struct statfs/statfs64 in linux-generic

[Chung-Lin Tang <cltang@codesourcery.com>]

Hi,

I'm currently working on the glibc port for Altera Nios II, and per the
kernel upstreaming requirements, we're making it a user of linux-generic
in glibc.

I've come across an issue about struct statfs/statfs64, where I've
listed the struct definitions in both glibc and the kernel below.

In linux-generic, both struct statfs/statfs64 has some fields as 64-bit
words, padded properly if need on 32-bit targets. Effectively, they have
to be same-format, to pass to the statfs64 syscall uniformly.

__SWORD_TYPE appears to be int/long on 32/64-bit targets. This means
that for 32-bit targets, struct statfs[64] will be made of 32-bit words,
with a few 64-bit fields embedded in the middle.


In the kernel however, the fields of importance in struct statfs is made
up of entirely '__statfs_word', defined to be 64-bit or 32-bit depending
on target (putting aside signedness for now).

Notice how that, while this does work for 64-bit targets, 32-bit targets
cannot properly define a compatible struct statfs[64], at least not with
simple typedefs.

Chris, as you seem the original developer/maintainer of linux-generic
and the tile ports (as I observed from the mail archives), I'm curious
if you saw any similar problems with tilegx -m32? The only users of
linux-generic appears to be only aarch64 and tile, and nios2 will be
another 32-bit user.

The exact FAIL I saw was posix/tst-getconf, which I traced to a failed
statfs64 call in pathconf(), due to a failed sizeof(struct statfs64)
check inside the kernel syscall code.

Thanks,
Chung-Lin


In glibc, ports/sysdeps/unix/sysv/linux/generic/bits/statfs.h:
struct statfs
  {
    __SWORD_TYPE f_type;
    __SWORD_TYPE f_bsize;
    __field64(__fsblkcnt_t, __fsblkcnt64_t, f_blocks);
    __field64(__fsblkcnt_t, __fsblkcnt64_t, f_bfree);
    __field64(__fsblkcnt_t, __fsblkcnt64_t, f_bavail);
    __field64(__fsfilcnt_t, __fsfilcnt64_t, f_files);
    __field64(__fsfilcnt_t, __fsfilcnt64_t, f_ffree);
    __fsid_t f_fsid;
    __SWORD_TYPE f_namelen;
    __SWORD_TYPE f_frsize;
    __SWORD_TYPE f_flags;
    __SWORD_TYPE f_spare[4];
  } __attribute__((__aligned__(8)));

#ifdef __USE_LARGEFILE64
struct statfs64
  {
    __SWORD_TYPE f_type;
    __SWORD_TYPE f_bsize;
    __fsblkcnt64_t f_blocks;
    __fsblkcnt64_t f_bfree;
    __fsblkcnt64_t f_bavail;
    __fsfilcnt64_t f_files;
    __fsfilcnt64_t f_ffree;
    __fsid_t f_fsid;
    __SWORD_TYPE f_namelen;
    __SWORD_TYPE f_frsize;
    __SWORD_TYPE f_flags;
    __SWORD_TYPE f_spare[4];
  } __attribute__((__aligned__(8)));
#endif


In Linux kernel, include/uapi/asm-generic/statfs.h:

#ifndef __statfs_word
#if __BITS_PER_LONG == 64
#define __statfs_word long
#else
#define __statfs_word __u32
#endif
#endif

struct statfs {
        __statfs_word f_type;
        __statfs_word f_bsize;
        __statfs_word f_blocks;
        __statfs_word f_bfree;
        __statfs_word f_bavail;
        __statfs_word f_files;
        __statfs_word f_ffree;
        __kernel_fsid_t f_fsid;
        __statfs_word f_namelen;
        __statfs_word f_frsize;
        __statfs_word f_flags;
        __statfs_word f_spare[4];
};

#ifndef ARCH_PACK_STATFS64
#define ARCH_PACK_STATFS64
#endif

struct statfs64 {
        __statfs_word f_type;
        __statfs_word f_bsize;
        __u64 f_blocks;
        __u64 f_bfree;
        __u64 f_bavail;
        __u64 f_files;
        __u64 f_ffree;
        __kernel_fsid_t f_fsid;
        __statfs_word f_namelen;
        __statfs_word f_frsize;
        __statfs_word f_flags;
        __statfs_word f_spare[4];
} ARCH_PACK_STATFS64;