From 71719cd57fc02ddfd91a4a3ca3f469bfb4d221bc Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Tue, 27 Oct 2020 00:05:54 -0500 Subject: nbd: Add new qemu:allocation-depth metadata context 'qemu-img map' provides a way to determine which extents of an image come from the top layer vs. inherited from a backing chain. This is useful information worth exposing over NBD. There is a proposal to add a QMP command block-dirty-bitmap-populate which can create a dirty bitmap that reflects allocation information, at which point the qemu:dirty-bitmap:NAME metadata context can expose that information via the creation of a temporary bitmap, but we can shorten the effort by adding a new qemu:allocation-depth metadata context that does the same thing without an intermediate bitmap (this patch does not eliminate the need for that proposal, as it will have other uses as well). While documenting things, remember that although the NBD protocol has NBD_OPT_SET_META_CONTEXT, the rest of its documentation refers to 'metadata context', which is a more apt description of what is actually being used by NBD_CMD_BLOCK_STATUS: the user is requesting metadata by passing one or more context names. So I also touched up some existing wording to prefer the term 'metadata context' where it makes sense. Note that this patch does not actually enable any way to request a server to enable this context; that will come in the next patch. Signed-off-by: Eric Blake Message-Id: <20201027050556.269064-10-eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy --- include/block/nbd.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'include') diff --git a/include/block/nbd.h b/include/block/nbd.h index 3dd9a04..4a52a43 100644 --- a/include/block/nbd.h +++ b/include/block/nbd.h @@ -1,5 +1,5 @@ /* - * Copyright (C) 2016-2019 Red Hat, Inc. + * Copyright (C) 2016-2020 Red Hat, Inc. * Copyright (C) 2005 Anthony Liguori * * Network Block Device @@ -47,7 +47,7 @@ typedef struct NBDOptionReply NBDOptionReply; typedef struct NBDOptionReplyMetaContext { NBDOptionReply h; /* h.type = NBD_REP_META_CONTEXT, h.length > 4 */ uint32_t context_id; - /* meta context name follows */ + /* metadata context name follows */ } QEMU_PACKED NBDOptionReplyMetaContext; /* Transmission phase structs @@ -229,7 +229,7 @@ enum { #define NBD_MAX_BUFFER_SIZE (32 * 1024 * 1024) /* - * Maximum size of a protocol string (export name, meta context name, + * Maximum size of a protocol string (export name, metadata context name, * etc.). Use malloc rather than stack allocation for storage of a * string. */ @@ -259,6 +259,8 @@ enum { /* Extent flags for qemu:dirty-bitmap in NBD_REPLY_TYPE_BLOCK_STATUS */ #define NBD_STATE_DIRTY (1 << 0) +/* No flags needed for qemu:allocation-depth in NBD_REPLY_TYPE_BLOCK_STATUS */ + static inline bool nbd_reply_type_is_error(int type) { return type & (1 << 15); -- cgit v1.1