[LTP] [PATCH COMMITTED] tst_device: do sync() before reading test block device stat file

[Yang Xu]

on 2020/01/03 15:25, Li Wang wrote:
> 
> 
> On Thu, Jan 2, 2020 at 2:46 PM Yang Xu <xuyang2018.jy@cn.fujitsu.com 
> <mailto:xuyang2018.jy@cn.fujitsu.com>> wrote:
> 
> 
> 
>     on 2020/01/02 14:31, Li Wang wrote:
>      >
>      >
>      > On Thu, Jan 2, 2020 at 10:10 AM Yang Xu
>     <xuyang2018.jy@cn.fujitsu.com <mailto:xuyang2018.jy@cn.fujitsu.com>
>      > <mailto:xuyang2018.jy@cn.fujitsu.com
>     <mailto:xuyang2018.jy@cn.fujitsu.com>>> wrote:
>      >
>      >
>      >
>      >     Hi Li
>      >      > To avoid FS deferred IO metadata/cache interferes test
>     result, so we
>      >      > do sync simply before the tst_dev_bytes_written invocation.
>      >      >
>      >     Looks good, acked. Also, I think we can mention it in
>      >     doc/test-writing-guidelines.txt when using this api.
>      >
>      >
>      > Ok, I will append one line as:
>      > --- a/doc/test-writing-guidelines.txt
>      > +++ b/doc/test-writing-guidelines.txt
>      > @@ -1072,7 +1072,9 @@ unsigned long tst_dev_bytes_written(const
>     char *dev);
>      > 
>       -------------------------------------------------------------------------------
>      >
>      >   This function reads test block device stat file
>      > (/sys/block/<device>/stat) and
>      > -returns the bytes written since the last invocation of this
>     function.
>      > +returns the bytes written since the last invocation of this
>     function.
>      > To avoid
>      > +FS deferred IO metadata/cache interferes the test result, we
>     suggest
>      > doing sync()
>      > +before the tst_dev_bytes_written first invocation.
>     OK.
> 
>     I also meet another problem when using this api on old kernel.
> 
>     tst_device.c:395: CONF: Test device stat file: /sys/block/loop0/stat
>     broken
> 
>     /sys/block/loop0/stat is all 0 and case reports TCONF. on new kernel,
>     this value is normal. This is a block layer or loop device driver
>     modifition several yeas ago?
> 
> 
> It sounds like a kernel issue, can you tell which kernel version you did 
> test?
> 
I test this on 3.10.0-1101.el7.x86_64. It also reports TCONF on old 
fedora such as fedora 20,21. I guess loop driver modification(I am 
verifying ...) causes it.
> 
>     ps:I know ltp used LOOP_SET_FD to make loop device simulate other
>     filesystems. I am trying to find a generic way about this api.
> 
>     Best Regards
>     Yang Xu
>      >
>      > --
>      > Regards,
>      > Li Wang
> 
> 
> 
> 
> -- 
> Regards,
> Li Wang