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[2620:137:e000::1:20]) by mx.google.com with ESMTP id fk7-20020a056402398700b0049e160ce989si384896edb.306.2023.01.25.19.41.12; Wed, 25 Jan 2023 19:41:36 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@invisiblethingslab.com header.s=fm3 header.b=shU7A7Qo; dkim=pass header.i=@messagingengine.com header.s=fm3 header.b=dSggqvsL; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236396AbjAZDeW (ORCPT + 99 others); Wed, 25 Jan 2023 22:34:22 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59336 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236248AbjAZDeP (ORCPT ); Wed, 25 Jan 2023 22:34:15 -0500 Received: from out3-smtp.messagingengine.com (out3-smtp.messagingengine.com [66.111.4.27]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8D27E46D42; Wed, 25 Jan 2023 19:34:10 -0800 (PST) Received: from compute1.internal (compute1.nyi.internal [10.202.2.41]) by mailout.nyi.internal (Postfix) with ESMTP id EBFE75C05BC; Wed, 25 Jan 2023 22:34:09 -0500 (EST) Received: from mailfrontend2 ([10.202.2.163]) by compute1.internal (MEProxy); Wed, 25 Jan 2023 22:34:09 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= invisiblethingslab.com; h=cc:cc:content-transfer-encoding:date :date:from:from:in-reply-to:in-reply-to:message-id:mime-version :references:reply-to:sender:subject:subject:to:to; s=fm3; t= 1674704049; x=1674790449; bh=x0BohMGPEmmAQv3ZigspASmDgPSDsM1UcU2 Bewuui3w=; b=shU7A7QoonmUIxllylGbEv6EGhkh3ywZhyPtFTIJi9Cge9Hx9Ls UhlSQF2iUaG6BwKSu3h0FPwfliYXD4a8HP87jwCImKMcJA14E7ZDcDYPkNl6ZG2T /n75zWlQAsBnaIMRX/7uFYTPNKL20RcmCeuHCmZaPUBtaECY4I/yt2PIIU0+hiE+ XxtdD4XKor0xsD6NrdHklI+NDC27+/E/sX3Pc0+1ApGiqOr3HZnFYwEarK1lFlhq 1nqTlZH8mg/y2IpjNYDyDg+S3hSVjG39PXN8RAwpHOkFJeE5lzlBXn4J0NlNDdnD P8ewJ4cUaysdFp2K0nPW3ddIUwVz4Zu99xQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-transfer-encoding:date:date :feedback-id:feedback-id:from:from:in-reply-to:in-reply-to :message-id:mime-version:references:reply-to:sender:subject :subject:to:to:x-me-proxy:x-me-proxy:x-me-sender:x-me-sender :x-sasl-enc; s=fm3; t=1674704049; x=1674790449; bh=x0BohMGPEmmAQ v3ZigspASmDgPSDsM1UcU2Bewuui3w=; b=dSggqvsLBPqOQbwC+RWEeOIhmcoRT 4MX2VBxayPzSZP0MIgy/eWWdbnXC+gSo9R/9PI/YLYBrhhcQliJtRtIySnOt+szp 3I+23QWpvJiqcCRmVtPLAIQA2zCEfK7GJQlsKg5UVFpHP/m1TliE4zdxLHC3ZXD/ xdg80sFRzQW4wnari/b4m7NUE3ooE2PzI0DAEw/3jL4c6LEPbGLWO1Qh9nINu0Nc EzCJlclWFJMEIJKvp2dK0bI6Cy50yQYYGrkLSOa1nTVxE+khbACOxhpJwAoFGoKR jPlKDmMugkqE32uOvxf2i519UuBqPi16f8y75Q4+pTT3+IvUyop08xzSA== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvhedruddvfedgheekucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhephffvvefufffkofgjfhgggfestdekredtredttdenucfhrhhomhepffgvmhhi ucforghrihgvucfqsggvnhhouhhruceouggvmhhisehinhhvihhsihgslhgvthhhihhngh hslhgrsgdrtghomheqnecuggftrfgrthhtvghrnhepjeffjefggfeugeduvedvjeekgfeh gffhhfffjeetkeelueefffetfffhtdduheetnecuvehluhhsthgvrhfuihiivgeptdenuc frrghrrghmpehmrghilhhfrhhomhepuggvmhhisehinhhvihhsihgslhgvthhhihhnghhs lhgrsgdrtghomh X-ME-Proxy: Feedback-ID: iac594737:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Wed, 25 Jan 2023 22:34:09 -0500 (EST) From: Demi Marie Obenour To: Jens Axboe Cc: Demi Marie Obenour , =?utf-8?q?Marek_Marczy?= =?utf-8?q?kowski-G=C3=B3recki?= , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [RFC PATCH 1/7] block: Support creating a struct file from a block device Date: Wed, 25 Jan 2023 22:33:53 -0500 Message-Id: <20230126033358.1880-2-demi@invisiblethingslab.com> X-Mailer: git-send-email 2.39.1 In-Reply-To: <20230126033358.1880-1-demi@invisiblethingslab.com> References: <20230126033358.1880-1-demi@invisiblethingslab.com> MIME-Version: 1.0 X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1756054941796345760?= X-GMAIL-MSGID: =?utf-8?q?1756054941796345760?