Re: [PATCH] qemu: fix memory leak in qemuAgentGetFSInfo

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On Tue, Mar 10, 2015 at 10:32:04AM +0100, Ján Tomko wrote:
> On Tue, Mar 10, 2015 at 01:56:11PM +0800, Chen Fan wrote:
> > in virDomainFSInfoFree(), don't free the virDomainFSInfo data.
> > 
> > ==10670== 80 bytes in 2 blocks are definitely lost in loss record 576 of 793
> > ==10670==    at 0x4A06BC3: calloc (vg_replace_malloc.c:618)
> > ==10670==    by 0x509DEBD: virAlloc (viralloc.c:144)
> > ==10670==    by 0x19FBD558: qemuAgentGetFSInfo (qemu_agent.c:1837)
> > ==10670==    by 0x1A03CF91: qemuDomainGetFSInfo (qemu_driver.c:19238)
> > 
> > Signed-off-by: Chen Fan <chen.fan.fnst@xxxxxxxxxxxxxx>
> > ---
> >  src/libvirt-domain.c | 2 ++
> >  1 file changed, 2 insertions(+)
> 
> This does fix the memory leak and makes the function behave like it's
> documented in virDomainGetFSInfo and virDomainFSInfoFree:
> http://libvirt.org/html/libvirt-libvirt-domain.html#virDomainGetFSInfo
> http://libvirt.org/html/libvirt-libvirt-domain.html#virDomainFSInfoFree
> 
> But it changes the public API - if there are applications that already
> work around this function by freeing the info, this change would
> introduce a double free.

Well, this is a good point that we might break somebody's application, but the
virDomainFSInfoFree is the only one *Free API that doesn't call free/unref on
passed argument.  In the documentation the @info is an array and we specifically
says that calling virDomainFSInfoFree on each element and then just free the
@info is sufficient, but it isn't and there will be a memory leak.  It changes
behavior of public API to correctly free the allocated memory as documentation
says.  Let's hear another opinion, but I'm for fixing it.

Pavel

> 
> I would NACK this if the documentation for both APIs didn't say that's
> how this function should behave.
> 
> I'd like to hear a second opinion.
> 
> Jan
> 
> > 
> > diff --git a/src/libvirt-domain.c b/src/libvirt-domain.c
> > index 04545fd..7f8a7ce 100644
> > --- a/src/libvirt-domain.c
> > +++ b/src/libvirt-domain.c
> > @@ -11337,4 +11337,6 @@ virDomainFSInfoFree(virDomainFSInfoPtr info)
> >      for (i = 0; i < info->ndevAlias; i++)
> >          VIR_FREE(info->devAlias[i]);
> >      VIR_FREE(info->devAlias);
> > +
> > +    VIR_FREE(info);
> >  }
> > -- 
> > 1.9.3
> > 
> > --
> > libvir-list mailing list
> > libvir-list@xxxxxxxxxx
> > https://www.redhat.com/mailman/listinfo/libvir-list
> --
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