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

[Laurent Vivier]

Le 12/07/2018 à 09:00, Shivaprasad G Bhat a écrit :
> 
> 
> 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 <address@hidden>
>>>> ---
>>>>   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 Shivaprasad,

> Hi Laurent, Thanks for the comments. I agree to the comments,
> sending the v2 accordingly.

Thank you.

I did some tests, (qemu-hppa on ppc64 with dpkg), and we need the
conversion with TARGET_NR_fcntl64 too because it also calls safe_fcntl()
for TARGET_F_SETLK64 and TARGET_F_SETLKW64.

Thanks,
Laurent