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Mon, 13 Jul 2020 10:04:38 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 8F976AED7; Mon, 13 Jul 2020 14:04:38 +0000 (UTC) Subject: Re: [PATCH] btrfs_show_devname don't traverse into the seed fsid To: Anand Jain , linux-btrfs@vger.kernel.org References: <20200710063738.28368-1-anand.jain@oracle.com> From: Nikolay Borisov Autocrypt: addr=nborisov@suse.com; prefer-encrypt=mutual; keydata= xsFNBFiKBz4BEADNHZmqwhuN6EAzXj9SpPpH/nSSP8YgfwoOqwrP+JR4pIqRK0AWWeWCSwmZ T7g+RbfPFlmQp+EwFWOtABXlKC54zgSf+uulGwx5JAUFVUIRBmnHOYi/lUiE0yhpnb1KCA7f u/W+DkwGerXqhhe9TvQoGwgCKNfzFPZoM+gZrm+kWv03QLUCr210n4cwaCPJ0Nr9Z3c582xc bCUVbsjt7BN0CFa2BByulrx5xD9sDAYIqfLCcZetAqsTRGxM7LD0kh5WlKzOeAXj5r8DOrU2 GdZS33uKZI/kZJZVytSmZpswDsKhnGzRN1BANGP8sC+WD4eRXajOmNh2HL4P+meO1TlM3GLl EQd2shHFY0qjEo7wxKZI1RyZZ5AgJnSmehrPCyuIyVY210CbMaIKHUIsTqRgY5GaNME24w7h TyyVCy2qAM8fLJ4Vw5bycM/u5xfWm7gyTb9V1TkZ3o1MTrEsrcqFiRrBY94Rs0oQkZvunqia c+NprYSaOG1Cta14o94eMH271Kka/reEwSZkC7T+o9hZ4zi2CcLcY0DXj0qdId7vUKSJjEep c++s8ncFekh1MPhkOgNj8pk17OAESanmDwksmzh1j12lgA5lTFPrJeRNu6/isC2zyZhTwMWs k3LkcTa8ZXxh0RfWAqgx/ogKPk4ZxOXQEZetkEyTFghbRH2BIwARAQABzSJOaWtvbGF5IEJv cmlzb3YgPG5ib3Jpc292QHN1c2UuZGU+wsF4BBMBAgAiBQJYijkSAhsDBgsJCAcDAgYVCAIJ CgsEFgIDAQIeAQIXgAAKCRBxvoJG5T8oV/B6D/9a8EcRPdHg8uLEPywuJR8URwXzkofT5bZE IfGF0Z+Lt2ADe+nLOXrwKsamhweUFAvwEUxxnndovRLPOpWerTOAl47lxad08080jXnGfYFS Dc+ew7C3SFI4tFFHln8Y22Q9075saZ2yQS1ywJy+TFPADIprAZXnPbbbNbGtJLoq0LTiESnD w/SUC6sfikYwGRS94Dc9qO4nWyEvBK3Ql8NkoY0Sjky3B0vL572Gq0ytILDDGYuZVo4alUs8 LeXS5ukoZIw1QYXVstDJQnYjFxYgoQ5uGVi4t7FsFM/6ykYDzbIPNOx49Rbh9W4uKsLVhTzG BDTzdvX4ARl9La2kCQIjjWRg+XGuBM5rxT/NaTS78PXjhqWNYlGc5OhO0l8e5DIS2tXwYMDY LuHYNkkpMFksBslldvNttSNei7xr5VwjVqW4vASk2Aak5AleXZS+xIq2FADPS/XSgIaepyTV tkfnyreep1pk09cjfXY4A7qpEFwazCRZg9LLvYVc2M2eFQHDMtXsH59nOMstXx2OtNMcx5p8 0a5FHXE/HoXz3p9bD0uIUq6p04VYOHsMasHqHPbsMAq9V2OCytJQPWwe46bBjYZCOwG0+x58 fBFreP/NiJNeTQPOa6FoxLOLXMuVtpbcXIqKQDoEte9aMpoj9L24f60G4q+pL/54ql2VRscK d87BTQRYigc+ARAAyJSq9EFk28++SLfg791xOh28tLI6Yr8wwEOvM3wKeTfTZd+caVb9gBBy wxYhIopKlK1zq2YP7ZjTP1aPJGoWvcQZ8fVFdK/1nW+Z8/NTjaOx1mfrrtTGtFxVBdSCgqBB jHTnlDYV1R5plJqK+ggEP1a0mr/rpQ9dFGvgf/5jkVpRnH6BY0aYFPprRL8ZCcdv2DeeicOO YMobD5g7g/poQzHLLeT0+y1qiLIFefNABLN06Lf0GBZC5l8hCM3Rpb4ObyQ4B9PmL/KTn2FV Xq/c0scGMdXD2QeWLePC+yLMhf1fZby1vVJ59pXGq+o7XXfYA7xX0JsTUNxVPx/MgK8aLjYW