From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44908) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dUYlG-0004PT-Co for qemu-devel@nongnu.org; Mon, 10 Jul 2017 09:30:06 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dUYlD-0001zQ-65 for qemu-devel@nongnu.org; Mon, 10 Jul 2017 09:30:02 -0400 Received: from mx01.kamp.de ([82.141.2.16]:45860) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dUYlC-0001yc-TT for qemu-devel@nongnu.org; Mon, 10 Jul 2017 09:29:59 -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> From: Peter Lieven Message-ID: Date: Mon, 10 Jul 2017 15:29:54 +0200 MIME-Version: 1.0 In-Reply-To: <20170710132546.GG5772@noname.redhat.com> Content-Type: text/plain; charset=windows-1252; 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: Kevin Wolf Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, lersek@redhat.com, den@openvz.org, mreitz@redhat.com, eblake@redhat.com, berrange@redhat.com 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. Peter