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Date: Tue, 08 Oct 2013 15:05:46 +0100
From: =?ISO-8859-1?Q?P=E1draig_Brady?= <P@draigBrady.com>
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To: "Richard W.M. Jones" <rjones@redhat.com>
CC: util-linux@vger.kernel.org
Subject: Re: [PATCH] blockdev: Remove the --setbsz (set blocksize) option
 which has never worked.
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On 10/08/2013 09:54 AM, Richard W.M. Jones wrote:
> From: "Richard W.M. Jones" <rjones@redhat.com>
> 
> This option has never worked.  If you try setting the block size on a
> block device, and then read it using --getbsz, you will see that the
> block size never changes.
> 
> The reason for this is because the block size is specific to the
> current file descriptor opening the block device, so the change of
> block size only persists for as long as blockdev has the device open,
> and is lost once blockdev exits.
> 
> Also the block size is not really used anywhere.  Filesystems, for
> example, have their own idea of block size and ignore this setting
> completely.
> 
> (Thanks Masayoshi Mizuma for diagnosing the problem)
> 
> Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> ---
>  bash-completion/blockdev | 7 +------
>  disk-utils/blockdev.8    | 2 --
>  disk-utils/blockdev.c    | 7 -------
>  3 files changed, 1 insertion(+), 15 deletions(-)
> 
> diff --git a/bash-completion/blockdev b/bash-completion/blockdev
> index ce986cb..5889955 100644
> --- a/bash-completion/blockdev
> +++ b/bash-completion/blockdev
> @@ -19,7 +19,6 @@ _blockdev_module()
>  		--getalignoff
>  		--getmaxsect
>  		--getbsz
> -		--setbsz
>  		--getsize64
>  		--setra
>  		--getra
> @@ -29,11 +28,7 @@ _blockdev_module()
>  		--rereadpt
>  		$DEVS"
>  	case $prev in
> -		'--setbsz')
> -			COMPREPLY=( $(compgen -W "bytes" -- $cur) )
> -			return 0
> -			;;
> -		'--setbsz'|'--setfra')
> +		'--setfra')
>  			COMPREPLY=( $(compgen -W "sectors" -- $cur) )
>  			return 0
>  			;;
> diff --git a/disk-utils/blockdev.8 b/disk-utils/blockdev.8
> index 2b3d64c..6ab4324 100644
> --- a/disk-utils/blockdev.8
> +++ b/disk-utils/blockdev.8
> @@ -67,8 +67,6 @@ Print sectorsize in bytes - usually 512.
>  Get size in 512-byte sectors.
>  .IP "\fB\-\-rereadpt\fP"
>  Reread partition table
> -.IP "\fB\-\-setbsz\fP \fIbytes\fP"
> -Set blocksize.
>  .IP "\fB\-\-setfra\fP \fIsectors\fP"
>  Set filesystem readahead (same like --setra on 2.6 kernels).
>  .IP "\fB\-\-setra\fP \fIsectors\fP"
> diff --git a/disk-utils/blockdev.c b/disk-utils/blockdev.c
> index 4543818..dc02d48 100644
> --- a/disk-utils/blockdev.c
> +++ b/disk-utils/blockdev.c
> @@ -122,13 +122,6 @@ static const struct bdc bdcms[] =
>  		.argval = -1,
>  		.help = N_("get blocksize")
>  	},{
> -		IOCTL_ENTRY(BLKBSZSET),
> -		.name = "--setbsz",
> -		.argname = "<bytes>",
> -		.argtype = ARG_INT,
> -		.flags = FL_NORESULT,
> -	        .help = N_("set blocksize")
> -	},{
>  		IOCTL_ENTRY(BLKGETSIZE),
>  		.name = "--getsize",
>  		.argtype = ARG_ULONG,
> 

Might one process the adjusted block device in a subshell?

$ (blockdev --setbsz 2048 /dev/stdin; blockdev --getbsz /dev/stdin) < /dev/loop0
2048

cheers,
Pádraig.