On Tue, Oct 08, 2013 at 03:05:46PM +0100, Pádraig Brady wrote:
> 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
Yes .. if that was documented anywhere, if it wasn't so obscure, and
if it was useful for anything except changing a handle property that
nothing uses.
There's an informative but unfortunately private exchange on the
subject in this bug:
https://bugzilla.redhat.com/show_bug.cgi?id=1002825
I have asked if we can make the contents of this bug public.
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-top is 'top' for virtual machines. Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://people.redhat.com/~rjones/virt-top
--
To unsubscribe from this list: send the line "unsubscribe util-linux" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
