[Libguestfs] [PATCH nbdkit v4 13/15] data, memory: Implement extents.

[Richard W.M. Jones]

These plugins are both based on the same sparse array structure which
supports a simple implementation of extents.
---
 common/sparse/sparse.h  |  7 ++++++-
 common/sparse/sparse.c  | 29 ++++++++++++++++++++++++++++-
 plugins/data/data.c     | 16 +++++++++++++++-
 plugins/memory/memory.c | 16 +++++++++++++++-
 4 files changed, 64 insertions(+), 4 deletions(-)

diff --git a/common/sparse/sparse.h b/common/sparse/sparse.h
index 818d804..eb24a0b 100644
--- a/common/sparse/sparse.h
+++ b/common/sparse/sparse.h
@@ -1,5 +1,5 @@
 /* nbdkit
- * Copyright (C) 2017-2018 Red Hat Inc.
+ * Copyright (C) 2017-2019 Red Hat Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -87,4 +87,9 @@ extern void sparse_array_zero (struct sparse_array *sa,
                                uint32_t count, uint64_t offset)
   __attribute__((__nonnull__ (1)));
 
+/* Return information about allocated pages and holes. */
+extern int sparse_array_extents (struct sparse_array *sa,
+                                 uint32_t count, uint64_t offset,
+                                 struct nbdkit_extents *extents);
+
 #endif /* NBDKIT_SPARSE_H */
diff --git a/common/sparse/sparse.c b/common/sparse/sparse.c
index a5ace48..f388cd4 100644
--- a/common/sparse/sparse.c
+++ b/common/sparse/sparse.c
@@ -1,5 +1,5 @@
 /* nbdkit
- * Copyright (C) 2017-2018 Red Hat Inc.
+ * Copyright (C) 2017-2019 Red Hat Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -360,3 +360,30 @@ sparse_array_zero (struct sparse_array *sa, uint32_t count, uint64_t offset)
     offset += n;
   }
 }
+
+int
+sparse_array_extents (struct sparse_array *sa,
+                      uint32_t count, uint64_t offset,
+                      struct nbdkit_extents *extents)
+{
+  uint32_t n, type;
+  void *p;
+
+  while (count > 0) {
+    p = lookup (sa, offset, false, &n, NULL);
+
+    if (p == NULL)
+      type = NBDKIT_EXTENT_HOLE | NBDKIT_EXTENT_ZERO;
+    else
+      type = 0; /* allocated data */
+    if (nbdkit_add_extent (extents, offset, n, type) == -1)
+      return -1;
+
+    if (n > count)
+      n = count;
+    count -= n;
+    offset += n;
+  }
+
+  return 0;
+}
diff --git a/plugins/data/data.c b/plugins/data/data.c
index f9d3881..c5540f6 100644
--- a/plugins/data/data.c
+++ b/plugins/data/data.c
@@ -1,5 +1,5 @@
 /* nbdkit
- * Copyright (C) 2018 Red Hat Inc.
+ * Copyright (C) 2018-2019 Red Hat Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -378,6 +378,19 @@ data_trim (void *handle, uint32_t count, uint64_t offset)
   return 0;
 }
 
+/* Extents. */
+static int
+data_extents (void *handle, uint32_t count, uint64_t offset,
+              uint32_t flags, struct nbdkit_extents *extents)
+{
+  int r;
+
+  pthread_mutex_lock (&lock);
+  r = sparse_array_extents (sa, count, offset, extents);
+  pthread_mutex_unlock (&lock);
+  return r;
+}
+
 static struct nbdkit_plugin plugin = {
   .name              = "data",
   .version           = PACKAGE_VERSION,
@@ -394,6 +407,7 @@ static struct nbdkit_plugin plugin = {
   .pwrite            = data_pwrite,
   .zero              = data_zero,
   .trim              = data_trim,
+  .extents           = data_extents,
   /* In this plugin, errno is preserved properly along error return
    * paths from failed system calls.
    */
diff --git a/plugins/memory/memory.c b/plugins/memory/memory.c
index e27e127..741eaad 100644
--- a/plugins/memory/memory.c
+++ b/plugins/memory/memory.c
@@ -1,5 +1,5 @@
 /* nbdkit
- * Copyright (C) 2017-2018 Red Hat Inc.
+ * Copyright (C) 2017-2019 Red Hat Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -170,6 +170,19 @@ memory_trim (void *handle, uint32_t count, uint64_t offset)
   return 0;
 }
 
+/* Extents. */
+static int
+memory_extents (void *handle, uint32_t count, uint64_t offset,
+                uint32_t flags, struct nbdkit_extents *extents)
+{
+  int r;
+
+  pthread_mutex_lock (&lock);
+  r = sparse_array_extents (sa, count, offset, extents);
+  pthread_mutex_unlock (&lock);
+  return r;
+}
+
 static struct nbdkit_plugin plugin = {
   .name              = "memory",
   .version           = PACKAGE_VERSION,
@@ -185,6 +198,7 @@ static struct nbdkit_plugin plugin = {
   .pwrite            = memory_pwrite,
   .zero              = memory_zero,
   .trim              = memory_trim,
+  .extents           = memory_extents,
   /* In this plugin, errno is preserved properly along error return
    * paths from failed system calls.
    */
-- 
2.20.1