Re: [Xen-devel] [v5][PATCH 1/2] xen:x86:mm:p2m: introduce set_identity_p2m_entry

["Chen, Tiejun" <tiejun.chen@xxxxxxxxx>]

On 2014/7/29 15:05, Jan Beulich wrote:
> > > > On 29.07.14 at 08:40, <tiejun.chen@xxxxxxxxx> wrote:
> > +int set_identity_p2m_entry(struct domain *d, unsigned long gfn)
> > +{
> > +    p2m_type_t p2mt;
> > +    p2m_access_t a;
> > +    mfn_t tmp_mfn, mfn = _mfn(gfn);
> No need for the mfn variable; instead what currently is tmp_mfn
> should be named just mfn, and the _mfn(gfn) construction can be
> done right in the function call.
Okay.

> > +    struct p2m_domain *p2m = p2m_get_hostp2m(d);
> > +    int ret = -EBUSY;
> > +
> > +    gfn_lock(p2m, gfn, 0);
> > +
> > +    tmp_mfn = p2m->get_entry(p2m, gfn, &p2mt, &a, 0, NULL);
> > +
> > +    if ( mfn_valid(tmp_mfn) )
> > +    {
> > +        gdprintk(XENLOG_ERR,
> > +                 "Overlapping RMRRs at %"PRIx64".\n", (paddr_t)gfn);
> Pointless cast: Just use %lx in the format string. Additionally I don't
> think the message text is correct: You don't really know whether
> what's there is another RMRR (or that the context you're being
> called in refers to an RMRR at all). On the contrary - if it was an
> RMRR (or to be precise, a previously established identity mapping),
> you'd want to report success. And generally we have no stop at
> the end of log messages.
So just print this,

+        gdprintk(XENLOG_ERR,
+                 "Overlapping at %lx.\n", (paddr_t)gfn);


> > +        goto out;
> Once again, when error handling is that simple please avoid using
> "goto".
Its make no sense to me.

Did you see this function in this same file,

int clear_mmio_p2m_entry(struct domain *d, unsigned long gfn)
{
    int rc = -EINVAL;
    mfn_t mfn;
    p2m_access_t a;
    p2m_type_t t;
    struct p2m_domain *p2m = p2m_get_hostp2m(d);

    if ( !paging_mode_translate(d) )
        return -EIO;

    gfn_lock(p2m, gfn, 0);
    mfn = p2m->get_entry(p2m, gfn, &t, &a, 0, NULL);

    /* Do not use mfn_valid() here as it will usually fail for MMIO 
pages. */
    if ( (INVALID_MFN == mfn_x(mfn)) || (t != p2m_mmio_direct) )
    {
        gdprintk(XENLOG_ERR,
                 "gfn_to_mfn failed! gfn=%08lx type:%d\n", gfn, t);
        goto out;
    }
    rc = p2m_set_entry(p2m, gfn, _mfn(INVALID_MFN), PAGE_ORDER_4K, 
p2m_invalid,
                       p2m->default_access);

 out:
    gfn_unlock(p2m, gfn, 0);

    return rc;
}

Yes, previously I really can't understand what's that code style in xen. 
So as I remember I ask you guy if xen has checkpatch.pl like Linux, qemu 
or other stuff, but you didn't reply this point. So I have to try 
following existing codes. Now I'm curious what we should abide.
Thanks
Tiejun

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