Re: [Qemu-devel] [PATCH v3] linux-user: ppc64: use the correct values for F_*LK64s

[Laurent Vivier]

Le 13/07/2018 à 08:16, Shivaprasad G Bhat a écrit :
> Qemu includes the glibc headers for the host defines and target headers are
> part of the qemu source themselves. The glibc has the F_GETLK64, F_SETLK64
> and F_SETLKW64 defined to 12, 13 and 14 for all archs in
> sysdeps/unix/sysv/linux/bits/fcntl-linux.h. The linux kernel generic
> definition for F_*LK is 5, 6 & 7 and F_*LK64* is 12,13, and 14 as seen in
> include/uapi/asm-generic/fcntl.h. On 64bit machine, by default the kernel
> assumes all F_*LK to 64bit calls and doesnt support use of F_*LK64* as
> can be seen in include/linux/fcntl.h in linux source.
> 
> On x86_64 host, the values for F_*LK64* are set to 5, 6 and 7
> explicitly in /usr/include/x86_64-linux-gnu/bits/fcntl.h by the glibc.
> Whereas, a PPC64 host doesn't have such a definition in
> /usr/include/powerpc64le-linux-gnu/bits/fcntl.h by the glibc. So,
> the sources on PPC64 host sees the default value of F_*LK64*
> as 12, 13 & 14(fcntl-linux.h).
> 
> Since the 64bit kernel doesnt support 12, 13 & 14; the glibc fcntl syscall
> implementation(__libc_fcntl*(), __fcntl64_nocancel) does the F_*LK64* value
> convertion back to F_*LK* values on PPC64 as seen in
> sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h with FCNTL_ADJUST_CMD()
> macro. Whereas on x86_64 host the values for F_*LK64* are set to 5, 6 and 7
> and no adjustments are needed.
> 
> Since qemu doesnt use the glibc fcntl, but makes the safe_syscall* on its
> own, the PPC64 qemu is calling the syscall with 12, 13, and 14(without
> adjustment) and they all fail. The fcntl calls to F_GETLK/F_SETLK|W all
> fail by all pplications run on PPC64 host user emulation.
> 
> The fix here could be to see why on PPC64 the glibc is still keeping
> F_*LK64* different from F_*LK and why adjusting them to 5, 6 and 7 before
> the syscall for PPC only. See if we can make the
> /usr/include/powerpc64le-linux-gnu/bits/fcntl.h to have the values
> 5, 6 & 7 just like x86_64 and remove the adjustment code in glibc. That
> way, qemu sources see the kernel supported values in glibc headers.
> 
> OR
> 
> On PPC64 host, qemu sources see both F_*LK & F_*LK64* as same and set to
> 12, 13 and 14 because __USE_FILE_OFFSET64 is defined in qemu
> sources(also refer sysdeps/unix/sysv/linux/bits/fcntl-linux.h).
> Do the value adjustment just like it is done by glibc source by using
> F_GETLK value of 5. That way, we make the syscalls with the actual
> supported values in Qemu. The patch is taking this approach.
> 
> Signed-off-by: Shivaprasad G Bhat <address@hidden>
> ---
>  v2 - https://lists.gnu.org/archive/html/qemu-devel/2018-07/msg02920.html
>  Changes from v2:
>     - Fixed the braces, and indentation for comments.
>  v1 - https://lists.gnu.org/archive/html/qemu-devel/2018-07/msg02567.html
>  Changes from v1:
>     - Changed the overwrite of F*LK64* with 5, 6 and 7 in using #define
>       instead using the adjustment code similar to glibc as suggested.
>     - Dropped __linux__ check for the adjustment code as suggested.
>     - Moved the adjustment code inside target_to_host_fcntl_cmd to address
>       all possible|future cases.
> 
>  linux-user/syscall.c |   74 
> ++++++++++++++++++++++++++++++++++++--------------
>  1 file changed, 53 insertions(+), 21 deletions(-)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 643b8833de..7fb595269f 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -6475,63 +6475,95 @@ static int do_fork(CPUArchState *env, unsigned int 
> flags, abi_ulong newsp,
>  /* warning : doesn't handle linux specific flags... */
>  static int target_to_host_fcntl_cmd(int cmd)
>  {
> +    int ret = -TARGET_EINVAL;

as you have a default case in the switch, you don't need to initialize
it here.

