Merge remote-tracking branch 'remotes/ericb/tags/pull-nbd-2018-06-20-v2' into staging

nbd patches for 2018-06-20

Add experimental x-nbd-server-add-bitmap to expose a disabled
bitmap over NBD, in preparation for a pull model incremental
backup scheme. Also fix a corner case protocol issue with
NBD_CMD_BLOCK_STATUS, and add new NBD_CMD_CACHE.

- Eric Blake: tests: Simplify .gitignore
- Eric Blake: nbd/server: Reject 0-length block status request
- Vladimir Sementsov-Ogievskiy: 0/6 NBD export bitmaps
- Vladimir Sementsov-Ogievskiy: nbd/server: introduce NBD_CMD_CACHE

# gpg: Signature made Thu 21 Jun 2018 15:53:55 BST
# gpg:                using RSA key A7A16B4A2527436A
# gpg: Good signature from "Eric Blake <eblake@redhat.com>"
# gpg:                 aka "Eric Blake (Free Software Programmer) <ebb9@byu.net>"
# gpg:                 aka "[jpeg image of size 6874]"
# Primary key fingerprint: 71C2 CC22 B1C4 6029 27D2  F3AA A7A1 6B4A 2527 436A

* remotes/ericb/tags/pull-nbd-2018-06-20-v2:
  nbd/server: introduce NBD_CMD_CACHE
  docs/interop: add nbd.txt
  qapi: new qmp command nbd-server-add-bitmap
  nbd/server: implement dirty bitmap export
  nbd/server: add nbd_meta_empty_or_pattern helper
  nbd/server: refactor NBDExportMetaContexts
  nbd/server: fix trace
  nbd/server: Reject 0-length block status request
  tests: Simplify .gitignore

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

9 files changed, 433 insertions, 144 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index da91501c7a..efb17e6ac0 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1972,6 +1972,7 @@ F: nbd/
 F: include/block/nbd*
 F: qemu-nbd.*
 F: blockdev-nbd.c
+F: docs/interop/nbd.txt
 T: git git://repo.or.cz/qemu/ericb.git nbd
 
 NFS
diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index 65a84739ed..1ef11041a7 100644
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -220,3 +220,26 @@ void qmp_nbd_server_stop(Error **errp)
     nbd_server_free(nbd_server);
     nbd_server = NULL;
 }
+
+void qmp_x_nbd_server_add_bitmap(const char *name, const char *bitmap,
+                                 bool has_bitmap_export_name,
+                                 const char *bitmap_export_name,
+                                 Error **errp)
+{
+    NBDExport *exp;
+
+    if (!nbd_server) {
+        error_setg(errp, "NBD server not running");
+        return;
+    }
+
+    exp = nbd_export_find(name);
+    if (exp == NULL) {
+        error_setg(errp, "Export '%s' is not found", name);
+        return;
+    }
+
+    nbd_export_bitmap(exp, bitmap,
+                      has_bitmap_export_name ? bitmap_export_name : bitmap,
+                      errp);
+}
diff --git a/docs/interop/nbd.txt b/docs/interop/nbd.txt
new file mode 100644
index 0000000000..77b5f45911
--- /dev/null
+++ b/docs/interop/nbd.txt
@@ -0,0 +1,38 @@
+Qemu supports the NBD protocol, and has an internal NBD client (see
+block/nbd.c), an internal NBD server (see blockdev-nbd.c), and an
+external NBD server tool (see qemu-nbd.c). The common code is placed
+in nbd/*.
+
+The NBD protocol is specified here:
+https://github.com/NetworkBlockDevice/nbd/blob/master/doc/proto.md
+
+The following paragraphs describe some specific properties of NBD
+protocol realization in Qemu.
+
+= Metadata namespaces =
+
+Qemu supports the "base:allocation" metadata context as defined in the
+NBD protocol specification, and also defines an additional metadata
+namespace "qemu".
+
+
+== "qemu" namespace ==
+
+The "qemu" namespace currently contains only one type of context,
+related to exposing the contents of a dirty bitmap alongside the
+associated disk contents.  That context has the following form:
+
+    qemu:dirty-bitmap:<dirty-bitmap-export-name>
+
+Each dirty-bitmap metadata context defines only one flag for extents
+in reply for NBD_CMD_BLOCK_STATUS:
+
+    bit 0: NBD_STATE_DIRTY, means that the extent is "dirty"
+
+For NBD_OPT_LIST_META_CONTEXT the following queries are supported
+in addition to "qemu:dirty-bitmap:<dirty-bitmap-export-name>":
+
+* "qemu:" - returns list of all available metadata contexts in the
+            namespace.
+* "qemu:dirty-bitmap:" - returns list of all available dirty-bitmap
+                         metadata contexts.
diff --git a/include/block/nbd.h b/include/block/nbd.h
index fcdcd54502..daaeae61bf 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -135,6 +135,7 @@ typedef struct NBDExtent {
 #define NBD_FLAG_SEND_TRIM         (1 << 5) /* Send TRIM (discard) */
 #define NBD_FLAG_SEND_WRITE_ZEROES (1 << 6) /* Send WRITE_ZEROES */
 #define NBD_FLAG_SEND_DF           (1 << 7) /* Send DF (Do not Fragment) */
+#define NBD_FLAG_SEND_CACHE        (1 << 8) /* Send CACHE (prefetch) */
 
