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Date: Tue, 20 Feb 2024 12:42:50 +0530
From: Ojaswin Mujoo <ojaswin@linux.ibm.com>
To: John Garry <john.g.garry@oracle.com>
Cc: axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me,
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Subject: Re: [PATCH v4 09/11] scsi: scsi_debug: Atomic write support
Message-ID: <ZdRQ8mPGRVidvjQI@li-bb2b2a4c-3307-11b2-a85c-8fa5c3a69313.ibm.com>
References: <20240219130109.341523-1-john.g.garry@oracle.com>
 <20240219130109.341523-10-john.g.garry@oracle.com>
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In-Reply-To: <20240219130109.341523-10-john.g.garry@oracle.com>

On Mon, Feb 19, 2024 at 01:01:07PM +0000, John Garry wrote:
> Add initial support for atomic writes.
> 
> As is standard method, feed device properties via modules param, those
> being:
> - atomic_max_size_blks
> - atomic_alignment_blks
> - atomic_granularity_blks
> - atomic_max_size_with_boundary_blks
> - atomic_max_boundary_blks
> 
> These just match sbc4r22 section 6.6.4 - Block limits VPD page.
> 
> We just support ATOMIC WRITE (16).
> 
> The major change in the driver is how we lock the device for RW accesses.
> 
> Currently the driver uses a per-device lock for accessing device metadata
> and "media" data (calls to do_device_access()) atomically for the duration
> of the whole read/write command.
> 
> This should not suit verifying atomic writes. Reason being that currently
> all reads/writes are atomic, so using atomic writes does not prove
> anything.
> 
> Change device access model to basis that regular writes only atomic on a
> per-sector basis, while reads and atomic writes are fully atomic.
> 
> As mentioned, since accessing metadata and device media is atomic,
> continue to have regular writes involving metadata - like discard or PI -
> as atomic. We can improve this later.
> 
> Currently we only support model where overlapping going reads or writes
> wait for current access to complete before commencing an atomic write.
> This is described in 4.29.3.2 section of the SBC. However, we simplify,
> things and wait for all accesses to complete (when issuing an atomic
> write).
> 
> Signed-off-by: John Garry <john.g.garry@oracle.com>
> ---

<snip>

> +#define DEF_ATOMIC_WR 0

<snip>

> +static unsigned int sdebug_atomic_wr = DEF_ATOMIC_WR;

<snip>

> +MODULE_PARM_DESC(atomic_write, "enable ATOMIC WRITE support, support WRITE ATOMIC(16) (def=1)");
Hi John,

The default value here seems to be 0 and not 1. Got me a bit confused
while testing :) 

Regards,
ojaswin

>  MODULE_PARM_DESC(lowest_aligned, "lowest aligned lba (def=0)");
>  MODULE_PARM_DESC(lun_format, "LUN format: 0->peripheral (def); 1 --> flat address method");
>  MODULE_PARM_DESC(max_luns, "number of LUNs per target to simulate(def=1)");
> @@ -6260,6 +6575,11 @@ MODULE_PARM_DESC(unmap_alignment, "lowest aligned thin provisioning lba (def=0)"
>  MODULE_PARM_DESC(unmap_granularity, "thin provisioning granularity in blocks (def=1)");
>  MODULE_PARM_DESC(unmap_max_blocks, "max # of blocks can be unmapped in one cmd (def=0xffffffff)");
>  MODULE_PARM_DESC(unmap_max_desc, "max # of ranges that can be unmapped in one cmd (def=256)");
> +MODULE_PARM_DESC(atomic_wr_max_length, "max # of blocks can be atomically written in one cmd (def=8192)");
> +MODULE_PARM_DESC(atomic_wr_align, "minimum alignment of atomic write in blocks (def=2)");
> +MODULE_PARM_DESC(atomic_wr_gran, "minimum granularity of atomic write in blocks (def=2)");
> +MODULE_PARM_DESC(atomic_wr_max_length_bndry, "max # of blocks can be atomically written in one cmd with boundary set (def=8192)");
> +MODULE_PARM_DESC(atomic_wr_max_bndry, "max # boundaries per atomic write (def=128)");
>  MODULE_PARM_DESC(uuid_ctl,
>  		 "1->use uuid for lu name, 0->don't, 2->all use same (def=0)");
>  MODULE_PARM_DESC(virtual_gb, "virtual gigabyte (GiB) size (def=0 -> use dev_size_mb)");
> @@ -7406,6 +7726,7 @@ static int __init scsi_debug_init(void)
>  			return -EINVAL;
>  		}
>  	}
> +
>  	xa_init_flags(per_store_ap, XA_FLAGS_ALLOC | XA_FLAGS_LOCK_IRQ);
>  	if (want_store) {
>  		idx = sdebug_add_store();
> @@ -7613,7 +7934,9 @@ static int sdebug_add_store(void)
>  			map_region(sip, 0, 2);
>  	}
>  
> -	rwlock_init(&sip->macc_lck);
> +	rwlock_init(&sip->macc_data_lck);
> +	rwlock_init(&sip->macc_meta_lck);
> +	rwlock_init(&sip->macc_sector_lck);
>  	return (int)n_idx;
>  err:
>  	sdebug_erase_store((int)n_idx, sip);
> -- 
> 2.31.1
>