Re: [Qemu-devel] [PATCH] virtiofsd: fix compile error if 'F_OFD_GETLK' not defined

[piaojun]

Hi Eric,

On 2019/7/30 21:28, Eric Blake wrote:
> On 7/29/19 7:27 PM, piaojun wrote:
>> Use F_GETLK for fcntl when F_OFD_GETLK not defined.
> 
> Which system are you hitting this problem on?
> 
> The problem with F_GETLK is that it is NOT as safe as F_OFD_GETLK.
> 
> We already have fcntl_op_getlk and qemu_probe_lock_ops() in util/osdep.c
> to not only determine which form to use, but also to emit a warning to
> the end user if we had to fall back to the unsafe F_GETLK. Why is your
> code not reusing that logic?

virtiofsd compile error due to missed 'F_OFD_GETLK'. My kernel version is
3.10.

linux-PUALcm:/home/code/virtiofs/qemu # make -j 8 virtiofsd

make[1]: Entering directory `/home/code/virtiofs/qemu/slirp'
make[1]: Nothing to be done for `all'.
make[1]: Leaving directory `/home/code/virtiofs/qemu/slirp'
        CHK version_gen.h
  CC      contrib/virtiofsd/passthrough_ll.o
  CC      qapi/qapi-clone-visitor.o
  CC      qapi/qmp-event.o
  CC      qapi/qapi-util.o
  CC      qapi/qapi-builtin-types.o
  CC      qapi/qapi-types-audio.o
  CC      qapi/qapi-types-authz.o
  CC      qapi/qapi-types-block-core.o
contrib/virtiofsd/passthrough_ll.c: In function ‘lo_getlk’:
contrib/virtiofsd/passthrough_ll.c:1622:25: error: ‘F_OFD_GETLK’ undeclared 
(first use in this function)
  ret = fcntl(plock->fd, F_OFD_GETLK, lock);
                         ^
contrib/virtiofsd/passthrough_ll.c:1622:25: note: each undeclared identifier is 
reported only once for each function it appears in
contrib/virtiofsd/passthrough_ll.c: In function ‘lo_setlk’:
contrib/virtiofsd/passthrough_ll.c:1671:25: error: ‘F_OFD_SETLK’ undeclared 
(first use in this function)

> 
>>
>> Signed-off-by: Jun Piao <address@hidden>
>> ---
>>  contrib/virtiofsd/passthrough_ll.c | 9 +++++++++
>>  1 file changed, 9 insertions(+)
>>
>> diff --git a/contrib/virtiofsd/passthrough_ll.c 
>> b/contrib/virtiofsd/passthrough_ll.c
>> index 9ae1381..757785b 100644
>> --- a/contrib/virtiofsd/passthrough_ll.c
>> +++ b/contrib/virtiofsd/passthrough_ll.c
>> @@ -1619,7 +1619,11 @@ static void lo_getlk(fuse_req_t req, fuse_ino_t ino,
>>              return;
>>      }
>>
>> +#ifdef F_OFD_GETLK
>>      ret = fcntl(plock->fd, F_OFD_GETLK, lock);
>> +#else
>> +    ret = fcntl(plock->fd, F_GETLK, lock);
>> +#endif
> 
> Hmm. Since this is in contrib, you are trying to compile something that
> is independent of util/osdep.c (at least, I assume that's the case, as
> contrib/virtiofsd/ is not even part of qemu.git master yet - in which
> case, why is this not being squashed in to the patch introducing that
> file, rather than sent standalone).  On the other hand, that raises the
> question - who is trying to use virtiofsd on a kernel that is too old to
> provid F_OFD_GETLK?  Isn't the whole point of virtiofsd to be speeding
> up modern usage, at which point an old kernel is just gumming up the
> works?  It seems like you are better off letting compilation fail on a
> system that is too old to support decent F_OFD_GETLK, rather than
> silently falling back to something that is unsafe.

Perhaps reusing qemu_lock_fd() looks a better way to solve this.

Thanks,
Jun

>