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

[David Gibson <david@gibson.dropbear.id.au>]

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On Sat, Jul 14, 2018 at 07:37:43AM +0200, Laurent Vivier wrote:
> 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 <sbhat@linux.vnet.ibm.com>
> > 
> > Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> > 
> > 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.

Great, thanks.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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