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Tue, 22 Sep 2020 02:37:35 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxpZAyhisLGV3J/wtNyb29WZ2YaCd/Z8yHGecpiMZ8HjsfGSXB2Wc1gWdxiTXT2nRR454fKsQ== X-Received: by 2002:a1c:f612:: with SMTP id w18mr16018wmc.47.1600767455389; Tue, 22 Sep 2020 02:37:35 -0700 (PDT) Received: from [192.168.10.165] ([93.56.170.5]) by smtp.gmail.com with ESMTPSA id l10sm23958875wru.59.2020.09.22.02.37.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Sep 2020 02:37:34 -0700 (PDT) Subject: Re: [PATCH] char: fix logging when chardev write fails To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , qemu-devel@nongnu.org References: <20200914103109.1327875-1-berrange@redhat.com> From: Paolo Bonzini Message-ID: Date: Tue, 22 Sep 2020 11:37:34 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200914103109.1327875-1-berrange@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=pbonzini@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US Received-SPF: pass client-ip=63.128.21.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/22 02:07:04 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.455, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 14/09/20 12:31, Daniel P. Berrangé wrote: > The qemu_chr_write_buffer() method sends data to the chardev backend for > writing, and then also writes to the log file. In case the chardev > backend only writes part of the data buffer, we need to make sure we > only log the same subset. qemu_chr_write_buffer() will be invoked again > later to write the rest of the buffer. > > In the case the chardev backend returns an error though, no further > attempts to likely to be made to write the data. We must therefore write > the entire buffer to the log immediately. > > An example where this is important is with the socket backend. This will > return -1 for all writes if no client is currently connected. We still > wish to write data to the log file when no client is present though. > This used to work because the chardev would return "len" to pretend it > had written all data when no client is connected, but this changed to > return an error in > > commit 271094474b65de1ad7aaf729938de3d9b9d0d36f > Author: Dima Stepanov > Date: Thu May 28 12:11:18 2020 +0300 > > char-socket: return -1 in case of disconnect during tcp_chr_write > > and this broke the logging, resulting in all data being discarded when > no client is present. > > Fixes: https://bugs.launchpad.net/qemu/+bug/1893691 > Signed-off-by: Daniel P. Berrangé > --- > chardev/char.c | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/chardev/char.c b/chardev/char.c > index 77e7ec814f..e30cd025f5 100644 > --- a/chardev/char.c > +++ b/chardev/char.c > @@ -138,7 +138,20 @@ static int qemu_chr_write_buffer(Chardev *s, > } > } > if (*offset > 0) { > + /* > + * If some data was written by backend, we should > + * only log what was actually written. This method > + * may be invoked again to write the remaining > + * method, thus we'll log the remainder at that time. > + */ > qemu_chr_write_log(s, buf, *offset); > + } else if (res < 0) { > + /* > + * If a fatal error was reported by the backend, > + * assume this method won't be invoked again with > + * this buffer, so log it all right away. > + */ > + qemu_chr_write_log(s, buf, len); > } > qemu_mutex_unlock(&s->chr_write_lock); > > Queued, thanks. Paolo