linux-kernel - Re: [PATCH v3 2/4] selftests: cgroup: return the errno of write() in cg

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Date:   Fri, 8 Apr 2022 18:44:41 -0700
From:   Roman Gushchin <roman.gushchin@...ux.dev>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <shuah@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Wei Xu <weixugc@...gle.com>, Greg Thelen <gthelen@...gle.com>,
        Chen Wandun <chenwandun@...wei.com>,
        Vaibhav Jain <vaibhav@...ux.ibm.com>,
        Michal Koutný <mkoutny@...e.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>, cgroups@...r.kernel.org,
        linux-doc@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 2/4] selftests: cgroup: return the errno of write() in
 cg_write() on failure

On Fri, Apr 08, 2022 at 06:21:55PM -0700, Yosry Ahmed wrote:
> On Thu, Apr 7, 2022 at 9:57 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
> >
> > Currently, cg_write() returns 0 on success and -1 on failure. Modify it
> > to return the errno of write() syscall when write() fails.
> >
> > Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
> > ---
> >  tools/testing/selftests/cgroup/cgroup_util.c | 32 +++++++++++---------
> >  1 file changed, 17 insertions(+), 15 deletions(-)
> >
> > diff --git a/tools/testing/selftests/cgroup/cgroup_util.c b/tools/testing/selftests/cgroup/cgroup_util.c
> > index dbaa7aabbb4a..3b6bb09985fa 100644
> > --- a/tools/testing/selftests/cgroup/cgroup_util.c
> > +++ b/tools/testing/selftests/cgroup/cgroup_util.c
> > @@ -38,23 +38,23 @@ static ssize_t read_text(const char *path, char *buf, size_t max_len)
> >         return len;
> >  }
> >
> > -static ssize_t write_text(const char *path, char *buf, ssize_t len)
> > +/*
> > + * Returns:
> > + *     success -> 0
> > + *     open() failure -> -1
> > + *     write() failure -> errno
> > + */
> > +static int write_text(const char *path, char *buf, ssize_t len)
> >  {
> > -       int fd;
> > +       int fd, ret;
> >
> >         fd = open(path, O_WRONLY | O_APPEND);
> >         if (fd < 0)
> >                 return fd;
> >
> > -       len = write(fd, buf, len);
> > -       if (len < 0) {
> > -               close(fd);
> > -               return len;
> > -       }
> > -
> > +       ret = write(fd, buf, len) < 0 ? errno : 0;
> >         close(fd);
> > -
> > -       return len;
> > +       return ret;
> >  }
> >
> >  char *cg_name(const char *root, const char *name)
> > @@ -177,17 +177,19 @@ long cg_read_lc(const char *cgroup, const char *control)
> >         return cnt;
> >  }
> >
> > +/*
> > + * Returns:
> > + *     success -> 0
> > + *     open() failure -> -1
> > + *     write() failure -> errno
> > + */
> >  int cg_write(const char *cgroup, const char *control, char *buf)
> >  {
> >         char path[PATH_MAX];
> >         ssize_t len = strlen(buf);
> >
> >         snprintf(path, sizeof(path), "%s/%s", cgroup, control);
> > -
> > -       if (write_text(path, buf, len) == len)
> > -               return 0;
> > -
> > -       return -1;
> > +       return write_text(path, buf, len);
> >  }
> 
> I have changed this in v4 to a cleaner implementation that either
> returns 0 on success or -errno on failure. I also made sure to check
> that the full buffer was being written, and updated cg_read() as well
> for the interface to be consistent.
> 
> Will send out once the discussion on patch 1 in v3 reaches a consensus.

Ok, sounds good, please feel free to add my
Acked-by: Roman Gushchin <roman.gushchin@...ux.dev>
for the whole series. It looks really nice and ready for merging upstream to me.

Thanks!