On 03/21/2014 08:36 AM, 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 should significantly speed up file system initialization and > should speed zero write test used to test backend storage performance. > > the difference can simply be tested by e.g. > > dd if=/dev/zero of=/dev/vdX bs=1M > > Signed-off-by: Peter Lieven <[email protected]> > --- > v1->v2: - add detect-zeroes=off|on|unmap knob to drive cmdline parameter > - call zero detection only for format (bs->file != NULL) >
> +static int bdrv_set_detect_zeroes(BlockDriverState *bs,
> + const char *detect_zeroes,
> + Error **errp)
> +{
> + if (!detect_zeroes || !strncmp(detect_zeroes, "off", 3)) {
> + bs->detect_zeroes = BDRV_DETECT_ZEROES_OFF;
This parses "offer"
> + } else if (!strncmp(detect_zeroes, "on", 2)) {
> + bs->detect_zeroes = BDRV_DETECT_ZEROES_ON;
and this parses "onto".
> + } else if (!strncmp(detect_zeroes, "unmap", 5)) {
> + bs->detect_zeroes = BDRV_DETECT_ZEROES_UNMAP;
In all three cases, shouldn't you be using strcmp() instead of strncmp()?
> + } else {
> + error_setg(errp, "invalid value for detect-zeroes: %s",
> + detect_zeroes);
Especially since you warn about other unknown spellings, it feels weird
to not warn about the spellings where the prefix matches but the overall
spelling is unknown.
> file sectors into the image file.
> +@item detect-zeroes=@var{detect-zeroes}
> +@var{detect-zeroes} is "off", "on" or "unmap" and enables the automatic
> +conversion of plain zero writes by the OS to driver specific optimized
> +zero write commands. If "unmap" is choosen and @var{discard} is "on"
s/choosen/chosen/
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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