linux-kernel - Re: [PATCH v2 3/5] pstore: support multiple pmsg instances

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Date:   Thu, 8 Sep 2016 14:33:52 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Nobuhiro Iwamatsu <nobuhiro.iwamatsu.kw@...achi.com>
Cc:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Hiraku Toyooka <hiraku.toyooka.gu@...achi.com>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Seiji Aguchi <seiji.aguchi.tr@...achi.com>
Subject: Re: [PATCH v2 3/5] pstore: support multiple pmsg instances

On Sun, Jul 24, 2016 at 8:56 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: Mark Salyzyn <salyzyn@...roid.com>
> Cc: Seiji Aguchi <seiji.aguchi.tr@...achi.com>
> ---
>  fs/pstore/pmsg.c       | 20 ++++++++++++++++++--
>  include/linux/pstore.h |  1 +
>  2 files changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/fs/pstore/pmsg.c b/fs/pstore/pmsg.c
> index 7de20cd..2e281ed 100644
> --- a/fs/pstore/pmsg.c
> +++ b/fs/pstore/pmsg.c
> @@ -52,8 +52,8 @@ static ssize_t write_pmsg(struct file *file, const char __user *buf,
>                         vfree(buffer);
>                         return -EFAULT;
>                 }
> -               psinfo->write_buf(PSTORE_TYPE_PMSG, 0, &id, 0, buffer, 0, c,
> -                                 psinfo);
> +               psinfo->write_buf(PSTORE_TYPE_PMSG, 0, &id,
> +                                 iminor(file->f_inode), buffer, 0, c, psinfo);
>
>                 i += c;
>         }
> @@ -85,6 +85,7 @@ static char *pmsg_devnode(struct device *dev, umode_t *mode)
>  void pstore_register_pmsg(void)
>  {
>         struct device *pmsg_device;
> +       int i = 0;
>
>         pmsg_major = register_chrdev(0, PMSG_NAME, &pmsg_fops);
>         if (pmsg_major < 0) {
> @@ -105,9 +106,24 @@ void pstore_register_pmsg(void)
>                 pr_err("failed to create device\n");
>                 goto err_device;
>         }
> +
> +       /* allocate additional /dev/pmsg[ID] */
> +       for (i = 1; 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;
> +               }
> +       }

This should just be merged into the first device_create call (i.e.
drop the first one, keep your loop, but have "i" start at 0). There's
no reason that I can see to do it separately.

>         return;
>
>  err_device:
> +       for (i--; i >= 0; i--)
> +               device_destroy(pmsg_class, MKDEV(pmsg_major, i));

Was the device_destroy() for /dev/pmsg0 missing before? (i.e. does
class_destroy() or unregister_chrdev() already clean up the devices?)

>         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 831479f..b0c24cc 100644
> --- a/include/linux/pstore.h
> +++ b/include/linux/pstore.h
> @@ -54,6 +54,7 @@ struct pstore_info {
>         size_t          bufsize;
>         struct mutex    read_mutex;     /* serialize open/read/close */
>         int             flags;
> +       unsigned int    num_pmsg;
>         int             (*open)(struct pstore_info *psi);
>         int             (*close)(struct pstore_info *psi);
>         ssize_t         (*read)(u64 *id, enum pstore_type_id *type,
> --
> 2.8.1
>
>

-Kees


-- 
Kees Cook
Nexus Security