From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp1040.oracle.com ([141.146.126.69]:40389 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755532AbaHZW46 (ORCPT ); Tue, 26 Aug 2014 18:56:58 -0400 Message-ID: <53FD10AC.8050906@oracle.com> Date: Wed, 27 Aug 2014 06:56:44 +0800 From: Anand Jain MIME-Version: 1.0 To: Chris Mason CC: Eric Sandeen , dsterba@suse.cz, Goffredo Baroncelli , linux-btrfs Subject: Re: [PATCH 0/3] btrfs-progs: remove full /dev scanning References: <53F51F4D.2090203@redhat.com> <53F635B9.6050900@libero.it> <20140826105522.GN29981@twin.jikos.cz> <53FC9EFE.8050105@redhat.com> <53FC9F80.6070608@fb.com> In-Reply-To: <53FC9F80.6070608@fb.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 26/08/2014 22:53, Chris Mason wrote: > On 08/26/2014 10:51 AM, Eric Sandeen wrote: >> On 8/26/14, 5:55 AM, David Sterba wrote: >>> On Thu, Aug 21, 2014 at 08:08:57PM +0200, Goffredo Baroncelli wrote: >>>> Of course I (we) don't care cdrom and/or floppy, but this raises >>>> the question: are there other block devices which aren't showed in >>>> proc/partitions ? >>> >>> cdrom appears as /dev/sr0, floppy is /dev/fd0 if the respective modules >>> are loaded, no breakage here. >>> >>>> I am thinking to some less common hardware like >>>> NON USB sd disk (I saw this kind of hardware, but now I don't have >>>> it in my hands....). >>> >>> A block device whose driver calls register_blkdev should appear in >>> proc/partitions, if not then I think it's a bug or a very non-standard >>> interface. >>> >>> I don't know about any other cases where full /dev scan would reveal >>> something that /proc/partitions not, so I guess it's safe to remove it. >> >> Yesterday, Chris did mention about /dev/mapper/* >> >> [12:57] I got inconsistent results from /proc/partitions >> [12:57] this was 3 years ago now >> [12:58] it didn't find everything for dm devices, yeah >> [12:58] especially dm multipath got really confused >> >> and I'll be honest, I didn't test with devicemapper devices, much >> less dm multipath, so I suppose that's warranted prior to removal. >> >> I'll see what I can do. >> >> If there's a problem, I bet there's a solution that doesn't involve >> scanning everything under /dev ... > > That's definitely the problem I hit, but it was years ago. I'm willing > to bet we're safe to keep /proc/partitions now. I was tempted to remove BTRFS_SCAN_PROC completely when I introduced BTRFS_SCAN_LBLKID, but then there was less clarity on this as it is now. The point I am trying to make is that we could remove BTRFS_SCAN_PROC all together and keep only the BTRFS_SCAN_LBLKID. (Which means we shall remove the -d option under btrfs filesystem show and btrfs device scan). We could remove scanning /proc/partition (the BTRFS_SCAN_PROC) because the libblkid (under scan method BTRFS_SCAN_LBLKID) would scan both udev and /proc/partition by default. (as in the libblkid man page). Further libblkid is end user configurable. end user can override the default configuration and can scan either of udev /dev/disk/by-* symlinks or /proc/partitions only. Further if still some device is not found then it would be a libblkid bug/enhancement, so we need to fix it under libblkid. The scan method BTRFS_SCAN_PROC is redundant. Thanks, Anand > -chris > > -- > 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 >