 /* New-style handshake (global) flags, sent from server to client, and
    control what will happen during handshake phase. */
@@ -195,7 +196,7 @@ enum {
     NBD_CMD_DISC = 2,
     NBD_CMD_FLUSH = 3,
     NBD_CMD_TRIM = 4,
-    /* 5 reserved for failed experiment NBD_CMD_CACHE */
+    NBD_CMD_CACHE = 5,
     NBD_CMD_WRITE_ZEROES = 6,
     NBD_CMD_BLOCK_STATUS = 7,
 };
@@ -229,11 +230,13 @@ enum {
 #define NBD_REPLY_TYPE_ERROR         NBD_REPLY_ERR(1)
 #define NBD_REPLY_TYPE_ERROR_OFFSET  NBD_REPLY_ERR(2)
 
-/* Flags for extents (NBDExtent.flags) of NBD_REPLY_TYPE_BLOCK_STATUS,
- * for base:allocation meta context */
+/* Extent flags for base:allocation in NBD_REPLY_TYPE_BLOCK_STATUS */
 #define NBD_STATE_HOLE (1 << 0)
 #define NBD_STATE_ZERO (1 << 1)
 
+/* Extent flags for qemu:dirty-bitmap in NBD_REPLY_TYPE_BLOCK_STATUS */
+#define NBD_STATE_DIRTY (1 << 0)
+
 static inline bool nbd_reply_type_is_error(int type)
 {
     return type & (1 << 15);
@@ -315,6 +318,8 @@ void nbd_client_put(NBDClient *client);
 void nbd_server_start(SocketAddress *addr, const char *tls_creds,
                       Error **errp);
 
+void nbd_export_bitmap(NBDExport *exp, const char *bitmap,
+                       const char *bitmap_export_name, Error **errp);
 
 /* nbd_read
  * Reads @size bytes from @ioc. Returns 0 on success.
diff --git a/nbd/common.c b/nbd/common.c
index 8c95c1d606..41f5ed8d9f 100644
--- a/nbd/common.c
+++ b/nbd/common.c
@@ -148,6 +148,8 @@ const char *nbd_cmd_lookup(uint16_t cmd)
         return "flush";
     case NBD_CMD_TRIM:
         return "trim";
+    case NBD_CMD_CACHE:
+        return "cache";
     case NBD_CMD_WRITE_ZEROES:
         return "write zeroes";
     case NBD_CMD_BLOCK_STATUS:
diff --git a/nbd/server.c b/nbd/server.c
index 9e1f227178..274604609f 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -23,6 +23,13 @@
 #include "nbd-internal.h"
 
 #define NBD_META_ID_BASE_ALLOCATION 0
+#define NBD_META_ID_DIRTY_BITMAP 1
+
+/* NBD_MAX_BITMAP_EXTENTS: 1 mb of extents data. An empirical
+ * constant. If an increase is needed, note that the NBD protocol
+ * recommends no larger than 32 mb, so that the client won't consider
+ * the reply as a denial of service attack. */
+#define NBD_MAX_BITMAP_EXTENTS (0x100000 / 8)
 
 static int system_errno_to_nbd_errno(int err)
 {
@@ -80,6 +87,9 @@ struct NBDExport {
 
     BlockBackend *eject_notifier_blk;
     Notifier eject_notifier;
+
+    BdrvDirtyBitmap *export_bitmap;
+    char *export_bitmap_context;
 };
 
 static QTAILQ_HEAD(, NBDExport) exports = QTAILQ_HEAD_INITIALIZER(exports);
@@ -88,10 +98,11 @@ static QTAILQ_HEAD(, NBDExport) exports = QTAILQ_HEAD_INITIALIZER(exports);
  * as selected by NBD_OPT_SET_META_CONTEXT. Also used for
  * NBD_OPT_LIST_META_CONTEXT. */
 typedef struct NBDExportMetaContexts {
-    char export_name[NBD_MAX_NAME_SIZE + 1];
+    NBDExport *exp;
     bool valid; /* means that negotiation of the option finished without
                    errors */
     bool base_allocation; /* export base:allocation context (block status) */
+    bool bitmap; /* export qemu:dirty-bitmap:<export bitmap name> */
 } NBDExportMetaContexts;
 
 struct NBDClient {
@@ -399,10 +410,9 @@ static int nbd_negotiate_handle_list(NBDClient *client, Error **errp)
     return nbd_negotiate_send_rep(client, NBD_REP_ACK, errp);
 }
 
