From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49627) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dUYza-0005RQ-1y for qemu-devel@nongnu.org; Mon, 10 Jul 2017 09:44:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dUYzZ-0001Kd-0C for qemu-devel@nongnu.org; Mon, 10 Jul 2017 09:44:50 -0400 Date: Mon, 10 Jul 2017 14:44:36 +0100 From: "Daniel P. Berrange" Message-ID: <20170710134436.GB6770@redhat.com> Reply-To: "Daniel P. Berrange" References: <1498733831-15254-1-git-send-email-pl@kamp.de> <1498733831-15254-6-git-send-email-pl@kamp.de> <20170710132546.GG5772@noname.redhat.com> <20170710133459.GI5772@noname.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20170710133459.GI5772@noname.redhat.com> Subject: Re: [Qemu-devel] [PATCH V2 5/8] block/qcow2: read and write the compress format extension List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: Peter Lieven , qemu-block@nongnu.org, qemu-devel@nongnu.org, lersek@redhat.com, den@openvz.org, mreitz@redhat.com, eblake@redhat.com On Mon, Jul 10, 2017 at 03:34:59PM +0200, Kevin Wolf wrote: > Am 10.07.2017 um 15:29 hat Peter Lieven geschrieben: > > Am 10.07.2017 um 15:25 schrieb Kevin Wolf: > > >Am 29.06.2017 um 12:57 hat Peter Lieven geschrieben: > > >>we now read the extension on open and write it on update, but > > >>do not yet use it. > > >> > > >>Signed-off-by: Peter Lieven > > >>--- > > >> block/qcow2.c | 100 ++++++++++++++++++++++++++++++++++++++++++++++++++-------- > > >> block/qcow2.h | 23 +++++++++++--- > > >> 2 files changed, 104 insertions(+), 19 deletions(-) > > >> > > >>diff --git a/block/qcow2.c b/block/qcow2.c > > >>index 308121a..39a8afc 100644 > > >>--- a/block/qcow2.c > > >>+++ b/block/qcow2.c > > >>@@ -63,6 +63,7 @@ typedef struct { > > >> #define QCOW2_EXT_MAGIC_END 0 > > >> #define QCOW2_EXT_MAGIC_BACKING_FORMAT 0xE2792ACA > > >> #define QCOW2_EXT_MAGIC_FEATURE_TABLE 0x6803f857 > > >>+#define QCOW2_EXT_MAGIC_COMPRESS_FORMAT 0xC03183A3 > > >> static int qcow2_probe(const uint8_t *buf, int buf_size, const char *filename) > > >> { > > >>@@ -76,6 +77,26 @@ static int qcow2_probe(const uint8_t *buf, int buf_size, const char *filename) > > >> return 0; > > >> } > > >>+static int qcow2_compress_format_from_name(char *fmt) > > >>+{ > > >>+ if (!fmt || !fmt[0]) { > > >>+ return QCOW2_COMPRESS_ZLIB_COMPAT; > > >>+ } else if (g_str_equal(fmt, "zlib")) { > > >>+ return QCOW2_COMPRESS_ZLIB; > > >>+ } else { > > >>+ return -EINVAL; > > >>+ } > > >>+} > > >It might make sense to allow specifying the old compression format in > > >the compression header. But I'm not so sure about using the empty string > > >rather than a proper name for it, and even less about not documenting > > >it. > > > > The old format is used if and only if the compression header is absent. > > It makes no sense to write a header and use the old format. The old > > settings are suboptimal and old versions can't open a qcow2 with a > > compression header anyway. > > Your code allows an empty string in the header extension. If you don't > want it there, you need to reject it. This is a good reason to use the QAPI schema to parse the create options instead of doing it using qemu_opts - the QAPI schema will generate correct code to parse & validate enum values Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|