On Mon, Sep 26, 2016 at 04:30:46PM -0700, Song Liu wrote:
> r5c_state have 4 states:
> * no-cache;
> * write-through (write journal only);
> * write-back (w/ write cache);
> * cache-broken (journal missing or Faulty)
>
> When there is functional write cache, r5c_state is a knob to
> switch between write-back and write-through.
>
> When the journal device is broken, the raid array is forced
> in readonly mode. In this case, r5c_state can be used to
> remove "journal feature", and thus make the array read-write
> without journal. By writing into r5c_cache_mode, the array
> can transit from cache-broken to no-cache, which removes
> journal feature for the array.
How will user use the new interface? I suppose
-raid array is forced readonly mode (by kernel)
-user uses the new interface to remove journal
-user forces array read-write
-kernel will update superblock and array can run read/write
please describe
>
> Signed-off-by: Song Liu <songliubraving@xxxxxx>
> ---
> drivers/md/raid5-cache.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++++
> drivers/md/raid5.c | 1 +
> drivers/md/raid5.h | 2 ++
> 3 files changed, 60 insertions(+)
>
> diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
> index 6b28461..0a0b16a 100644
> --- a/drivers/md/raid5-cache.c
> +++ b/drivers/md/raid5-cache.c
> @@ -54,6 +54,9 @@ enum r5c_state {
> R5C_STATE_CACHE_BROKEN = 3,
> };
>
> +static char *r5c_state_str[] = {"no-cache", "write-through",
> + "write-back", "cache-broken"};
> +
> struct r5l_log {
> struct md_rdev *rdev;
>
> @@ -1242,6 +1245,60 @@ int r5c_flush_cache(struct r5conf *conf, int num)
> return count;
> }
>
> +ssize_t r5c_state_show(struct mddev *mddev, char *page)
> +{
> + struct r5conf *conf = mddev->private;
> + int val = 0;
> + int ret = 0;
> +
> + if (conf->log)
> + val = conf->log->r5c_state;
> + else if (test_bit(MD_HAS_JOURNAL, &mddev->flags))
> + val = R5C_STATE_CACHE_BROKEN;
> + ret += snprintf(page, PAGE_SIZE - ret, "%d: %s\n",
> + val, r5c_state_str[val]);
> + return ret;
> +}
> +
> +ssize_t r5c_state_store(struct mddev *mddev, const char *page, size_t len)
> +{
> + struct r5conf *conf = mddev->private;
> + struct r5l_log *log = conf->log;
> + int val;
> +
> + if (kstrtoint(page, 10, &val))
> + return -EINVAL;
> + if (!log && val != R5C_STATE_NO_CACHE)
> + return -EINVAL;
> +
> + if (val < R5C_STATE_NO_CACHE || val > R5C_STATE_WRITE_BACK)
> + return -EINVAL;
> + if (val == R5C_STATE_NO_CACHE) {
> + if (conf->log &&
> + !test_bit(Faulty, &log->rdev->flags)) {
> + pr_err("md/raid:%s: journal device is in use, cannot remove it\n",
> + mdname(mddev));
> + return -EINVAL;
> + }
> + }
> +
> + spin_lock_irq(&conf->device_lock);
> + if (log)
> + conf->log->r5c_state = val;
> + if (val == R5C_STATE_NO_CACHE) {
> + clear_bit(MD_HAS_JOURNAL, &mddev->flags);
> + set_bit(MD_UPDATE_SB_FLAGS, &mddev->flags);
> + }
> + spin_unlock_irq(&conf->device_lock);
> + pr_info("md/raid:%s: setting r5c cache mode to %d: %s\n",
> + mdname(mddev), val, r5c_state_str[val]);
> + return len;
> +}
Is this safe? Eg, switching from writethrough to writeback or vice versa in
runtime with IO running? I think you'd better call mddev_suspend/mddev_resume.
Thanks,
Shaohua
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