-static void nbd_check_meta_export_name(NBDClient *client)
+static void nbd_check_meta_export(NBDClient *client)
 {
-    client->export_meta.valid &= !strcmp(client->exp->name,
-                                         client->export_meta.export_name);
+    client->export_meta.valid &= client->exp == client->export_meta.exp;
 }
 
 /* Send a reply to NBD_OPT_EXPORT_NAME.
@@ -456,7 +466,7 @@ static int nbd_negotiate_handle_export_name(NBDClient *client,
 
     QTAILQ_INSERT_TAIL(&client->exp->clients, client, next);
     nbd_export_get(client->exp);
-    nbd_check_meta_export_name(client);
+    nbd_check_meta_export(client);
 
     return 0;
 }
@@ -650,7 +660,7 @@ static int nbd_negotiate_handle_info(NBDClient *client, uint16_t myflags,
         client->exp = exp;
         QTAILQ_INSERT_TAIL(&client->exp->clients, client, next);
         nbd_export_get(client->exp);
-        nbd_check_meta_export_name(client);
+        nbd_check_meta_export(client);
         rc = 1;
     }
     return rc;
@@ -734,45 +744,135 @@ static int nbd_negotiate_send_meta_context(NBDClient *client,
     return qio_channel_writev_all(client->ioc, iov, 2, errp) < 0 ? -EIO : 0;
 }
 
+/* Read strlen(@pattern) bytes, and set @match to true if they match @pattern.
+ * @match is never set to false.
+ *
+ * Return -errno on I/O error, 0 if option was completely handled by
+ * sending a reply about inconsistent lengths, or 1 on success.
+ *
+ * Note: return code = 1 doesn't mean that we've read exactly @pattern.
+ * It only means that there are no errors.
+ */
+static int nbd_meta_pattern(NBDClient *client, const char *pattern, bool *match,
+                            Error **errp)
+{
+    int ret;
+    char *query;
+    size_t len = strlen(pattern);
+
+    assert(len);
+
+    query = g_malloc(len);
+    ret = nbd_opt_read(client, query, len, errp);
+    if (ret <= 0) {
+        g_free(query);
+        return ret;
+    }
+
+    if (strncmp(query, pattern, len) == 0) {
+        trace_nbd_negotiate_meta_query_parse(pattern);
+        *match = true;
+    } else {
+        trace_nbd_negotiate_meta_query_skip("pattern not matched");
+    }
+    g_free(query);
+
+    return 1;
+}
+
+/*
+ * Read @len bytes, and set @match to true if they match @pattern, or if @len
+ * is 0 and the client is performing _LIST_. @match is never set to false.
+ *
+ * Return -errno on I/O error, 0 if option was completely handled by
+ * sending a reply about inconsistent lengths, or 1 on success.
+ *
+ * Note: return code = 1 doesn't mean that we've read exactly @pattern.
+ * It only means that there are no errors.
+ */
+static int nbd_meta_empty_or_pattern(NBDClient *client, const char *pattern,
+                                     uint32_t len, bool *match, Error **errp)
+{
+    if (len == 0) {
+        if (client->opt == NBD_OPT_LIST_META_CONTEXT) {
+            *match = true;
+        }
+        trace_nbd_negotiate_meta_query_parse("empty");
+        return 1;
+    }
+
+    if (len != strlen(pattern)) {
+        trace_nbd_negotiate_meta_query_skip("different lengths");
+        return nbd_opt_skip(client, len, errp);
+    }
+
+    return nbd_meta_pattern(client, pattern, match, errp);
+}
+
 /* nbd_meta_base_query
  *
- * Handle query to 'base' namespace. For now, only base:allocation context is
- * available in it.  'len' is the amount of text remaining to be read from
+ * Handle queries to 'base' namespace. For now, only the base:allocation
+ * context is available.  'len' is the amount of text remaining to be read from
  * the current name, after the 'base:' portion has been stripped.
  *
  * Return -errno on I/O error, 0 if option was completely handled by
- * sending a reply about inconsistent lengths, or 1 on success. */
+ * sending a reply about inconsistent lengths, or 1 on success.
+ */
 static int nbd_meta_base_query(NBDClient *client, NBDExportMetaContexts *meta,
                                uint32_t len, Error **errp)
 {
+    return nbd_meta_empty_or_pattern(client, "allocation", len,
+                                     &meta->base_allocation, errp);
+}
+
+/* nbd_meta_bitmap_query
+ *
+ * Handle query to 'qemu:' namespace.
+ * @len is the amount of text remaining to be read from the current name, after
+ * the 'qemu:' portion has been stripped.
+ *
+ * Return -errno on I/O error, 0 if option was completely handled by
+ * sending a reply about inconsistent lengths, or 1 on success. */
+static int nbd_meta_qemu_query(NBDClient *client, NBDExportMetaContexts *meta,
+                               uint32_t len, Error **errp)
+{
+    bool dirty_bitmap = false;
+    size_t dirty_bitmap_len = strlen("dirty-bitmap:");
     int ret;
-    char query[sizeof("allocation") - 1];
-    size_t alen = strlen("allocation");
+
+    if (!meta->exp->export_bitmap) {
+        trace_nbd_negotiate_meta_query_skip("no dirty-bitmap exported");
+        return nbd_opt_skip(client, len, errp);
+    }
 