= The newly added blkdev_get_file() function allows kernel code to create a struct file for any block device. The main use-case is for the struct file to be exposed to userspace as a file descriptor. A future patch will modify the DM_DEV_CREATE_CREATE ioctl to allow userspace to get a file descriptor to the newly created block device, avoiding nasty race conditions. Signed-off-by: Demi Marie Obenour --- block/bdev.c | 77 +++++++++++++++++++++++++++++++++++------- include/linux/blkdev.h | 5 +++ 2 files changed, 70 insertions(+), 12 deletions(-) diff --git a/block/bdev.c b/block/bdev.c index edc110d90df4041e7d337976951bd0d17525f1f7..09cb5ef900ca9ad5b21250bb63e64cc2a79f9289 100644 --- a/block/bdev.c +++ b/block/bdev.c @@ -459,10 +459,33 @@ static struct file_system_type bd_type = { struct super_block *blockdev_superblock __read_mostly; EXPORT_SYMBOL_GPL(blockdev_superblock); +static struct vfsmount *bd_mnt __read_mostly; + +struct file * +blkdev_get_file(struct block_device *bdev, fmode_t flags, void *holder) +{ + struct inode *inode; + struct file *filp; + int ret; + + ret = blkdev_do_open(bdev, flags, holder); + if (ret) + return ERR_PTR(ret); + inode = bdev->bd_inode; + filp = alloc_file_pseudo(inode, bd_mnt, "[block]", flags | O_CLOEXEC, &def_blk_fops); + if (IS_ERR(filp)) { + blkdev_put(bdev, flags); + } else { + filp->f_mapping = inode->i_mapping; + filp->f_wb_err = filemap_sample_wb_err(filp->f_mapping); + } + return filp; +} +EXPORT_SYMBOL(blkdev_get_file); + void __init bdev_cache_init(void) { int err; - static struct vfsmount *bd_mnt; bdev_cachep = kmem_cache_create("bdev_cache", sizeof(struct bdev_inode), 0, (SLAB_HWCACHE_ALIGN|SLAB_RECLAIM_ACCOUNT| @@ -775,7 +798,7 @@ void blkdev_put_no_open(struct block_device *bdev) * * Use this interface ONLY if you really do not have anything better - i.e. when * you are behind a truly sucky interface and all you are given is a device - * number. Everything else should use blkdev_get_by_path(). + * number. Everything else should use blkdev_get_by_path() or blkdev_do_open(). * * CONTEXT: * Might sleep. @@ -785,9 +808,7 @@ void blkdev_put_no_open(struct block_device *bdev) */ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder) { - bool unblock_events = true; struct block_device *bdev; - struct gendisk *disk; int ret; ret = devcgroup_check_permission(DEVCG_DEV_BLOCK, @@ -800,18 +821,52 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder) bdev = blkdev_get_no_open(dev); if (!bdev) return ERR_PTR(-ENXIO); - disk = bdev->bd_disk; + + ret = blkdev_do_open(bdev, mode, holder); + if (ret) { + blkdev_put_no_open(bdev); + return ERR_PTR(ret); + } + + return bdev; +} +EXPORT_SYMBOL(blkdev_get_by_dev); + +/** + * blkdev_do_open - open a block device by device pointer + * @bdev: pointer to the device to open + * @mode: FMODE_* mask + * @holder: exclusive holder identifier + * + * Open the block device pointed to by @bdev. If @mode includes + * %FMODE_EXCL, the block device is opened with exclusive access. Specifying + * %FMODE_EXCL with a %NULL @holder is invalid. Exclusive opens may nest for + * the same @holder. + * + * Unlike blkdev_get_by_dev() and bldev_get_by_path(), this function does not + * do any permission checks. The most common use-case is where the device + * was freshly created by userspace. + * + * CONTEXT: + * Might sleep. + * + * RETURNS: + * Reference 0 on success, -errno on failure. + */ +int blkdev_do_open(struct block_device *bdev, fmode_t mode, void *holder) { + struct gendisk *disk = bdev->bd_disk; + int ret = -ENXIO; + bool unblock_events = true; if (mode & FMODE_EXCL) { ret = bd_prepare_to_claim(bdev, holder); if (ret) - goto put_blkdev; + return ret; } disk_block_events(disk); mutex_lock(&disk->open_mutex); - ret = -ENXIO; if (!disk_live(disk)) goto abort_claiming; if (!try_module_get(disk->fops->owner)) @@ -842,7 +897,7 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder) if (unblock_events) disk_unblock_events(disk); - return bdev; + return 0; put_module: module_put(disk->fops->owner); abort_claiming: @@ -850,11 +905,9 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder) bd_abort_claiming(bdev, holder); mutex_unlock(&disk->open_mutex); disk_unblock_events(disk); -put_blkdev: - blkdev_put_no_open(bdev); - return ERR_PTR(ret); + return