Question about fcntl64

[Hongzhi, Song]

Append source code link:

https://github.com/linux-test-project/ltp/blob/7599ff232b98b4f8440e1410e8721822995877e2/testcases/kernel/syscalls/fcntl/fcntl34.c#L79

The problem is prompt on qemux86.


Thanks,
Hongzhi


On 2018年09月13日 09:10, Hongzhi, Song wrote:
>
>
> On 2018年09月13日 01:32, Florian Weimer wrote:
>> On 09/12/2018 04:23 PM, Hongzhi, Song wrote:
>>> Testcase source code: ltp/testcases/kernel/syscalls/fcntl/fcntl34.c
>>>
>>>
>>> In function 'thread_fn_01', struct flock64 lck.l_len is set '1'.
>>>
>>> thread_fn_01 ---> SAFE_FCNTL(fd, F_OFD_SETLKW, &lck) ---> fcntl64
>>
>> Please quote the relevant parts of the source code.  What is SAFE_FNCTL?
>>
>
> OK,
>
> 1.part of source code: ltp/testcases/kernel/syscalls/fcntl/fcntl34.c
> ---
> struct flock64 lck = {
> Â Â Â  Â Â Â Â Â  .l_whence = SEEK_SET,
>           .l_start  = 0,
> --->    .l_len    = 1, <---
> };
> lck.l_type = F_WRLCK
> SAFE_FCNTL(fd, F_OFD_SETLKW, &lck);
> ---
>
> 2.SAFE_FCNTL is defined as a macro:
> ---
> #define SAFE_FCNTL(fd, cmd, ...)Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  \
> Â Â  ---> ({int tst_ret_ = fcntl(fd, cmd, ##__VA_ARGS__);Â Â Â Â  \ <---
>       tst_ret_ == -1 ?                                  \
>        tst_brk(TBROK | TERRNO,                          \
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  "fcntl(%i,%s,...) failed", fd, #cmd), 0 \
> Â Â Â Â  : tst_ret_;})
> ---
>
> 3. I used "strace -f ./fcntl34" found that: l_len was changed to '0'.
>
> fcntl64(6, F_OFD_SETLKW, {l_type=F_WRLCK, l_whence=SEEK_SET, 
> l_start=0, ---> l_len=0 <---}
>
> 4. The question is that l_len was set '1', but why it is changed to 
> '0' when it is passed to fcntl64.
>
> Thanks,
> --Hongzhi
>
>> Thanks,
>> Florian
>>
>
>