Re: [Qemu-devel] [PATCH 5/5] block: Avoid bdrv_get_geometry() where errors should be detected

[Kevin Wolf]

Am 09.05.2014 um 11:48 hat Markus Armbruster geschrieben:
> bdrv_get_geometry() hides errors.  Use bdrv_nb_sectors() or
> bdrv_getlength() instead where that's obviously inappropriate.
> 
> Signed-off-by: Markus Armbruster <address@hidden>

> @@ -1167,7 +1174,7 @@ static int img_convert(int argc, char **argv)
>      BlockDriver *drv, *proto_drv;
>      BlockDriverState **bs = NULL, *out_bs = NULL;
>      int64_t total_sectors, nb_sectors, sector_num, bs_offset;
> -    uint64_t bs_sectors;
> +    int64_t *bs_sectors = NULL;
>      uint8_t * buf = NULL;
>      size_t bufsectors = IO_BUF_SIZE / BDRV_SECTOR_SIZE;
>      const uint8_t *buf1;
> @@ -1307,7 +1314,8 @@ static int img_convert(int argc, char **argv)
>  
>      qemu_progress_print(0, 100);
>  
> -    bs = g_malloc0(bs_n * sizeof(BlockDriverState *));
> +    bs = g_new(BlockDriverState *, bs_n);
> +    bs_sectors = g_new(int64_t, bs_n);
>  
>      total_sectors = 0;
>      for (bs_i = 0; bs_i < bs_n; bs_i++) {
> @@ -1321,8 +1329,14 @@ static int img_convert(int argc, char **argv)
>              ret = -1;
>              goto out;
>          }
> -        bdrv_get_geometry(bs[bs_i], &bs_sectors);
> -        total_sectors += bs_sectors;
> +        bs_sectors[bs_i] = bdrv_nb_sectors(bs[bs_i]);
> +        if (bs_sectors[bs_i] < 0) {
> +            error_report("Could not get size of %s: %s",
> +                         argv[optind + bs_i], strerror(-bs_sectors[bs_i]));
> +            ret = -1;
> +            goto out;
> +        }
> +        total_sectors += bs_sectors[bs_i];
>      }
>  
>      if (sn_opts) {
> @@ -1446,7 +1460,6 @@ static int img_convert(int argc, char **argv)
>  
>      bs_i = 0;
>      bs_offset = 0;
> -    bdrv_get_geometry(bs[0], &bs_sectors);
>  
>      /* increase bufsectors from the default 4096 (2M) if opt_transfer_length
>       * or discard_alignment of the out_bs is greater. Limit to 32768 (16MB)
> @@ -1512,19 +1525,19 @@ static int img_convert(int argc, char **argv)
>              buf2 = buf;
>              while (remainder > 0) {
>                  int nlow;
> -                while (bs_num == bs_sectors) {
> +                while (bs_num == bs_sectors[bs_i]) {
>                      bs_i++;
>                      assert (bs_i < bs_n);
> -                    bs_offset += bs_sectors;
> -                    bdrv_get_geometry(bs[bs_i], &bs_sectors);
> +                    bs_offset += bs_sectors[bs_i];

bs_i is already incremented here, so you're accessing the new bs_sectors
instead of the old one.

>                      bs_num = 0;
>                      /* printf("changing part: sector_num=%" PRId64 ", "
>                         "bs_i=%d, bs_offset=%" PRId64 ", bs_sectors=%" PRId64
> -                       "\n", sector_num, bs_i, bs_offset, bs_sectors); */
> +                       "\n", sector_num, bs_i, bs_offset, bs_sectors[bs_i]); 
> */
>                  }
> -                assert (bs_num < bs_sectors);
> +                assert (bs_num < bs_sectors[bs_i]);
>  
> -                nlow = (remainder > bs_sectors - bs_num) ? bs_sectors - 
> bs_num : remainder;
> +                nlow = remainder > bs_sectors[bs_i] - bs_num
> +                    ? bs_sectors[bs_i] - bs_num : remainder;
>  
>                  ret = bdrv_read(bs[bs_i], bs_num, buf2, nlow);
>                  if (ret < 0) {
> @@ -1585,14 +1598,13 @@ restart:
>                  break;
>              }
>  
> -            while (sector_num - bs_offset >= bs_sectors) {
> +            while (sector_num - bs_offset >= bs_sectors[bs_i]) {
> +                bs_offset += bs_sectors[bs_i];
>                  bs_i ++;

Here you got the order right.

>                  assert (bs_i < bs_n);
> -                bs_offset += bs_sectors;
> -                bdrv_get_geometry(bs[bs_i], &bs_sectors);
>                  /* printf("changing part: sector_num=%" PRId64 ", bs_i=%d, "
>                    "bs_offset=%" PRId64 ", bs_sectors=%" PRId64 "\n",
> -                   sector_num, bs_i, bs_offset, bs_sectors); */
> +                   sector_num, bs_i, bs_offset, bs_sectors[bs_i]); */
>              }
>  
>              if ((out_baseimg || has_zero_init) &&
> @@ -1645,7 +1657,7 @@ restart:
>                  }
>              }
>  
> -            n = MIN(n, bs_sectors - (sector_num - bs_offset));
> +            n = MIN(n, bs_sectors[bs_i] - (sector_num - bs_offset));
>  
>              sectors_read += n;
>              if (count_allocated_sectors) {
> @@ -1703,6 +1715,7 @@ out:
>          }
>          g_free(bs);
>      }
> +    g_free(bs_sectors);
>  fail_getopt:
>      g_free(options);

This is not a trivial change that can be done while you're touching the
code for fixing the error paths. The error checking is only a small part
of it, while the main objective seems to be caching image sizes so that
bdrv_getlength() needs to be called only once. I'm not sure if this
optimisation is worthwhile, but if so, it should be a separate patch.

Kevin