ret; } -EXPORT_SYMBOL(blkdev_get_by_dev); +EXPORT_SYMBOL(blkdev_do_open); /** * blkdev_get_by_path - open a block device by name diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 43d4e073b1115e4628a001081fbf08b296d342df..04635cb5ee29d22394a34c65eb34bea4e7847d8d 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -325,6 +325,11 @@ typedef int (*report_zones_cb)(struct blk_zone *zone, unsigned int idx, void disk_set_zoned(struct gendisk *disk, enum blk_zoned_model model); +struct file * +blkdev_get_file(struct block_device *bdev, fmode_t flags, void *holder); + +int blkdev_do_open(struct block_device *bdev, fmode_t flags, void *holder); + #ifdef CONFIG_BLK_DEV_ZONED #define BLK_ALL_ZONES ((unsigned int)-1) From patchwork Thu Jan 26 03:33:54 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Demi Marie Obenour X-Patchwork-Id: 48483 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:adf:eb09:0:0:0:0:0 with SMTP id s9csp76293wrn; Wed, 25 Jan 2023 19:39:56 -0800 (PST) X-Google-Smtp-Source: AMrXdXuaVEbz+OAuqEQUXauR6FLBeBaR7mb0luYqGiSqD+Zd3mdPPgQdBeDO8lWiFMCEuYBBWwnZ X-Received: by 2002:a17:906:b215:b0:871:2060:c4c4 with SMTP id p21-20020a170906b21500b008712060c4c4mr36649179ejz.68.1674704396755; Wed, 25 Jan 2023 19:39:56 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1674704396; cv=none; d=google.com; s=arc-20160816; b=Ccuvp0CLPtOR3dzvDHVSSeTurBYajjwxF5ouo9/IZ1DUB4pNN/ykj8443cM1qmnEXV DUMlon5DMI8qQJe/PYTMG5+BB4UImHi8BV+whTg2XiUYSijwmmWLavldzNBnPcD7yxZQ AFudMM6qee2ZeFu/oM7JrCu/1mSt7PxuUyyux1sDMvDdkovX8nqGx2Bt4wRZx+z+UxYU HC2LaWBIFvMtH/OSi9RM3bY9Fchu5Gx3WQWJyGFHxWvqNiX96WvxRPCWptNPMyLhdNc+ v7XmY7SaZVc/xUn0opb5gq09giR31TUxC9eOQCdFu5hpN+AYgCtLnsUSuXt6NpypH/FS iLkQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :feedback-id:dkim-signature:dkim-signature; bh=daYdDSxsQizEcNPbMbpsOlpi5qeRBNOt+BqQaw5kD0w=; b=wcFR1RTQAQsIfAglNBte1TSJaopVP1D+6kU7V8ZqZ5RTfsbuKgesOQRRxqtb3bTRHn UzJCUSCT52YPkN9MWpCBZmjLocv0BdmrNm89izoApWf0es1R/D8NcIMUE09w30qd+okH aNlan05jIYy81hUP6C9iZ0ss9VtAp19u54IqxUYGkYvlYFNTpG34FnRq041jF8ZaA3QQ Pg7+s+FdC0a4NXYzUYMByqAc2AvuH+zbG+bycttVmhe334EH3Ip9pYWeE7HCtmbK5DFA R9AG8cyQVUZydzXKQvqO/0Q+Fsuo4mF0H/nED5Up8a/u2zCLB0tRXuGkXPrp8U4qQ8R+ bfFQ== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@invisiblethingslab.com header.s=fm3 header.b="Gz2/2Xbq"; dkim=pass header.i=@messagingengine.com header.s=fm3 header.b=NutHK5vz; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: from out1.vger.email (out1.vger.email. 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Signed-off-by: Demi Marie Obenour --- drivers/md/dm-ioctl.c | 67 +++++++++++++++++++++++++++++------ include/uapi/linux/dm-ioctl.h | 16 ++++++++- 2 files changed, 72 insertions(+), 11 deletions(-) diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c index 36fc6ae4737a05ab53ab67a8ccee525cb5fda082..05438dedcd17b7cac470fcc5a9721d67daad4bfb 100644 --- a/drivers/md/dm-ioctl.c +++ b/drivers/md/dm-ioctl.c @@ -853,9 +853,21 @@ static void __dev_status(struct mapped_device *md, struct dm_ioctl *param) static int dev_create(struct file *filp, struct dm_ioctl *param, size_t param_size) { - int r, m = DM_ANY_MINOR; + int r, m = DM_ANY_MINOR, fd; struct mapped_device *md; + /* Do not allow unknown flags */ + if (param->flags > (2 * DM_FILE_DESCRIPTOR_FLAG - 1)) + return -EINVAL; + + /* + * Do not allow creating a device that would just be destroyed + * before the ioctl returns. + */ + if ((param->flags & DM_DEFERRED_REMOVE) && + !