Re: [Qemu-devel] [PATCH v4] linux-user: ppc64: use the correct values for F_*LK64s

[Laurent Vivier]

Le 14/07/2018 à 03:07, David Gibson a écrit :
> On Fri, Jul 13, 2018 at 07:34:46AM -0500, Shivaprasad G Bhat wrote:
>> 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>
> 
> Reviewed-by: David Gibson <address@hidden>
> 
> I'm not sure if this should go in through my tree or not.

I will take it through my linux-user tree, I have some fixes to send for
the next -rc.

Thanks,
Laurent

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