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Re: [Xen-devel] [PATCH v2] introduce grant copy for user land
On 12/02/2014 11:13 AM, Thanos Makatos wrote:
This patch introduces the interface to allow user-space applications
execute grant-copy operations. This is done by sending an ioctl to the
grant device.
Signed-off-by: Thanos Makatos <thanos.makatos@xxxxxxxxxx>
---
drivers/xen/gntdev.c | 171 +++++++++++++++++++++++++++++++++++++++++++++
include/uapi/xen/gntdev.h | 69 ++++++++++++++++++
2 files changed, 240 insertions(+)
diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 51f4c95..7b4a8e0 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -705,6 +705,174 @@ static long gntdev_ioctl_notify(struct gntdev_priv *priv,
void __user *u)
return rc;
}
+static int gntdev_gcopy_batch(int nr_segments, unsigned long gcopy_cb,
+ struct gntdev_grant_copy_segment __user *__segments, int dir,
+ int src, int dst) {
+
+ static const int batch_size = PAGE_SIZE / (sizeof(struct page*) +
+ sizeof(struct gnttab_copy) + sizeof(struct
gntdev_grant_copy_segment));
+ struct page **pages = (struct page **)gcopy_cb;
+ struct gnttab_copy *batch = (struct gnttab_copy *)((unsigned long)pages
+
+ sizeof(struct page*) * batch_size);
+ struct gntdev_grant_copy_segment *segments =
+ (struct gntdev_grant_copy_segment *)((unsigned long)batch +
+ sizeof(struct gnttab_copy) * batch_size);
+ unsigned int nr_pinned = 0, nr_segs2cp = 0;
+ int err = 0, i;
+ const int write = dir == GNTCOPY_IOCTL_g2s;
+
+ nr_segments = min(nr_segments, batch_size);
+
+ if (unlikely(copy_from_user(segments, __segments,
+ sizeof(struct gntdev_grant_copy_segment) *
nr_segments))) {
+ pr_debug("failed to copy %d segments from user", nr_segments);
+ err = -EFAULT;
+ goto out;
+ }
+
+ for (i = 0; i < nr_segments; i++) {
+
+ xen_pfn_t pgaddr;
+ unsigned long start, offset;
+ struct gntdev_grant_copy_segment *seg = &segments[i];
+
+ if (dir == GNTCOPY_IOCTL_s2g || dir == GNTCOPY_IOCTL_g2s) {
+
+ start = (unsigned long)seg->self.iov.iov_base &
PAGE_MASK;
+ offset = (unsigned long)seg->self.iov.iov_base &
~PAGE_MASK;
+ if (unlikely(offset + seg->self.iov.iov_len >
PAGE_SIZE)) {
+ pr_warn("segments crossing page boundaries not yet
"
+ "implemented\n");
+ err = -ENOSYS;
+ goto out;
+ }
+
+ err = get_user_pages_fast(start, 1, write, &pages[i]);
+ if (unlikely(err != 1)) {
+ pr_debug("failed to get user page %lu", start);
+ err = -EFAULT;
+ goto out;
+ }
+
+ nr_pinned++;
+
+ pgaddr = pfn_to_mfn(page_to_pfn(pages[i]));
+ }
+
+ nr_segs2cp++;
+
+ switch (dir) {
+ case GNTCOPY_IOCTL_g2s: /* copy from guest */
+ batch[i].len = seg->self.iov.iov_len;
+ batch[i].source.u.ref = seg->self.ref;
+ batch[i].source.domid = src;
+ batch[i].source.offset = seg->self.offset;
+ batch[i].dest.u.gmfn = pgaddr;
+ batch[i].dest.domid = DOMID_SELF;
+ batch[i].dest.offset = offset;
+ batch[i].flags = GNTCOPY_source_gref;
+ break;
+ case GNTCOPY_IOCTL_s2g: /* copy to guest */
+ batch[i].len = seg->self.iov.iov_len;
+ batch[i].source.u.gmfn = pgaddr;
+ batch[i].source.domid = DOMID_SELF;
+ batch[i].source.offset = offset;
+ batch[i].dest.u.ref = seg->self.ref;
+ batch[i].dest.domid = dst;
+ batch[i].dest.offset = seg->self.offset;
+ batch[i].flags = GNTCOPY_dest_gref;
+ break;
+ case GNTCOPY_IOCTL_g2g: /* copy guest to guest */
+ batch[i].len = seg->g2g.len;
+ batch[i].source.u.ref = seg->g2g.src.ref;
+ batch[i].source.domid = src;
+ batch[i].source.offset = seg->g2g.src.offset;
+ batch[i].dest.u.ref = seg->g2g.dst.ref;
+ batch[i].dest.domid = dst;
+ batch[i].dest.offset = seg->g2g.dst.offset;
+ batch[i].flags = GNTCOPY_source_gref |
GNTCOPY_dest_gref;
+ break;
+ default:
+ pr_debug("invalid grant-copy direction %d\n", dir);
+ err = -EINVAL;
+ goto out;
+ }
+ }
+
+ gnttab_batch_copy(batch, nr_segs2cp);
+ for (i = 0; i < nr_segs2cp; i++) {
Can nr_segs2cp be not equal to nr_segments here? If you got to this
point you have gone through the full loop.
+ err = put_user(batch[i].status, &__segments[i].status);
+ if (unlikely(err)) {
+ pr_debug("failed to copy error code %d to user: %d\n",
+ batch[i].status, err);
+ goto out;
+ }
+ }
+
+out:
+ for (i = 0; i < nr_pinned; i++)
+ put_page(pages[i]);
+
+ if (unlikely(err))
+ return err;
+
+ return nr_segs2cp;
And I think here it can be either 0 (which is the case of an error) or
nr_segments. If you error out of the 'for' loop you haven't actually
copied anything, even though nr_segs2cp might be non-zero.
-boris
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