[stgt] [PATCH] null backing store

[FUJITA Tomonori]

On Thu, 02 Oct 2008 15:24:08 +0300
Alexander Nezhinsky <nezhinsky at gmail.com> wrote:

> Implements a NULL I/O backing store, which shortcuts all scsi commands
> and returns a success status without actually performing them. 
> Useful for performance measurements, by eliminating or significantly 
> reducing I/O side bottleneck. Not based on bs_threads, commands
> are handled immediately from the context they are submitted from.
> To add a device backed by this, "-E null" should be used with tgtadm,
> also a dummy device name (any string) should be supplied, 
> because bs_null does not use any real devices but the current 
> code won't admit a null-string device name. 
> 
> Signed-off-by: Alexander Nezhinsky <nezhinsky at gmail.com>
> ---
> 
> diff --git a/usr/Makefile b/usr/Makefile
> index 82ddf07..23215ef 100644
> --- a/usr/Makefile
> +++ b/usr/Makefile
> @@ -11,7 +11,7 @@ CFLAGS += -DISCSI
>  TGTD_OBJS += $(addprefix iscsi/, conn.o param.o session.o \
>  		iscsid.o target.o chap.o transport.o iscsi_tcp.o \
>  		isns.o libcrc32c.o)
> -TGTD_OBJS += bs_rdwr.o bs_aio.o
> +TGTD_OBJS += bs_rdwr.o bs_aio.o bs_null.o
>  
>  LIBS += -lcrypto
>  ifneq ($(ISCSI_RDMA),)
> diff --git a/usr/bs_null.c b/usr/bs_null.c
> new file mode 100644
> index 0000000..bb93d38
> --- /dev/null
> +++ b/usr/bs_null.c
> @@ -0,0 +1,103 @@
> +/*
> + * NULL I/O backing store routine
> + *
> + * Copyright (C) 2008 Alexander Nezhinsky <nezhinskyf at gmail.com>
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License as
> + * published by the Free Software Foundation, version 2 of the
> + * License.
> + *
> + * This program is distributed in the hope that it will be useful, but
> + * WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + * General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
> + * 02110-1301 USA
> + */
> +
> +#include <errno.h>
> +#include <inttypes.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +
> +#include "list.h"
> +#include "tgtd.h"
> +#include "scsi.h"
> +#include "bs_thread.h"

No need to include bs_thread.h.


> +#define NULL_BS_DEV_SIZE        (1ULL << 40)
> +
> +int bs_null_cmd_submit(struct scsi_cmd *cmd)
> +{
> +	int result = SAM_STAT_GOOD;
> +	uint16_t asc = 0;
> +	uint8_t key = 0;
> +	uint8_t scb_op = cmd->scb[0];
> +
> +	set_cmd_async(cmd);
> +
> +	if (scb_op == SYNCHRONIZE_CACHE || scb_op == SYNCHRONIZE_CACHE_16) {
> +		if (cmd->scb[1] & 0x2) {
> +			result = SAM_STAT_CHECK_CONDITION;
> +			key = ILLEGAL_REQUEST;
> +			asc = ASC_INVALID_FIELD_IN_CDB;
> +		}
> +	}
> +
> +	scsi_set_result(cmd, result);
> +
> +	if (result != SAM_STAT_GOOD) {
> +		eprintf("io error %p %x %" PRIu64 ", %m\n",
> +			cmd, scb_op, cmd->offset);
> +		sense_data_build(cmd, key, asc);
> +	}
> +
> +	cmd->scsi_cmd_done(cmd, scsi_get_result(cmd));
> +	return 0;
> +}
> +
> +static int bs_null_open(struct scsi_lu *lu, char *path,
> +			int *fd, uint64_t *size)
> +{
> +	*size = NULL_BS_DEV_SIZE;
> +	dprintf("NULL backing store open, size: %" PRIu64 "\n", *size);
> +	return 0;
> +}
> +
> +static void bs_null_close(struct scsi_lu *lu)
> +{
> +}
> +
> +static int bs_null_init(struct scsi_lu *lu)
> +{
> +	return 0;
> +}
> +
> +static void bs_null_exit(struct scsi_lu *lu)
> +{
> +}

No need to define bs_init and bs_exit.
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