(param->flags & DM_FILE_DESCRIPTOR_FLAG)) + return -EINVAL; + r = check_name(param->name); if (r) return r; @@ -867,20 +879,55 @@ static int dev_create(struct file *filp, struct dm_ioctl *param, size_t param_si if (r) return r; - r = dm_hash_insert(param->name, *param->uuid ? param->uuid : NULL, md); - if (r) { - dm_put(md); - dm_destroy(md); - return r; - } - param->flags &= ~DM_INACTIVE_PRESENT_FLAG; + r = dm_hash_insert(param->name, *param->uuid ? param->uuid : NULL, md); + if (r) + goto out_put; + + if (param->flags & DM_FILE_DESCRIPTOR_FLAG) { + struct block_device *bdev = dm_disk(md)->part0; + struct file *file; + + fd = get_unused_fd_flags(O_RDWR | O_CLOEXEC); + if (fd < 0) { + r = fd; + goto out_put; + } + + file = blkdev_get_file(bdev, O_RDWR|O_CLOEXEC, NULL); + if (IS_ERR(file)) { + r = PTR_ERR(file); + goto out_put_fd; + } + + /* + * Simulate opening the device. The other checks in + * dm_blk_open() are not necessary becuase we have a reference + * to the `struct md`. + */ + atomic_inc(&md->open_count); + fd_install(fd, file); + param->file_descriptor = fd; + } + + /* + * If userspace requests it, automatically delete the device + * when it is no longer used + */ + if (param->flags & DM_DEFERRED_REMOVE) + set_bit(DMF_DEFERRED_REMOVE, &md->flags); + __dev_status(md, param); - dm_put(md); - return 0; + +out_put_fd: + put_unused_fd(fd); +out_put: + dm_put(md); + dm_destroy(md); + return r; } /* diff --git a/include/uapi/linux/dm-ioctl.h b/include/uapi/linux/dm-ioctl.h index 7edf335778bae1cb206f6dd4d44e9cf7fb9da35c..30a6260ed7e06ff71fad1675dd4e7f9325d752a6 100644 --- a/include/uapi/linux/dm-ioctl.h +++ b/include/uapi/linux/dm-ioctl.h @@ -136,7 +136,13 @@ struct dm_ioctl { * For output, the ioctls return the event number, not the cookie. */ __u32 event_nr; /* in/out */ - __u32 padding; + + union { + /* Padding for named devices */ + __u32 padding; + /* For anonymous devices, this is a file descriptor. */ + __u32 file_descriptor; + }; __u64 dev; /* in/out */ @@ -382,4 +388,12 @@ enum { */ #define DM_IMA_MEASUREMENT_FLAG (1 << 19) /* In */ +/* + * If set in a DM_DEV_CREATE ioctl(), sets the file_descriptor field + * to a valid file descriptor. This can be combined with DM_DEFERRED_REMOVE + * to cause the device to be destroyed when the file descriptor is closed + * and is otherwise unused. + */ +#define DM_FILE_DESCRIPTOR_FLAG (1 << 20) /* In */ + #endif /* _LINUX_DM_IOCTL_H */ From patchwork Thu Jan 26 03:33:55 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Demi Marie Obenour X-Patchwork-Id: 48487 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:adf:eb09:0:0:0:0:0 with SMTP id s9csp77105wrn; Wed, 25 Jan 2023 19:43:06 -0800 (PST) X-Google-Smtp-Source: AMrXdXvYddkA5AlR3//K3AwUrBB49B007+a+fGDwsP3/O2gALDyjyVE/TX+AnRzjp6GfLZxPxu6i X-Received: by 2002:a17:906:e13:b0:870:f0c8:8187 with SMTP id l19-20020a1709060e1300b00870f0c88187mr34766982eji.24.1674704586240; Wed, 25 Jan 2023 19:43:06 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1674704586; cv=none; d=google.com; s=arc-20160816; b=IMMtnLeNQgFhcnjxlv5d9lzObkV/qVyvfYhy7XPJudHUvoAAMBRRAKoY948lwVEncc AqdEYgUZpaSdN8rLpksOKz6fgeKxUDh2FRQDs0ioQs7hk5AtmsOi39hF1dknZZthJz4+ pMYWwf4+NmfGRrDqVDIy98WlE+NhY0Izi1Uld8DfpvRZW20oB1Qckb70VEF5oYB9LlaF nKGcwX8MqOkitamvQ/HWPZMX5vWuXQETKUkn1RlHankOsJpAdsnQNUPbG4r6u4f5uM+T zSyaIdaFiZcue70MecGZ8jgg2+gRPj5snTH4urlO8FNIb+s2CDDhpYsYOk1JV1Mk7Yy/ A5Rw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :feedback-id:dkim-signature:dkim-signature; bh=sHxeYo7zgfjFccvxCuuph95svfpElxK2vn8+J41Up4A=; b=gB6GPjW0wKf2SwLcspVGMmPkUNM4gFtflodmh2xn9sPphTlIvLRDWLk24xYB9thjMj h33Dt5YyBfMvWmPb/T0dHz4TarRVCalRQb07XjARUv6lNeXYW7dzLc5j6R58yd6NRSOW azC3u92Hi/FIfjSSwKAvTDXhRrnsP2zu71/WMZL4mfy3TjDpml+ESXSAl/GlLO+fE8FT 27AdKHosrTTD5tMjjPvQxpvzeTxhHa8bhC2NqKh6rc/6hbEqjEatfv/Mi7nODwkLWJXF 35Zj4kWS1Umnh8BlAJmxGAHFNdnkwlrxy7Ll3phJ3AfhST1iVjrwBDq0q90Dmi4gIwfU Eriw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@invisiblethingslab.com header.s=fm3 header.b="adUQaXp/"; dkim=pass header.i=@messagingengine.com header.s=fm3 header.b=XIQCpZ3l; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: from out1.vger.email (out1.vger.email. 