Re: [PATCH] perf trace beautify: Beautify flags of mount(2) and umount(2).

[Benjamin Peterson <benjamin@python.org>]

Hi Arnaldo,
Did you get a chance to look at this again?

On Thu, Aug 30, 2018, at 14:50, Benjamin Peterson wrote:
> Thanks for the review.
> 
> On Thu, Aug 30, 2018, at 11:28, Arnaldo Carvalho de Melo wrote:
> > Em Mon, Aug 27, 2018 at 08:53:44PM -0700, Benjamin Peterson escreveu:
> > > Example output of perf trace -e mount,umount2:
> > > 
> > >   6243.930 ( 0.052 ms): mount/30976 mount(dev_name: 0x55dc541bb920, dir_name: 0x55dc541bc960, type: 0x55dc541b9c40, flags: BIND) = 0
> > >   7851.821 (26.015 ms): umount/30983 umount2(name: 0x558daa82cf50, flags: MNT_FORCE                        ) = 0
> > > 
> > > Signed-off-by: Benjamin Peterson <benjamin@python.org>
> > 
> > So, I tried:
> > 
> > Before your patch:
> > 
> >   # perf trace -e *mount* mount /dev/mapper/fedora-home /s
> >      0.000 ( 4.335 ms): mount/3126 mount(dev_name: 0x55deecc4d480, 
> > dir_name: 0x55deecc4d4a0, type: 0x55deecc53880, flags: 3236757504) = 0
> >   #
> >   # perf trace -e *mount* umount /dev/mapper/fedora-home /s
> >          ? (         ): umount/3138  ... [continued]: umount2()) = 0
> >     11.576 (umount:  0.004 ms): /s: not mounted.umount/
> > 3138 umount2(arg0: 94501956754656, arg1: 0, arg2: 1, arg3: 
> > 140051050083104, arg4: 4, arg5: 94501956755136) = -1 EINVAL Invalid 
> > argument
> >   #
> > 
> > After:
> > 
> > [root@jouet ~]# perf trace -e *mount* mount /dev/mapper/fedora-home /s
> >      0.000 ( 1.213 ms): mount/5244 mount(dev_name: 0x5558c1169480, 
> > dir_name: 0x5558c11694a0, type: 0x5558c116f880, flags: ) = 0
> > [root@jouet ~]# perf trace -e *mount* umount /s
> >      0.000 ( 9.241 ms): umount/5251 umount2(name: 
> > 0x55f74a986480                                          ) = 0
> > 
> > The flags for mount got empty? Can you pleaes check that? I.e. using the
> > default mount options, not specifying a 'bind' mount like you did.
> 
> That comes from these lines in syscall_arg__scnprintf_mount_flags:
> 
> if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
> 	flags &= ~MS_MGC_MSK;
> 
> The reason for this is explained in the comment for do_mount in fs/namespace.c:
> 
> /*
>  * Pre-0.97 versions of mount() didn't have a flags word.
>  * When the flags word was introduced its top half was required
>  * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
>  * Therefore, if this magic number is present, it carries no information
>  * and must be discarded.
> */
> 
> (I used a bind mount for my commit message example because a "default" 
> mount() doesn't use any flags.)
> 
> > 
> > I'm splitting this patch so that the aliasing of 'umount2' to 'umount'
> > gets merged now,
> > 
> > Check my perf/core branch at:
> > 
> > git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git
> 
> LGTM. Thanks
>