hX+TRA4bCr4uYt/S3ThDRywSX6Hr1lyp4FJBwgyb8iv42it8KvoeOsHqVbuCIGRCXqGGiaeX Wa0M/oxN1vJjMSIEVzBAPi16tztL/wQtFHJtZAdCnuzFAz8ue6GzvsyBj97pzkBVacwp3/Mw qbiu7sDz7yB0d7J2tFBJYNpVt/Lce6nQhrvon0VqiWeMHxgtQ4k92Eja9u80JDaKnHDdjdwq FUikZirB28UiLPQV6PvCckgIiukmz/5ctAfKpyYRGfez+JbAGl6iCvHYt/wAZ7Oqe/3Cirs5 KhaXBcMmJR1qo8QH8eYZ+qhFE3bSPH446+5oEw8A9v5oonKV7zMAEQEAAcLBXwQYAQIACQUC WIoHPgIbDAAKCRBxvoJG5T8oV1pyD/4zdXdOL0lhkSIjJWGqz7Idvo0wjVHSSQCbOwZDWNTN JBTP0BUxHpPu/Z8gRNNP9/k6i63T4eL1xjy4umTwJaej1X15H8Hsh+zakADyWHadbjcUXCkg OJK4NsfqhMuaIYIHbToi9K5pAKnV953xTrK6oYVyd/Rmkmb+wgsbYQJ0Ur1Ficwhp6qU1CaJ mJwFjaWaVgUERoxcejL4ruds66LM9Z1Qqgoer62ZneID6ovmzpCWbi2sfbz98+kW46aA/w8r 7sulgs1KXWhBSv5aWqKU8C4twKjlV2XsztUUsyrjHFj91j31pnHRklBgXHTD/pSRsN0UvM26 lPs0g3ryVlG5wiZ9+JbI3sKMfbdfdOeLxtL25ujs443rw1s/PVghphoeadVAKMPINeRCgoJH zZV/2Z/myWPRWWl/79amy/9MfxffZqO9rfugRBORY0ywPHLDdo9Kmzoxoxp9w3uTrTLZaT9M KIuxEcV8wcVjr+Wr9zRl06waOCkgrQbTPp631hToxo+4rA1jiQF2M80HAet65ytBVR2pFGZF zGYYLqiG+mpUZ+FPjxk9kpkRYz61mTLSY7tuFljExfJWMGfgSg1OxfLV631jV1TcdUnx+h3l Sqs2vMhAVt14zT8mpIuu2VNxcontxgVr1kzYA/tQg32fVRbGr449j1gw57BV9i0vww== Message-ID: <88241a07-9994-bf83-c06f-374611bc03c7@suse.com> Date: Mon, 13 Jul 2020 17:04:35 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200710063738.28368-1-anand.jain@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 10.07.20 г. 9:37 ч., Anand Jain wrote: > ->show_devname currently shows the lowest devid in the list. As the seed > devices have the lowest devid in the sprouted filesystem, the userland > tool such as findmnt end up seeing seed device instead of the device from > the read-writable sprouted filesystem. As shown below. > > mount /dev/sda /btrfs > mount: /btrfs: WARNING: device write-protected, mounted read-only. > > findmnt --output SOURCE,TARGET,UUID /btrfs > SOURCE TARGET UUID > /dev/sda /btrfs 899f7027-3e46-4626-93e7-7d4c9ad19111 > > btrfs dev add -f /dev/sdb /btrfs > > umount /btrfs > mount /dev/sdb /btrfs > > findmnt --output SOURCE,TARGET,UUID /btrfs > SOURCE TARGET UUID > /dev/sda /btrfs 899f7027-3e46-4626-93e7-7d4c9ad19111 > > > All sprouts from a single seed will show the same seed device and the > same fsid. That's messy. > This is causing problems in our prototype as there isn't any reference > to the sprout file-system(s) which is being used for actual read and > write. > > This was added in the patch