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If it does not match the disk sequence number of the underlying device, the device will not be exported and a warning will be logged. Userspace can use this to eliminate race conditions due to major/minor number reuse. Older kernels will ignore this, so it is safe for userspace to set it unconditionally. This also makes physical-device parsing stricter. I do not believe this will break any extant userspace tools. Signed-off-by: Demi Marie Obenour --- drivers/block/xen-blkback/xenbus.c | 137 +++++++++++++++++++++-------- 1 file changed, 100 insertions(+), 37 deletions(-) diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index 4807af1d58059394d7a992335dabaf2bc3901721..2c43bfc7ab5ba6954f11d4b949a5668660dbd290 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -24,6 +24,7 @@ struct backend_info { struct xenbus_watch backend_watch; unsigned major; unsigned minor; + unsigned long long diskseq; char *mode; }; @@ -479,7 +480,7 @@ static void xen_vbd_free(struct xen_vbd *vbd) static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle, unsigned major, unsigned minor, int readonly, - int cdrom) + bool cdrom, u64 diskseq) { struct xen_vbd *vbd; struct block_device *bdev; @@ -507,6 +508,25 @@ static int xen_vbd_create(struct xen_blkif *blkif, blkif_vdev_t handle, xen_vbd_free(vbd); return -ENOENT; } + + if (diskseq) { + struct gendisk *disk = bdev->bd_disk; + if (unlikely(disk == NULL)) { + pr_err("xen_vbd_create: device %08x has no gendisk\n", + vbd->pdevice); + xen_vbd_free(vbd); + return -EFAULT; + } + + if (unlikely(disk->diskseq != diskseq)) { + pr_warn("xen_vbd_create: device %08x has incorrect sequence " + "number 0x%llx (expected 0x%llx)\n", + vbd->pdevice, disk->diskseq, diskseq); + xen_vbd_free(vbd); + return -ENODEV; + } + } + vbd->size = vbd_sz(vbd); if (cdrom || disk_to_cdi(vbd->bdev->bd_disk)) @@ -690,6 +710,55 @@ static int xen_blkbk_probe(struct xenbus_device *dev, return err; } +static bool read_physical_device(struct xenbus_device *dev, + unsigned long long *diskseq, + unsigned *major, unsigned *minor) +{ + char *physical_device, *problem; + int i, physical_device_length; + char junk; + + physical_device = xenbus_read(XBT_NIL, dev->nodename, "physical-device", + &physical_device_length); + + if (IS_ERR(physical_device)) { + int err = PTR_ERR(physical_device); + /* + * Since this watch will fire once immediately after it is + * registered, we expect "does not exist" errors. Ignore + * them and wait for the hotplug scripts. + */ + if (unlikely(!XENBUS_EXIST_ERR(err))) + xenbus_dev_fatal(dev, err, "reading physical-device"); + return false; + } + + for (i = 0; i < physical_device_length; ++i) + if (unlikely(physical_device[i] <= 0x20 || physical_device[i] >= 0x7F)) { + problem = "bad byte in physical-device"; + goto fail; + } + + if (sscanf(physical_device, "%16llx@%8x:%8x%c", + diskseq, major, minor, &junk) == 3) { + if (*diskseq == 0) { + problem = "diskseq 0 is invalid"; + goto fail; + } + } else if (sscanf(physical_device, "%8x:%8x%c", major, minor, &junk) == 2) { + *diskseq = 0; + } else { + problem = "invalid physical-device"; + goto fail; + } + kfree(physical_device); + return true; +fail: + kfree(physical_device); + xenbus_dev_fatal(dev, -EINVAL, problem); + return false; +} + /* * Callback received when the hotplug scripts have placed the physical-device * node. Read it and the mode node, and create a vbd. If the frontend is @@ -707,28 +776,17 @@ static void backend_changed(struct xenbus_watch *watch, int cdrom = 0; unsigned long handle; char *device_type; + unsigned long long diskseq; pr_debug("%s %p %d\n", __func__, dev, dev->otherend_id); - - err = xenbus_scanf(XBT_NIL, dev->nodename, "physical-device", "%x:%x", - &major, &minor); - if (XENBUS_EXIST_ERR(err)) { - /* - * Since this watch will fire once immediately after it is - * registered, we expect this. Ignore it, and wait for the - * hotplug scripts. - */ + if (!read_physical_device(dev, &diskseq, &major, &minor)) return; - } - if (err != 2) { - xenbus_dev_fatal(dev, err, "reading physical-device"); - return; - } - if (be->major | be->minor) { - if (be->major != major || be->minor != minor) - pr_warn("changing physical device (from %x:%x to %x:%x) not supported.\n", - be->major, be->minor, major, minor); + if (be->major | be->minor | be->diskseq) { + if (be->major != major || be->minor != minor || be->diskseq != diskseq) + pr_warn("changing physical device (from %x:%x:%llx to %x:%x:%llx)" + " not supported.