     if (len == 0) {
         if (client->opt == NBD_OPT_LIST_META_CONTEXT) {
-            meta->base_allocation = true;
+            meta->bitmap = true;
         }
-        trace_nbd_negotiate_meta_query_parse("base:");
+        trace_nbd_negotiate_meta_query_parse("empty");
         return 1;
     }
 
-    if (len != alen) {
-        trace_nbd_negotiate_meta_query_skip("not base:allocation");
+    if (len < dirty_bitmap_len) {
+        trace_nbd_negotiate_meta_query_skip("not dirty-bitmap:");
         return nbd_opt_skip(client, len, errp);
     }
 
-    ret = nbd_opt_read(client, query, len, errp);
+    len -= dirty_bitmap_len;
+    ret = nbd_meta_pattern(client, "dirty-bitmap:", &dirty_bitmap, errp);
     if (ret <= 0) {
         return ret;
     }
-
-    if (strncmp(query, "allocation", alen) == 0) {
-        meta->base_allocation = true;
+    if (!dirty_bitmap) {
+        trace_nbd_negotiate_meta_query_skip("not dirty-bitmap:");
+        return nbd_opt_skip(client, len, errp);
     }
 
-    trace_nbd_negotiate_meta_query_parse("base:allocation");
-    return 1;
+    trace_nbd_negotiate_meta_query_parse("dirty-bitmap:");
+
+    return nbd_meta_empty_or_pattern(
+            client, meta->exp->export_bitmap_context +
+            strlen("qemu:dirty_bitmap:"), len, &meta->bitmap, errp);
 }
 
 /* nbd_negotiate_meta_query
@@ -790,9 +890,14 @@ static int nbd_meta_base_query(NBDClient *client, NBDExportMetaContexts *meta,
 static int nbd_negotiate_meta_query(NBDClient *client,
                                     NBDExportMetaContexts *meta, Error **errp)
 {
+    /*
+     * Both 'qemu' and 'base' namespaces have length = 5 including a
+     * colon. If another length namespace is later introduced, this
+     * should certainly be refactored.
+     */
     int ret;
-    char query[sizeof("base:") - 1];
-    size_t baselen = strlen("base:");
+    size_t ns_len = 5;
+    char ns[5];
     uint32_t len;
 
     ret = nbd_opt_read(client, &len, sizeof(len), errp);
@@ -801,24 +906,27 @@ static int nbd_negotiate_meta_query(NBDClient *client,
     }
     cpu_to_be32s(&len);
 
-    /* The only supported namespace for now is 'base'. So query should start
-     * with 'base:'. Otherwise, we can ignore it and skip the remainder. */
-    if (len < baselen) {
+    if (len < ns_len) {
         trace_nbd_negotiate_meta_query_skip("length too short");
         return nbd_opt_skip(client, len, errp);
     }
 
-    len -= baselen;
-    ret = nbd_opt_read(client, query, baselen, errp);
+    len -= ns_len;
+    ret = nbd_opt_read(client, ns, ns_len, errp);
     if (ret <= 0) {
         return ret;
     }
-    if (strncmp(query, "base:", baselen) != 0) {
-        trace_nbd_negotiate_meta_query_skip("not for base: namespace");
-        return nbd_opt_skip(client, len, errp);
+
+    if (!strncmp(ns, "base:", ns_len)) {
+        trace_nbd_negotiate_meta_query_parse("base:");
+        return nbd_meta_base_query(client, meta, len, errp);
+    } else if (!strncmp(ns, "qemu:", ns_len)) {
+        trace_nbd_negotiate_meta_query_parse("qemu:");
+        return nbd_meta_qemu_query(client, meta, len, errp);
     }
 
