> > > 
> > > This is wrong. How can you know if the area pointed to by p is at least
> > > new_size bytes long?
> > > 
> > Agreed, I revisited the code and will remove _xrealloc and use xfree and 
> > _xmalloc instead.
> 
> I am not sure why you choose to drop it completely. xfree is able to know
> the size of the buffer to free.
> 
> So you could find out the size and copy the right amount of data.
> 
> Note that having _xrealloc would be my preference over an open-coded version
> in the code.

I would vouch for a properly implemented _xrealloc. :-)

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