From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from firstgate.proxmox.com (firstgate.proxmox.com [212.224.123.68]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.proxmox.com (Postfix) with ESMTPS id 619AF948D2 for ; Fri, 13 Jan 2023 12:50:09 +0100 (CET) Received: from firstgate.proxmox.com (localhost [127.0.0.1]) by firstgate.proxmox.com (Proxmox) with ESMTP id 40D7A4DED for ; Fri, 13 Jan 2023 12:50:09 +0100 (CET) Received: from proxmox-new.maurer-it.com (proxmox-new.maurer-it.com [94.136.29.106]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by firstgate.proxmox.com (Proxmox) with ESMTPS for ; Fri, 13 Jan 2023 12:50:08 +0100 (CET) Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1]) by proxmox-new.maurer-it.com (Proxmox) with ESMTP id 5443C44D9E for ; Fri, 13 Jan 2023 12:50:06 +0100 (CET) Date: Fri, 13 Jan 2023 12:50:04 +0100 From: Wolfgang Bumiller To: Fiona Ebner Cc: Thomas Lamprecht , Proxmox VE development discussion Message-ID: <20230113115004.cwfuh7wi4qcqo7fz@fwblub> References: <20221128155509.142996-1-f.ebner@proxmox.com> <81b59658-e60d-6899-dc73-4e5b02b151b9@proxmox.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <81b59658-e60d-6899-dc73-4e5b02b151b9@proxmox.com> X-SPAM-LEVEL: Spam detection results: 0 AWL 0.060 Adjusted score from AWL reputation of From: address BAYES_00 -1.9 Bayes spam probability is 0 to 1% KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment POISEN_SPAM_PILL 0.1 Meta: its spam POISEN_SPAM_PILL_1 0.1 random spam to be learned in bayes POISEN_SPAM_PILL_3 0.1 random spam to be learned in bayes SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record SPF_PASS -0.001 SPF: sender matches SPF record URIBL_BLOCKED 0.001 ADMINISTRATOR NOTICE: The query to URIBL was blocked. See http://wiki.apache.org/spamassassin/DnsBlocklists#dnsbl-block for more information. [proxmox.com, plugin.pm] Subject: Re: [pve-devel] [PATCH storage] plugin: file size info: use fallback for actual size X-BeenThere: pve-devel@lists.proxmox.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: Proxmox VE development discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 13 Jan 2023 11:50:09 -0000 On Thu, Jan 12, 2023 at 09:33:51AM +0100, Fiona Ebner wrote: > Am 11.01.23 um 16:46 schrieb Thomas Lamprecht: > > Am 28/11/2022 um 16:55 schrieb Fiona Ebner: > >> The actual-size property is an optional property in the QAPI > >> definition for ImageInfo. If it's not set, simply use the information > >> from stat() as a fallback. This is essentially the same > >> raw_get_allocated_file_size() in QEMU does anyways. > >> > >> Reported in the community forum: > >> https://forum.proxmox.com/threads/118443/post-513421 > >> > >> Signed-off-by: Fiona Ebner > >> --- > >> > >> Thanks to Mira for setting up a GlusterFS instance and discussing the > >> issue with me! > >> > >> I'm not sure why QEMU fails here, didn't see much that could go wrong > >> beside the fstat() call failing. But our stat() call in the beginning > >> of file_size_info already succeeded at that point :/ The mysteries of > >> QEMU+GlusterFS. > >> > >> Also, it's a bit strange to call qemu-img info regardless of whether > >> the image is a VM image or not. E.g., this results in the format > >> property for backups to always be raw, rather than the backup format. > >> Should we change that (for 8.0)? > >> > >> PVE/Storage/Plugin.pm | 1 + > >> 1 file changed, 1 insertion(+) > >> > >> diff --git a/PVE/Storage/Plugin.pm b/PVE/Storage/Plugin.pm > >> index 8a41df1..7773ac3 100644 > >> --- a/PVE/Storage/Plugin.pm > >> +++ b/PVE/Storage/Plugin.pm > >> @@ -899,6 +899,7 @@ sub file_size_info { > >> } > >> > >> my ($size, $format, $used, $parent) = $info->@{qw(virtual-size format actual-size backing-filename)}; > >> + $used ||= $st->blocks * 512; > > > > in general OK, but can we really be sure that blocks are always 512 bytes? > > > > Initially, I only checked 'man 2 stat' where this is the case: > > blkcnt_t st_blocks; /* Number of 512B blocks allocated */ > > But checking again now, 'perldoc -f stat' (File::stat mentions it uses > Perl's builtin stat()) actually states: > > 12 blocks actual number of system-specific blocks allocated > > on disk (often, but not always, 512 bytes each) > > Trying to decipher the Perl 5 source code, I /think/ it will just use > stat(2) on Linux (a quick check with strace seems to confirm this) and > I'd say it would be surprising if not, but I'm not 100% sure. There aren't too many choices there. It may switch to `statx` at some point where there's only `stx_blocks` which is specifically documented as "Number of 512B blocks allocated". The terminology in the I/O layer around blocks, sectors and "groups of 512 bytes" is quite annoying really. But hey, at least it's not `statvfs` which fills a struct with "garbage" on some systems (see `man 3 statvfs` on freebsd14) As for why glusterfs would fail with our stat() having succeeded, that's just glusterfs. Don't question it... > > That said, the original issue here was GlusterFS reporting an incorrect > value (see the forum thread). The new fallback introduced by this patch > would only help if 'qemu-img info' fails to determine the size for some > other reason (it also just does st_blocks * 512 in > raw_get_allocated_file_size()), so I'm not sure the patch is even worth > it after all.