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Mon, 27 Jan 2020 15:32:04 +0000 (UTC) Received: from redhat.com (ovpn-116-91.ams2.redhat.com [10.36.116.91]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 748295C1D6; Mon, 27 Jan 2020 15:32:03 +0000 (UTC) From: Juan Quintela To: "Dr. David Alan Gilbert" Subject: Re: [PATCH 1/2] migration/compress: compress QEMUFile is not writable In-Reply-To: <20191107115910.GG2816@work-vm> (David Alan Gilbert's message of "Thu, 7 Nov 2019 11:59:10 +0000") References: <20191012023932.1863-1-richardw.yang@linux.intel.com> <20191012023932.1863-2-richardw.yang@linux.intel.com> <20191107115910.GG2816@work-vm> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) Date: Mon, 27 Jan 2020 16:32:01 +0100 Message-ID: <87v9ow29vy.fsf@secure.laptop> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-MC-Unique: uVGiV0w0Mk-Z3-MOH_VbAw-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 207.211.31.120 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: , Reply-To: quintela@redhat.com Cc: Wei Yang , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" "Dr. David Alan Gilbert" wrote: > * Wei Yang (richardw.yang@linux.intel.com) wrote: >> We open a file with empty_ops for compress QEMUFile, which means this is >> not writable. > > That explanation sounds reasonable; but I'm confused by the history of > this; the code was added by Liang Li in : > > b3be289 qemu-file: Fix qemu_put_compression_data flaw > > ( https://www.mail-archive.com/qemu-devel@nongnu.org/msg368974.html ) > > with almost exactly the opposite argument; can we figure out why? Comment of that patch is wrong, code agrees with this patch. The patch that went in does: - return 0; + if (!qemu_file_is_writable(f)) { + return -1; + } + qemu_fflush(f); + blen =3D IO_BUF_SIZE - sizeof(int32_t); + if (blen < compressBound(size)) { + return -1; + } i.e. it move from return 0 to return -1 if we are not able to write, or if we are not able to get enough space. >> @@ -756,14 +753,7 @@ ssize_t qemu_put_compression_data(QEMUFile *f, z_st= ream *stream, >> ssize_t blen =3D IO_BUF_SIZE - f->buf_index - sizeof(int32_t); >> =20 >> if (blen < compressBound(size)) { >> - if (!qemu_file_is_writable(f)) { >> - return -1; >> - } >> - qemu_fflush(f); >> - blen =3D IO_BUF_SIZE - sizeof(int32_t); >> - if (blen < compressBound(size)) { >> - return -1; >> - } >> + return -1; >> } This moves from trying some things to just return -1. And patch is ok. compression file has a file with empty_os, so qemu_fflush() will not help at all. Reviewed-by: Juan Quintela Thanks, Juan.