Re: [PATCH v3 2/3] linux: statvfs: allocate spare for f_type

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 03/07/23 11:59, наб via Libc-alpha wrote:
> This is the only missing part in struct statvfs.
> The LSB calls [f]statfs() deprecated, and its weird types are definitely
> off-putting. However, its use is required to get f_type.
> 
> Instead, allocate one of the six spares to f_type,
> copied directly from struct .
> This then becomes a small glibc extension to the standard interface
> on Linux and the Hurd, instead of two different interfaces, one of which
> is quite odd due to being an ABI type, and there no longer is any reason
> to use statfs().
> 
> The underlying kernel type is a mess, but all architectures agree on u32
> (or more) for the ABI, and all filesystem magicks are 32-bit integers.
> 
> Link: https://lore.kernel.org/linux-man/f54kudgblgk643u32tb6at4cd3kkzha6hslahv24szs4raroaz@ogivjbfdaqtb/t/#u
> Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
> ---
>  sysdeps/unix/sysv/linux/bits/statvfs.h     | 6 ++++--
>  sysdeps/unix/sysv/linux/internal_statvfs.c | 2 ++
>  2 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/bits/statvfs.h b/sysdeps/unix/sysv/linux/bits/statvfs.h
> index 8dfb5ce761..cf98460e00 100644
> --- a/sysdeps/unix/sysv/linux/bits/statvfs.h
> +++ b/sysdeps/unix/sysv/linux/bits/statvfs.h
> @@ -51,7 +51,8 @@ struct statvfs
>  #endif
>      unsigned long int f_flag;
>      unsigned long int f_namemax;
> -    int __f_spare[6];
> +    unsigned int f_type;
> +    int __f_spare[5];
>    };
>  
>  #ifdef __USE_LARGEFILE64
> @@ -71,7 +72,8 @@ struct statvfs64
>  #endif
>      unsigned long int f_flag;
>      unsigned long int f_namemax;
> -    int __f_spare[6];
> +    unsigned int f_type;
> +    int __f_spare[5];
>    };
>  #endif
>  

All ABIs define fstatfs/statfs64 as signed, as the constants in include/uapi/linux/magic.h.
Should we do the same here?

> diff --git a/sysdeps/unix/sysv/linux/internal_statvfs.c b/sysdeps/unix/sysv/linux/internal_statvfs.c
> index 6a1b7b755f..112d3c241a 100644
> --- a/sysdeps/unix/sysv/linux/internal_statvfs.c
> +++ b/sysdeps/unix/sysv/linux/internal_statvfs.c
> @@ -57,6 +57,7 @@ __internal_statvfs (struct statvfs *buf, const struct statfs *fsbuf)
>    buf->__f_unused = 0;
>  #endif
>    buf->f_namemax = fsbuf->f_namelen;
> +  buf->f_type = fsbuf->f_type;
>    memset (buf->__f_spare, '\0', sizeof (buf->__f_spare));
>  
>    /* What remains to do is to fill the fields f_favail and f_flag.  */
> @@ -99,6 +100,7 @@ __internal_statvfs64 (struct statvfs64 *buf, const struct statfs64 *fsbuf)
>    buf->__f_unused = 0;
>  #endif
>    buf->f_namemax = fsbuf->f_namelen;
> +  buf->f_type = fsbuf->f_type;
>    memset (buf->__f_spare, '\0', sizeof (buf->__f_spare));
>  
>    /* What remains to do is to fill the fields f_favail and f_flag.  */