From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cn.fujitsu.com ([59.151.112.132]:42364 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1750982AbaDPCJA convert rfc822-to-8bit (ORCPT ); Tue, 15 Apr 2014 22:09:00 -0400 Message-ID: <534DE66E.8060203@cn.fujitsu.com> Date: Wed, 16 Apr 2014 10:09:50 +0800 From: Qu Wenruo MIME-Version: 1.0 To: , Subject: Re: [PATCH] btrfs-progs: Force 'btrfs dev scan' not using old libblkid cache References: <1397115021-30426-1-git-send-email-quwenruo@cn.fujitsu.com> <20140414162919.GO29256@twin.jikos.cz> <534DDBDF.4050408@cn.fujitsu.com> In-Reply-To: <534DDBDF.4050408@cn.fujitsu.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: -------- Original Message -------- Subject: Re: [PATCH] btrfs-progs: Force 'btrfs dev scan' not using old libblkid cache From: Qu Wenruo To: dsterba@suse.cz, linux-btrfs@vger.kernel.org Date: 2014年04月16日 09:24 > > -------- Original Message -------- > Subject: Re: [PATCH] btrfs-progs: Force 'btrfs dev scan' not using old > libblkid cache > From: David Sterba > To: Qu Wenruo > Date: 2014年04月15日 00:29 >> On Thu, Apr 10, 2014 at 03:30:21PM +0800, Qu Wenruo wrote: >>> 'btrfs scan' uses libblkid to scan devices by default, and libblkid >>> uses >>> cache to reduce the probe. >>> >>> But if operations below is done in less than 2 >>> seconds(BLKID_PROBE_MIN), >>> 'btrfs scan' will still use the uncorrect cache and scan on the >>> deleted device. >>> 0. /dev/sda[1-4] mounted on /mnt using single data/metadata >>> 1. btrfs dev scan >>> 2. btrfs dev del /dev/sda3 /mnt >>> 3. btrfs dev scan >>> >>> Since the cache made by step 1 is still validated, step 3 will use the >>> cache and consider /dev/sda3 as a btrfs filesystem and try to scan it. >>> But the superblock(at least the first one) is wiped and failed to scan, >>> a error message, which can be avoided and is unneeded, is output. >>> >>> This patch will force scan_for_btrfs() not to use cache to avoid the >>> problem. >>> --- a/utils.c >>> +++ b/utils.c >>> @@ -2057,7 +2057,8 @@ int btrfs_scan_lblkid(int update_kernel) >>> blkid_cache cache = NULL; >>> char path[PATH_MAX]; >>> - if (blkid_get_cache(&cache, 0) < 0) { >>> + /* No to use libblkid cache to avoid old data */ >>> + if (blkid_get_cache(&cache, "/dev/null") < 0) { >> This effectively avoid the blkid cache for all devices but the point of >> blkid was to use it so repeated probes are not done. >> >> I think it's not right to skip the whole cache because one entry may be >> stale, more that we know which one and when. >> >> We should rather explicitly invalidate the removed device after delete, >> I don't what's the right way to do that. Maybe blkid_do_probe() or >> blkid_gc_cache() > Please ignore this patch, since after consulting with libblkid mail > list, the real problem is that btrfs ioctl for remove device > does not update the mtime/ctime for the device. I'm sorry that kernel updates the mtime/ctime, but it seems there is some small latency, which caused libblkd fail to detect the modification and use old cache. Will go on investigation. Thanks, Qu > > Libblkid will only use cache when the device's mtime/ctime stay > unchanged, if mtime/ctime changed libblkid will do the lowprobe. > > I'll try to fix it in kernel space. > > Thanks, > Qu > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html