linux-kernel - RE: [PATCH v4 2nd 2/4] pstore: support multiple pmsg instances

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Date:   Tue, 7 Feb 2017 08:44:54 +0000
From:   岩松信洋 / IWAMATSU，NOBUHIRO 
        <nobuhiro.iwamatsu.kw@...achi.com>
To:     Kees Cook <keescook@...omium.org>
CC:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        "Tony Luck" <tony.luck@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Mark Salyzyn <salyzyn@...roid.com>,
        阿口誠司 / AGUCHI，SEIJI 
        <seiji.aguchi.tr@...achi.com>
Subject: RE: [PATCH v4 2nd 2/4] pstore: support multiple pmsg instances

Hi,

Thanks for your review.

> -----Original Message-----
> From: keescook@...gle.com [mailto:keescook@...gle.com] On Behalf Of Kees
> Cook
> Sent: Thursday, February 02, 2017 5:29 AM
> To: 岩松信洋 / IWAMATSU，NOBUHIRO
> Cc: Anton Vorontsov; Colin Cross; Tony Luck; LKML; Hiraku Toyooka; Mark
> Salyzyn; 阿口誠司 / AGUCHI，SEIJI
> Subject: Re: [PATCH v4 2nd 2/4] pstore: support multiple pmsg instances
> 
> On Mon, Jan 30, 2017 at 5:58 PM, Nobuhiro Iwamatsu
> <nobuhiro.iwamatsu.kw@...achi.com> wrote:
> > From: Hiraku Toyooka <hiraku.toyooka.gu@...achi.com>
> >
> > This enables pmsg to deal with multiple instances. One possible use is
> > content priority control on limited persistent store space. By using
> > different buffers, we can prevent important messages from being
> > overwritten by less important messages.
> >
> > When pstore backend module specifies the number of instances
> > (num_pmsg) in pstore_info, multiple /dev/pmsg[ID] appear. (ID is an
> > integer starting at 0. It corresponds to minor number of the each char
> > device.) Writes to each /dev/pmsg[ID] are isolated each other. After
> > reboot, the contents are available in
> /sys/fs/pstore/pmsg-[backend]-[ID].
> >
> > Signed-off-by: Hiraku Toyooka <hiraku.toyooka.gu@...achi.com>
> > Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.kw@...achi.com>
> > Cc: Anton Vorontsov <anton@...msg.org>
> > Cc: Colin Cross <ccross@...roid.com>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Mark Salyzyn <salyzyn@...roid.com>
> > Cc: Seiji Aguchi <seiji.aguchi.tr@...achi.com>
> > Cc: Tony Luck <tony.luck@...el.com>
> >
> > V4:
> >     Rebase.
> > V3:
> >     rebase.
> >     merged device_create().
> > ---
> >  fs/pstore/pmsg.c       | 23 ++++++++++++++++-------
> >  include/linux/pstore.h |  1 +
> >  2 files changed, 17 insertions(+), 7 deletions(-)
> >
> > diff --git a/fs/pstore/pmsg.c b/fs/pstore/pmsg.c index
> > 78f6176c020f..5da5cba4b387 100644
> > --- a/fs/pstore/pmsg.c
> > +++ b/fs/pstore/pmsg.c
> > @@ -34,7 +34,8 @@ static ssize_t write_pmsg(struct file *file, const char
> __user *buf,
> >                 return -EFAULT;
> >
> >         mutex_lock(&pmsg_lock);
> > -       ret = psinfo->write_buf_user(PSTORE_TYPE_PMSG, 0, &id, 0, buf,
> 0, count,
> > +       ret = psinfo->write_buf_user(PSTORE_TYPE_PMSG, 0, &id,
> > +                                    iminor(file->f_inode), buf, 0,
> > + count,
> >                                      psinfo);
> >         mutex_unlock(&pmsg_lock);
> >         return ret ? ret : count;
> > @@ -61,7 +62,7 @@ static char *pmsg_devnode(struct device *dev,
> > umode_t *mode)
> >
> >  void pstore_register_pmsg(void)
> >  {
> > -       struct device *pmsg_device;
> > +       int i;
> >
> >         pmsg_major = register_chrdev(0, PMSG_NAME, &pmsg_fops);
> >         if (pmsg_major < 0) {
> > @@ -76,15 +77,23 @@ void pstore_register_pmsg(void)
> >         }
> >         pmsg_class->devnode = pmsg_devnode;
> >
> > -       pmsg_device = device_create(pmsg_class, NULL, MKDEV(pmsg_major,
> 0),
> > -                                       NULL, "%s%d", PMSG_NAME, 0);
> > -       if (IS_ERR(pmsg_device)) {
> > -               pr_err("failed to create device\n");
> > -               goto err_device;
> > +       /* allocate additional /dev/pmsg[ID] */
> 
> This isn't "additional" any more, but rather "Allocate each pmsg device"
> or something.

OK, I will fix.
> 
> > +       for (i = 0; i < psinfo->num_pmsg; i++) {
> > +               struct device *pmsg_device;
> > +
> > +               pmsg_device = device_create(pmsg_class, NULL,
> > +                                           MKDEV(pmsg_major, i), NULL,
> "%s%d",
> > +                                           PMSG_NAME, i);
> > +               if (IS_ERR(pmsg_device)) {
> > +                       pr_err("failed to create device\n");
> > +                       goto err_device;
> > +               }
> >         }
> >         return;
> >
> >  err_device:
> > +       for (i--; i >= 0; i--)
> > +               device_destroy(pmsg_class, MKDEV(pmsg_major, i));
> >         class_destroy(pmsg_class);
> >  err_class:
> >         unregister_chrdev(pmsg_major, PMSG_NAME); diff --git
> > a/include/linux/pstore.h b/include/linux/pstore.h index
> > 0da29cae009b..7a5db4833b8a 100644
> > --- a/include/linux/pstore.h
> > +++ b/include/linux/pstore.h
> > @@ -55,6 +55,7 @@ struct pstore_info {
> >         size_t          bufsize;
> >         struct mutex    read_mutex;     /* serialize open/read/close
> */
> >         int             flags;
> > +       unsigned int    num_pmsg;
> 
> Something in this patch needs to set num_pmsg to 1 unconditionally, so that
> bisectability is retained. I.e. after this patch, I should still get a
> /dev/pmsg0 device. Right now, it will be skipped since num_pmsg will always
> == 0.

Indeed, I will fix too.

Best regards,
  Nobuhiro