From owner-freebsd-hackers@freebsd.org Fri Apr 12 15:40:08 2019 Return-Path: Delivered-To: freebsd-hackers@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 D30F3157F779 for ; Fri, 12 Apr 2019 15:40:07 +0000 (UTC) (envelope-from wlosh@bsdimp.com) Received: from mail-qk1-x732.google.com (mail-qk1-x732.google.com [IPv6:2607:f8b0:4864:20::732]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "GTS CA 1O1" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 1354480534 for ; Fri, 12 Apr 2019 15:40:07 +0000 (UTC) (envelope-from wlosh@bsdimp.com) Received: by mail-qk1-x732.google.com with SMTP id a71so5914116qkg.2 for ; Fri, 12 Apr 2019 08:40:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bsdimp-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=VjreV3vKf5M7EBDuNy6Y3C0CF0CwbztSVHdP0B0Xamg=; b=OHvc4JFsd/66NxcZ08CB4uUd82OnqL6sE3Ns3SWCRXXrdFjmPKgf1gWZWU4O+v4kHJ Nb+BKCaXrtkklFsYKxEZRU6h+6czMmp826rWuD0/zbV4x4Axob+HLOCKRj3HGbQ5ONm9 D+knDVKbkuKRJx2woaua9nnlC2T38OCG14FWgw2BCjuna6vuwJVzMRRVoYVFryABBXSS Q/rmcGQJhXxbdD0Nnr8V1iWpe1BW60SnK+Utqsm8uk/Xm5piYIlxd2VDvvMRmYJfhSpG waFfzgAsoqLDqc07m3HINcVEGbMRrmkvxdnRY+b/AwTocB93geGhouzDcm2nJGRS64zK EtUw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=VjreV3vKf5M7EBDuNy6Y3C0CF0CwbztSVHdP0B0Xamg=; b=Fyml3eDd6gSI9RvkFlVUoGdwpNMgSn0NgEiTr+dFYwv5L3S6Sdw0HGf6GZ4jzsYMM/ WDxqQBzMfW1gqQJ8wwNVyf6oKOASej/VzbFMKexLaDomDtTPHoJLiBirrlTxlBw/YqRM 0GNAsgPeEHEfNl+2jlmkDHi/E3st+6LlgbfXW0qMUgIo3xv5OO5hqWXe80MeP8MXzE3G fwHltJWzYB3hca2MNQ4PZhdCK/L7v2FgNFIrW0R3ImWHOfzQqL/SNdCinQy3rWdW6mFk dYdF7soc3KecKo5Hz0aoukmnQjlGE1935gATxRyYRrLgEGGQFtdKgBbWTLY82NkqcrVx mhsQ== X-Gm-Message-State: APjAAAXw0tLRzzUEq/pOB7RzQ0SbgaBW3PRpN3AmqB5et9tlT21ny0HL 5e/wMOcq3s817VgYxjaCU/OILleGU2OWoH7hnYmUpg== X-Google-Smtp-Source: APXvYqwP5+Ows3OUJQB9WWhSMwBn1494SyjPzFA//MX/JK6mlfRDT40hSmPPqt/hRYST3BemRnr10yT2x6e/Gne8528= X-Received: by 2002:a37:a310:: with SMTP id m16mr3818806qke.140.1555083606341; Fri, 12 Apr 2019 08:40:06 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Warner Losh Date: Fri, 12 Apr 2019 09:39:55 -0600 Message-ID: Subject: Re: When can a struct buf's b_lblkno field by < 0 ? To: Alan Somers Cc: FreeBSD Hackers X-Rspamd-Queue-Id: 1354480534 X-Spamd-Bar: ---- Authentication-Results: mx1.freebsd.org; dkim=pass header.d=bsdimp-com.20150623.gappssmtp.com header.s=20150623 header.b=OHvc4JFs X-Spamd-Result: default: False [-4.80 / 15.00]; ARC_NA(0.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-0.998,0]; R_DKIM_ALLOW(-0.20)[bsdimp-com.20150623.gappssmtp.com:s=20150623]; FROM_HAS_DN(0.00)[]; NEURAL_HAM_SHORT(-0.98)[-0.977,0]; IP_SCORE(-2.82)[ip: (-8.90), ipnet: 2607:f8b0::/32(-2.94), asn: 15169(-2.18), country: US(-0.06)]; MIME_GOOD(-0.10)[multipart/alternative,text/plain]; PREVIOUSLY_DELIVERED(0.00)[freebsd-hackers@freebsd.org]; DMARC_NA(0.00)[bsdimp.com]; NEURAL_HAM_LONG(-1.00)[-1.000,0]; TO_MATCH_ENVRCPT_SOME(0.00)[]; TO_DN_ALL(0.00)[]; DKIM_TRACE(0.00)[bsdimp-com.20150623.gappssmtp.com:+]; RCPT_COUNT_TWO(0.00)[2]; RCVD_IN_DNSWL_NONE(0.00)[2.3.7.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.0.0.4.6.8.4.0.b.8.f.7.0.6.2.list.dnswl.org : 127.0.5.0]; MX_GOOD(-0.01)[cached: ALT1.aspmx.l.google.com]; R_SPF_NA(0.00)[]; FORGED_SENDER(0.30)[imp@bsdimp.com,wlosh@bsdimp.com]; SUBJECT_ENDS_QUESTION(1.00)[]; MIME_TRACE(0.00)[0:+,1:+]; ASN(0.00)[asn:15169, ipnet:2607:f8b0::/32, country:US]; FROM_NEQ_ENVFROM(0.00)[imp@bsdimp.com,wlosh@bsdimp.com]; RCVD_TLS_LAST(0.00)[]; RCVD_COUNT_TWO(0.00)[2] Content-Type: text/plain; charset="UTF-8" X-Content-Filtered-By: Mailman/MimeDel 2.1.29 X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 12 Apr 2019 15:40:08 -0000 On Fri, Apr 12, 2019 at 9:12 AM Alan Somers wrote: > In struct buf, b_lblkno is documented as "Logical block number". I > would expect that to always be nonnegative. However, vtruncbuf loops > through a list of buffers, skipping those where "bp->b_lblkno > 0". > Maybe that's just an awkward way of writing "do something for the > buffer where b_lblkno == 0", but SVN archaeology suggests otherwise. > Before r112182, the code looked like this, implying that the b_lblkno > could actually be negative: > > if ((bp->b_flags & B_DELWRI) && (bp->b_lblkno < 0)) { > > Does anybody know under what circumstances that field might be > negative? Also, was r112182 a correct change? It appears to have > negated "<" and gotten ">", neglecting the "==" case. > > https://svnweb.freebsd.org/base/head/sys/kern/vfs_subr.c?r1=112182&r2=112181&pathrev=112182 b_lblkno can be negative when it describes the meta-data for a file, non-negative when it describes data for the file. Warner