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

[Vladimir Sementsov-Ogievskiy]

03.06.2021 16:37, 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.

I assume, you keep /sys/dev/block code branch here only for following 
converting of the function to be hdev_get_max_hw_transfer()? Worth mentioning 
here?

> 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)) {

Should it be instead "if (bs->sg) {" ? As SG_GET_SG_TABLESIZE looks like 
sg-specific, not for any chardev.

Also, st is not a pointer, so here and in the next if condition it should be 
s/st->/st./

> +        if (ioctl(fd, SG_GET_SG_TABLESIZE, &ret) == 0) {
> +            return ret;
> +        }
> +        return -EIO;
> +    }
> +
> +    if (!S_ISBLK(st->st_mode)) {
> +        return -ENOTSUP;
> +    }
> +
>       sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/max_segments",
>                                   major(st.st_rdev), minor(st.st_rdev));
>       sysfd = open(sysfspath, O_RDONLY);


--
Best regards,
Vladimir