-    return nbd_meta_base_query(client, meta, len, errp);
+    trace_nbd_negotiate_meta_query_skip("unknown namespace");
+    return nbd_opt_skip(client, len, errp);
 }
 
 /* nbd_negotiate_meta_queries
@@ -829,7 +937,7 @@ static int nbd_negotiate_meta_queries(NBDClient *client,
                                       NBDExportMetaContexts *meta, Error **errp)
 {
     int ret;
-    NBDExport *exp;
+    char export_name[NBD_MAX_NAME_SIZE + 1];
     NBDExportMetaContexts local_meta;
     uint32_t nb_queries;
     int i;
@@ -848,15 +956,15 @@ static int nbd_negotiate_meta_queries(NBDClient *client,
 
     memset(meta, 0, sizeof(*meta));
 
-    ret = nbd_opt_read_name(client, meta->export_name, NULL, errp);
+    ret = nbd_opt_read_name(client, export_name, NULL, errp);
     if (ret <= 0) {
         return ret;
     }
 
-    exp = nbd_export_find(meta->export_name);
-    if (exp == NULL) {
+    meta->exp = nbd_export_find(export_name);
+    if (meta->exp == NULL) {
         return nbd_opt_drop(client, NBD_REP_ERR_UNKNOWN, errp,
-                            "export '%s' not present", meta->export_name);
+                            "export '%s' not present", export_name);
     }
 
     ret = nbd_opt_read(client, &nb_queries, sizeof(nb_queries), errp);
@@ -865,7 +973,7 @@ static int nbd_negotiate_meta_queries(NBDClient *client,
     }
     cpu_to_be32s(&nb_queries);
     trace_nbd_negotiate_meta_context(nbd_opt_lookup(client->opt),
-                                     meta->export_name, nb_queries);
+                                     export_name, nb_queries);
 
     if (client->opt == NBD_OPT_LIST_META_CONTEXT && !nb_queries) {
         /* enable all known contexts */
@@ -888,6 +996,16 @@ static int nbd_negotiate_meta_queries(NBDClient *client,
         }
     }
 
+    if (meta->bitmap) {
+        ret = nbd_negotiate_send_meta_context(client,
+                                              meta->exp->export_bitmap_context,
+                                              NBD_META_ID_DIRTY_BITMAP,
+                                              errp);
+        if (ret < 0) {
+            return ret;
+        }
+    }
+
     ret = nbd_negotiate_send_rep(client, NBD_REP_ACK, errp);
     if (ret == 0) {
         meta->valid = true;
@@ -1134,7 +1252,7 @@ static coroutine_fn int nbd_negotiate(NBDClient *client, Error **errp)
     int ret;
     const uint16_t myflags = (NBD_FLAG_HAS_FLAGS | NBD_FLAG_SEND_TRIM |
                               NBD_FLAG_SEND_FLUSH | NBD_FLAG_SEND_FUA |
-                              NBD_FLAG_SEND_WRITE_ZEROES);
+                              NBD_FLAG_SEND_WRITE_ZEROES | NBD_FLAG_SEND_CACHE);
     bool oldStyle;
 
     /* Old style negotiation header, no room for options
@@ -1516,6 +1634,11 @@ void nbd_export_put(NBDExport *exp)
             exp->blk = NULL;
         }
 
+        if (exp->export_bitmap) {
+            bdrv_dirty_bitmap_set_qmp_locked(exp->export_bitmap, false);
+            g_free(exp->export_bitmap_context);
+        }
+
         g_free(exp);
     }
 }
@@ -1757,9 +1880,15 @@ static int blockstatus_to_extent_be(BlockDriverState *bs, uint64_t offset,
 }
 
 /* nbd_co_send_extents
- * @extents should be in big-endian */
+ *
+ * @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.
+ */
 static int nbd_co_send_extents(NBDClient *client, uint64_t handle,
-                               NBDExtent *extents, unsigned nb_extents,
+                               NBDExtent *extents, unsigned int nb_extents,
+                               uint64_t length, bool last,
                                uint32_t context_id, Error **errp)
 {
     NBDStructuredMeta chunk;
@@ -1769,7 +1898,9 @@ static int nbd_co_send_extents(NBDClient *client, uint64_t handle,
         {.iov_base = extents, .iov_len = nb_extents * sizeof(extents[0])}
     };
 
-    set_be_chunk(&chunk.h, NBD_REPLY_FLAG_DONE, NBD_REPLY_TYPE_BLOCK_STATUS,
+    trace_nbd_co_send_extents(handle, nb_extents, context_id, 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);
     stl_be_p(&chunk.context_id, context_id);
 
