linux-kernel - Re: [PATCH v11 13/22] vfio: Introduce common function to add capabilities

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Date:   Tue, 8 Nov 2016 14:42:29 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Kirti Wankhede <kwankhede@...dia.com>
Cc:     Alexey Kardashevskiy <aik@...abs.ru>, <pbonzini@...hat.com>,
        <kraxel@...hat.com>, <cjia@...dia.com>, <qemu-devel@...gnu.org>,
        <kvm@...r.kernel.org>, <kevin.tian@...el.com>,
        <jike.song@...el.com>, <bjsdjshi@...ux.vnet.ibm.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v11 13/22] vfio: Introduce common function to add
 capabilities

On Wed, 9 Nov 2016 02:16:17 +0530
Kirti Wankhede <kwankhede@...dia.com> wrote:

> On 11/8/2016 12:59 PM, Alexey Kardashevskiy wrote:
> > On 05/11/16 08:10, Kirti Wankhede wrote:  
> >> Vendor driver using mediated device framework should use
> >> vfio_info_add_capability() to add capabilities.
> >> Introduced this function to reduce code duplication in vendor drivers.
> >>
> >> Signed-off-by: Kirti Wankhede <kwankhede@...dia.com>
> >> Signed-off-by: Neo Jia <cjia@...dia.com>
> >> Change-Id: I6fca329fa2291f37a2c859d0bc97574d9e2ce1a6
> >> ---
> >>  drivers/vfio/vfio.c  | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++-
> >>  include/linux/vfio.h |  3 +++
> >>  2 files changed, 62 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> >> index 4ed1a6a247c6..9a03be0942a1 100644
> >> --- a/drivers/vfio/vfio.c
> >> +++ b/drivers/vfio/vfio.c
> >> @@ -1797,8 +1797,66 @@ void vfio_info_cap_shift(struct vfio_info_cap *caps, size_t offset)
> >>  	for (tmp = caps->buf; tmp->next; tmp = (void *)tmp + tmp->next - offset)
> >>  		tmp->next += offset;
> >>  }
> >> -EXPORT_SYMBOL_GPL(vfio_info_cap_shift);
> >> +EXPORT_SYMBOL(vfio_info_cap_shift);  
> > 
> > 
> > Why this change?
> > 
> >   
> 
> We want this symbol to be available to all drivers.

IOW, from proprietary drivers.  It makes me uncomfortable how many
non-GPL symbols we're adding (or converting) in this effort, but I'm
trying to look objectively at every export as to whether a non-GPL
caller of the function is legitimately separate from in-kernel code.
For instance are they making use of data structures intrinsic to GPL'd
code.  In this case we're converting a symbol that's just manipulating
a data buffer to add an offset to each element in a chain.  The entries
are documented in a uapi header.  Kirti asked me about this one, and I
couldn't find any basis to raise an objection.  If you spot any reason
that any of the export symbols in these series really should be GPL,
please raise the issue.

> >>  
> >> +static int sparse_mmap_cap(struct vfio_info_cap *caps, void *cap_type)
> >> +{
> >> +	struct vfio_info_cap_header *header;
> >> +	struct vfio_region_info_cap_sparse_mmap *sparse_cap, *sparse = cap_type;
> >> +	size_t size;
> >> +
> >> +	size = sizeof(*sparse) + sparse->nr_areas *  sizeof(*sparse->areas);
> >> +	header = vfio_info_cap_add(caps, size,
> >> +				   VFIO_REGION_INFO_CAP_SPARSE_MMAP, 1);
> >> +	if (IS_ERR(header))
> >> +		return PTR_ERR(header);
> >> +
> >> +	sparse_cap = container_of(header,
> >> +			struct vfio_region_info_cap_sparse_mmap, header);
> >> +	sparse_cap->nr_areas = sparse->nr_areas;
> >> +	memcpy(sparse_cap->areas, sparse->areas,
> >> +	       sparse->nr_areas * sizeof(*sparse->areas));
> >> +	return 0;
> >> +}
> >> +
> >> +static int region_type_cap(struct vfio_info_cap *caps, void *cap_type)
> >> +{
> >> +	struct vfio_info_cap_header *header;
> >> +	struct vfio_region_info_cap_type *type_cap, *cap = cap_type;
> >> +
> >> +	header = vfio_info_cap_add(caps, sizeof(*cap),
> >> +				   VFIO_REGION_INFO_CAP_TYPE, 1);
> >> +	if (IS_ERR(header))
> >> +		return PTR_ERR(header);
> >> +
> >> +	type_cap = container_of(header, struct vfio_region_info_cap_type,
> >> +				header);
> >> +	type_cap->type = cap->type;
> >> +	type_cap->subtype = cap->subtype;
> >> +	return 0;
> >> +}
> >> +
> >> +int vfio_info_add_capability(struct vfio_info_cap *caps, int cap_type_id,
> >> +			     void *cap_type)
> >> +{
> >> +	int ret = -EINVAL;
> >> +
> >> +	if (!cap_type)
> >> +		return 0;
> >> +
> >> +	switch (cap_type_id) {
> >> +	case VFIO_REGION_INFO_CAP_SPARSE_MMAP:
> >> +		ret = sparse_mmap_cap(caps, cap_type);
> >> +		break;
> >> +
> >> +	case VFIO_REGION_INFO_CAP_TYPE:
> >> +		ret = region_type_cap(caps, cap_type);
> >> +		break;
> >> +	}
> >> +
> >> +	return ret;
> >> +}
> >> +EXPORT_SYMBOL(vfio_info_add_capability);
> >>  
> >>  /*
> >>   * Pin a set of guest PFNs and return their associated host PFNs for local
> >> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> >> index dcda8fccefab..cf90393a11e2 100644
> >> --- a/include/linux/vfio.h
> >> +++ b/include/linux/vfio.h
> >> @@ -113,6 +113,9 @@ extern struct vfio_info_cap_header *vfio_info_cap_add(
> >>  		struct vfio_info_cap *caps, size_t size, u16 id, u16 version);
> >>  extern void vfio_info_cap_shift(struct vfio_info_cap *caps, size_t offset);
> >>  
> >> +extern int vfio_info_add_capability(struct vfio_info_cap *caps,
> >> +				    int cap_type_id, void *cap_type);
> >> +  
> > 
> > 
> > It would make it easier to review and bisect if 14/22 was squashed into
> > this one.   
> 
> This was split based on Alex's suggestion on earlier version of this
> patchset.

Yeah, generally squashing patches together is the opposite of what we
want for review and bisect.  In this case the symbol exports should
avoid any defined-but-unused warnings.  Thanks,

Alex