which implemented the show_devname in btrfs > commit 9c5085c14798 (Btrfs: implement ->show_devname). > I tried to look for any particular reason that we need to show the seed > device, there isn't any. > > So instead, do not traverse through the seed devices, just show the > lowest devid in the sprouted fsid. > > After the patch: > > mount /dev/sda /btrfs > mount: /btrfs: WARNING: device write-protected, mounted read-only. > > findmnt --output SOURCE,TARGET,UUID /btrfs > SOURCE TARGET UUID > /dev/sda /btrfs 899f7027-3e46-4626-93e7-7d4c9ad19111 > > btrfs dev add -f /dev/sdb /btrfs > mount -o rw,remount /dev/sdb /btrfs > > findmnt --output SOURCE,TARGET,UUID /btrfs > SOURCE TARGET UUID > /dev/sdb /btrfs 595ca0e6-b82e-46b5-b9e2-c72a6928be48 > > mount /dev/sda /btrfs1 > mount: /btrfs1: WARNING: device write-protected, mounted read-only. > > btrfs dev add -f /dev/sdc /btrfs1 > > findmnt --output SOURCE,TARGET,UUID /btrfs1 > SOURCE TARGET UUID > /dev/sdc /btrfs1 ca1dbb7a-8446-4f95-853c-a20f3f82bdbb > > cat /proc/self/mounts | grep btrfs > /dev/sdb /btrfs btrfs rw,relatime,noacl,space_cache,subvolid=5,subvol=/ 0 0 > /dev/sdc /btrfs1 btrfs ro,relatime,noacl,space_cache,subvolid=5,subvol=/ 0 0 > > Signed-off-by: Anand Jain Reviewed-by: Nikolay Borisov Tested-by: Nikolay Borisov > --- > This has passed the xfstests/btrfs sucessfully with no new > regressions. Thanks. > > fs/btrfs/super.c | 21 +++++++-------------- > 1 file changed, 7 insertions(+), 14 deletions(-) > > diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c > index c7ee119cffa1..1e2a36f5c792 100644 > --- a/fs/btrfs/super.c > +++ b/fs/btrfs/super.c > @@ -2377,9 +2377,7 @@ 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_fs_devices *cur_devices; > struct btrfs_device *dev, *first_dev = NULL; > - struct list_head *head; > > /* > * Lightweight locking of the devices. We should not need > @@ -2389,18 +2387,13 @@ static int btrfs_show_devname(struct seq_file *m, struct dentry *root) > * least until the rcu_read_unlock. > */ > rcu_read_lock(); > - cur_devices = fs_info->fs_devices; > - while (cur_devices) { > - head = &cur_devices->devices; > - list_for_each_entry_rcu(dev, head, 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; > - } > - cur_devices = cur_devices->seed; > + 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; > } > > if (first_dev) >