linux-kernel - Re: [PATCH 1/2]pstore: Move timestamp collection code to common pstore place

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Date:   Mon, 22 May 2017 16:37:37 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Ankit Kumar <ankit@...ux.vnet.ibm.com>
Cc:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "mahesh@...ux.vnet.ibm.com" <mahesh@...ux.vnet.ibm.com>,
        Hari Bathini <hbathini@...ux.vnet.ibm.com>,
        hegdevasant@...ux.vnet.ibm.com
Subject: Re: [PATCH 1/2]pstore: Move timestamp collection code to common
 pstore place

On Mon, May 22, 2017 at 3:20 AM, Ankit Kumar <ankit@...ux.vnet.ibm.com> wrote:
> Current pstore code(ram.c) gets dump timestamp and make it part of header.
> Different diffent architecture uses different header format and hence it
> won't be good idea to make ramoops_write_kmsg_hdr/ramoops_read_kmsg_hdr
> part of generic pstore code.
>
> ramoops_write_kmsg_hdr calls __getnstimeofday to get timestamp and also
> takes care of condition if timekeeping has not resumed.
>
> This patch moves code for retrieving timestamp to common place and hence
> can be used by other functions as well.

Ah! Heh, funny, I had just done a version of this while working on EFI
pstore fixes. Here's what I did instead:

https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?h=pstore/fixes&id=ea209b760f104daf0cf62953090b66c5628b0842

This makes it so the time field is prepopulated for all backend
writes, which should simplify things (no need to have the backends
call out).

-Kees

>
> Signed-off-by: Ankit Kumar <ankit@...ux.vnet.ibm.com>
> ---
>  fs/pstore/internal.h |  1 +
>  fs/pstore/platform.c | 13 +++++++++++++
>  fs/pstore/ram.c      |  9 ++++-----
>  3 files changed, 18 insertions(+), 5 deletions(-)
>
> diff --git a/fs/pstore/internal.h b/fs/pstore/internal.h
> index c416e65..339dcdc 100644
> --- a/fs/pstore/internal.h
> +++ b/fs/pstore/internal.h
> @@ -22,6 +22,7 @@ static inline void pstore_unregister_pmsg(void) {}
>  #endif
>
>  extern struct pstore_info *psinfo;
> +void pstore_get_timestamp(struct timespec *timestamp);
>
>  extern void    pstore_set_kmsg_bytes(int);
>  extern void    pstore_get_records(int);
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index d468eec..5cb25b0 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -474,6 +474,19 @@ static size_t copy_kmsg_to_buffer(int hsize, size_t len)
>         return total_len;
>  }
>
> +void pstore_get_timestamp(struct timespec *timestamp)
> +{
> +       if (!timestamp)
> +               return;
> +
> +       /* Report zeroed timestamp if called before timekeeping has resumed. */
> +       if (__getnstimeofday(timestamp)) {
> +               timestamp->tv_sec = 0;
> +               timestamp->tv_nsec = 0;
> +       }
> +}
> +EXPORT_SYMBOL_GPL(pstore_get_timestamp);
> +
>  /*
>   * callback from kmsg_dump. (s2,l2) has the most recently
>   * written bytes, older bytes are in (s1,l1). Save as much
> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> index 5cb022c..e39297d 100644
> --- a/fs/pstore/ram.c
> +++ b/fs/pstore/ram.c
> @@ -37,6 +37,8 @@
>  #include <linux/of.h>
>  #include <linux/of_address.h>
>
> +#include "internal.h"
> +
>  #define RAMOOPS_KERNMSG_HDR "===="
>  #define MIN_MEM_SIZE 4096UL
>
> @@ -362,11 +364,8 @@ static size_t ramoops_write_kmsg_hdr(struct persistent_ram_zone *prz,
>         struct timespec timestamp;
>         size_t len;
>
> -       /* Report zeroed timestamp if called before timekeeping has resumed. */
> -       if (__getnstimeofday(&timestamp)) {
> -               timestamp.tv_sec = 0;
> -               timestamp.tv_nsec = 0;
> -       }
> +       pstore_get_timestamp(&timestamp);
> +
>         hdr = kasprintf(GFP_ATOMIC, RAMOOPS_KERNMSG_HDR "%lu.%lu-%c\n",
>                 (long)timestamp.tv_sec, (long)(timestamp.tv_nsec / 1000),
>                 compressed ? 'C' : 'D');
> --
> 2.7.4
>



-- 
Kees Cook
Pixel Security