From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1D43DC433EF for ; Fri, 24 Jun 2022 21:51:12 +0000 (UTC) Received: from localhost ([::1]:35090 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1o4rCo-0007Uf-GG for qemu-devel@archiver.kernel.org; Fri, 24 Jun 2022 17:51:10 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60968) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1o4qs6-0000aF-3X; Fri, 24 Jun 2022 17:29:48 -0400 Received: from forwardcorp1j.mail.yandex.net ([2a02:6b8:0:1619::183]:41252) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1o4qs3-0004Tk-DC; Fri, 24 Jun 2022 17:29:45 -0400 Received: from myt5-23f0be3aa648.qloud-c.yandex.net (myt5-23f0be3aa648.qloud-c.yandex.net [IPv6:2a02:6b8:c12:3e29:0:640:23f0:be3a]) by forwardcorp1j.mail.yandex.net (Yandex) with ESMTP id 8F00F2E2FB3; Sat, 25 Jun 2022 00:29:35 +0300 (MSK) Received: from myt6-81d8ab6a9f9d.qloud-c.yandex.net (myt6-81d8ab6a9f9d.qloud-c.yandex.net [2a02:6b8:c12:520a:0:640:81d8:ab6a]) by myt5-23f0be3aa648.qloud-c.yandex.net (mxbackcorp/Yandex) with ESMTP id lyN1QBwti6-TYKac3B0; Sat, 25 Jun 2022 00:29:35 +0300 X-Yandex-Fwd: 2 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yandex-team.ru; s=default; t=1656106175; bh=Rk0bDHnb7E+qRgGa2/pn8ZWtLRCliajv6M+eQdsi/5k=; h=Message-Id:References:Date:Subject:In-Reply-To:Cc:To:From; b=E2dGL7yN7PrI6D3cht1jr+sCzWyn3fUQfcRy9fZDC1XDdXYx7BtJyQto1qlGtF40y IEep5/pXSoyD8M24UZ5Kk0UV+s1FiJ4ISxCFnkqPS9adX+uscw6FEc9woxpcwYCBAT wSeA8fBozbnUuGCI6DB76YykqHRJcVz2KeT2yH/o= Authentication-Results: myt5-23f0be3aa648.qloud-c.yandex.net; dkim=pass header.i=@yandex-team.ru Received: from vsementsov-win.yandex-team.ru (unknown [2a02:6b8:b081:b64c::1:2c]) by myt6-81d8ab6a9f9d.qloud-c.yandex.net (smtpcorp/Yandex) with ESMTPSA id KXs24KJ458-TYMSQwJg; Sat, 25 Jun 2022 00:29:34 +0300 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)) (Client certificate not present) From: Vladimir Sementsov-Ogievskiy To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, kwolf@redhat.com, hreitz@redhat.com, vsementsov@yandex-team.ru, John Snow Subject: [PATCH v6 13/15] block: Manipulate bs->file / bs->backing pointers in .attach/.detach Date: Sat, 25 Jun 2022 00:28:28 +0300 Message-Id: <20220624212830.316919-14-vsementsov@yandex-team.ru> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220624212830.316919-1-vsementsov@yandex-team.ru> References: <20220624212830.316919-1-vsementsov@yandex-team.ru> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a02:6b8:0:1619::183; envelope-from=vsementsov@yandex-team.ru; helo=forwardcorp1j.mail.yandex.net X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" bs->file and bs->backing are a kind of duplication of part of bs->children. But very useful diplication, so let's not drop them at all:) We should manage bs->file and bs->backing in same place, where we manage bs->children, to keep them in sync. Moreover, generic io paths are unprepared to BdrvChild without a bs, so it's double good to clear bs->file / bs->backing when we detach the child. Detach is simple: if we detach bs->file or bs->backing child, just set corresponding field to NULL. Attach is a bit more complicated. But we still can precisely detect should we set one of bs->file / bs->backing or not: - if role is BDRV_CHILD_COW, we definitely deal with bs->backing - else, if role is BDRV_CHILD_FILTERED (it must be also BDRV_CHILD_PRIMARY), it's a filtered child. Use bs->drv->filtered_child_is_backing to chose the pointer field to modify. - else, if role is