On 10/08/2013 09:54 AM, Richard W.M. Jones wrote:
> From: "Richard W.M. Jones" <rjones@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> ---
> 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.
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