[libvirt] [PATCHv3] Add unsafe cache mode support for disk driver

[Eric Blake]

On 09/22/2011 01:33 PM, Oskari Saarenmaa wrote:
> QEMU 0.13 introduced cache=unsafe for -drive, this patch exposes
> it in the libvirt layer.
>
>    * Introduced a new QEMU capability flag ($prefix_CACHE_UNSAFE),
>      as even if $prefix_CACHE_V2 is set, we can't known if unsafe

s/known/know/

>      is supported.
>
>    * Improved the reliability of qemu cache type detection.
> ---
>   Updated patch based on Eric Blake's comments and rebased it to c4111bd0
>

> +++ b/docs/formatdomain.html.in
> @@ -996,10 +996,15 @@
>             <li>
>               The optional<code>cache</code>  attribute controls the
>               cache mechanism, possible values are "default", "none",
> -            "writethrough", "writeback", and "directsync". "directsync"
> -            is like "writethrough", but it bypasses the host page
> -            cache.
> -<span class="since">Since 0.6.0</span>
> +            "writethrough", "writeback", "directsync" (like
> +            "writethrough", but it bypasses the host page cache) and
> +            "unsafe" (host may cache all disk io and sync requests from

s/io and/io, and/

> @@ -912,12 +914,16 @@ qemuCapsComputeCmdFlags(const char *help,
>       else if (strstr(help, "-domid"))
>           qemuCapsSet(flags, QEMU_CAPS_DOMID);
>       if (strstr(help, "-drive")) {
> +        const char *cache = strstr(help, "cache=");
> +
>           qemuCapsSet(flags, QEMU_CAPS_DRIVE);
> -        if (strstr(help, "cache=")&&
> -            !strstr(help, "cache=on|off")) {
> -            qemuCapsSet(flags, QEMU_CAPS_DRIVE_CACHE_V2);
> -            if (strstr(help, "directsync"))
> +        if (cache&&  (p = strchr(cache, ']'))) {
> +            if (memmem(cache, p - cache, "on|off", sizeof("on|off") - 1) == NULL)
> +                qemuCapsSet(flags, QEMU_CAPS_DRIVE_CACHE_V2);
> +            if (memmem(cache, p - cache, "directsync", sizeof("directsync") - 1))
>                   qemuCapsSet(flags, QEMU_CAPS_DRIVE_CACHE_DIRECTSYNC);
> +            if (memmem(cache, p - cache, "unsafe", sizeof("unsafe") - 1))
> +                qemuCapsSet(flags, QEMU_CAPS_DRIVE_CACHE_UNSAFE);

Nice!  And indeed, unsafe but not directsync is present in qemu 0.14.0, 
so this does need another capability bit.

ACK and pushed.

-- 
Eric Blake   eblake at redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org