Re: [PATCH v3 1/7] file-posix: fix max_iov for /dev/sg devices

[Max Reitz]

On 03.06.21 15:37, Paolo Bonzini wrote:
> Even though it was only called for devices that have bs->sg set (which
> must be character devices),
> sg_get_max_segments looked at /sys/dev/block which only works for
> block devices.
>
> On Linux the sg driver has its own way to provide the maximum number of
> iovecs in a scatter/gather list.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   block/file-posix.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)
>
> diff --git a/block/file-posix.c b/block/file-posix.c
> index f37dfc10b3..58db526cc2 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -1180,6 +1180,17 @@ static int sg_get_max_segments(int fd)
>           goto out;
>       }
>   
> +    if (S_ISCHR(st->st_mode)) {
> +        if (ioctl(fd, SG_GET_SG_TABLESIZE, &ret) == 0) {
> +            return ret;
> +        }
> +        return -EIO;
> +    }
> +
> +    if (!S_ISBLK(st->st_mode)) {
> +        return -ENOTSUP;
> +    }
> +

With %s/->/./:

Reviewed-by: Max Reitz <mreitz@redhat.com>

(To answer Vladimir’s question, I don’t believe the condition should be 
bs->sg, because bs->sg == true is a given for this function anyway. 
Therefore, there’s no need to check whether the char device is an SG 
device.)