-----Original Message-----
From: Alexander Atanasov <alexander.atana...@virtuozzo.com>
Date: Tuesday, 18 October 2022 at 9:12 PM
To: Kui Liu <kui....@acronis.com>, Konstantin Khorenko
<khore...@virtuozzo.com>, Alexey Kuznetsov <kuz...@acronis.com>
Cc: Devel <devel@openvz.org>
Subject: Re: [Devel] [PATCH RH9] dm-ploop: port the standby mode feature.
On 18.10.22 15:47, Kui Liu wrote:
> Hello,
>
> -----Original Message-----
> From: Alexander Atanasov <alexander.atana...@virtuozzo.com>
> Date: Tuesday, 18 October 2022 at 7:40 PM
> To: Kui Liu <kui....@acronis.com>, Konstantin Khorenko
<khore...@virtuozzo.com>, Alexey Kuznetsov <kuz...@acronis.com>
> Cc: Devel <devel@openvz.org>
> Subject: Re: [Devel] [PATCH RH9] dm-ploop: port the standby mode feature.
> >
> > diff --git a/drivers/md/dm-ploop-target.c
b/drivers/md/dm-ploop-target.c
> > index 4f7dc36eee0c..dda0fe957c1f 100644
> > --- a/drivers/md/dm-ploop-target.c
> > +++ b/drivers/md/dm-ploop-target.c
> > @@ -21,6 +21,7 @@
> > #include <linux/uio.h>
> > #include <linux/error-injection.h>
> > #include "dm-ploop.h"
> > +#include "dm-core.h"
> >
> > #define DM_MSG_PREFIX "ploop"
> >
> > @@ -32,6 +33,7 @@
MODULE_PARM_DESC(ignore_signature_disk_in_use,
> > static struct kmem_cache *prq_cache;
> > static struct kmem_cache *pio_cache;
> > struct kmem_cache *cow_cache;
> > +extern struct static_key ploop_standby_check;
> >
> > static void ploop_aio_do_completion(struct pio *pio)
> > {
> > @@ -406,6 +408,14 @@ static int ploop_ctr(struct dm_target
*ti, unsigned
> > int argc, char **argv)
> > ti->private = ploop;
> > ploop->ti = ti;
> >
> > + if (blk_queue_standby_en(ploop_blk_queue(ploop))) {
> > + blk_queue_flag_clear(QUEUE_FLAG_STANDBY,
ploop_blk_queue(ploop));
> > + if (!static_key_enabled(&ploop_standby_check)) {
> > + static_key_enable(&ploop_standby_check);
> > + pr_info("ploop: standby mode check
enabled\n");
> > + }
> > + }
> > +
> >
> > [LIU]: This may not work, because normally a ploop device is
created first before being attached to SCST, which means 'ploop_ctr' is called
before QUEUE_FLAG_STANDBY_EN can be set. We need to put "
static_key_enable(&ploop_standby_check))" somewhere else.
>
> I am not sure i undestand that correctly but dm-ploop maps the ploop
> device over existing device. It first opens the files that are on the
> existing device then passes the fds to dm-ploop. To do this the
target
> must be up and running. device mapper setups the table before calling
> the ploop ctr. You already checked the queue lifecycle.
> Is there any other precodition for the target to set the EN flag?
>
>
> There is one more alternative to pass the stanby enable flag enable
from
> userspace .
>
> [LIU]: well, you are right about the dm-ploop setup process. However SCST
can only set the EN flag after the ploop device is assigned to
> SCST, before which the table could have been loaded. So if setup sequence
is 1) create ploop device -> 2) load table -> 3) assign ploop
> device to SCST, then the outer if condition won't be true, hence not
triggering static_key_enable().
> My concern is this should not be the only place where the static key can
be enabled. Now that there is one more alternative in user space
> , above code is OK.
Ok - for the user space there are two options:
1. add an argument to enable at creation time
2. command standby_enable /if using the enable it is possible to
implement a disable command too/.
I prefer the second approach but let's hear other opinions too.
And yes we can possibly do both but is there a use case ?
[LIU]: Since the static key is a global option, I also think the second
approach is better.
In case of nodes with vStorage + ploop + iSCSI setup, we just need to enable
the static
key early in system init or iSCSI service init. I don't think it is necessary
to implement both.
> > +++ b/include/linux/blkdev.h
> > @@ -434,6 +434,8 @@ struct request_queue {
> > #define QUEUE_FLAG_RQ_ALLOC_TIME 27 /* record
rq->alloc_time_ns */
> > #define QUEUE_FLAG_HCTX_ACTIVE 28 /* at least one
blk-mq hctx is active */
> > #define QUEUE_FLAG_NOWAIT 29 /* device supports
NOWAIT */
> > +#define QUEUE_FLAG_STANDBY 30 /* unable to handle
read/write
> > requests */
> > +#define QUEUE_FLAG_STANDBY_EN 30 /* enable standby
queue flag */
> >
> > [LIU]: Should use a different number for QUEUE_FLAG_STANDBY_EN.
>
> yes, definitely
>
> >
> > #define QUEUE_FLAG_MQ_DEFAULT ((1 <<
QUEUE_FLAG_IO_STAT) | \
> > (1 << QUEUE_FLAG_SAME_COMP) |
\
> > @@ -480,6 +482,8 @@ bool blk_queue_flag_test_and_set(unsigned
int flag,
> > struct request_queue *q);
> > #define blk_queue_fua(q) test_bit(QUEUE_FLAG_FUA,
&(q)->queue_flags)
> > #define blk_queue_registered(q)
test_bit(QUEUE_FLAG_REGISTERED,
> > &(q)->queue_flags)
> > #define blk_queue_nowait(q) test_bit(QUEUE_FLAG_NOWAIT,
&(q)->queue_flags)
> > +#define blk_queue_standby(q) test_bit(QUEUE_FLAG_STANDBY,
> > &(q)->queue_flags)
> > +#define blk_queue_standby_en(q)
test_bit(QUEUE_FLAG_STANDBY_EN,
> > &(q)->queue_flags)
> >
> > extern void blk_set_pm_only(struct request_queue *q);
> > extern void blk_clear_pm_only(struct request_queue *q);
> >
> >
> >
>
> --
> Regards,
> Alexander Atanasov
>
>
--
Regards,
Alexander Atanasov
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