[PATCH v3 3/7] tools/foreignmem: Support querying the size of a resource

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

With the Xen side of this interface fixed to return real sizes, userspace
needs to be able to make the query.

Introduce xenforeignmemory_resource_size() for the purpose, bumping the
library minor version.

Update both Linux and FreeBSD's osdep_xenforeignmemory_map_resource() to
understand size requests, skip the mmap() operation, and copy back the
nr_frames field.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
CC: Wei Liu <wl@xxxxxxx>
CC: Paul Durrant <paul@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Juergen Gross <jgross@xxxxxxxx>
CC: Ian Jackson <iwj@xxxxxxxxxxxxxx>
CC: Michał Leszczyński <michal.leszczynski@xxxxxxx>
CC: Hubert Jasudowicz <hubert.jasudowicz@xxxxxxx>
CC: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>

This depends on a bugfix to the Linux IOCTL to understand size requests and
pass them on to Xen.

  
https://lore.kernel.org/xen-devel/20210112115358.23346-1-roger.pau@xxxxxxxxxx/T/#u

v3:
 * Rewrite from scratch, to avoid breaking restricted domid situations.  In
   particular, we cannot open a xencall interface and issue blind hypercalls.
---
 tools/include/xenforeignmemory.h                 | 15 +++++++++++++++
 tools/libs/foreignmemory/Makefile                |  2 +-
 tools/libs/foreignmemory/core.c                  | 18 ++++++++++++++++++
 tools/libs/foreignmemory/freebsd.c               | 18 +++++++++++++++---
 tools/libs/foreignmemory/libxenforeignmemory.map |  4 ++++
 tools/libs/foreignmemory/linux.c                 | 18 +++++++++++++++---
 6 files changed, 68 insertions(+), 7 deletions(-)

diff --git a/tools/include/xenforeignmemory.h b/tools/include/xenforeignmemory.h
index d594be8df0..1ba2f5316b 100644
--- a/tools/include/xenforeignmemory.h
+++ b/tools/include/xenforeignmemory.h
@@ -179,6 +179,21 @@ xenforeignmemory_resource_handle 
*xenforeignmemory_map_resource(
 int xenforeignmemory_unmap_resource(
     xenforeignmemory_handle *fmem, xenforeignmemory_resource_handle *fres);
 
+/**
+ * Determine the maximum size of a specific resource.
+ *
+ * @parm fmem handle to the open foreignmemory interface
+ * @parm domid the domain id
+ * @parm type the resource type
+ * @parm id the type-specific resource identifier
+ *
+ * Return 0 on success and fills in *nr_frames.  Sets errno and return -1 on
+ * error.
+ */
+int xenforeignmemory_resource_size(
+    xenforeignmemory_handle *fmem, domid_t domid, unsigned int type,
+    unsigned int id, unsigned long *nr_frames);
+
 #endif
 
 /*
diff --git a/tools/libs/foreignmemory/Makefile 
b/tools/libs/foreignmemory/Makefile
index 13850f7988..90d80a49ae 100644
--- a/tools/libs/foreignmemory/Makefile
+++ b/tools/libs/foreignmemory/Makefile
@@ -2,7 +2,7 @@ XEN_ROOT = $(CURDIR)/../../..
 include $(XEN_ROOT)/tools/Rules.mk
 
 MAJOR    = 1
-MINOR    = 3
+MINOR    = 4
 
 SRCS-y                 += core.c
 SRCS-$(CONFIG_Linux)   += linux.c
diff --git a/tools/libs/foreignmemory/core.c b/tools/libs/foreignmemory/core.c
index 63f12e2450..1e92c567e1 100644
--- a/tools/libs/foreignmemory/core.c
+++ b/tools/libs/foreignmemory/core.c
@@ -188,6 +188,24 @@ int xenforeignmemory_unmap_resource(
     return rc;
 }
 
+int xenforeignmemory_resource_size(
+    xenforeignmemory_handle *fmem, domid_t domid, unsigned int type,
+    unsigned int id, unsigned long *nr_frames)
+{
+    xenforeignmemory_resource_handle fres = {
+        .domid = domid,
+        .type  = type,
+        .id    = id,
+    };
+    int rc = osdep_xenforeignmemory_map_resource(fmem, &fres);
+
+    if ( rc )
+        return rc;
+
+    *nr_frames = fres.nr_frames;
+    return 0;
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/tools/libs/foreignmemory/freebsd.c 
b/tools/libs/foreignmemory/freebsd.c
index 3d403a7cd0..9a2796f0b7 100644
--- a/tools/libs/foreignmemory/freebsd.c
+++ b/tools/libs/foreignmemory/freebsd.c
@@ -119,6 +119,10 @@ int 
osdep_xenforeignmemory_map_resource(xenforeignmemory_handle *fmem,
     };
     int rc;
 