BDRV_CHILD_PRIMARY, we deal with bs->file - in all other cases, it's neither bs->backing nor bs->file. It's some other child and we shouldn't care OK. This change brings one more good thing: we can (and should) get rid of all indirect pointers in the block-graph-change transactions: bdrv_attach_child_common() stores BdrvChild** into transaction to clear it on abort. bdrv_attach_child_common() has two callers: bdrv_attach_child_noperm() just pass-through this feature, bdrv_root_attach_child() doesn't need the feature. Look at bdrv_attach_child_noperm() callers: - bdrv_attach_child() doesn't need the feature - bdrv_set_file_or_backing_noperm() uses the feature to manage bs->file and bs->backing, we don't want it anymore - bdrv_append() uses the feature to manage bs->backing, again we don't want it anymore So, we should drop this stuff! Great! We could probably keep BdrvChild** argument to keep the int return value, but it seems not worth the complexity. Finally, we now set .file / .backing automatically in generic code and want to restring setting them by hand outside of .attach/.detach. So, this patch cleanups all remaining places where they were set. To find such places I use: git grep '\->file =' git grep '\->backing =' git grep '&.*\' git grep '&.*\' Signed-off-by: Vladimir Sementsov-Ogievskiy --- block.c | 234 ++++++++++++++----------------- block/raw-format.c | 4 +- block/snapshot-access.c | 6 +- block/snapshot.c | 1 - include/block/block_int-common.h | 15 +- tests/unit/test-bdrv-drain.c | 10 +- 6 files changed, 126 insertions(+), 144 deletions(-) diff --git a/block.c b/block.c index ca86cd86d3..6b08d20d8c 100644 --- a/block.c +++ b/block.c @@ -1438,9 +1438,39 @@ static void bdrv_child_cb_attach(BdrvChild *child) assert_bdrv_graph_writable(bs); QLIST_INSERT_HEAD(&bs->children, child, next); - - if (child->role & BDRV_CHILD_COW) { + if (bs->drv->is_filter || (child->role & BDRV_CHILD_FILTERED)) { + /* + * Here we handle filters and block/raw-format.c when it behave like + * filter. They generally have a single PRIMARY child, which is also the + * FILTERED child, and that they may have multiple more children, which + * are neither PRIMARY nor FILTERED. And never we have a COW child here. + * So bs->file will be the PRIMARY child, unless the PRIMARY child goes + * into bs->backing on exceptional cases; and bs->backing will be + * nothing else. + */ + assert(!(child->role & BDRV_CHILD_COW)); + if (child->role & BDRV_CHILD_PRIMARY) { + assert(child->role & BDRV_CHILD_FILTERED); + assert(!bs->backing); + assert(!bs->file); + + if (bs->drv->filtered_child_is_backing) { + bs->backing = child; + } else { + bs->file = child; + } + } else { + assert(!(child->role & BDRV_CHILD_FILTERED)); + } + } else if (child->role & BDRV_CHILD_COW) { + assert(bs->drv->supports_backing); + assert(!(child->role & BDRV_CHILD_PRIMARY)); + assert(!bs->backing); + bs->backing = child; bdrv_backing_attach(child); + } else if (child->role & BDRV_CHILD_PRIMARY) { + assert(!bs->file); + bs->file = child; } bdrv_apply_subtree_drain(child, bs); @@ -1458,6 +1488,12 @@ static void bdrv_child_cb_detach(BdrvChild *child) assert_bdrv_graph_writable(bs); QLIST_REMOVE(child, next); + if (child == bs->backing) { + assert(child != bs->file); + bs->backing = NULL; + } else if (child == bs->file) { + bs->file = NULL; + } } static int bdrv_child_cb_update_filename(BdrvChild *c, BlockDriverState *base, @@ -1663,7 +1699,7 @@ open_failed: bs->drv = NULL; if (bs->file != NULL) { bdrv_unref_child(bs, bs->file); - bs->file = NULL; + assert(!bs->file); } g_free(bs->opaque); bs->opaque = NULL; @@ -2852,7 +2888,7 @@ static void bdrv_child_free(BdrvChild *child) } typedef struct BdrvAttachChildCommonState { - BdrvChild **child; + BdrvChild *child; AioContext *old_parent_ctx; AioContext *old_child_ctx; } BdrvAttachChildCommonState; @@ -2860,33 +2896,31 @@ typedef struct BdrvAttachChildCommonState { static void bdrv_attach_child_common_abort(void *opaque) { BdrvAttachChildCommonState *s = opaque; - BdrvChild *child = *s->child; - BlockDriverState *bs = child->bs; + BlockDriverState *bs = s->child->bs; GLOBAL_STATE_CODE(); - bdrv_replace_child_noperm(child, NULL); + bdrv_replace_child_noperm(s->child, NULL); if (bdrv_get_aio_context(bs) != s->old_child_ctx) { bdrv_try_set_aio_context(bs, s->old_child_ctx, &error_abort); } - if (bdrv_child_get_parent_aio_context(child) != s->old_parent_ctx) { + if (bdrv_child_get_parent_aio_context(s->child) != s->old_parent_ctx) { GSList *ignore; /* No need to ignore `child`, because it has been detached already */ ignore = NULL; - child->klass->can_set_aio_ctx(child, s->old_parent_ctx, &ignore, - &error_abort); + s->child->klass->can_set_aio_ctx(s->child, s->old_parent_ctx, &ignore, + &error_abort); g_slist_free(ignore); ignore = NULL; - child->klass->set_aio_ctx(child, s->old_parent_ctx, &ignore); + s->child->klass->set_aio_ctx(s->child, s->old_parent_ctx, &ignore); g_slist_free(ignore); } bdrv_unref(bs); - bdrv_child_free(child); - *s->child = NULL; + bdrv_child_free(s->child); } static TransactionActionDrv bdrv_attach_child_common_drv = { @@ -2897,28 +2931,22 @@ static TransactionActionDrv bdrv_attach_child_common_drv = { /* * Common part of attaching bdrv child to bs or to blk or to job * - * Resulting new child is returned through @child. - * At start *@child must be NULL. - * @child is saved to a new entry of @tran, so that *@child could be reverted to - * NULL on abort(). So referenced variable must live at least until transaction - * end. - * * Function doesn't update permissions, caller is responsible for this. + * + * Returns new created child. */ -static int bdrv_attach_child_common(BlockDriverState *child_bs, - const char *child_name, - const BdrvChildClass *child_class, - BdrvChildRole child_role, - uint64_t perm, uint64_t shared_perm, - void *opaque, BdrvChild **child, - Transaction *tran, Error **errp) +static BdrvChild *bdrv_attach_child_common(BlockDriverState *child_bs, + const char *child_name, + const BdrvChildClass *child_class, + BdrvChildRole child_role, + uint64_t perm, uint64_t shared_perm, + void *opaque, + Transaction *tran, Error **errp) { BdrvChild *new_child; AioContext *parent_ctx; AioContext *child_ctx = bdrv_get_aio_context(child_bs); - assert(child); - assert(*child == NULL); assert(child_class->get_parent_desc); GLOBAL_STATE_CODE(); @@ -2960,42 +2988,35 @@ static int bdrv_attach_child_common(BlockDriverState *child_bs, if (ret < 0) { error_propagate(errp, local_err); bdrv_child_free(new_child); - return ret; + return NULL; } } bdrv_ref(child_bs); bdrv_replace_child_noperm(new_child, child_bs); - *child = new_child; - BdrvAttachChildCommonState *s = g_new(BdrvAttachChildCommonState, 1); *s = (BdrvAttachChildCommonState) { - .child = child, + .child = new_child, .old_parent_ctx = parent_ctx, .old_child_ctx = child_ctx, }; tran_add(tran, &bdrv_attach_child_common_drv, s); - return 0; + return new_child; } /* - * Variable referenced by @child must live at least until transaction end. - * (see bdrv_attach_child_common() doc