Re: [Qemu-devel] [PATCH v2 2/4] nvdimm: warn if the backend is not a DAX device

[Stefan Hajnoczi]

On Tue, Jun 06, 2017 at 03:22:27PM +0800, Haozhong Zhang wrote:
> diff --git a/util/osdep.c b/util/osdep.c
> index a2863c8e53..02881f96bc 100644
> --- a/util/osdep.c
> +++ b/util/osdep.c
> @@ -471,3 +471,64 @@ writev(int fd, const struct iovec *iov, int iov_cnt)
>      return readv_writev(fd, iov, iov_cnt, true);
>  }
>  #endif
> +
> +#ifdef __linux__
> +static ssize_t qemu_dev_dax_sysfs_read(int fd, const char *entry,
> +                                       char *buf, size_t len)
> +{
> +    ssize_t read_bytes;
> +    struct stat st;
> +    unsigned int major, minor;
> +    char *path, *pos;
> +    int sysfs_fd;
> +
> +    if (fstat(fd, &st)) {
> +        return 0;
> +    }
> +
> +    major = major(st.st_rdev);
> +    minor = minor(st.st_rdev);
> +    path = g_strdup_printf("/sys/dev/char/%u:%u/%s", major, minor, entry);
> +
> +    sysfs_fd = open(path, O_RDONLY);
> +    g_free(path);
> +    if (sysfs_fd == -1) {
> +        return 0;
> +    }
> +
> +    read_bytes = read(sysfs_fd, buf, len - 1);
> +    close(sysfs_fd);
> +    if (read_bytes > 0) {
> +        buf[read_bytes] = '\0';
> +        pos = g_strstr_len(buf, read_bytes, "\n");
> +        if (pos) {
> +            *pos = '\0';
> +        }

Should read_bytes be adjusted since we made the string shorter?

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