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From: | Peter Lieven |
Subject: | Re: [Qemu-devel] [PATCH V2 5/8] block/qcow2: read and write the compress format extension |
Date: | Mon, 10 Jul 2017 15:46:21 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 |
Am 10.07.2017 um 15:44 schrieb Daniel P. Berrange:
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 <address@hidden> --- 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
Can you then please advise where to add the schematas and which functions to use for parsing it? You wrote that it is a bit hackish at the moment as not everything is available in qcow2_create path. Thank you, Peter
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