On Fri, Aug 26, 2011 at 5:04 PM, Kevin Wolf <kw...@redhat.com> wrote:
> @@ -571,6 +573,48 @@ 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.
> + */
> +static int is_allocated_sectors_min(const uint8_t *buf, int n, int *pnum,
> + 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 += 512 * *pnum;
BDRV_SECTOR_SIZE
> + n -= *pnum;
> + num_checked = num_used;
> +
> + while (n > 0) {
> + ret = is_allocated_sectors(buf, n, pnum);
> +
> + buf += 512 * *pnum;
> + n -= *pnum;
> + num_checked += *pnum;
> + if (ret) {
> + num_used = num_checked;
> + } else if (*pnum >= min) {
> + break;
> + }
> + }
> +
> + *pnum = num_used;
> + return 1;
> +}
> +
> +/*
> * Compares two buffers sector by sector. Returns 0 if the first sector of
> both
> * buffers matches, non-zero otherwise.
> *
> @@ -620,6 +664,7 @@ static int img_convert(int argc, char **argv)
> char *options = NULL;
> const char *snapshot_name = NULL;
> float local_progress;
> + int min_sparse = 8; /* Need at least 4k of zeros for sparse detection */
>
> fmt = NULL;
> out_fmt = "raw";
> @@ -627,7 +672,7 @@ static int img_convert(int argc, char **argv)
> out_baseimg = NULL;
> compress = 0;
> for(;;) {
> - c = getopt(argc, argv, "f:O:B:s:hce6o:pt:");
> + c = getopt(argc, argv, "f:O:B:s:hce6o:pS:t:");
> if (c == -1) {
> break;
> }
> @@ -662,6 +707,18 @@ static int img_convert(int argc, char **argv)
> case 's':
> snapshot_name = optarg;
> break;
> + case 'S':
> + {
> + int64_t sval;
> + sval = strtosz_suffix(optarg, NULL, STRTOSZ_DEFSUFFIX_B);
> + if (sval < 0) {
> + error_report("Invalid minimum zero buffer size for sparse
> output specified");
> + return 1;
> + }
> +
> + min_sparse = sval / BDRV_SECTOR_SIZE;
> + break;
> + }
> case 'p':
> progress = 1;
> break;
> @@ -970,7 +1027,7 @@ static int img_convert(int argc, char **argv)
> sectors that are entirely 0, since whatever data was
> already there is garbage, not 0s. */
> if (!has_zero_init || out_baseimg ||
> - is_allocated_sectors(buf1, n, &n1)) {
> + is_allocated_sectors_min(buf1, n, &n1, min_sparse)) {
> ret = bdrv_write(out_bs, sector_num, buf1, n1);
> if (ret < 0) {
> error_report("error while writing sector %" PRId64
> diff --git a/qemu-img.texi b/qemu-img.texi
> index 495a1b6..a0579e7 100644
> --- a/qemu-img.texi
> +++ b/qemu-img.texi
> @@ -40,6 +40,9 @@ indicates that target image must be compressed (qcow format
> only)
> with or without a command shows help and lists the supported formats
> @item -p
> display progress bar (convert and rebase commands only)
> +@item -S @var{size}
> +indicates the consecutive number of bytes that must contain only zeros
> +for qemu-img to create a sparse image during conversion
For completeness (and to encourage people to use 1024 multiples
instead of 1000):
"This value is rounded down to the nearest 512 bytes."
> @end table
>
> Parameters to snapshot subcommand:
> @@ -86,7 +89,7 @@ it doesn't need to be specified separately in this case.
>
> Commit the changes recorded in @var{filename} in its base image.
>
> -@item convert [-c] [-p] [-f @var{fmt}] [-O @var{output_fmt}] [-o
> @var{options}] [-s @var{snapshot_name}] @var{filename} [@var{filename2}
> [...]] @var{output_filename}
> +@item convert [-c] [-p] [-f @var{fmt}] [-O @var{output_fmt}] [-o
> @var{options}] [-s @var{snapshot_name}] [-S @var{sprase_size}] @var{filename}
> [@var{filename2} [...]] @var{output_filename}
s/sprase_size/sparse_size/
Stefan
