[PATCH v3 08/10] nbd/server: introduce NBDExtentArray

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

Introduce NBDExtentArray class, to handle extents list creation in more
controlled way and with less OUT parameters in functions.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 nbd/server.c | 201 ++++++++++++++++++++++++++++-----------------------
 1 file changed, 109 insertions(+), 92 deletions(-)

diff --git a/nbd/server.c b/nbd/server.c
index a4b348eb32..cc722adc31 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1909,27 +1909,89 @@ static int coroutine_fn nbd_co_send_sparse_read(NBDClient *client,
     return ret;
 }
 
+typedef struct NBDExtentArray {
+    NBDExtent *extents;
+    unsigned int nb_alloc;
+    unsigned int count;
+    uint64_t total_length;
+    bool converted; /* extents are converted to BE, no more changes allowed */
+} NBDExtentArray;
+
+static NBDExtentArray *nbd_extent_array_new(unsigned int nb_alloc)
+{
+    NBDExtentArray *ea = g_new0(NBDExtentArray, 1);
+
+    ea->nb_alloc = nb_alloc;
+    ea->extents = g_new(NBDExtent, nb_alloc);
+
+    return ea;
+}
+
+static void nbd_extent_array_free(NBDExtentArray *ea)
+{
+    g_free(ea->extents);
+    g_free(ea);
+}
+G_DEFINE_AUTOPTR_CLEANUP_FUNC(NBDExtentArray, nbd_extent_array_free);
+
+/* Further modifications of the array after conversion are abandoned */
+static void nbd_extent_array_convert_to_be(NBDExtentArray *ea)
+{
+    int i;
+
+    if (ea->converted) {
+        return;
+    }
+    ea->converted = true;
+
+    for (i = 0; i < ea->count; i++) {
+        ea->extents[i].flags = cpu_to_be32(ea->extents[i].flags);
+        ea->extents[i].length = cpu_to_be32(ea->extents[i].length);
+    }
+}
+
 /*
- * Populate @extents from block status. Update @bytes to be the actual
- * length encoded (which may be smaller than the original), and update
- * @nb_extents to the number of extents used.
- *
- * Returns zero on success and -errno on bdrv_block_status_above failure.
+ * Add extent to NBDExtentArray. If extent can't be added (no available space),
+ * return -1.
+ * For safety, when returning -1 for the first time, the array is converted
+ * to BE and further modifications are abandoned.
  */
-static int blockstatus_to_extents(BlockDriverState *bs, uint64_t offset,
-                                  uint64_t *bytes, NBDExtent *extents,
-                                  unsigned int *nb_extents)
+static int nbd_extent_array_add(NBDExtentArray *ea,
+                                uint32_t length, uint32_t flags)
 {
-    uint64_t remaining_bytes = *bytes;
-    NBDExtent *extent = extents, *extents_end = extents + *nb_extents;
-    bool first_extent = true;
+    assert(!ea->converted);
+
+    if (!length) {
+        return 0;
+    }
+
+    /* Extend previous extent if flags are the same */
+    if (ea->count > 0 && flags == ea->extents[ea->count - 1].flags) {
+        ea->extents[ea->count - 1].length += length;
+        ea->total_length += length;
+        return 0;
+    }
+
+    if (ea->count >= ea->nb_alloc) {
+        nbd_extent_array_convert_to_be(ea);
+        return -1;
+    }
+
+    ea->total_length += length;
+    ea->extents[ea->count] = (NBDExtent) {.length = length, .flags = flags};
+    ea->count++;
 
