Re: [Xen-devel] [PATCH RESEND 1/4] libs, gnttab, libxc: Interface for grant copy operation

[Paulina Szubarczyk <paulinaszubarczyk@xxxxxxxxx>]

On Tue, 2016-05-31 at 10:25 +0100, David Vrabel wrote:
> 
> On 31/05/2016 05:44, Paulina Szubarczyk wrote:
> > Implentation of interface to grant copy operation called through
> > libxc. An ioctl(gntdev, IOCTL_GNTDEV_GRANT_COPY, ..) system call is
> > invoked for linux. In the mini-os the operation is yet not
> > implemented.
> > 
> > * In the file "tools/include/xen-sys/Linux/gntdev.h" added
> >   - 'struct ioctl_gntdev_grant_copy_segment'
> >     The structure is analogous to 'struct gntdev_grant_copy_segment'
> >     defined in linux code include/uapi/xen/gntdev.h. Typdefs are
> >     replaced by they original types:
> >       typedef uint16_t domid_t;
> >       typedef uint32_t grant_ref_t;
> >     That leads to defining domids array with type uint16_t in libs,
> >     differently then in other functions concerning grant table
> >     operations in that library.
> > 
> > ` - macro #define IOCTL_GNTDEV_GRANT_COPY
> > 
> >   - 'struct ioctl_gntdev_grant_copy'
> >     taken from linux code as higher. Structure aggregating
> >     'struct gntdev_grant_copy_segment'
> > 
> > * In the file libs/gnttab/linux.c
> >   - function int osdep_gnttab_grant_copy(xengnttab_handle *xgt,
> >                               uint32_t count,
> >                               uint16_t *domids, uint32_t *refs, void
> >                               **bufs, uint32_t *offset, uint32_t *len,
> >                               int type, uint32_t notify_offset,
> >                               evtchn_port_t notify_port)
> > 
> >     It is a function used to perform grant copy opertion. It allocats
> >     'ioctl_gntdev_grant_copy' and 'ioctl_gntdev_grant_copy_segment'.
> >     Segments are filled from the passed values.
> > 
> >     When @type is different then zero the source to copy from are guest
> >     domain grant pages addressed by @refs and the destination is local
> >     memory accessed from @bufs, the operation flag is then set to
> >     'GNTCOPY_source_gref', contrarily for @type equal zero.
> > 
> >     @offset is the offset on the page
> >     @len is the amount of data to copy,
> >     @offset[i] + @len[i] should not exceed XEN_PAGE_SIZE
> >         - the condition is checked in gntdev device.
> > 
> >     Notification is yet not implemented.
> 
> I'm not sure what you mean by "notifcation" here.
There is notify interface for grant map operations to communicate a
failure to the peer in case of teardown if the notify_port is given
to allow it to take care of resources. I have not checked yet how is it
used.
> 
> > index caf6fb4..0ca07c9 100644
> > --- a/tools/include/xen-sys/Linux/gntdev.h
> > +++ b/tools/include/xen-sys/Linux/gntdev.h
> > @@ -147,4 +147,25 @@ struct ioctl_gntdev_unmap_notify {
> >  /* Send an interrupt on the indicated event channel */
> >  #define UNMAP_NOTIFY_SEND_EVENT 0x2
> >  
> > +struct ioctl_gntdev_grant_copy_segment {
> > +    union {
> > +        void *virt;
> > +        struct {
> > +            uint32_t ref;
> > +            uint16_t offset;
> > +            uint16_t domid;
> > +        } foreign;
> > +    } source, dest;
> > +    uint16_t len;
> > +    uint16_t flags;
> > +    int16_t status;
> > +};
> > +
> > +#define IOCTL_GNTDEV_GRANT_COPY \
> > +_IOC(_IOC_NONE, 'G', 8, sizeof(struct ioctl_gntdev_grant_copy))
> > +struct ioctl_gntdev_grant_copy {
> > +    unsigned int count;
> > +    struct ioctl_gntdev_grant_copy_segment *segments;
> > +};
> > +
> >  #endif /* __LINUX_PUBLIC_GNTDEV_H__ */
> > diff --git a/tools/libs/gnttab/gnttab_core.c 
> > b/tools/libs/gnttab/gnttab_core.c
> > index 5d0474d..1e014f8 100644
> > --- a/tools/libs/gnttab/gnttab_core.c
> > +++ b/tools/libs/gnttab/gnttab_core.c
> > @@ -113,6 +113,18 @@ int xengnttab_unmap(xengnttab_handle *xgt, void 
> > *start_address, uint32_t count)
> >      return osdep_gnttab_unmap(xgt, start_address, count);
> >  }
> >  
> > +int xengnttab_copy_grant(xengnttab_handle *xgt,
> > +                         uint32_t count,
> > +                         uint16_t *domids,
> > +                         uint32_t *refs,
> > +                         void **bufs,
> > +                         uint32_t *offset, 
> > +                         uint32_t *len,
> > +                         int type)
> 
> This interface should match the ioctl which matches the hypercall.  In
> particular the ioctl (and hypercall) allows copies to and from grant
> references in the same call and returns a per-op status.
> 
I followed the pattern of declaration for the grant map in this file
which as I believe is generic due to the use of it by both linux and
mini-os. 

The header with 'struct ioctl_gntdev_copy_segment' is linked only to the
linux part which issues the hypercall by gntdev, whereas mini-os does
not use gntdev it is not accessible at the higher level.

> Using the same structure in libxc would also allow you to a) remove the
> memory allocations; and b) avoid having to fill in a different structure.
> 
> I would suggest:
> 
> int xengnttab_copy_grant(xengnttab_handle *xgt,
>       unsigned int count,
>       xengnttab_copy_segment_t *segs);
> 
> With:
> 
> typedef struct ioctl_gntdev_copy_segment xengnttab_copy_segment_t;
> 
> You should put the required struct ioctl_gntdev_grant_copy on the stack
> since it is small.
> 
> David

Paulina



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