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Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension |
Date: |
Mon, 10 Jul 2017 15:52:18 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
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 <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
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.
Kevin
- Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension, Kevin Wolf, 2017/07/10
- Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension, Peter Lieven, 2017/07/10
- Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension, Kevin Wolf, 2017/07/10
- Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension,
Kevin Wolf <=
- Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension, Daniel P. Berrange, 2017/07/10
- Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension, Peter Lieven, 2017/07/13
- Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension, Daniel P. Berrange, 2017/07/13
- Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension, Peter Lieven, 2017/07/13
- Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension, Daniel P. Berrange, 2017/07/13
- Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension, Peter Lieven, 2017/07/13
- Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension, Daniel P. Berrange, 2017/07/13
- Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension, Peter Lieven, 2017/07/13
- Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension, Daniel P. Berrange, 2017/07/13
- Re: [Qemu-block] [PATCH V2 5/8] block/qcow2: read and write the compress format extension, Peter Lieven, 2017/07/13