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Date:   Wed, 4 Mar 2020 18:55:56 +0100
From:   Karel Zak <kzak@redhat.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Ian Kent <raven@themaw.net>, Miklos Szeredi <miklos@szeredi.hu>,
        David Howells <dhowells@redhat.com>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        James Bottomley <James.Bottomley@hansenpartnership.com>,
        Steven Whitehouse <swhiteho@redhat.com>,
        Miklos Szeredi <mszeredi@redhat.com>,
        viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <christian@brauner.io>,
        Jann Horn <jannh@google.com>,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        Linux API <linux-api@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 00/17] VFS: Filesystem information and notifications [ver
 #17]
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On Wed, Mar 04, 2020 at 05:49:13PM +0100, Greg Kroah-Hartman wrote:
> On Wed, Mar 04, 2020 at 04:22:41PM +0100, Karel Zak wrote:
> > $ strace -e openat,read,close -c ps aux
> > ...
> > % time     seconds  usecs/call     calls    errors syscall
> > ------ ----------- ----------- --------- --------- ----------------
> >  43.32    0.004190           4       987           read
> >  31.42    0.003039           3       844         4 openat
> >  25.26    0.002443           2       842           close
> > ------ ----------- ----------- --------- --------- ----------------
> > 100.00    0.009672                  2673         4 total
> >=20
> > $ strace -e openat,read,close -c lsns
> > ...
> > % time     seconds  usecs/call     calls    errors syscall
> > ------ ----------- ----------- --------- --------- ----------------
> >  39.95    0.001567           2       593           openat
> >  30.93    0.001213           2       597           close
> >  29.12    0.001142           3       365           read
> > ------ ----------- ----------- --------- --------- ----------------
> > 100.00    0.003922                  1555           total
> >=20
> >=20
> > $ strace -e openat,read,close -c lscpu
> > ...
> > % time     seconds  usecs/call     calls    errors syscall
> > ------ ----------- ----------- --------- --------- ----------------
> >  44.67    0.001480           7       189        52 openat
> >  34.77    0.001152           6       180           read
> >  20.56    0.000681           4       140           close
> > ------ ----------- ----------- --------- --------- ----------------
> > 100.00    0.003313                   509        52 total
>=20
> As a "real-world" test, would you recommend me converting one of the
> above tools to my implementation of readfile to see how/if it actually
> makes sense, or do you have some other tool you would rather see me try=
?

See lib/path.c and lib/sysfs.c in util-linux (https://github.com/karelzak=
/util-linux).=20
For example ul_path_read() and ul_path_scanf().=20

We use it for lsblk, lsmem, lscpu, etc.

=A0$ git grep -c ul_path_read misc-utils/lsblk.c sys-utils/lscpu.c
 misc-utils/lsblk.c:30
 sys-utils/lscpu.c:31

We're probably a little bit off-topic here, no problem to continue on
util-linux@vger.kernel.org or by private mails. Thanks!

    Karel

--=20
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com