docs/interop/qcow2.txt: fix description about "zlib" clusters

[PATCH qemu] docs/interop/qcow2.txt: fix description about "zlib" clusters

Posted by ~akihirosuda 11 months, 2 weeks ago

From: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

"zlib" clusters are actually raw deflate (RFC1951) clusters without
zlib headers.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>
---
 docs/interop/qcow2.txt | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt
index f7dc304ff6..e7f036c286 100644
--- a/docs/interop/qcow2.txt
+++ b/docs/interop/qcow2.txt
@@ -214,14 +214,18 @@ version 2.
                     type.
 
                     If the incompatible bit "Compression type" is set: the field
-                    must be present and non-zero (which means non-zlib
+                    must be present and non-zero (which means non-deflate
                     compression type). Otherwise, this field must not be present
-                    or must be zero (which means zlib).
+                    or must be zero (which means deflate).
 
                     Available compression type values:
-                        0: zlib <https://www.zlib.net/>
+                        0: deflate <https://www.ietf.org/rfc/rfc1951.txt>
                         1: zstd <http://github.com/facebook/zstd>
 
+                    The deflate compression type is called "zlib"
+                    <https://www.zlib.net/> in QEMU. However, clusters with the
+                    deflate compression type do not have zlib headers.
+
 
 === Header padding ===
 
-- 
2.38.4

Re: [PATCH qemu] docs/interop/qcow2.txt: fix description about "zlib" clusters

Posted by Kevin Wolf 11 months, 2 weeks ago

Am 16.05.2023 um 16:32 hat ~akihirosuda geschrieben:
> From: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>
> 
> "zlib" clusters are actually raw deflate (RFC1951) clusters without
> zlib headers.
> 
> Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

Thanks, applied to the block branch.

Kevin

Re: [PATCH qemu] docs/interop/qcow2.txt: fix description about "zlib" clusters

Posted by Eric Blake 11 months, 2 weeks ago

On Tue, May 16, 2023 at 11:32:27PM +0900, ~akihirosuda wrote:
> 
> From: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>
> 
> "zlib" clusters are actually raw deflate (RFC1951) clusters without
> zlib headers.
> 
> Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>
> ---
>  docs/interop/qcow2.txt | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)

Seems like a useful clarification to me (there's a difference between
the encoding name and the program used to create/parse that encoding).

Reviewed-by: Eric Blake <eblake@redhat.com>

> 
> diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt
> index f7dc304ff6..e7f036c286 100644
> --- a/docs/interop/qcow2.txt
> +++ b/docs/interop/qcow2.txt
> @@ -214,14 +214,18 @@ version 2.
>                      type.
>  
>                      If the incompatible bit "Compression type" is set: the field
> -                    must be present and non-zero (which means non-zlib
> +                    must be present and non-zero (which means non-deflate
>                      compression type). Otherwise, this field must not be present
> -                    or must be zero (which means zlib).
> +                    or must be zero (which means deflate).
>  
>                      Available compression type values:
> -                        0: zlib <https://www.zlib.net/>
> +                        0: deflate <https://www.ietf.org/rfc/rfc1951.txt>
>                          1: zstd <http://github.com/facebook/zstd>
>  
> +                    The deflate compression type is called "zlib"
> +                    <https://www.zlib.net/> in QEMU. However, clusters with the
> +                    deflate compression type do not have zlib headers.
> +
>  
>  === Header padding ===
>  
> -- 
> 2.38.4
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org