linux-kernel - RE: [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs

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Message-ID: <33710E6CAA200E4583255F4FB666C4E21B120583@G01JPEXMBYT03>
Date:   Mon, 30 Oct 2017 11:07:20 +0000
From:   "Hatayama, Daisuke" <d.hatayama@...fujitsu.com>
To:     "'marcandre.lureau@...hat.com'" <marcandre.lureau@...hat.com>
CC:     "'somlo@....edu'" <somlo@....edu>,
        "'mst@...hat.com'" <mst@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "'qemu-devel@...gnu.org'" <qemu-devel@...gnu.org>
Subject: RE: [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs

> From: Marc-André Lureau <marcandre.lureau@...hat.com>
>
> Since qemu 2.9, DMA write operations are allowed. However, usage of this
> interface from kernel or user-space is strongly discouraged by the
> maintainers. This patch is meant for experimentations for now.
>

Could you (or maintainers?) tell me how experimental the DMA write
operations from kernel are?

From some technical reason?
Or simply there has not been enough test yet so far?

> Signed-off-by: Marc-André Lureau <marcandre.lureau@...hat.com>
> ---
>  drivers/firmware/qemu_fw_cfg.c | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
> index 54b569da3257..e2f2ad1c9c0c 100644
> --- a/drivers/firmware/qemu_fw_cfg.c
> +++ b/drivers/firmware/qemu_fw_cfg.c
> @@ -524,9 +524,28 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
>       return fw_cfg_read_blob(entry->f.select, buf, pos, count, true);
>  }
>
> +static ssize_t fw_cfg_sysfs_write_raw(struct file *filp, struct kobject *kobj,
> +                                   struct bin_attribute *bin_attr,
> +                                   char *buf, loff_t pos, size_t count)
> +{
> +     struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
> +
> +     if (!fw_cfg_dma_enabled())
> +             return -ENOTSUPP;
> +
> +     if (pos > entry->f.size)
> +             return -EINVAL;
> +
> +     if (count > entry->f.size - pos)
> +             count = entry->f.size - pos;
> +
> +     return fw_cfg_write_blob(entry->f.select, buf, pos, count);
> +}
> +
>  static struct bin_attribute fw_cfg_sysfs_attr_raw = {
> -     .attr = { .name = "raw", .mode = S_IRUSR },
> +     .attr = { .name = "raw", .mode = S_IRUSR | S_IWUSR },
>       .read = fw_cfg_sysfs_read_raw,
> +     .write = fw_cfg_sysfs_write_raw,
>  };
>
>  /*
> --
> 2.14.1.146.gd35faa819

Thanks.
HATAYAMA, Daisuke