From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from firstgate.proxmox.com (firstgate.proxmox.com [IPv6:2a01:7e0:0:424::9]) by lore.proxmox.com (Postfix) with ESMTPS id BCD3B1FF13B for ; Wed, 25 Feb 2026 13:05:53 +0100 (CET) Received: from firstgate.proxmox.com (localhost [127.0.0.1]) by firstgate.proxmox.com (Proxmox) with ESMTP id 0E75E37700; Wed, 25 Feb 2026 13:06:34 +0100 (CET) From: Markus Ebner To: pve-devel@lists.proxmox.com Subject: [PATCH qemu-server v2 3/3] agent: file-read: Allow specifying byte offset to start reading at Date: Wed, 25 Feb 2026 12:28:49 +0100 Message-ID: <20260225112851.124188-4-info@ebner-markus.de> In-Reply-To: <20260225112851.124188-1-info@ebner-markus.de> References: <20260225112851.124188-1-info@ebner-markus.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-SPAM-LEVEL: Spam detection results: 0 AWL -0.531 Adjusted score from AWL reputation of From: address BAYES_00 -1.9 Bayes spam probability is 0 to 1% DMARC_PASS -0.1 DMARC pass policy KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment RCVD_IN_VALIDITY_CERTIFIED_BLOCKED 1.113 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. RCVD_IN_VALIDITY_RPBL_BLOCKED 0.358 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. RCVD_IN_VALIDITY_SAFE_BLOCKED 0.659 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record SPF_PASS -0.001 SPF: sender matches SPF record X-MailFrom: info@ebner-markus.de X-Mailman-Rule-Hits: nonmember-moderation X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; loop; banned-address; emergency; member-moderation Message-ID-Hash: 3CNFGYCVNRCJ3R273UFWAVA5RMKPEPUO X-Message-ID-Hash: 3CNFGYCVNRCJ3R273UFWAVA5RMKPEPUO X-Mailman-Approved-At: Wed, 25 Feb 2026 13:06:35 +0100 CC: Markus Ebner X-Mailman-Version: 3.3.10 Precedence: list List-Id: Proxmox VE development discussion List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: The previous implementation only allowed reads of fixed size starting at byte offset 0. This made the Proxmox's agent/file-read unsuitable for reading large files. The new offset parameter allows specifying a byte offset position relative to the start of the file (offset 0) from which the following read should be performed. The implementation's behavior follows the lseek semantics - directly following qemu-guest-agent's behavior: - fseek() does not perform validation against the file size - Seeking beyond the end of the file is not an error but explicitly allowed and specified behavior - Subsequent fread() calls at positions beyond the file size return zero bytes Additionally, this is equivalent to the behavior of POSIX pread(). Reading a large file block-by-block thus becomes (pseudo-code): let content = []; while(response.truncated) { response = proxmox.agent_file_read(offset = content.length); content .= response.content; } To be backwards compatible, offset defaults to 0. Signed-off-by: Markus Ebner --- src/PVE/API2/Qemu/Agent.pm | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/src/PVE/API2/Qemu/Agent.pm b/src/PVE/API2/Qemu/Agent.pm index 1f5962e9..ba96d77e 100644 --- a/src/PVE/API2/Qemu/Agent.pm +++ b/src/PVE/API2/Qemu/Agent.pm @@ -485,6 +485,13 @@ __PACKAGE__->register_method({ type => 'string', description => 'The path to the file', }, + offset => { + type => 'integer', + optional => 1, + minimum => 0, + default => 0, + description => "Offset to start reading at", + }, }, }, returns => { @@ -506,6 +513,7 @@ __PACKAGE__->register_method({ my ($param) = @_; my $count = int($param->{count} // $MAX_READ_SIZE); my $decode = $param->{decode} // 1; + my $offset = $param->{offset} // 0; my $vmid = $param->{vmid}; my $conf = PVE::QemuConfig->load_config($vmid); @@ -513,6 +521,16 @@ __PACKAGE__->register_method({ my $qgafh = agent_cmd($vmid, $conf, "file-open", { path => $param->{file} }, "can't open file"); + if ($offset > 0) { + my $seek = mon_cmd( + $vmid, "guest-file-seek", + handle => $qgafh, + offset => int($offset), + whence => 'set', + ); + check_agent_error($seek, "can't seek to offset position"); + } + my $bytes_read = 0; my $eof = 0; my $read_size = 1024 * 1024; -- 2.53.0