Re: [PATCH v6 3/8] file-posix: introduce get_sysfs_str_val for device zoned model

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Fri, Aug 05, 2022 at 03:57:46PM +0800, Sam Li wrote:
> Use sysfs attribute files to get the string value of device
> zoned model. Then get_sysfs_zoned_model can convert it to
> BlockZoneModel type in QEMU.
> 
> Signed-off-by: Sam Li <faithilikerun@gmail.com>
> Reviewed-by: Hannes Reinecke <hare@suse.de>
> ---
>  block/file-posix.c               | 70 ++++++++++++++++++++++++++++++++
>  include/block/block_int-common.h |  3 ++
>  2 files changed, 73 insertions(+)
> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index a40eab64a2..4785203eea 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -1264,6 +1264,68 @@ out:
>  #endif
>  }
>  
> +/*
> + * Convert the zoned attribute file in sysfs to internal value.
> + */
> +static int get_sysfs_str_val(int fd, struct stat *st,
> +                              const char *attribute,
> +                              char **val) {

The fd argument is unused and can be dropped.

> +#ifdef CONFIG_LINUX
> +    char *buf = NULL;
> +    g_autofree char *sysfspath = NULL;
> +    int ret;
> +    size_t len;
> +
> +    if (!S_ISBLK(st->st_mode)) {
> +        return -ENOTSUP;
> +    }
> +
> +    sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/%s",
> +                                major(st->st_rdev), minor(st->st_rdev),
> +                                attribute);
> +    ret = g_file_get_contents(sysfspath, &buf, &len, NULL);
> +    if (ret == -1) {
> +        ret = -errno;

g_file_get_contents() does not set errno. You can either pass in a
GError and report the message string by converting it into a QEMU Error
object (grep for g_file_get_contents() to see example), or you can
return a fixed error code like -ENOENT.

> +        return ret;
> +    }
> +
> +    /* The file is ended with '\n' */
> +    if (buf[len - 1] == '\n') {
> +        buf[len - 1] = '\0';
> +    }
> +
> +    if (!strncpy(*val, buf, len)) {
> +        ret = -errno;
> +        return ret;
> +    }
> +    g_free(buf);

buf is not necessary. val can be passed directly to g_file_get_contents().

> +    return 0;
> +#else
> +    return -ENOTSUP;
> +#endif
> +}

Now get_sysfs_long_val() can be written using get_sysfs_str_val():

  static long get_sysfs_long_val(struct stat *st, const char *attribute)
  {
      g_autofree char *str = NULL;
      const char *end;
      long val;
      int ret;

      ret = get_sysfs_str_val(st, attribute, &str);
      if (ret < 0) {
          return ret;
      }

      ret = qemu_strtol(str, &end, 10, &val);
      if (ret == 0 && end && *end == '\0') {
          ret = val;
      }
      return ret;
  }

The get_sysfs_long_val() patch can be moved after the
get_sysfs_str_val() patch.

> +
> +static int get_sysfs_zoned_model(int fd, struct stat *st,
> +                                 BlockZoneModel *zoned) {
> +    g_autofree char *val = NULL;
> +    val = g_malloc(32);
> +    get_sysfs_str_val(fd, st, "zoned", &val);

Once get_sysfs_str_val() passes val through to g_get_file_contents() the
caller will no longer have to g_malloc() val themselves.

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