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Date: Thu, 2 Jun 2016 14:52:34 +0800
From: Fam Zheng <famz@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 1/2] raw-posix: Fetch max sectors for host
 block device from sysfs
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To: qemu-devel@nongnu.org, kwolf@redhat.com, mreitz@redhat.com
Cc: qemu-block@nongnu.org

On Thu, 05/26 14:15, Fam Zheng wrote:
> This is sometimes a useful value we should count in.

Kevin, Max, could you review this please?

Fam

> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  block/raw-posix.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 47 insertions(+)
> 
> diff --git a/block/raw-posix.c b/block/raw-posix.c
> index a4f5a1b..d3796ad 100644
> --- a/block/raw-posix.c
> +++ b/block/raw-posix.c
> @@ -729,9 +729,56 @@ static void raw_reopen_abort(BDRVReopenState *state)
>      state->opaque = NULL;
>  }
>  
> +static int hdev_get_max_transfer_length(dev_t dev)
> +{
> +    int ret;
> +    int fd;
> +    char *path;
> +    const char *end;
> +    char buf[32];
> +    long len;
> +
> +    path = g_strdup_printf("/sys/dev/block/%u:%u/queue/max_sectors_kb",
> +                           major(dev), minor(dev));
> +    fd = open(path, O_RDONLY);
> +    if (fd < 0) {
> +        ret = -errno;
> +        goto out;
> +    }
> +    ret = read(fd, buf, sizeof(buf));
> +    if (ret < 0) {
> +        ret = -errno;
> +        goto out;
> +    } else if (ret == 0) {
> +        ret = -EIO;
> +        goto out;
> +    }
> +    buf[ret] = 0;
> +    /* The file is ended with '\n', pass 'end' to accept that. */
> +    ret = qemu_strtol(buf, &end, 10, &len);
> +    if (ret == 0 && end && *end == '\n') {
> +        ret = len * 1024 / BDRV_SECTOR_SIZE;
> +    }
> +
> +    close(fd);
> +out:
> +    g_free(path);
> +    return ret;
> +}
> +
>  static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
>  {
>      BDRVRawState *s = bs->opaque;
> +    struct stat st;
> +
> +    if (!fstat(s->fd, &st)) {
> +        if (S_ISBLK(st.st_mode)) {
> +            int ret = hdev_get_max_transfer_length(st.st_rdev);
> +            if (ret >= 0) {
> +                bs->bl.max_transfer_length = ret;
> +            }
> +        }
> +    }
>  
>      raw_probe_alignment(bs, s->fd, errp);
>      bs->bl.min_mem_alignment = s->buf_align;
> -- 
> 2.8.2
> 
>