[LTP] [PATCH] syscalls/statx06: use a fine-grained timestamp for the second time fetch

[LTP] [PATCH] syscalls/statx06: use a fine-grained timestamp for the second time fetch

[Jeff Layton]

I have a patchset in progress to change the kernel to sometimes use
fine-grained timestamps for the mtime/ctime. With this, the statx06 test
sometimes fails.

Change the test to grab a fine-grained timestamp for the "after" value,
which fixes the issue.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 testcases/kernel/syscalls/statx/statx06.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/testcases/kernel/syscalls/statx/statx06.c b/testcases/kernel/syscalls/statx/statx06.c
index ce82b905bebd..fa75982b0901 100644
--- a/testcases/kernel/syscalls/statx/statx06.c
+++ b/testcases/kernel/syscalls/statx/statx06.c
@@ -109,7 +109,7 @@ static void test_statx(unsigned int test_nr)
 	clock_wait_tick();
 	tc->operation();
 	clock_wait_tick();
-	SAFE_CLOCK_GETTIME(CLOCK_REALTIME_COARSE, &after_time);
+	SAFE_CLOCK_GETTIME(CLOCK_REALTIME, &after_time);
 
 	TEST(statx(AT_FDCWD, TEST_FILE, 0, STATX_ALL, &buff));
 	if (TST_RET != 0) {
-- 
2.40.1


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Re: [LTP] [PATCH] syscalls/statx06: use a fine-grained timestamp for the second time fetch

[Yang Xu (Fujitsu)]

on 2023/05/18 19:32, Jeff Layton wrote:
> I have a patchset in progress to change the kernel to sometimes use
> fine-grained timestamps for the mtime/ctime. With this, the statx06 test
> sometimes fails.
> 
> Change the test to grab a fine-grained timestamp for the "after" value,
> which fixes the issue.

Now, it is not a right time to review this patch,  I prefer to review 
this when your kernel patchset is merged into linux master or 
linux-next. Then we can add a comment or a kernel commit id to explain 
this..

Best Regard
Yang Xu

> 
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>   testcases/kernel/syscalls/statx/statx06.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/testcases/kernel/syscalls/statx/statx06.c b/testcases/kernel/syscalls/statx/statx06.c
> index ce82b905bebd..fa75982b0901 100644
> --- a/testcases/kernel/syscalls/statx/statx06.c
> +++ b/testcases/kernel/syscalls/statx/statx06.c
> @@ -109,7 +109,7 @@ static void test_statx(unsigned int test_nr)
>   	clock_wait_tick();
>   	tc->operation();
>   	clock_wait_tick();
> -	SAFE_CLOCK_GETTIME(CLOCK_REALTIME_COARSE, &after_time);
> +	SAFE_CLOCK_GETTIME(CLOCK_REALTIME, &after_time);
>   
>   	TEST(statx(AT_FDCWD, TEST_FILE, 0, STATX_ALL, &buff));
>   	if (TST_RET != 0) {

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Re: [LTP] [PATCH] syscalls/statx06: use a fine-grained timestamp for the second time fetch

[Jeff Layton]

On Fri, 2023-05-19 at 09:16 +0000, Yang Xu (Fujitsu) wrote:
> 
> on 2023/05/18 19:32, Jeff Layton wrote:
> > I have a patchset in progress to change the kernel to sometimes use
> > fine-grained timestamps for the mtime/ctime. With this, the statx06 test
> > sometimes fails.
> > 
> > Change the test to grab a fine-grained timestamp for the "after" value,
> > which fixes the issue.
> 
> Now, it is not a right time to review this patch,  I prefer to review 
> this when your kernel patchset is merged into linux master or 
> linux-next. Then we can add a comment or a kernel commit id to explain 
> this..
> 
> 

Fair enough. I don't think there is any issue with taking this patch in
earlier however.

The problem with this test is that it makes the assumption that coarse-
grained timestamps are sufficient to bracket a filesystem operation.
While that has largely been true in the past, it's certainly not
specified by any standard.