for details) - * * Function doesn't update permissions, caller is responsible for this. */ -static int bdrv_attach_child_noperm(BlockDriverState *parent_bs, - BlockDriverState *child_bs, - const char *child_name, - const BdrvChildClass *child_class, - BdrvChildRole child_role, - BdrvChild **child, - Transaction *tran, - Error **errp) +static BdrvChild *bdrv_attach_child_noperm(BlockDriverState *parent_bs, + BlockDriverState *child_bs, + const char *child_name, + const BdrvChildClass *child_class, + BdrvChildRole child_role, + Transaction *tran, + Error **errp) { - int ret; uint64_t perm, shared_perm; assert(parent_bs->drv); @@ -3004,21 +3025,16 @@ static int bdrv_attach_child_noperm(BlockDriverState *parent_bs, if (bdrv_recurse_has_child(child_bs, parent_bs)) { error_setg(errp, "Making '%s' a %s child of '%s' would create a cycle", child_bs->node_name, child_name, parent_bs->node_name); - return -EINVAL; + return NULL; } bdrv_get_cumulative_perm(parent_bs, &perm, &shared_perm); bdrv_child_perm(parent_bs, child_bs, NULL, child_role, NULL, perm, shared_perm, &perm, &shared_perm); - ret = bdrv_attach_child_common(child_bs, child_name, child_class, - child_role, perm, shared_perm, parent_bs, - child, tran, errp); - if (ret < 0) { - return ret; - } - - return 0; + return bdrv_attach_child_common(child_bs, child_name, child_class, + child_role, perm, shared_perm, parent_bs, + tran, errp); } static void bdrv_detach_child(BdrvChild *child) @@ -3063,15 +3079,16 @@ BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs, void *opaque, Error **errp) { int ret; - BdrvChild *child = NULL; + BdrvChild *child; Transaction *tran = tran_new(); GLOBAL_STATE_CODE(); - ret = bdrv_attach_child_common(child_bs, child_name, child_class, + child = bdrv_attach_child_common(child_bs, child_name, child_class, child_role, perm, shared_perm, opaque, - &child, tran, errp); - if (ret < 0) { + tran, errp); + if (!child) { + ret = -EINVAL; goto out; } @@ -3079,11 +3096,10 @@ BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs, out: tran_finalize(tran, ret); - /* child is unset on failure by bdrv_attach_child_common_abort() */ - assert((ret < 0) == !child); bdrv_unref(child_bs); - return child; + + return ret < 0 ? NULL : child; } /* @@ -3105,14 +3121,15 @@ BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs, Error **errp) { int ret; - BdrvChild *child = NULL; + BdrvChild *child; Transaction *tran = tran_new(); GLOBAL_STATE_CODE(); - ret = bdrv_attach_child_noperm(parent_bs, child_bs, child_name, child_class, - child_role, &child, tran, errp); - if (ret < 0) { + child = bdrv_attach_child_noperm(parent_bs, child_bs, child_name, + child_class, child_role, tran, errp); + if (!child) { + ret = -EINVAL; goto out; } @@ -3123,12 +3140,10 @@ BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs, out: tran_finalize(tran, ret); - /* child is unset on failure by bdrv_attach_child_common_abort() */ - assert((ret < 0) == !child); bdrv_unref(child_bs); - return child; + return ret < 0 ? NULL : child; } /* Callers must ensure that child->frozen is false. */ @@ -3270,7 +3285,6 @@ static int bdrv_set_file_or_backing_noperm(BlockDriverState *parent_bs, bool is_backing, Transaction *tran, Error **errp) { - int ret = 0; bool update_inherits_from = bdrv_inherits_from_recursive(child_bs, parent_bs); BdrvChild *child = is_backing ? parent_bs->backing : parent_bs->file; @@ -3328,14 +3342,12 @@ static int bdrv_set_file_or_backing_noperm(BlockDriverState *parent_bs, goto out; } - ret = bdrv_attach_child_noperm(parent_bs, child_bs, - is_backing ? "backing" : "file", - &child_of_bds, role, - is_backing ? &parent_bs->backing : - &parent_bs->file, - tran, errp); - if (ret < 0) { - return ret; + child = bdrv_attach_child_noperm(parent_bs, child_bs, + is_backing ? "backing" : "file", + &child_of_bds, role, + tran, errp); + if (!child) { + return -EINVAL; } @@ -3591,14 +3603,16 @@ int bdrv_open_file_child(const char *filename, /* commit_top and mirror_top don't use this function */ assert(!parent->drv->filtered_child_is_backing); - role = parent->drv->is_filter ? (BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY) : BDRV_CHILD_IMAGE; - parent->file = bdrv_open_child(filename, options, bdref_key, parent, - &child_of_bds, role, false, errp); + if (!bdrv_open_child(filename, options, bdref_key, parent, + &child_of_bds, role, false, errp)) + { + return -EINVAL; + } - return parent->file ? 0 : -EINVAL; + return 0; } /* @@ -4873,8 +4887,8 @@ static void bdrv_close(BlockDriverState *bs) bdrv_unref_child(bs, child); } - bs->backing = NULL; - bs->file = NULL; + assert(!bs->backing); + assert(!bs->file); g_free(bs->opaque); bs->opaque = NULL; qatomic_set(&bs->copy_on_read, 0); @@ -5005,41 +5019,14 @@ static bool should_update_child(BdrvChild *c, BlockDriverState *to) return ret; } -typedef struct BdrvRemoveFilterOrCowChild { - BdrvChild *child; - bool is_backing; -} BdrvRemoveFilterOrCowChild; - -static void bdrv_remove_filter_or_cow_child_abort(void *opaque) -{ - BdrvRemoveFilterOrCowChild *s = opaque; - BlockDriverState *parent_bs = s->child->opaque; - - if (s->is_backing) { - parent_bs->backing = s->child; - } else { - parent_bs->file = s->child; - } - - /* - * We don't have to restore child->bs here to undo bdrv_replace_child_tran() - * because that function is transactionable and it registered own completion - * entries in @tran, so .abort() for bdrv_replace_child_safe() will be - * called automatically. - */ -} - static void bdrv_remove_filter_or_cow_child_commit(void *opaque) { - BdrvRemoveFilterOrCowChild *s = opaque; GLOBAL_STATE_CODE(); - bdrv_child_free(s->child); + bdrv_child_free(opaque); } static TransactionActionDrv bdrv_remove_filter_or_cow_child_drv = { - .abort = bdrv_remove_filter_or_cow_child_abort, .commit = bdrv_remove_filter_or_cow_child_commit, - .clean = g_free, }; /* @@ -5050,8 +5037,6 @@ static void bdrv_remove_file_or_backing_child(BlockDriverState *bs, BdrvChild *child, Transaction *tran) { - BdrvRemoveFilterOrCowChild *s; - assert(child == bs->backing || child == bs->file); if (!child) { @@ -5062,18 +5047,7 @@ static void bdrv_remove_file_or_backing_child(BlockDriverState *bs, bdrv_replace_child_tran(child, NULL, tran); } - s = g_new(BdrvRemoveFilterOrCowChild, 1); - *s = (BdrvRemoveFilterOrCowChild) { - .child = child, - .is_backing = (child == bs->backing), - }; - tran_add(tran, &bdrv_remove_filter_or_cow_child_drv, s); - - if (s->is_backing) { - bs->backing = NULL; - } else { - bs->file = NULL; - } + tran_add(tran, &bdrv_remove_filter_or_cow_child_drv, child); } /* @@ -5227,16 +5201,18 @@ int bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top, Error **errp) { int ret; + BdrvChild *child; Transaction *tran = tran_new(); GLOBAL_STATE_CODE(); assert(!bs_new->backing); - ret = bdrv_attach_child_noperm(bs_new, bs_top, "backing", - &child_of_bds, bdrv_backing_role(bs_new), - &bs_new->backing, tran, errp); - if (ret < 0) { + child = bdrv_attach_child_noperm(bs_new, bs_top, "backing", + &child_of_bds, bdrv_backing_role(bs_new), + tran, errp); + if (!child) { + ret = -EINVAL; goto out; } diff --git a/block/raw-format.c b/block/raw-format.c index 69fd650eaf..d8ca8ee3a9 100644 --- a/block/raw-format.c +++ b/block/raw-format.c @@ -457,8 +457,8 @@ static int raw_open(BlockDriverState *bs, QDict *options, int flags, file_role = BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY; } - bs->file = bdrv_open_child(NULL, options, "file", bs, &child_of_bds, - file_role, false, errp); + bdrv_open_child(NULL, options, "file", bs, &child_of_bds, + file_role, false, errp); if (!bs->file) { return -EINVAL; } diff --git a/block/snapshot-access.c b/block/snapshot-access.c index 77b87c1946..0a30ec6cd9 100644 --- a/block/snapshot-access.c +++ b/block/snapshot-access.c @@ -82,9 +82,9 @@ static void snapshot_access_refresh_filename(BlockDriverState *bs) static int snapshot_access_open(BlockDriverState *bs, QDict *options, int flags, Error **errp) { - bs->file = bdrv_open_child(NULL, options, "file", bs, &child_of_bds, - BDRV_CHILD_DATA | BDRV_CHILD_PRIMARY, - false, errp); + bdrv_open_child(NULL, options, "file", bs, &child_of_bds, + BDRV_CHILD_DATA | BDRV_CHILD_PRIMARY, + false, errp); if (!bs->file) { return -EINVAL; } diff --git a/block/snapshot.c b/block/snapshot.c index 75e8d3a937..f3971ac2bd 100644 --- a/block/snapshot.c +++ b/block/snapshot.c @@ -288,7 +288,6 @@ int bdrv_snapshot_goto(BlockDriverState *bs, /* .bdrv_open() will re-attach it */ bdrv_unref_child(bs, *fallback_ptr); - *fallback_ptr = NULL; ret = bdrv_snapshot_goto(fallback_bs, snapshot_id, errp); open_ret = drv->bdrv_open(bs, options, bs->open_flags, &local_err); diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h index d68adc6ff3..c4d8b11dbb 100644 --- a/include/block/block_int-common.h +++ b/include/block/block_int-common.h @@ -1056,9 +1056,6 @@ struct BlockDriverState { QDict *full_open_options; char exact_filename[PATH_MAX]; - BdrvChild *backing; - BdrvChild *file; - /* I/O Limits */ BlockLimits bl; @@ -1117,7 +1114,19 @@ struct BlockDriverState { * parent node of this node. */ BlockDriverState *inherits_from; + + /* + * @backing and @file are some of @children or NULL. All these three fields + * (@file, @backing and @children) are modified only in + * bdrv_child_cb_attach() and bdrv_child_cb_detach(). + * + * See also comment in include/block/block.h, to learn how backing and file + * are connected with BdrvChildRole. + */ QLIST_HEAD(, BdrvChild) children; + BdrvChild *backing; + BdrvChild *file; + QLIST_HEAD(, BdrvChild) parents; QDict *options; diff --git a/tests/unit/test-bdrv-drain.c b/tests/unit/test-bdrv-drain.c index 23d425a494..4cf99edf5b 100644 --- a/tests/unit/test-bdrv-drain.c +++ b/tests/unit/test-bdrv-drain.c @@ -1808,9 +1808,8 @@ static void test_drop_intermediate_poll(void) for (i = 0; i < 3; i++) { if (i) { /* Takes the reference to chain[i - 1] */ - chain[i]->backing = bdrv_attach_child(chain[i], chain[i - 1], - "chain", &chain_child_class, - BDRV_CHILD_COW, &error_abort); + bdrv_attach_child(chain[i], chain[i - 1], "chain", + &chain_child_class, BDRV_CHILD_COW, &error_abort); } } @@ -2028,9 +2027,8 @@ static void do_test_replace_child_mid_drain(int old_drain_count, new_child_bs->total_sectors = 1; bdrv_ref(old_child_bs); - parent_bs->backing = bdrv_attach_child(parent_bs, old_child_bs, "child", - &child_of_bds, BDRV_CHILD_COW, - &error_abort); + bdrv_attach_child(parent_bs, old_child_bs, "child", &child_of_bds, + BDRV_CHILD_COW, &error_abort); for (i = 0; i < old_drain_count; i++) { bdrv_drained_begin(old_child_bs); -- 2.25.1