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dkim=none (message not signed) header.d=none;nongnu.org; dmarc=none action=none header.from=virtuozzo.com; Received: from AM7PR08MB5494.eurprd08.prod.outlook.com (2603:10a6:20b:dc::15) by AM6PR08MB3445.eurprd08.prod.outlook.com (2603:10a6:20b:43::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4042.19; Fri, 23 Apr 2021 15:17:11 +0000 Received: from AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b403:c1a9:6bb7:133]) by AM7PR08MB5494.eurprd08.prod.outlook.com ([fe80::b403:c1a9:6bb7:133%7]) with mapi id 15.20.4065.021; Fri, 23 Apr 2021 15:17:11 +0000 Subject: Re: [PATCH v2 2/2] qemu-img convert: Unshare write permission for source To: Kevin Wolf , qemu-block@nongnu.org Cc: qemu-devel@nongnu.org References: <20210422164344.283389-1-kwolf@redhat.com> <20210422164344.283389-3-kwolf@redhat.com> From: Vladimir Sementsov-Ogievskiy Message-ID: Date: Fri, 23 Apr 2021 18:17:09 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 In-Reply-To: <20210422164344.283389-3-kwolf@redhat.com> Content-Type: text/plain; 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envelope-from=vsementsov@virtuozzo.com; helo=EUR05-DB8-obe.outbound.protection.outlook.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 22.04.2021 19:43, Kevin Wolf wrote: > For a successful conversion of an image, we must make sure that its > content doesn't change during the conversion. > > A special case of this is using the same image file both as the source > and as the destination. If both input and output format are raw, the > operation would just be useless work, with other formats it is a sure > way to destroy the image. This will now fail because the image file > can't be opened a second time for the output when opening it for the > input has already acquired file locks to unshare BLK_PERM_WRITE. > > Nevertheless, if there is some reason in a special case why it is > actually okay to allow writes to the image while it is being converted, > -U can still be used to force sharing all permissions. > > Note that for most image formats, BLK_PERM_WRITE would already be > unshared by the format driver, so this only really makes a difference > for raw source images (but any output format). > > Reported-by: Xueqiang Wei > Signed-off-by: Kevin Wolf > Reviewed-by: Eric Blake > --- > qemu-img.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/qemu-img.c b/qemu-img.c > index babb5573ab..a5993682aa 100644 > --- a/qemu-img.c > +++ b/qemu-img.c > @@ -2146,7 +2146,7 @@ static void set_rate_limit(BlockBackend *blk, int64_t rate_limit) > > static int img_convert(int argc, char **argv) > { > - int c, bs_i, flags, src_flags = 0; > + int c, bs_i, flags, src_flags = BDRV_O_NO_SHARE; > const char *fmt = NULL, *out_fmt = NULL, *cache = "unsafe", > *src_cache = BDRV_DEFAULT_CACHE, *out_baseimg = NULL, > *out_filename, *out_baseimg_param, *snapshot_name = NULL; > Reviewed-by: Vladimir Sementsov-Ogievskiy -- Best regards, Vladimir