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

[Shivaprasad G Bhat <sbhat@linux.vnet.ibm.com>]

On 07/12/2018 02:21 AM, Laurent Vivier wrote:
> Le 11/07/2018 à 15:04, Laurent Vivier a écrit :
>> Le 11/07/2018 à 12:55, 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(generic) 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).
>>> Since F_*LK and F_*LK64 are same, the value adjument like done by glibc in
>>> qemu sources is difficult. So, Overwrite the glibc defaults with the actual
>>> supported values in Qemu. The current patch is doing this.
>>>
>>> Signed-off-by: Shivaprasad G Bhat <sbhat@linux.vnet.ibm.com>
>>> ---
>>>   linux-user/syscall.c |   14 ++++++++++++++
>>>   1 file changed, 14 insertions(+)
>>>
>>> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
>>> index 7b9ac3b408..1693e69ce0 100644
>>> --- a/linux-user/syscall.c
>>> +++ b/linux-user/syscall.c
>>> @@ -250,6 +250,20 @@ static type name (type1 arg1,type2 arg2,type3 arg3,type4 arg4,type5 arg5,	\
>>>   #define TARGET_NR__llseek TARGET_NR_llseek
>>>   #endif
>>>   
>>> +/* glibc headers has these defined to 12, 13 and 14 and is not supported
>>> + * by kernel. The glibc fcntl call actually adjusts them back to 5, 6 and 7
>>> + * before making the syscall(). Since we make the syscall directly,
>>> + * overwite/adjust to what is supported by the kernel.
>>> + */
>>> +#if defined(__linux__) && defined(__powerpc64__)
>>> +#undef F_GETLK64
>>> +#define F_GETLK64      5       /* Get record locking info.  */
>>> +#undef F_SETLK64
>>> +#define F_SETLK64      6       /* Set record locking info (non-blocking).  */
>>> +#undef F_SETLKW64
>>> +#define F_SETLKW64     7       /* Set record locking info (blocking).  */
>>> +#endif
>>> +
>>>   #ifdef __NR_gettid
>>>   _syscall0(int, gettid)
>>>   #else
>>>
>> These macros are used in target_to_host_fcntl_cmd(), and this function
>> is used with safe_fcntl() and fcntl().
>>
>> So I think it would be cleaner to do the change after
>> target_to_host_fcntl_cmd() in do_fcntl() as it is done in glibc instead
>> of redefining system values. Something like:
>>
>> --- a/linux-user/syscall.c
>> +++ b/linux-user/syscall.c
>> @@ -6782,6 +6782,12 @@ static abi_long do_fcntl(int fd, int cmd,
>> abi_ulong arg)
>>       if (host_cmd == -TARGET_EINVAL)
>>              return host_cmd;
>>
>> +#if defined(__linux__) && defined(__powerpc64__)
>> +    if (host_cmd >= F_GETLK64 && host_cmd <= F_SETLKW64) {
>> +        host_cmd -= F_GETLK64 - F_GETLK;
> But as you said, __USE_FILE_OFFSET64 is defined in qemu, and F_GETLK is
> equal to F_GETLK64, so we should use something like:
>
> ...
>      host_cmd -= F_GETLK64 - 5;
> ...
Hi Laurent, Thanks for the comments. I agree to the comments,
sending the v2 accordingly.

Thanks,
Shivaprasad

>
> Thanks,
> Laurent
>