Re: [Qemu-devel] [PATCH for-2.9] block: Don't check permissions for copy on read

["Richard W.M. Jones" <rjones@redhat.com>]

On Fri, Apr 07, 2017 at 12:32:45PM +0200, Kevin Wolf wrote:
> The assertion is currently failing. We can't require callers to have
> write permissions when all they are doing is a read, so comment it out.
> Add a FIXME comment in the code so that the check is re-enabled when
> copy on read is refactored into its own filter driver.
> 
> Reported-by: Richard W.M. Jones <rjones@redhat.com>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Thanks Kevin.  As this is essentially the same as the patch I tested
last night,

  Reviewed-by: Richard W.M. Jones <rjones@redhat.com>

Rich.

>  block/io.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/block/io.c b/block/io.c
> index 2709a70..7321dda 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -945,7 +945,14 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild *child,
>      size_t skip_bytes;
>      int ret;
>  
> -    assert(child->perm & (BLK_PERM_WRITE_UNCHANGED | BLK_PERM_WRITE));
> +    /* FIXME We cannot require callers to have write permissions when all they
> +     * are doing is a read request. If we did things right, write permissions
> +     * would be obtained anyway, but internally by the copy-on-read code. As
> +     * long as it is implemented here rather than in a separat filter driver,
> +     * the copy-on-read code doesn't have its own BdrvChild, however, for which
> +     * it could request permissions. Therefore we have to bypass the permission
> +     * system for the moment. */
> +    // assert(child->perm & (BLK_PERM_WRITE_UNCHANGED | BLK_PERM_WRITE));
>  
>      /* Cover entire cluster so no additional backing file I/O is required when
>       * allocating cluster in the image file.
> -- 
> 1.8.3.1

-- 
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