On Tue, Jun 08, 2021 at 03:16:28PM +0200, 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, so add support for it. The block device
> path is kept because it will be reinstated in the next patches.
>
> Signed-off-by: Paolo Bonzini <pbonz...@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..536998a1d6 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) {
Do we need to do any conditional compilation based on whether
SG_GET_SG_TABLESIZE is a known ioctl, or is it old enough to be
assumed present on all platforms we care about?
> + return ret;
> + }
> + return -ENOTSUP;
> + }
> +
> + 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);
Otherwise looks good to me.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
