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Fri, 20 Aug 2021 11:06:11 +0000 Subject: Re: [PATCH RFC v2 3/4] btrfs: use latest_dev in btrfs_show_devname From: Anand Jain To: linux-btrfs@vger.kernel.org References: <7c09f4adb27f4dc9de47ec9a4b8b4b540036534e.1629452691.git.anand.jain@oracle.com> Message-ID: Date: Fri, 20 Aug 2021 19:06:02 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 In-Reply-To: <7c09f4adb27f4dc9de47ec9a4b8b4b540036534e.1629452691.git.anand.jain@oracle.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SG2PR01CA0156.apcprd01.prod.exchangelabs.com (2603:1096:4:8f::36) To MN2PR10MB4128.namprd10.prod.outlook.com (2603:10b6:208:1d2::24) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.10.109] (39.109.186.25) by SG2PR01CA0156.apcprd01.prod.exchangelabs.com (2603:1096:4:8f::36) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4436.19 via Frontend Transport; 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So this patch makes that change. > > Signed-off-by: Anand Jain > --- > RFC because, > 1. With this patch, /proc/self/mounts might not show the lowest devid > device as we did before. We show the device that has the greatest > generation and, we used it to build the tree. Are we ok with this change > and, it won't affect the ABI? IMO it should be ok. > > v2 use latest_dev so that device path is also shown > > fs/btrfs/super.c | 24 ++---------------------- > 1 file changed, 2 insertions(+), 22 deletions(-) > > diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c > index 64ecbdb50c1a..6da62ebda979 100644 > --- a/fs/btrfs/super.c > +++ b/fs/btrfs/super.c > @@ -2464,30 +2464,10 @@ static int btrfs_unfreeze(struct super_block *sb) > static int btrfs_show_devname(struct seq_file *m, struct dentry *root) > { > struct btrfs_fs_info *fs_info = btrfs_sb(root->d_sb); > - struct btrfs_device *dev, *first_dev = NULL; > > - /* > - * Lightweight locking of the devices. We should not need > - * device_list_mutex here as we only read the device data and the list > - * is protected by RCU. Even if a device is deleted during the list > - * traversals, we'll get valid data, the freeing callback will wait at > - * least until the rcu_read_unlock. > - */ > - rcu_read_lock(); > - list_for_each_entry_rcu(dev, &fs_info->fs_devices->devices, dev_list) { > - if (test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state)) > - continue; > - if (!dev->name) > - continue; > - if (!first_dev || dev->devid < first_dev->devid) > - first_dev = dev; > - } > + seq_escape(m, rcu_str_deref(fs_info->fs_devices->latest_dev->name), > + " \t\n\\"); > I missed rcu_lock here. I am fixing it in v3. Thx. > - if (first_dev) > - seq_escape(m, rcu_str_deref(first_dev->name), " \t\n\\"); > - else > - WARN_ON(1); > - rcu_read_unlock(); > return 0; > } > >