[Libguestfs] [PATCH nbdkit 5/9] offset: Implement mapping of extents.

[Richard W.M. Jones]

Allows you to safely use nbdkit-offset-filter on top of a plugin
supporting extents.
---
 filters/offset/offset.c | 43 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/filters/offset/offset.c b/filters/offset/offset.c
index 058571d..4e3f74d 100644
--- a/filters/offset/offset.c
+++ b/filters/offset/offset.c
@@ -37,6 +37,7 @@
 #include <stdlib.h>
 #include <stdint.h>
 #include <string.h>
+#include <assert.h>
 
 #include <nbdkit-filter.h>
 
@@ -132,6 +133,47 @@ offset_zero (struct nbdkit_next_ops *next_ops, void *nxdata,
   return next_ops->zero (nxdata, count, offs + offset, flags, err);
 }
 
+/* Extents. */
+static int
+subtract_offset (uint64_t offs, uint64_t length, uint32_t type,
+                 void *vp)
+{
+  struct nbdkit_extents_map *extents_map = vp;
+
+  assert (offs >= offset);
+  offs -= offset;
+  return nbdkit_extent_add (extents_map, offs, length, type);
+}
+
+static int
+offset_extents (struct nbdkit_next_ops *next_ops, void *nxdata,
+                void *handle, uint32_t count, uint64_t offs, uint32_t flags,
+                struct nbdkit_extents_map *extents_map,
+                int *err)
+{
+  struct nbdkit_extents_map *map2;
+
+  map2 = nbdkit_extents_new ();
+  if (map2 == NULL)
+    return -1;
+  if (next_ops->extents (nxdata, count, offs + offset,
+                         flags, map2, err) == -1) {
+    nbdkit_extents_free (map2);
+    return -1;
+  }
+
+  /* Transform offsets in map2, return result in extents_map. */
+  if (nbdkit_extents_foreach (map2, subtract_offset, extents_map,
+                              NBDKIT_EXTENTS_FOREACH_FLAG_RANGE,
+                              offset, range) == -1) {
+    nbdkit_extents_free (map2);
+    return -1;
+  }
+  nbdkit_extents_free (map2);
+
+  return 0;
+}
+
 static struct nbdkit_filter filter = {
   .name              = "offset",
   .longname          = "nbdkit offset filter",
@@ -144,6 +186,7 @@ static struct nbdkit_filter filter = {
   .pwrite            = offset_pwrite,
   .trim              = offset_trim,
   .zero              = offset_zero,
+  .extents           = offset_extents,
 };
 
 NBDKIT_REGISTER_FILTER(filter)
-- 
2.20.1