@@ -1779,8 +1910,8 @@ static int nbd_co_send_extents(NBDClient *client, uint64_t handle,
 /* Get block status from the exported device and send it to the client */
 static int nbd_co_send_block_status(NBDClient *client, uint64_t handle,
                                     BlockDriverState *bs, uint64_t offset,
-                                    uint64_t length, uint32_t context_id,
-                                    Error **errp)
+                                    uint64_t length, bool last,
+                                    uint32_t context_id, Error **errp)
 {
     int ret;
     NBDExtent extent;
@@ -1791,7 +1922,84 @@ static int nbd_co_send_block_status(NBDClient *client, uint64_t handle,
                 client, handle, -ret, "can't get block status", errp);
     }
 
-    return nbd_co_send_extents(client, handle, &extent, 1, context_id, errp);
+    return nbd_co_send_extents(client, handle, &extent, 1, length, 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.
+ */
+static unsigned int bitmap_to_extents(BdrvDirtyBitmap *bitmap, uint64_t offset,
+                                      uint64_t *length, NBDExtent *extents,
+                                      unsigned int nb_extents,
+                                      bool dont_fragment)
+{
+    uint64_t begin = offset, end;
+    uint64_t overall_end = offset + *length;
+    unsigned int i = 0;
+    BdrvDirtyBitmapIter *it;
+    bool dirty;
+
+    bdrv_dirty_bitmap_lock(bitmap);
+
+    it = bdrv_dirty_iter_new(bitmap);
+    dirty = bdrv_get_dirty_locked(NULL, bitmap, offset);
+
+    assert(begin < overall_end && nb_extents);
+    while (begin < overall_end && i < nb_extents) {
+        if (dirty) {
+            end = bdrv_dirty_bitmap_next_zero(bitmap, begin);
+        } else {
+            bdrv_set_dirty_iter(it, begin);
+            end = bdrv_dirty_iter_next(it);
+        }
+        if (end == -1 || end - begin > UINT32_MAX) {
+            /* Cap to an aligned value < 4G beyond begin. */
+            end = MIN(bdrv_dirty_bitmap_size(bitmap),
+                      begin + UINT32_MAX + 1 -
+                      bdrv_dirty_bitmap_granularity(bitmap));
+        }
+        if (dont_fragment && end > overall_end) {
+            end = overall_end;
+        }
+
+        extents[i].length = cpu_to_be32(end - begin);
+        extents[i].flags = cpu_to_be32(dirty ? NBD_STATE_DIRTY : 0);
+        i++;
+        begin = end;
+        dirty = !dirty;
+    }
+
+    bdrv_dirty_iter_free(it);
+
+    bdrv_dirty_bitmap_unlock(bitmap);
+
+    *length = end - offset;
+    return i;
+}
+
+static int nbd_co_send_bitmap(NBDClient *client, uint64_t handle,
+                              BdrvDirtyBitmap *bitmap, uint64_t offset,
+                              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_BITMAP_EXTENTS;
+    NBDExtent *extents = g_new(NBDExtent, nb_extents);
+    uint64_t final_length = length;
+
+    nb_extents = bitmap_to_extents(bitmap, offset, &final_length, extents,
+                                   nb_extents, dont_fragment);
+
+    ret = nbd_co_send_extents(client, handle, extents, nb_extents,
+                              final_length, last, context_id, errp);
+
+    g_free(extents);
+
+    return ret;
 }
 
 /* nbd_co_receive_request
@@ -1826,7 +2034,9 @@ static int nbd_co_receive_request(NBDRequestData *req, NBDRequest *request,
         return -EIO;
     }
 
-    if (request->type == NBD_CMD_READ || request->type == NBD_CMD_WRITE) {
+    if (request->type == NBD_CMD_READ || request->type == NBD_CMD_WRITE ||
+        request->type == NBD_CMD_CACHE)
+    {
         if (request->len > NBD_MAX_BUFFER_SIZE) {
             error_setg(errp, "len (%" PRIu32" ) is larger than max len (%u)",
                        request->len, NBD_MAX_BUFFER_SIZE);
@@ -1911,7 +2121,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *client, NBDRequest *request,
     int ret;
     NBDExport *exp = client->exp;
 
-    assert(request->type == NBD_CMD_READ);
+    assert(request->type == NBD_CMD_READ || request->type == NBD_CMD_CACHE);
 