-    assert(*nb_extents);
-    while (remaining_bytes) {
+    return 0;
+}
+
+static int blockstatus_to_extents(BlockDriverState *bs, uint64_t offset,
+                                  uint64_t bytes, NBDExtentArray *ea)
+{
+    while (bytes) {
         uint32_t flags;
         int64_t num;
-        int ret = bdrv_block_status_above(bs, NULL, offset, remaining_bytes,
-                                          &num, NULL, NULL);
+        int ret = bdrv_block_status_above(bs, NULL, offset, bytes, &num,
+                                          NULL, NULL);
 
         if (ret < 0) {
             return ret;
@@ -1938,60 +2000,37 @@ static int blockstatus_to_extents(BlockDriverState *bs, uint64_t offset,
         flags = (ret & BDRV_BLOCK_ALLOCATED ? 0 : NBD_STATE_HOLE) |
                 (ret & BDRV_BLOCK_ZERO      ? NBD_STATE_ZERO : 0);
 
-        if (first_extent) {
-            extent->flags = flags;
-            extent->length = num;
-            first_extent = false;
-        } else if (flags == extent->flags) {
-            /* extend current extent */
-            extent->length += num;
-        } else {
-            if (extent + 1 == extents_end) {
-                break;
-            }
-
-            /* start new extent */
-            extent++;
-            extent->flags = flags;
-            extent->length = num;
+        if (nbd_extent_array_add(ea, num, flags) < 0) {
+            return 0;
         }
-        offset += num;
-        remaining_bytes -= num;
-    }
-
-    extents_end = extent + 1;
 
-    for (extent = extents; extent < extents_end; extent++) {
-        extent->flags = cpu_to_be32(extent->flags);
-        extent->length = cpu_to_be32(extent->length);
+        offset += num;
+        bytes -= num;
     }
 
-    *bytes -= remaining_bytes;
-    *nb_extents = extents_end - extents;
-
     return 0;
 }
 
-/* nbd_co_send_extents
+/*
+ * nbd_co_send_extents
  *
- * @length is only for tracing purposes (and may be smaller or larger
- * than the client's original request). @last controls whether
- * NBD_REPLY_FLAG_DONE is sent. @extents should already be in
- * big-endian format.
+ * @ea is converted to BE by the function
+ * @last controls whether NBD_REPLY_FLAG_DONE is sent.
  */
 static int nbd_co_send_extents(NBDClient *client, uint64_t handle,
-                               NBDExtent *extents, unsigned int nb_extents,
-                               uint64_t length, bool last,
-                               uint32_t context_id, Error **errp)
+                               NBDExtentArray *ea,
+                               bool last, uint32_t context_id, Error **errp)
 {
     NBDStructuredMeta chunk;
-
     struct iovec iov[] = {
         {.iov_base = &chunk, .iov_len = sizeof(chunk)},
-        {.iov_base = extents, .iov_len = nb_extents * sizeof(extents[0])}
+        {.iov_base = ea->extents, .iov_len = ea->count * sizeof(ea->extents[0])}
     };
 
-    trace_nbd_co_send_extents(handle, nb_extents, context_id, length, last);
+    nbd_extent_array_convert_to_be(ea);
+
+    trace_nbd_co_send_extents(handle, ea->count, context_id, ea->total_length,
+                              last);
     set_be_chunk(&chunk.h, last ? NBD_REPLY_FLAG_DONE : 0,
                  NBD_REPLY_TYPE_BLOCK_STATUS,
                  handle, sizeof(chunk) - sizeof(chunk.h) + iov[1].iov_len);
@@ -2009,39 +2048,27 @@ static int nbd_co_send_block_status(NBDClient *client, uint64_t handle,
 {
     int ret;
     unsigned int nb_extents = dont_fragment ? 1 : NBD_MAX_BLOCK_STATUS_EXTENTS;
-    NBDExtent *extents = g_new(NBDExtent, nb_extents);
-    uint64_t final_length = length;
+    g_autoptr(NBDExtentArray) ea = nbd_extent_array_new(nb_extents);
 
-    ret = blockstatus_to_extents(bs, offset, &final_length, extents,
-                                 &nb_extents);
+    ret = blockstatus_to_extents(bs, offset, length, ea);
     if (ret < 0) {
-        g_free(extents);
         return nbd_co_send_structured_error(
                 client, handle, -ret, "can't get block status", errp);
     }
 
