Re: [Qemu-devel] [PATCHv3] block: optimize zero writes with bdrv_write_zeroes

[Kevin Wolf]

Am 07.05.2014 um 16:26 hat Peter Lieven geschrieben:
> On 07.05.2014 04:52, Eric Blake wrote:
> >On 05/06/2014 06:23 PM, Peter Lieven wrote:
> >>this patch tries to optimize zero write requests
> >>by automatically using bdrv_write_zeroes if it is
> >>supported by the format.
> >>
> >>This significantly speeds up file system initialization and
> >>should speed zero write test used to test backend storage
> >>performance.
> >>
> >>Signed-off-by: Peter Lieven <address@hidden>
> >>---
> >>v2->v3: - moved parameter parsing to blockdev_init
> >>         - added per device detect_zeroes status to
> >>           hmp (info block -v) and qmp (query-block) [Eric]
> >>         - added support to enable detect-zeroes also
> >>           for hot added devices [Eric]
> >>         - added missing entry to qemu_common_drive_opts
> >>         - fixed description of qemu_iovec_is_zero [Fam]
> >>
> >>+static BdrvDetectZeroes parse_detect_zeroes(const char *buf, Error **errp)
> >>+{
> >>+    if (!buf || !strcmp(buf, "off")) {
> >>+        return BDRV_DETECT_ZEROES_OFF;
> >>+    } else if (!strcmp(buf, "on")) {
> >>+        return BDRV_DETECT_ZEROES_ON;
> >>+    } else if (!strcmp(buf, "unmap")) {
> >>+        return BDRV_DETECT_ZEROES_UNMAP;
> >>+    } else {
> >>+        error_setg(errp, "invalid value for detect-zeroes: %s",
> >>+                   buf);
> >>+    }
> >>+    return BDRV_DETECT_ZEROES_OFF;
> >>+}
> >Isn't there QAPI generated code that you can use instead of open-coding
> >this conversion between string and enum values?
> 
> Actually I have no idea. As you pointed out in the qapi patch I sent
> it was quite hard for me to crawl through the whole stuff as one who is not
> familiar with it. Can somebody advise here? Anyhow, I wonder
> how this would work since qapi doesn't know the C Macros.

QAPI does generate C enums, so you should take whatever identifier it
uses instead of defining your own macros. You may need to include
qapi-types.h for this. It also creates a *_lookup array that maps enum
IDs to strings.

Kevin