     /* XXX: NBD Protocol only documents use of FUA with WRITE */
     if (request->flags & NBD_CMD_FLAG_FUA) {
@@ -1930,7 +2140,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *client, NBDRequest *request,
 
     ret = blk_pread(exp->blk, request->from + exp->dev_offset, data,
                     request->len);
-    if (ret < 0) {
+    if (ret < 0 || request->type == NBD_CMD_CACHE) {
         return nbd_send_generic_reply(client, request->handle, ret,
                                       "reading from file failed", errp);
     }
@@ -1963,6 +2173,7 @@ static coroutine_fn int nbd_handle_request(NBDClient *client,
 
     switch (request->type) {
     case NBD_CMD_READ:
+    case NBD_CMD_CACHE:
         return nbd_do_cmd_read(client, request, data, errp);
 
     case NBD_CMD_WRITE:
@@ -2007,11 +2218,38 @@ static coroutine_fn int nbd_handle_request(NBDClient *client,
                                       "discard failed", errp);
 
     case NBD_CMD_BLOCK_STATUS:
-        if (client->export_meta.valid && client->export_meta.base_allocation) {
-            return nbd_co_send_block_status(client, request->handle,
-                                            blk_bs(exp->blk), request->from,
-                                            request->len,
-                                            NBD_META_ID_BASE_ALLOCATION, errp);
+        if (!request->len) {
+            return nbd_send_generic_reply(client, request->handle, -EINVAL,
+                                          "need non-zero length", errp);
+        }
+        if (client->export_meta.valid &&
+            (client->export_meta.base_allocation ||
+             client->export_meta.bitmap))
+        {
+            if (client->export_meta.base_allocation) {
+                ret = nbd_co_send_block_status(client, request->handle,
+                                               blk_bs(exp->blk), request->from,
+                                               request->len,
+                                               !client->export_meta.bitmap,
+                                               NBD_META_ID_BASE_ALLOCATION,
+                                               errp);
+                if (ret < 0) {
+                    return ret;
+                }
+            }
+
+            if (client->export_meta.bitmap) {
+                ret = nbd_co_send_bitmap(client, request->handle,
+                                         client->exp->export_bitmap,
+                                         request->from, request->len,
+                                         request->flags & NBD_CMD_FLAG_REQ_ONE,
+                                         true, NBD_META_ID_DIRTY_BITMAP, errp);
+                if (ret < 0) {
+                    return ret;
+                }
+            }
+
+            return ret;
         } else {
             return nbd_send_generic_reply(client, request->handle, -EINVAL,
                                           "CMD_BLOCK_STATUS not negotiated",
@@ -2163,3 +2401,44 @@ void nbd_client_new(NBDExport *exp,
     co = qemu_coroutine_create(nbd_co_client_start, client);
     qemu_coroutine_enter(co);
 }
+
+void nbd_export_bitmap(NBDExport *exp, const char *bitmap,
+                       const char *bitmap_export_name, Error **errp)
+{
+    BdrvDirtyBitmap *bm = NULL;
+    BlockDriverState *bs = blk_bs(exp->blk);
+
+    if (exp->export_bitmap) {
+        error_setg(errp, "Export bitmap is already set");
+        return;
+    }
+
+    while (true) {
+        bm = bdrv_find_dirty_bitmap(bs, bitmap);
+        if (bm != NULL || bs->backing == NULL) {
+            break;
+        }
+
+        bs = bs->backing->bs;
+    }
+
+    if (bm == NULL) {
+        error_setg(errp, "Bitmap '%s' is not found", bitmap);
+        return;
+    }
+
+    if (bdrv_dirty_bitmap_enabled(bm)) {
+        error_setg(errp, "Bitmap '%s' is enabled", bitmap);
+        return;
+    }
+
+    if (bdrv_dirty_bitmap_qmp_locked(bm)) {
+        error_setg(errp, "Bitmap '%s' is locked", bitmap);
+        return;
+    }
+
+    bdrv_dirty_bitmap_set_qmp_locked(bm, true);
+    exp->export_bitmap = bm;
+    exp->export_bitmap_context =
+            g_strdup_printf("qemu:dirty-bitmap:%s", bitmap_export_name);
+}
diff --git a/nbd/trace-events b/nbd/trace-events
index dee081e775..5e1d4afe8e 100644
--- a/nbd/trace-events
+++ b/nbd/trace-events
@@ -64,6 +64,7 @@ nbd_co_send_simple_reply(uint64_t handle, uint32_t error, const char *errname, i
 nbd_co_send_structured_done(uint64_t handle) "Send structured reply done: handle = %" PRIu64
 nbd_co_send_structured_read(uint64_t handle, uint64_t offset, void *data, size_t size) "Send structured read data reply: handle = %" PRIu64 ", offset = %" PRIu64 ", data = %p, len = %zu"
 nbd_co_send_structured_read_hole(uint64_t handle, uint64_t offset, size_t size) "Send structured read hole reply: handle = %" PRIu64 ", offset = %" PRIu64 ", len = %zu"
+nbd_co_send_extents(uint64_t handle, unsigned int extents, uint32_t id, uint64_t length, int last) "Send block status reply: handle = %" PRIu64 ", extents = %u, context = %d (extents cover %" PRIu64 " bytes, last chunk = %d)"
 nbd_co_send_structured_error(uint64_t handle, int err, const char *errname, const char *msg) "Send structured error reply: handle = %" PRIu64 ", error = %d (%s), msg = '%s'"
 nbd_co_receive_request_decode_type(uint64_t handle, uint16_t type, const char *name) "Decoding type: handle = %" PRIu64 ", type = %" PRIu16 " (%s)"
 nbd_co_receive_request_payload_received(uint64_t handle, uint32_t len) "Payload received: handle = %" PRIu64 ", len = %" PRIu32
diff --git a/qapi/block.json b/qapi/block.json
index c694524002..ca807f176a 100644
--- a/qapi/block.json
+++ b/qapi/block.json
@@ -269,6 +269,29 @@
   'data': {'name': 'str', '*mode': 'NbdServerRemoveMode'} }
 
