From owner-freebsd-bugs@freebsd.org Sun Feb 3 22:49:54 2019 Return-Path: Delivered-To: freebsd-bugs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id B0FEE14B5F9B for ; Sun, 3 Feb 2019 22:49:54 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from mailman.ysv.freebsd.org (mailman.ysv.freebsd.org [IPv6:2001:1900:2254:206a::50:5]) by mx1.freebsd.org (Postfix) with ESMTP id 488908A17E for ; Sun, 3 Feb 2019 22:49:54 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: by mailman.ysv.freebsd.org (Postfix) id 0C20A14B5F9A; Sun, 3 Feb 2019 22:49:54 +0000 (UTC) Delivered-To: bugs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id DB9E514B5F99 for ; Sun, 3 Feb 2019 22:49:53 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from mxrelay.ysv.freebsd.org (mxrelay.ysv.freebsd.org [IPv6:2001:1900:2254:206a::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.ysv.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 75CC88A17A for ; Sun, 3 Feb 2019 22:49:53 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org (kenobi.freebsd.org [IPv6:2001:1900:2254:206a::16:76]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.ysv.freebsd.org (Postfix) with ESMTPS id BA6CF1A309 for ; Sun, 3 Feb 2019 22:49:52 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org ([127.0.1.118]) by kenobi.freebsd.org (8.15.2/8.15.2) with ESMTP id x13MnqcT053846 for ; Sun, 3 Feb 2019 22:49:52 GMT (envelope-from bugzilla-noreply@freebsd.org) Received: (from www@localhost) by kenobi.freebsd.org (8.15.2/8.15.2/Submit) id x13MnqOP053845 for bugs@FreeBSD.org; Sun, 3 Feb 2019 22:49:52 GMT (envelope-from bugzilla-noreply@freebsd.org) X-Authentication-Warning: kenobi.freebsd.org: www set sender to bugzilla-noreply@freebsd.org using -f From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 235473] gconcat online append Date: Sun, 03 Feb 2019 22:49:52 +0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Base System X-Bugzilla-Component: kern X-Bugzilla-Version: CURRENT X-Bugzilla-Keywords: X-Bugzilla-Severity: Affects Only Me X-Bugzilla-Who: noah.bergbauer@tum.de X-Bugzilla-Status: New X-Bugzilla-Resolution: X-Bugzilla-Priority: --- X-Bugzilla-Assigned-To: bugs@FreeBSD.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: bug_id short_desc product version rep_platform op_sys bug_status bug_severity priority component assigned_to reporter attachments.created Message-ID: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugs.freebsd.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: freebsd-bugs@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Bug reports List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 03 Feb 2019 22:49:54 -0000 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D235473 Bug ID: 235473 Summary: gconcat online append Product: Base System Version: CURRENT Hardware: Any OS: Any Status: New Severity: Affects Only Me Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: noah.bergbauer@tum.de Created attachment 201701 --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=3D201701&action= =3Dedit Initial patch draft It really shouldn't be necessary to rebuild a gconcat volume from scratch j= ust to add another disk. This is particularly inconvenient because it forces on= e to remount/restart any filesystems/geoms stacked on top of gconcat for no appa= rent reason. I attached my first attempt at hacking on this. It works! But since I have never worked with geoms (or rather any part of the kernel at all) before I = am very unsure about correctness, especially when it comes to locking and race conditions in general. Since the existing mutex appears to have a very specific purpose, I created= a new one. One obvious race is keeping the `g_access` levels in sync, so I'm locking over there as well. I would like to avoid locking a mutex in the regular IO path (g_concat_start) as this looks like a performance footgun to me, but given that I have to do array reallocation it seems to me that the = only alternative is to leak memory - perhaps an rwlock would be appropriate to s= olve this? Even after using FreeBSD for several years I never understood the hardcode option so I didn't implement that either. Incrementing G_CONCAT_VERSION did= n't work for some reason (userland tool wouldn't pick up the new version), did I miss something? Also I still need to update the manpage. I mean, the patch is quite literally a copy-pasted mix from gmultipath (resize/insert capability), gmirror (metadata update) and gconcat itself. It works but it really needs someone who actually knows how this stuff works to advise me on how to proceed. --=20 You are receiving this mail because: You are the assignee for the bug.=