Am 21.03.2014 15:50, schrieb Eric Blake: > 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 <p...@kamp.de> >> --- >> 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()?
yes, you are right. Thanks, Peter > >> + } 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/ >