\n", + be->major, be->minor, be->diskseq, major, minor, diskseq); return; } @@ -756,29 +814,34 @@ static void backend_changed(struct xenbus_watch *watch, be->major = major; be->minor = minor; + be->diskseq = diskseq; err = xen_vbd_create(be->blkif, handle, major, minor, - !strchr(be->mode, 'w'), cdrom); - - if (err) - xenbus_dev_fatal(dev, err, "creating vbd structure"); - else { - err = xenvbd_sysfs_addif(dev); - if (err) { - xen_vbd_free(&be->blkif->vbd); - xenbus_dev_fatal(dev, err, "creating sysfs entries"); - } - } + !strchr(be->mode, 'w'), cdrom, diskseq); if (err) { - kfree(be->mode); - be->mode = NULL; - be->major = 0; - be->minor = 0; - } else { - /* We're potentially connected now */ - xen_update_blkif_status(be->blkif); + xenbus_dev_fatal(dev, err, "creating vbd structure"); + goto fail; } + + err = xenvbd_sysfs_addif(dev); + if (err) { + xenbus_dev_fatal(dev, err, "creating sysfs entries"); + goto free_vbd; + } + + /* We're potentially connected now */ + xen_update_blkif_status(be->blkif); + return; + +free_vbd: + xen_vbd_free(&be->blkif->vbd); +fail: + kfree(be->mode); + be->mode = NULL; + be->major = 0; + be->minor = 0; + be->diskseq = 0; } /* From patchwork Thu Jan 26 03:33:56 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Demi Marie Obenour X-Patchwork-Id: 48488 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:adf:eb09:0:0:0:0:0 with SMTP id s9csp77291wrn; Wed, 25 Jan 2023 19:43:49 -0800 (PST) X-Google-Smtp-Source: AMrXdXst6bx5Yl8uAxLHzNqkJFPwCoNY/Tubg/sSYNblLKj9lKr0k3ZZz9+e/y9MwfXozSHsXxdm X-Received: by 2002:a17:906:25db:b0:877:6a03:9ad1 with SMTP id n27-20020a17090625db00b008776a039ad1mr24477236ejb.7.1674704629541; Wed, 25 Jan 2023 19:43:49 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1674704629; cv=none; d=google.com; s=arc-20160816; b=B0rh2PohZYrOjTg4c2K6RXtTe7nniTg/TxuxyPB9A9bGZvvsmLMW4ze6iRb4lzPn1O h9ZVq5+wwX6ZEwAAb56adD6LcQRSM9oA0+gFnUA03J2PqxIZ+Lhes0ZjQoxmczdAY9se rGY7FS+DkhnFL3UWclY0Gd1otBEEKVGYWAJ/o7wvwNyNRcGkRfh5yrUDx3YqzGRpD2R9 HUvgjgdKbIIixbKW4ZTdVlClOBXp4Xfh/zLAp6kRt1OGr5s+c7rKkb2wMYtYUVEMxpfC mzyx96diy0kb4kso/M+fSuBrGSba4UFzl9RKQXDX8/XFgBJriO6kw0iQ3q0FUruh/YMr Wqew== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :feedback-id:dkim-signature:dkim-signature; bh=z0ynB5y0JUWTzScYTn7Q3OC3bp6u5sO9TqW4X6XkP2I=; b=DsBv/KI2CtTLJGCLAsu2otCZ7Ywyct1tu9cwaHSgUPy9DlZWMLLgK3EJeaNEUWdv3x +tTo7HrzI77mwXNJT+EPMFgGEZeOJDoxhJ4uvKOPG6CiomjyKsTkKzVSBH0d7USgOpha E73PLjOSUYYmkxMdAPX6SFuozB2/DY5vqlNITMOcrSZfWPLBAY/zdnmI3FxTmEFE7DL4 FHf2vl/CofLTnPM7Vrmo4kEB8vUwwyXqj9LOCRkhuFFB6l/lHI4DIDAawHaOa0lkvHH2 gSElCZiUA+9EMk9aNdqx5ELXhDLRWOWNCDExBwH1Zzyypps1/6bbZyMELcpUQ2klLHbG HgTg== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@invisiblethingslab.com header.s=fm3 header.b=hDNnUBhG; dkim=pass header.i=@messagingengine.com header.s=fm3 header.b=UwYtMTzI; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: from out1.vger.email (out1.vger.email. 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Signed-off-by: Demi Marie Obenour --- block/genhd.c | 1 + drivers/block/loop.c | 6 ++++++ 2 files changed, 7 insertions(+) diff --git a/block/genhd.c b/block/genhd.c index 23cf83b3331cdea5c916fbf01cb5b92aeb2f7cf8..5bf7664273c66d04b40730434f17f7b65fbfe101 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -1490,3 +1490,4 @@ void inc_diskseq(struct gendisk *disk) { disk->diskseq = atomic64_inc_return(&diskseq); } +EXPORT_SYMBOL(inc_diskseq); diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 1518a6423279bc890221e8184a8f2e420cb16715..f862b0ab1dce43b3617b1381be8e2de3aab828b1 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1205,6 +1205,12 @@ static void __loop_clr_fd(struct loop_device *lo, bool release) if (!part_shift) set_bit(GD_SUPPRESS_PART_SCAN, &lo->lo_disk->state); mutex_lock(&lo->lo_mutex); + + /* + * Increment the disk sequence number, so that userspace knows this + * device now points to something else. + */ + inc_diskseq(lo->lo_disk); lo->lo_state = Lo_unbound; mutex_unlock(&lo->lo_mutex); From patchwork Thu Jan 26 03:33:57 