>      switch(cmd) {
>       case TARGET_F_DUPFD:
>       case TARGET_F_GETFD:
>       case TARGET_F_SETFD:
>       case TARGET_F_GETFL:
>       case TARGET_F_SETFL:
> -            return cmd;
> +            ret = cmd;
> +            break;

As you change all the entries of the switch, could you modify the
indentation to follow the coding style of QEMU:
  - don't use tabulation
  - switch and case at the same indent
  - indentation increment is four spaces

>          case TARGET_F_GETLK:
> -            return F_GETLK64;
> +            ret = F_GETLK64;
> +            break;
>          case TARGET_F_SETLK:
> -            return F_SETLK64;
> +            ret = F_SETLK64;
> +            break;
>          case TARGET_F_SETLKW:
> -            return F_SETLKW64;
> +            ret = F_SETLKW64;
> +            break;
>       case TARGET_F_GETOWN:
> -         return F_GETOWN;
> +            ret = F_GETOWN;
> +            break;
>       case TARGET_F_SETOWN:
> -         return F_SETOWN;
> +            ret = F_SETOWN;
> +            break;
>       case TARGET_F_GETSIG:
> -         return F_GETSIG;
> +            ret = F_GETSIG;
> +            break;
>       case TARGET_F_SETSIG:
> -         return F_SETSIG;
> +            ret = F_SETSIG;
> +            break;
>  #if TARGET_ABI_BITS == 32
>          case TARGET_F_GETLK64:
> -         return F_GETLK64;
> +            ret = F_GETLK64;
> +            break;
>       case TARGET_F_SETLK64:
> -         return F_SETLK64;
> +            ret = F_SETLK64;
> +            break;
>       case TARGET_F_SETLKW64:
> -         return F_SETLKW64;
> +            ret = F_SETLKW64;
> +            break;
>  #endif
>          case TARGET_F_SETLEASE:
> -            return F_SETLEASE;
> +            ret = F_SETLEASE;
> +            break;
>          case TARGET_F_GETLEASE:
> -            return F_GETLEASE;
> +            ret = F_GETLEASE;
> +            break;
>  #ifdef F_DUPFD_CLOEXEC
>          case TARGET_F_DUPFD_CLOEXEC:
> -            return F_DUPFD_CLOEXEC;
> +            ret = F_DUPFD_CLOEXEC;
> +            break;
>  #endif
>          case TARGET_F_NOTIFY:
> -            return F_NOTIFY;
> +            ret = F_NOTIFY;
> +            break;
>  #ifdef F_GETOWN_EX
>       case TARGET_F_GETOWN_EX:
> -         return F_GETOWN_EX;
> +            ret = F_GETOWN_EX;
> +            break;
>  #endif
>  #ifdef F_SETOWN_EX
>       case TARGET_F_SETOWN_EX:
> -         return F_SETOWN_EX;
> +            ret = F_SETOWN_EX;
> +            break;
>  #endif
>  #ifdef F_SETPIPE_SZ
>          case TARGET_F_SETPIPE_SZ:
> -            return F_SETPIPE_SZ;
> +            ret = F_SETPIPE_SZ;
> +            break;
>          case TARGET_F_GETPIPE_SZ:
> -            return F_GETPIPE_SZ;
> +            ret = F_GETPIPE_SZ;
> +            break;
>  #endif
>       default:
> -            return -TARGET_EINVAL;
> +            ret = -TARGET_EINVAL;

Could you add the "break" here, even if it is useless, we always add it.

> +    }
> +
> +#if defined(__powerpc64__)
> +    /* On PPC64, glibc headers has the F_*LK* defined to 12, 13 and 14 and
> +     * is not supported by kernel. The glibc fcntl call actually adjusts
> +     * them to 5, 6 and 7 before making the syscall(). Since we make the
> +     * syscall directly, adjust to what is supported by the kernel.
> +     */
> +    if (ret >= F_GETLK64 && ret <= F_SETLKW64) {
> +        ret -= F_GETLK64 - 5;
>      }
> -    return -TARGET_EINVAL;
> +#endif
> +
> +    return ret;
>  }
>  
>  #define TRANSTBL_CONVERT(a) { -1, TARGET_##a, -1, a }
> 

otherwise, the patch looks good.

Thanks,
Laurent