[PATCH v10 5/10] libs/guest: add xg_foreignmemory_copy_{from,to}

[Frediano Ziglio <freddy77@gmail.com>]

This change prepare code to use a new "foreign copy" hypercall.
The new hypercall will copy memory from/to a foreign domain.
The new hypercall can be emulated with a sequence of:
- map foreign memory;
- copy memory;
- unmap foreign memory.

The reason to introduce the emulation first is that you can refactor on the
emulation without having to introduce the new hypercall.  Introducing the
hypercall first would make testing more complicated as bugs on the hypercall
have to be taken into account and considered.  Also it is easier that way to
enable or disable new code. For instance you want to test for performance
regression (in this case the code emulated should not perform worse).

Signed-off-by: Frediano Ziglio <frediano.ziglio@citrix.com>
---
Changes since v5:
- Do not overwrite errno if xenforeignmemory_map fails.

Changes since v6:
- improve commit message, explain order and changes.
---
 tools/libs/guest/xg_sr_common.c | 57 +++++++++++++++++++++++++++++++++
 tools/libs/guest/xg_sr_common.h |  8 +++++
 2 files changed, 65 insertions(+)

diff --git a/tools/libs/guest/xg_sr_common.c b/tools/libs/guest/xg_sr_common.c
index 9b2782b5cf..90da21c35f 100644
--- a/tools/libs/guest/xg_sr_common.c
+++ b/tools/libs/guest/xg_sr_common.c
@@ -156,6 +156,63 @@ static void __attribute__((unused)) build_assertions(void)
     BUILD_BUG_ON(sizeof(struct xc_sr_rec_hvm_params)        != 8);
 }
 
+enum {
+    foreigncopy_from,
+    foreigncopy_to
+};
+
+static int xg_foreignmemory_copy(xc_interface *xch, domid_t domid,
+                                 int dir, size_t nr_pages, void *buffer,
+                                 const xen_pfn_t foreign_pfns[nr_pages])
+{
+    if ( nr_pages == 0 )
+        return 0;
+
+    if ( !buffer || !foreign_pfns )
+    {
+        errno = EINVAL;
+        return -1;
+    }
+
+    int err[nr_pages];
+    const int prot = (dir == foreigncopy_from) ? PROT_READ : PROT_READ|PROT_WRITE;
+
+    void *p = xenforeignmemory_map(xch->fmem, domid, prot, nr_pages, foreign_pfns, err);
+    if ( !p )
+        return -1;
+
+    for ( size_t n = 0; n < nr_pages; ++n )
+        if ( err[n] )
+        {
+            xenforeignmemory_unmap(xch->fmem, p, nr_pages);
+            errno = -err[n];
+            return -1;
+        }
+
+    if ( dir == foreigncopy_from )
+        memcpy(buffer, p, nr_pages * XC_PAGE_SIZE);
+    else
+        memcpy(p, buffer, nr_pages * XC_PAGE_SIZE);
+
+    return xenforeignmemory_unmap(xch->fmem, p, nr_pages);
+}
+
+int xg_foreignmemory_copy_from(xc_interface *xch, domid_t dom,
+                               size_t nr_pages, void *dest,
+                               const xen_pfn_t source[nr_pages])
+{
+    return xg_foreignmemory_copy(xch, dom, foreigncopy_from,
+                                 nr_pages, dest, source);
+}
+
+int xg_foreignmemory_copy_to(xc_interface *xch, domid_t dom,
+                             size_t nr_pages, const xen_pfn_t dest[nr_pages],
+                             const void *source)
+{
+    return xg_foreignmemory_copy(xch, dom, foreigncopy_to,
+                                 nr_pages, (void *) source, dest);
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/tools/libs/guest/xg_sr_common.h b/tools/libs/guest/xg_sr_common.h
index 020b1a5272..50f235ba87 100644
--- a/tools/libs/guest/xg_sr_common.h
+++ b/tools/libs/guest/xg_sr_common.h
@@ -556,6 +556,14 @@ static inline bool page_type_has_stream_data(uint32_t type)
     }
 }
 
+int xg_foreignmemory_copy_from(xc_interface *xch, domid_t dom,
+                               size_t nr_pages, void *dest,
+                               const xen_pfn_t source[nr_pages]);
+
+int xg_foreignmemory_copy_to(xc_interface *xch, domid_t dom,
+                             size_t nr_pages, const xen_pfn_t dest[nr_pages],
+                             const void *source);
+
 #endif
 /*
  * Local variables:
-- 
2.43.0