Re: [RFC v5 03/11] file-posix: introduce get_sysfs_long_val for the long sysfs attribute

[Stefan Hajnoczi <stefanha@gmail.com>]

On Sun, 31 Jul 2022 at 21:39, Sam Li <faithilikerun@gmail.com> wrote:
>
> Use sysfs attribute files to get the long value of zoned device
> information.
>
> Signed-off-by: Sam Li <faithilikerun@gmail.com>
> ---
>  block/file-posix.c | 23 ++++++++++++++++-------
>  1 file changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 48cd096624..bcf898f0cb 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -1210,15 +1210,19 @@ static int hdev_get_max_hw_transfer(int fd, struct stat *st)
>  #endif
>  }
>
> -static int hdev_get_max_segments(int fd, struct stat *st)
> -{
> +/*
> + * Get zoned device information (chunk_sectors, zoned_append_max_bytes,
> + * max_open_zones, max_active_zones) through sysfs attribute files.
> + */
> +static long get_sysfs_long_val(int fd, struct stat *st,
> +                               const char *attribute) {
>  #ifdef CONFIG_LINUX
>      char buf[32];
>      const char *end;
>      char *sysfspath = NULL;
>      int ret;
>      int sysfd = -1;
> -    long max_segments;
> +    long val;
>
>      if (S_ISCHR(st->st_mode)) {
>          if (ioctl(fd, SG_GET_SG_TABLESIZE, &ret) == 0) {

This code is specific to max_segments and not relevant to other
attributes. It's an alternative code path for SCSI generic types of
devices. It should be moved into hdev_get_max_segments() before
get_sysfs_long_val() is called.

> @@ -1231,8 +1235,9 @@ static int hdev_get_max_segments(int fd, struct stat *st)
>          return -ENOTSUP;
>      }
>
> -    sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/max_segments",
> -                                major(st->st_rdev), minor(st->st_rdev));
> +    sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/%s",
> +                                major(st->st_rdev), minor(st->st_rdev),
> +                                attribute);
>      sysfd = open(sysfspath, O_RDONLY);
>      if (sysfd == -1) {
>          ret = -errno;
> @@ -1250,9 +1255,9 @@ static int hdev_get_max_segments(int fd, struct stat *st)
>      }
>      buf[ret] = 0;
>      /* The file is ended with '\n', pass 'end' to accept that. */
> -    ret = qemu_strtol(buf, &end, 10, &max_segments);
> +    ret = qemu_strtol(buf, &end, 10, &val);
>      if (ret == 0 && end && *end == '\n') {
> -        ret = max_segments;
> +        ret = val;
>      }
>
>  out:
> @@ -1266,6 +1271,10 @@ out:
>  #endif
>  }
>
> +static int hdev_get_max_segments(int fd, struct stat *st) {
> +    return get_sysfs_long_val(fd, st, "max_segments");
> +}
> +
>  static void raw_refresh_limits(BlockDriverState *bs, Error **errp)
>  {
>      BDRVRawState *s = bs->opaque;
> --
> 2.37.1
>
>