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Demi Marie Obenour X-Patchwork-Id: 48486 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:adf:eb09:0:0:0:0:0 with SMTP id s9csp77008wrn; Wed, 25 Jan 2023 19:42:38 -0800 (PST) X-Google-Smtp-Source: AK7set8GmjuU6mEeiJMKl0EKi5jrUC70HS31/MP1uGlNfM+8JkLZqYz74fZLTlMYkUdm+WHOEl/p X-Received: by 2002:a17:906:5857:b0:878:4379:f591 with SMTP id h23-20020a170906585700b008784379f591mr2605060ejs.5.1674704558624; Wed, 25 Jan 2023 19:42:38 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1674704558; cv=none; d=google.com; s=arc-20160816; b=ROENE2J8CJmFR03VotmNeSdGWEAKOEVBdQbI/bekCr46J1tBDE9sriIi650MExrgNO fJF5kBOHZqFxRK8VixGRnMaA4uQAbyyn8BWRFn7ZrnaIwvxENqiEFjwFcLCikURwzllA xu0d1MdAW/5EfIyHXv8F4NfsO75RLM2/R4nz7r6LtL+DA2XBeLd+CcUAKePub+V+g+2w Js/VEpabiWqnmFv8GCZJ+2t318cQ9IEhRh45fIy9FjYssCA0hHlae3jJiM0RheyWY/0g nbLe4IS6+WRYNFWm2Y6dMYhILUTOJaIFDCz29hO6nKWnd8YYMAwLHZ9Aw4IX6MRzNCP6 9eeQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :feedback-id:dkim-signature:dkim-signature; bh=fly1TGtjPYQFqq0ZAbmMb6xmSvsz35BqaEQbyQNg2OA=; b=diaXHHRvbBXZ7/9vWWNU7xrpnMxEsdIxYSukTYyIZ39GhoZgq7I6Ea+L0bj7f1FsxJ SQpgOg4muMkbpLPq+YYYNB8zVo6CmYgnIN4M1xdwjw6fVJIoHUQu1DynMXr3NCyTMNxy XQu8rt4oxQOvojnTU4i9qwEoesGtUmNnuKyOqOuokZjcgk5wnyY9BDx7fSzshUbV8ZuN XZ9xfoE5uvguQ3i4ztJqjHv+1/P4st51yFV8wqbE8tgoMmS7OQoAVlWECq1ZpqUU0GoD IZtmIOcKrEQ6za1KdFny2BZMcoClYyMW4HOUqASiEl/rSJ+tJxbp7JwLXgd141wOA81H 232g== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@invisiblethingslab.com header.s=fm3 header.b=D1MtYf7m; dkim=pass header.i=@messagingengine.com header.s=fm3 header.b=ctkpfx7S; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: from out1.vger.email (out1.vger.email. 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Signed-off-by: Demi Marie Obenour --- drivers/block/xen-blkback/blkback.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c index a5cf7f1e871c7f9ff397ab8ff1d7b9e3db686659..8a49cbe81d8895f89371bdf50d1b445c088c9b6a 100644 --- a/drivers/block/xen-blkback/blkback.c +++ b/drivers/block/xen-blkback/blkback.c @@ -1238,6 +1238,8 @@ static int dispatch_rw_block_io(struct xen_blkif_ring *ring, nseg = req->operation == BLKIF_OP_INDIRECT ? req->u.indirect.nr_segments : req->u.rw.nr_segments; + BUILD_BUG_ON(offsetof(struct blkif_request, u.rw.id) != 8); + BUILD_BUG_ON(offsetof(struct blkif_request, u.indirect.id) != 8); if (unlikely(nseg == 0 && operation_flags != REQ_PREFLUSH) || unlikely((req->operation != BLKIF_OP_INDIRECT) && (nseg > BLKIF_MAX_SEGMENTS_PER_REQUEST)) || @@ -1261,13 +1263,13 @@ static int dispatch_rw_block_io(struct xen_blkif_ring *ring, preq.sector_number = req->u.rw.sector_number; for (i = 0; i < nseg; i++) { pages[i]->gref = req->u.rw.seg[i].gref; - seg[i].nsec = req->u.rw.seg[i].last_sect - - req->u.rw.seg[i].first_sect + 1; - seg[i].offset = (req->u.rw.seg[i].first_sect << 9); if ((req->u.rw.seg[i].last_sect >= (XEN_PAGE_SIZE >> 9)) || (req->u.rw.seg[i].last_sect < req->u.rw.seg[i].first_sect)) goto fail_response; + seg[i].nsec = req->u.rw.seg[i].last_sect - + req->u.rw.seg[i].first_sect + 1; + seg[i].offset = (req->u.rw.seg[i].first_sect << 9); preq.nr_sects += seg[i].nsec; } } else { From patchwork Thu Jan 26 03:33:58 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Demi Marie Obenour X-Patchwork-Id: 48489 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:adf:eb09:0:0:0:0:0 with SMTP id s9csp77611wrn; Wed, 25 Jan 2023 19:44:55 -0800 (PST) X-Google-Smtp-Source: AMrXdXsea8nlmed1cr3s677AVcO+Li/IVCeBfwz1U1ePzv+mBbXAbCGfKQy54R/g/cSWAGd332Ez X-Received: by 2002:a17:907:20f6:b0:84d:21b2:735a with SMTP id rh22-20020a17090720f600b0084d21b2735amr33828350ejb.54.1674704695106; Wed, 25 Jan 2023 19:44:55 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1674704695; cv=none; d=google.com; s=arc-20160816; b=g3mBaQNT5k7Y8jofI8xLzGKZ3FIqYokqdZ6bkxvWVHaj8+H8GFmRtXqJFWVndu2bAF M7rSij6rvidV37AeTqUivt8jf5R5Q36nnP4XSBP+/VxLK2mrlj12si3S0NS1zVtY9JAA d1kpjfliAcBkGy7qbL0WxU6uhrl5uMuPWVOurwlOs4fj9RNUWoO36sRJGC/gLoKX86WK