[RFC PATCH v2 5/6] drm/shmem: Add a helper to check object's page backing status

["Adrián Larumbe" <adrian.larumbe@collabora.com>]

Provide a helper function that lets shmem API users know whether a given
object is backed by physical pages, or else in the case of a sparse
shmem object, at least one of them is populated.

The obvious user is fdinfo, which needs to know an object's resident
status.

Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 18 ++++++++++++++++++
 include/drm/drm_gem_shmem_helper.h     |  2 ++
 2 files changed, 20 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 1bf33e5a1c4c..79ac7c7c953f 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -1033,6 +1033,24 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
 }
 EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_sg_table);
 
+/**
+ * drm_gem_shmem_is_populated - Tell whether the shem object is backed by
+ *                 at least one page of physical memory
+ * @shmem: shmem GEM object
+ *
+ * Returns:
+ * A boolean, where the 'true' value depends on at least one page being preset
+ * in a sparse object's xarray, or all the shmem file pages for PRIME buffers
+ * and regular shmem objects.
+ */
+bool drm_gem_shmem_is_populated(struct drm_gem_shmem_object *shmem)
+{
+	return (shmem->base.import_attach ||
+		(!shmem->sparse && shmem->pages) ||
+		(shmem->sparse && !xa_empty(&shmem->xapages)));
+}
+EXPORT_SYMBOL_GPL(drm_gem_shmem_is_populated);
+
 MODULE_DESCRIPTION("DRM SHMEM memory-management helpers");
 MODULE_IMPORT_NS("DMA_BUF");
 MODULE_LICENSE("GPL v2");
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index cbe4548e3ff6..60d2b8ef230b 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -302,6 +302,8 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
 int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev,
 			      struct drm_mode_create_dumb *args);
 
+bool drm_gem_shmem_is_populated(struct drm_gem_shmem_object *shmem);
+
 /**
  * DRM_GEM_SHMEM_DRIVER_OPS - Default shmem GEM operations
  *
-- 
2.48.1