-    ret = nbd_co_send_extents(client, handle, extents, nb_extents,
-                              final_length, last, context_id, errp);
-
-    g_free(extents);
-
-    return ret;
+    return nbd_co_send_extents(client, handle, ea, last, context_id, errp);
 }
 
 /*
- * Populate @extents from a dirty bitmap. Unless @dont_fragment, the
- * final extent may exceed the original @length. Store in @length the
- * byte length encoded (which may be smaller or larger than the
- * original), and return the number of extents used.
+ * Populate @ea from a dirty bitmap. Unless @dont_fragment, the
+ * final extent may exceed the original @length.
  */
-static unsigned int bitmap_to_extents(BdrvDirtyBitmap *bitmap, uint64_t offset,
-                                      uint64_t *length, NBDExtent *extents,
-                                      unsigned int nb_extents,
-                                      bool dont_fragment)
+static void bitmap_to_extents(BdrvDirtyBitmap *bitmap,
+                              uint64_t offset, uint64_t length,
+                              NBDExtentArray *ea, bool dont_fragment)
 {
     uint64_t begin = offset, end = offset;
-    uint64_t overall_end = offset + *length;
-    unsigned int i = 0;
+    uint64_t overall_end = offset + length;
     BdrvDirtyBitmapIter *it;
     bool dirty;
 
@@ -2050,8 +2077,7 @@ static unsigned int bitmap_to_extents(BdrvDirtyBitmap *bitmap, uint64_t offset,
     it = bdrv_dirty_iter_new(bitmap);
     dirty = bdrv_dirty_bitmap_get_locked(bitmap, offset);
 
-    assert(begin < overall_end && nb_extents);
-    while (begin < overall_end && i < nb_extents) {
+    while (begin < overall_end) {
         bool next_dirty = !dirty;
 
         if (dirty) {
@@ -2071,9 +2097,10 @@ static unsigned int bitmap_to_extents(BdrvDirtyBitmap *bitmap, uint64_t offset,
             end = overall_end;
         }
 
-        extents[i].length = cpu_to_be32(end - begin);
-        extents[i].flags = cpu_to_be32(dirty ? NBD_STATE_DIRTY : 0);
-        i++;
+        if (nbd_extent_array_add(ea, end - begin,
+                                 dirty ? NBD_STATE_DIRTY : 0) < 0) {
+            break;
+        }
         begin = end;
         dirty = next_dirty;
     }
@@ -2083,8 +2110,6 @@ static unsigned int bitmap_to_extents(BdrvDirtyBitmap *bitmap, uint64_t offset,
     bdrv_dirty_bitmap_unlock(bitmap);
 
     assert(offset < end);
-    *length = end - offset;
-    return i;
 }
 
 static int nbd_co_send_bitmap(NBDClient *client, uint64_t handle,
@@ -2092,20 +2117,12 @@ static int nbd_co_send_bitmap(NBDClient *client, uint64_t handle,
                               uint32_t length, bool dont_fragment, bool last,
                               uint32_t context_id, Error **errp)
 {
-    int ret;
     unsigned int nb_extents = dont_fragment ? 1 : NBD_MAX_BLOCK_STATUS_EXTENTS;
-    NBDExtent *extents = g_new(NBDExtent, nb_extents);
-    uint64_t final_length = length;
+    g_autoptr(NBDExtentArray) ea = nbd_extent_array_new(nb_extents);
 
-    nb_extents = bitmap_to_extents(bitmap, offset, &final_length, extents,
-                                   nb_extents, dont_fragment);
+    bitmap_to_extents(bitmap, offset, length, ea, dont_fragment);
 
-    ret = nbd_co_send_extents(client, handle, extents, nb_extents,
-                              final_length, last, context_id, errp);
-
-    g_free(extents);
-
-    return ret;
+    return nbd_co_send_extents(client, handle, ea, last, context_id, errp);
 }
 
 /* nbd_co_receive_request
-- 
2.21.0