> > 
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> >   testcases/kernel/syscalls/statx/statx06.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/testcases/kernel/syscalls/statx/statx06.c b/testcases/kernel/syscalls/statx/statx06.c
> > index ce82b905bebd..fa75982b0901 100644
> > --- a/testcases/kernel/syscalls/statx/statx06.c
> > +++ b/testcases/kernel/syscalls/statx/statx06.c
> > @@ -109,7 +109,7 @@ static void test_statx(unsigned int test_nr)
> >   	clock_wait_tick();
> >   	tc->operation();
> >   	clock_wait_tick();
> > -	SAFE_CLOCK_GETTIME(CLOCK_REALTIME_COARSE, &after_time);
> > +	SAFE_CLOCK_GETTIME(CLOCK_REALTIME, &after_time);
> >   
> >   	TEST(statx(AT_FDCWD, TEST_FILE, 0, STATX_ALL, &buff));
> >   	if (TST_RET != 0) {

-- 
Jeff Layton <jlayton@kernel.org>

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Re: [LTP] [PATCH] syscalls/statx06: use a fine-grained timestamp for the second time fetch

[Cyril Hrubis]

Hi!
> > Now, it is not a right time to review this patch,  I prefer to review 
> > this when your kernel patchset is merged into linux master or 
> > linux-next. Then we can add a comment or a kernel commit id to explain 
> > this..
> > 
> > 
> 
> Fair enough. I don't think there is any issue with taking this patch in
> earlier however.
> 
> The problem with this test is that it makes the assumption that coarse-
> grained timestamps are sufficient to bracket a filesystem operation.
> While that has largely been true in the past, it's certainly not
> specified by any standard.

Do we have any API to ask the kernel what the granularity of filesystem
the timestamps is? Would that make sense to be added if it's not
present?

Apart from that I think that this patch is fine, since the
CLOCK_REALTIME value would be between CLOCK_REALTIME_COARSE and
CLOCK_REALTIME_COARSE + one tick. So the change is backward compatible
and we will not loose any precision in the assertions either.

Reviewed-by: Cyril Hrubis <chrubis@suse.cz>

-- 
Cyril Hrubis
chrubis@suse.cz

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Re: [LTP] [PATCH] syscalls/statx06: use a fine-grained timestamp for the second time fetch

[Jeff Layton]

On Wed, 2023-05-24 at 10:46 +0200, Cyril Hrubis wrote:
> Hi!
> > > Now, it is not a right time to review this patch,  I prefer to review 
> > > this when your kernel patchset is merged into linux master or 
> > > linux-next. Then we can add a comment or a kernel commit id to explain 
> > > this..
> > > 
> > > 
> > 
> > Fair enough. I don't think there is any issue with taking this patch in
> > earlier however.
> > 
> > The problem with this test is that it makes the assumption that coarse-
> > grained timestamps are sufficient to bracket a filesystem operation.
> > While that has largely been true in the past, it's certainly not
> > specified by any standard.
> 
> Do we have any API to ask the kernel what the granularity of filesystem
> the timestamps is? Would that make sense to be added if it's not
> present?
> 

No, we don't have such a thing now, and we don't really track that
information in the kernel.

We do have a sb->s_time_gran field which is in units of nanoseconds, but
that really is more about the granularity that the filesystem itself can
store on disk. It doesn't tell you whether the kernel decided to put a
coarse or fine grained timestamp in there.

> Apart from that I think that this patch is fine, since the
> CLOCK_REALTIME value would be between CLOCK_REALTIME_COARSE and
> CLOCK_REALTIME_COARSE + one tick. So the change is backward compatible
> and we will not loose any precision in the assertions either.
> 
> Reviewed-by: Cyril Hrubis <chrubis@suse.cz>
> 

Thanks, and yes. This should be safe to apply now even if the kernel
patch series never goes in.
-- 
Jeff Layton <jlayton@kernel.org>

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Re: [LTP] [PATCH] syscalls/statx06: use a fine-grained timestamp for the second time fetch

[Petr Vorel]

Hi all,

Reviewed-by: Petr Vorel <pvorel@suse.cz>

> Thanks, and yes. This should be safe to apply now even if the kernel
> patch series never goes in.

I'd be ok to merge this now. Xu, please let me know if you're against.

Kind regards,
Petr

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Re: [LTP] [PATCH] syscalls/statx06: use a fine-grained timestamp for the second time fetch

[Yang Xu (Fujitsu)]

Hi Petr

> Hi all,
> 
> Reviewed-by: Petr Vorel <pvorel@suse.cz>
> 
>> Thanks, and yes. This should be safe to apply now even if the kernel
>> patch series never goes in.
> 
> I'd be ok to merge this now. Xu, please let me know if you're against.

This patch is right, so please merged.

Reviewed-by: Yang Xu <xuyang2018.jy@fujitsu.com>

Best Regards
Yang Xu
> 
> Kind regards,
> Petr

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Re: [LTP] [PATCH] syscalls/statx06: use a fine-grained timestamp for the second time fetch

[Petr Vorel]

Hi all,

I merged the patchset, linking the original RFC patchset in kernel and
explaining that we merged it because the change is backward compatible anyway.

Thanks to all!

Kind regards,
Petr

[1] https://lore.kernel.org/lkml/20230411143702.64495-1-jlayton@kernel.org/

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