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Tue, 07 Sep 2021 02:58:36 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwbrKzt+0vdfWS44nrI2RjfXdKoxtZKcG05wwfyy2X2pP2H1aCPlcEP0Zl6bdOc1xGWjff4ZA== X-Received: by 2002:a1c:f314:: with SMTP id q20mr2978426wmq.154.1631008716439; Tue, 07 Sep 2021 02:58:36 -0700 (PDT) Received: from dresden.str.redhat.com ([2a02:908:1e42:9e20:fd73:7ee2:9975:24d9]) by smtp.gmail.com with ESMTPSA id t7sm11551684wrq.90.2021.09.07.02.58.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Sep 2021 02:58:36 -0700 (PDT) Subject: Re: [PATCH] qemu-img: Allow target be aligned to sector size To: qemu-block@nongnu.org References: <20210819101200.64235-1-hreitz@redhat.com> From: Hanna Reitz Message-ID: <089b83f0-6511-f4b1-5d1e-ccaa70ac236c@redhat.com> Date: Tue, 7 Sep 2021 11:58:35 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210819101200.64235-1-hreitz@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=hreitz@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Received-SPF: pass client-ip=170.10.133.124; envelope-from=hreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -47 X-Spam_score: -4.8 X-Spam_bar: ---- X-Spam_report: (-4.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.391, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-2.332, RCVD_IN_MSPIKE_H2=-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: Kevin Wolf , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Ping – any thoughts on this? Hanna On 19.08.21 12:12, Hanna Reitz wrote: > We cannot write to images opened with O_DIRECT unless we allow them to > be resized so they are aligned to the sector size: Since 9c60a5d1978, > bdrv_node_refresh_perm() ensures that for nodes whose length is not > aligned to the request alignment and where someone has taken a WRITE > permission, the RESIZE permission is taken, too). > > Let qemu-img convert pass the BDRV_O_RESIZE flag (which causes > blk_new_open() to take the RESIZE permission) when using cache=none for > the target, so that when writing to it, it can be aligned to the target > sector size. > > Without this patch, an error is returned: > > $ qemu-img convert -f raw -O raw -t none foo.img /mnt/tmp/foo.img > qemu-img: Could not open '/mnt/tmp/foo.img': Cannot get 'write' > permission without 'resize': Image size is not a multiple of request > alignment > > Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1994266 > Signed-off-by: Hanna Reitz > --- > As I have written in the BZ linked above, I am not sure what behavior we > want. It can be argued that the current behavior is perfectly OK > because we want the target to have the same size as the source, so if > this cannot be done, we should just print the above error (which I think > explains the problem well enough that users can figure out they need to > resize the source image). > > OTOH, it is difficult for me to imagine a case where the user would > prefer the above error to just having qemu-img align the target image's > length. > --- > qemu-img.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/qemu-img.c b/qemu-img.c > index 908fd0cce5..d4b29bf73e 100644 > --- a/qemu-img.c > +++ b/qemu-img.c > @@ -2628,6 +2628,14 @@ static int img_convert(int argc, char **argv) > goto out; > } > > + if (flags & BDRV_O_NOCACHE) { > + /* > + * If we open the target with O_DIRECT, it may be necessary to > + * extend its size to align to the physical sector size. > + */ > + flags |= BDRV_O_RESIZE; > + } > + > if (skip_create) { > s.target = img_open(tgt_image_opts, out_filename, out_fmt, > flags, writethrough, s.quiet, false);