On 12/11/20 12:39 PM, Vladimir Sementsov-Ogievskiy wrote:
> We are generally moving to int64_t for both offset and bytes parameters
> on all io paths.
>
> Main motivation is realization of 64-bit write_zeroes operation for
> fast zeroing large disk chunks, up to the whole disk.
>
> We chose signed type, to be consistent with off_t (which is signed) and
> with possibility for signed return type (where negative value means
> error).
>
> So, prepare bdrv_co_do_pwrite_zeroes() now.
>
> Callers are safe, as converting int to int64_t is safe. Concentrate on
> 'bytes' usage in the function (thx to Eric Blake):
>
> compute 'int tail' via % 'int alignment' - safe
> fragmentation loop 'int num' - still fragments with a cap on
> max_transfer
>
> use of 'num' within the loop
> MIN(bytes, max_transfer) as well as %alignment - still works, so
> calculations in if (head) {} are safe
> clamp size by 'int max_write_zeroes' - safe
> drv->bdrv_co_pwrite_zeroes(int) - safe because of clamping
> clamp size by 'int max_transfer' - safe
> buf allocation is still clamped to max_transfer
> qemu_iovec_init_buf(size_t) - safe because of clamping
> bdrv_driver_pwritev(uint64_t) - safe
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
> ---
> block/io.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
Reviewed-by: Eric Blake <ebl...@redhat.com>
And thanks for including the gist of my previous audit - that greatly
speeds things up this time through. ;)
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