qNRRBvV84Yf1ONubMr2xJgj4Vu2XMbapzs+FOx+6A4joj0euyY8vg42PmEir0bQzPOmU QOvOk8h7cmFYe+Szvym929/C7d1M/dfPmZDGBjiNMD02Lv5KIdLBE+ftrn4C01EJxsPn v9dg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :feedback-id:dkim-signature:dkim-signature; bh=V4qU6xBczXYBxuAJBBtWt5596TfV6Bd4Dyk+YpmwRl4=; b=JKgaEmwHq7ACq7TpjdiYLluPkOcwdKH7cPNsY3Xs0UqjzPhQoCJs5DukkEGxDRXecL 2QBG3j/D6IXasBMnlELmlIhbwY42lg6LyUcEfzT87Nzaa30FwVzK6OIckbkBiJWz5xYB dAIx4O8aQSkgZFqujDKudW7+veKewZTCqLAjj00jgevVLChjj8t0BwgDZhOj6EKkGgGQ bKbc5why7SryOcbiPIIh4Dl/jaGUswpz+y3Or8YjQgWMnvC70WGetPoTTHtYA5fhPx4B JZf0KZD7TifR4sHLNW2Y+lYfFHmGbo0IN+5F28g6WtnOmM6RIG6LBe1DYLjE5+WbWDga zRPg== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@invisiblethingslab.com header.s=fm3 header.b=CuRQlVlI; dkim=pass header.i=@messagingengine.com header.s=fm3 header.b=G9bxwKaZ; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: from out1.vger.email (out1.vger.email. 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Wed, 25 Jan 2023 22:34:21 -0500 (EST) From: Demi Marie Obenour To: Jens Axboe , =?utf-8?q?Roger_Pau_Monn=C3=A9?= , Juergen Gross Cc: Demi Marie Obenour , =?utf-8?q?Marek_Marczy?= =?utf-8?q?kowski-G=C3=B3recki?= , xen-devel@lists.xenproject.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [RFC PATCH 7/7] xen/blkback: Inform userspace that device has been opened Date: Wed, 25 Jan 2023 22:33:58 -0500 Message-Id: <20230126033358.1880-7-demi@invisiblethingslab.com> X-Mailer: git-send-email 2.39.1 In-Reply-To: <20230126033358.1880-1-demi@invisiblethingslab.com> References: <20230126033358.1880-1-demi@invisiblethingslab.com> MIME-Version: 1.0 X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1756055150414392846?= X-GMAIL-MSGID: =?utf-8?q?1756055150414392846?= This allows userspace to use block devices with delete-on-close behavior, which is necessary to ensure virtual devices (such as loop or device-mapper devices) are cleaned up automatically. Protocol details are included in comments. Signed-off-by: Demi Marie Obenour --- drivers/block/xen-blkback/xenbus.c | 34 ++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+) diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index 2c43bfc7ab5ba6954f11d4b949a5668660dbd290..ca8dae05985038da490c5ac93364509913f6b4c7 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -3,6 +3,19 @@ Copyright (C) 2005 Rusty Russell Copyright (C) 2005 XenSource Ltd +In addition to the XenStore nodes required by the Xen block device +specification, this implementation of blkback uses a new XenStore +node: "opened". blkback sets "opened" to "0" before the hotplug script +is called. Once the device node has been opened, blkback sets "opened" +to "1". + +"opened" is used exclusively by userspace. It serves two purposes: + +1. It tells userspace that diskseq@major:minor syntax for "physical-device" is + supported. +2. It tells userspace that it can wait for "opened" to be set to 1. Once + "opened" is 1, blkback has a reference to the device, so userspace doesn't + need to keep one. */ @@ -698,6 +711,14 @@ static int xen_blkbk_probe(struct xenbus_device *dev, if (err) pr_warn("%s write out 'max-ring-page-order' failed\n", __func__); + /* + * This informs userspace that the "opened" node will be set to "1" when + * the device has been opened successfully. + */ + err = xenbus_write(XBT_NIL, dev->nodename, "opened", "0"); + if (err) + goto fail; + err = xenbus_switch_state(dev, XenbusStateInitWait); if (err) goto fail; @@ -824,6 +845,19 @@ static void backend_changed(struct xenbus_watch *watch, goto fail; } + /* + * Tell userspace that the device has been opened and that blkback has a + * reference to it. Userspace can then close the device or mark it as + * delete-on-close, knowing that blkback will keep the device open as + * long as necessary. + */ + err = xenbus_write(XBT_NIL, dev->nodename, "opened", "1"); + if (err) { + xenbus_dev_fatal(dev, err, "%s: notifying userspace device has been opened", + dev->nodename); + goto free_vbd; + } + err = xenvbd_sysfs_addif(dev); if (err) { xenbus_dev_fatal(dev, err, "creating sysfs entries");