Forgot to CC Jeff?
On Sat, Dec 12, 2020 at 1:50 AM Sargun Dhillon <sargun@xxxxxxxxx> wrote:
>
> This adds the function errseq_counter_sample to allow for "subscribers"
> to take point-in-time snapshots of the errseq_counter, and store the
> counter + errseq_t.
>
> Signed-off-by: Sargun Dhillon <sargun@xxxxxxxxx>
> ---
> include/linux/errseq.h | 4 ++++
> lib/errseq.c | 51 ++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 55 insertions(+)
>
> diff --git a/include/linux/errseq.h b/include/linux/errseq.h
> index 35818c484290..8998df499a3b 100644
> --- a/include/linux/errseq.h
> +++ b/include/linux/errseq.h
> @@ -25,4 +25,8 @@ errseq_t errseq_set(errseq_t *eseq, int err);
> errseq_t errseq_sample(errseq_t *eseq);
> int errseq_check(errseq_t *eseq, errseq_t since);
> int errseq_check_and_advance(errseq_t *eseq, errseq_t *since);
> +void errseq_counter_sample(errseq_t *dst_errseq, int *dst_errors,
> + struct errseq_counter *counter);
> +int errseq_counter_check(struct errseq_counter *counter, errseq_t errseq_since,
> + int errors_since);
> #endif
> diff --git a/lib/errseq.c b/lib/errseq.c
> index d555e7fc18d2..98fcfafa3d97 100644
> --- a/lib/errseq.c
> +++ b/lib/errseq.c
> @@ -246,3 +246,54 @@ int errseq_check_and_advance(errseq_t *eseq, errseq_t *since)
> return err;
> }
> EXPORT_SYMBOL(errseq_check_and_advance);
> +
> +/**
> + * errseq_counter_sample() - Grab the current errseq_counter value
> + * @dst_errseq: The errseq_t to copy to
> + * @dst_errors: The destination overflow to copy to
> + * @counter: The errseq_counter to copy from
> + *
> + * Grabs a point in time sample of the errseq_counter for latter comparison
> + */
> +void errseq_counter_sample(errseq_t *dst_errseq, int *dst_errors,
Why 2 arguments and not struct errseq_counter *dst_counter?
> + struct errseq_counter *counter)
> +{
> + errseq_t cur;
> +
> + do {
> + cur = READ_ONCE(counter->errseq);
> + *dst_errors = atomic_read(&counter->errors);
> + } while (cur != READ_ONCE(counter->errseq));
This loop seems odd. I think the return value should reflect the fact that
the snapshot failed and let the caller decide if it wants to loop.
And about the one and only introduced caller, I think the answer is that
it shouldn't loop. If volatile overlayfs mount tries to sample the upper sb
error counter and an unseen error exists, I argued before that I think
mount should fail, so that the container orchestrator can decide what to do.
Failure to take an errseq_counter sample means than an unseen error
has been observed at least in the first or second check.
> +
> + /* Clear the seen bit to make checking later easier */
> + *dst_errseq = cur & ~ERRSEQ_SEEN;
> +}
> +EXPORT_SYMBOL(errseq_counter_sample);
> +
> +/**
> + * errseq_counter_check() - Has an error occurred since the sample
> + * @counter: The errseq_counter from which to check.
> + * @errseq_since: The errseq_t sampled with errseq_counter_sample to check
> + * @errors_since: The errors sampled with errseq_counter_sample to check
> + *
> + * Returns: The latest error set in the errseq_t or 0 if there have been none.
> + */
> +int errseq_counter_check(struct errseq_counter *counter, errseq_t errseq_since,
> + int errors_since)
> +{
> + errseq_t cur_errseq;
> + int cur_errors;
> +
> + cur_errors = atomic_read(&counter->errors);
> + /* To match the barrier in errseq_counter_set */
> + smp_rmb();
> +
> + /* Clear / ignore the seen bit as we do at sample time */
> + cur_errseq = READ_ONCE(counter->errseq) & ~ERRSEQ_SEEN;
> +
> + if (cur_errseq == errseq_since && errors_since == cur_errors)
> + return 0;
> +
> + return -(cur_errseq & MAX_ERRNO);
> +}
Same here. Why not pass an errseq_counter_since argument?
Thanks,
Amir.