 ##
+# @x-nbd-server-add-bitmap:
+#
+# Expose a dirty bitmap associated with the selected export. The bitmap search
+# starts at the device attached to the export, and includes all backing files.
+# The exported bitmap is then locked until the NBD export is removed.
+#
+# @name: Export name.
+#
+# @bitmap: Bitmap name to search for.
+#
+# @bitmap-export-name: How the bitmap will be seen by nbd clients
+#                      (default @bitmap)
+#
+# Note: the client must use NBD_OPT_SET_META_CONTEXT with a query of
+# "qemu:dirty-bitmap:NAME" (where NAME matches @bitmap-export-name) to access
+# the exposed bitmap.
+#
+# Since: 3.0
+##
+  { 'command': 'x-nbd-server-add-bitmap',
+    'data': {'name': 'str', 'bitmap': 'str', '*bitmap-export-name': 'str'} }
+
+##
 # @nbd-server-stop:
 #
 # Stop QEMU's embedded NBD server, and unregister all devices previously
diff --git a/tests/.gitignore b/tests/.gitignore
index 2bc61a9a58..08e2df1ce1 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -2,101 +2,18 @@ atomic_add-bench
 benchmark-crypto-cipher
 benchmark-crypto-hash
 benchmark-crypto-hmac
-check-qdict
-check-qnum
-check-qjson
-check-qlist
-check-qlit
-check-qnull
-check-qobject
-check-qstring
-check-qom-interface
-check-qom-proplist
+check-*
+!check-*.c
+!check-*.sh
 qht-bench
 rcutorture
-test-aio
-test-aio-multithread
-test-arm-mptimer
-test-base64
-test-bdrv-drain
-test-bitops
-test-bitcnt
-test-block-backend
-test-blockjob
-test-blockjob-txn
-test-bufferiszero
-test-char
-test-clone-visitor
-test-coroutine
-test-crypto-afsplit
-test-crypto-block
-test-crypto-cipher
-test-crypto-hash
-test-crypto-hmac
-test-crypto-ivgen
-test-crypto-pbkdf
-test-crypto-secret
-test-crypto-tlscredsx509
-test-crypto-tlscredsx509-work/
-test-crypto-tlscredsx509-certs/
-test-crypto-tlssession
-test-crypto-tlssession-work/
-test-crypto-tlssession-client/
-test-crypto-tlssession-server/
-test-crypto-xts
-test-cutils
-test-hbitmap
-test-hmp
-test-int128
-test-iov
-test-io-channel-buffer
-test-io-channel-command
-test-io-channel-command.fifo
-test-io-channel-file
-test-io-channel-file.txt
-test-io-channel-socket
-test-io-channel-tls
-test-io-task
-test-keyval
-test-logging
-test-mul64
-test-opts-visitor
+test-*
+!test-*.c
 test-qapi-commands.[ch]
 test-qapi-events.[ch]
 test-qapi-types.[ch]
-test-qapi-util
 test-qapi-visit.[ch]
-test-qdev-global-props
-test-qemu-opts
-test-qdist
-test-qga
-test-qht
-test-qht-par
-test-qmp-cmds
-test-qmp-event
-test-qobject-input-strict
-test-qobject-input-visitor
 test-qapi-introspect.[ch]
-test-qobject-output-visitor
-test-rcu-list
-test-replication
-test-shift128
-test-string-input-visitor
-test-string-output-visitor
-test-thread-pool
-test-throttle
-test-timed-average
-test-uuid
-test-util-sockets
-test-visitor-serialization
-test-vmstate
-test-write-threshold
-test-x86-cpuid
-test-x86-cpuid-compat
-test-xbzrle
-test-netfilter
-test-filter-mirror
-test-filter-redirector
 *-test
 qapi-schema/*.test.*
 vm/*.img