| Message ID | 1484841384-9938-1-git-send-email-pl@kamp.de |
|---|---|
| State | New |
| Headers | show |
Please ignore this one The code was suboptimal. Will send v2. Peter Am 19.01.2017 um 16:56 schrieb Peter Lieven: > the current implementation always splits requests if a buffer > begins or ends with zeroes independent of the length of the > zero area. Change this to really only split off zero areas > that have at least a length of 'min' bytes. > > Signed-off-by: Peter Lieven <pl@kamp.de> > --- > qemu-img.c | 38 ++++++++++++-------------------------- > 1 file changed, 12 insertions(+), 26 deletions(-) > > diff --git a/qemu-img.c b/qemu-img.c > index 5df66fe..046696f 100644 > --- a/qemu-img.c > +++ b/qemu-img.c > @@ -1010,45 +1010,31 @@ static int is_allocated_sectors(const uint8_t *buf, int n, int *pnum) > } > > /* > - * Like is_allocated_sectors, but if the buffer starts with a used sector, > - * up to 'min' consecutive sectors containing zeros are ignored. This avoids > - * breaking up write requests for only small sparse areas. > + * Like is_allocated_sectors, but only at least 'min' consecutive sectors > + * containing zeros are considered unallocated. This avoids breaking up write > + * requests for only small sparse areas. > */ > static int is_allocated_sectors_min(const uint8_t *buf, int n, int *pnum, > - int min) > + int min) > { > - int ret; > - int num_checked, num_used; > - > - if (n < min) { > - min = n; > - } > - > - ret = is_allocated_sectors(buf, n, pnum); > - if (!ret) { > - return ret; > - } > - > - num_used = *pnum; > - buf += BDRV_SECTOR_SIZE * *pnum; > - n -= *pnum; > - num_checked = num_used; > + int ret, num_checked = 0, num_used = 0; > > while (n > 0) { > ret = is_allocated_sectors(buf, n, pnum); > - > buf += BDRV_SECTOR_SIZE * *pnum; > n -= *pnum; > num_checked += *pnum; > - if (ret) { > - num_used = num_checked; > - } else if (*pnum >= min) { > + if (!ret && *pnum >= min) { > break; > } > + num_used = num_checked; > } > > - *pnum = num_used; > - return 1; > + if (num_used) { > + *pnum = num_used; > + } > + > + return !!num_used; > } > > /*
diff --git a/qemu-img.c b/qemu-img.c index 5df66fe..046696f 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -1010,45 +1010,31 @@ static int is_allocated_sectors(const uint8_t *buf, int n, int *pnum) } /* - * Like is_allocated_sectors, but if the buffer starts with a used sector, - * up to 'min' consecutive sectors containing zeros are ignored. This avoids - * breaking up write requests for only small sparse areas. + * Like is_allocated_sectors, but only at least 'min' consecutive sectors + * containing zeros are considered unallocated. This avoids breaking up write + * requests for only small sparse areas. */ static int is_allocated_sectors_min(const uint8_t *buf, int n, int *pnum, - int min) + int min) { - int ret; - int num_checked, num_used; - - if (n < min) { - min = n; - } - - ret = is_allocated_sectors(buf, n, pnum); - if (!ret) { - return ret; - } - - num_used = *pnum; - buf += BDRV_SECTOR_SIZE * *pnum; - n -= *pnum; - num_checked = num_used; + int ret, num_checked = 0, num_used = 0; while (n > 0) { ret = is_allocated_sectors(buf, n, pnum); - buf += BDRV_SECTOR_SIZE * *pnum; n -= *pnum; num_checked += *pnum; - if (ret) { - num_used = num_checked; - } else if (*pnum >= min) { + if (!ret && *pnum >= min) { break; } + num_used = num_checked; } - *pnum = num_used; - return 1; + if (num_used) { + *pnum = num_used; + } + + return !!num_used; } /*
the current implementation always splits requests if a buffer begins or ends with zeroes independent of the length of the zero area. Change this to really only split off zero areas that have at least a length of 'min' bytes. Signed-off-by: Peter Lieven <pl@kamp.de> --- qemu-img.c | 38 ++++++++++++-------------------------- 1 file changed, 12 insertions(+), 26 deletions(-)