From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35298) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dVZka-0005Q9-Vo for qemu-devel@nongnu.org; Thu, 13 Jul 2017 04:45:34 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dVZkX-0002dV-QZ for qemu-devel@nongnu.org; Thu, 13 Jul 2017 04:45:33 -0400 Received: from mx01.kamp.de ([82.141.2.16]:38734) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dVZkX-0002cK-HW for qemu-devel@nongnu.org; Thu, 13 Jul 2017 04:45:29 -0400 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> <20170710134436.GB6770@redhat.com> <20170710135218.GK5772@noname.redhat.com> <20170710135539.GD6770@redhat.com> From: Peter Lieven Message-ID: Date: Thu, 13 Jul 2017 10:44:53 +0200 MIME-Version: 1.0 In-Reply-To: <20170710135539.GD6770@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit 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: "Daniel P. Berrange" , Kevin Wolf Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, lersek@redhat.com, den@openvz.org, mreitz@redhat.com, eblake@redhat.com Am 10.07.2017 um 15:55 schrieb Daniel P. Berrange: > On Mon, Jul 10, 2017 at 03:52:18PM +0200, Kevin Wolf wrote: >> Am 10.07.2017 um 15:44 hat Daniel P. Berrange geschrieben: >>> 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 >> I'd really like to see QAPI used for bdrv_create(), but here we're in >> the bdrv_open() path and parsing qcow2 headers. So either way this one >> specifically wouldn't be fixed. > Sorry, yes, I was getting mixed up in the two different patches with > similar bits of code. > > We could still replace the qcow2_compress_format_from_name() method > though with a call to the qapi_enum_parse() passing in the > 'QcowCompressFormat_lookup' table. Can you advise how exactly I would do that? Sorry, but this is new stuff for me. Thanks, Peter