+    if ( !fres->addr && !fres->nr_frames )
+        /* Request for resource size.  Skip mmap(). */
+        goto skip_mmap;
+
     fres->addr = mmap(fres->addr, fres->nr_frames << PAGE_SHIFT,
                       fres->prot, fres->flags | MAP_SHARED, fmem->fd, 0);
     if ( fres->addr == MAP_FAILED )
@@ -126,6 +130,7 @@ int 
osdep_xenforeignmemory_map_resource(xenforeignmemory_handle *fmem,
 
     mr.addr = (uintptr_t)fres->addr;
 
+ skip_mmap:
     rc = ioctl(fmem->fd, IOCTL_PRIVCMD_MMAP_RESOURCE, &mr);
     if ( rc )
     {
@@ -136,13 +141,20 @@ int 
osdep_xenforeignmemory_map_resource(xenforeignmemory_handle *fmem,
         else
             errno = EOPNOTSUPP;
 
-        saved_errno = errno;
-        osdep_xenforeignmemory_unmap_resource(fmem, fres);
-        errno = saved_errno;
+        if ( fres->addr )
+        {
+            saved_errno = errno;
+            osdep_xenforeignmemory_unmap_resource(fmem, fres);
+            errno = saved_errno;
+        }
 
         return -1;
     }
 
+    /* If requesting size, copy back. */
+    if ( !fres->addr )
+        fres->nr_frames = mr.num;
+
     return 0;
 }
 
diff --git a/tools/libs/foreignmemory/libxenforeignmemory.map 
b/tools/libs/foreignmemory/libxenforeignmemory.map
index d5323c87d9..8aca341b99 100644
--- a/tools/libs/foreignmemory/libxenforeignmemory.map
+++ b/tools/libs/foreignmemory/libxenforeignmemory.map
@@ -19,3 +19,7 @@ VERS_1.3 {
                xenforeignmemory_map_resource;
                xenforeignmemory_unmap_resource;
 } VERS_1.2;
+VERS_1.4 {
+       global:
+               xenforeignmemory_resource_size;
+} VERS_1.3;
diff --git a/tools/libs/foreignmemory/linux.c b/tools/libs/foreignmemory/linux.c
index fe73d5ab72..d0eead1196 100644
--- a/tools/libs/foreignmemory/linux.c
+++ b/tools/libs/foreignmemory/linux.c
@@ -312,6 +312,10 @@ int osdep_xenforeignmemory_map_resource(
     };
     int rc;
 
+    if ( !fres->addr && !fres->nr_frames )
+        /* Request for resource size.  Skip mmap(). */
+        goto skip_mmap;
+
     fres->addr = mmap(fres->addr, fres->nr_frames << PAGE_SHIFT,
                       fres->prot, fres->flags | MAP_SHARED, fmem->fd, 0);
     if ( fres->addr == MAP_FAILED )
@@ -319,6 +323,7 @@ int osdep_xenforeignmemory_map_resource(
 
     mr.addr = (uintptr_t)fres->addr;
 
+ skip_mmap:
     rc = ioctl(fmem->fd, IOCTL_PRIVCMD_MMAP_RESOURCE, &mr);
     if ( rc )
     {
@@ -329,13 +334,20 @@ int osdep_xenforeignmemory_map_resource(
         else
             errno = EOPNOTSUPP;
 
-        saved_errno = errno;
-        (void)osdep_xenforeignmemory_unmap_resource(fmem, fres);
-        errno = saved_errno;
+        if ( fres->addr )
+        {
+            saved_errno = errno;
+            osdep_xenforeignmemory_unmap_resource(fmem, fres);
+            errno = saved_errno;
+        }
 
         return -1;
     }
 
+    /* If requesting size, copy back. */
+    if ( !fres->addr )
+        fres->nr_frames = mr.num;
+
     return 0;
 }
 
-- 
2.11.0