Re: [PATCH] btrfs: Add a new mount option to grow the FS to the limit of the device

[Chris Mason <chris.mason@oracle.com>]

On Wed, Aug 04, 2010 at 10:45:00PM +0900, Kyungmin Park wrote:
> On Wed, Aug 4, 2010 at 10:30 PM, Chris Mason <chris.mason@oracle.com>=
 wrote:
> > On Wed, Aug 04, 2010 at 08:34:43PM +0900, Donggeun Kim wrote:
> >> Chris Mason wrote:
> >> > On Mon, Aug 02, 2010 at 05:42:00PM +0900, Donggeun Kim wrote:
> >> >> In some cases, resizing a file system to the maximum device siz=
e is required.
> >> >> When flashing a file system image to a block device,
> >> >> the file system does not fit into the block device's size.
> >> >> Currently, executing 'btrfsctl' application is the only way
> >> >> to grow the file system to the limit of the device.
> >> >> If the mount option which alters the device size of a file syst=
em
> >> >> to the limit of the device is supported,
> >> >> it can be useful regardless of the existence of 'btrfsctl' prog=
ram.
> >> >> This patch allows the file system to grow to the maximum size o=
f the device
> >> >> on mount time.
> >> >> The new mount option name is 'maxsize'.
> >> >
> >> > I think this is a very useful feature, but could you please chan=
ge the
> >> > patch to allow controlling which device is resized?
> >> >
> >> > The ioctl allows you to pass in a device number (where the numbe=
r comes
> >> > from btrfs-show)
> >> >
> >> > Thanks!
> >> >
> >> > -chris
> >> >
> >> I'm sorry not to fully understand your comment.
> >> Do you mean that device file name for being resized is specified a=
fter 'maxsize' mount option?
> >> e.g) #mount -o maxsize=3D/dev/sda1 ...
> >
> > In the resize ioctl you can pass a device number, something like 2:=
max,
> > which allows you to say make device #2 the full size of the device.
> >
> > btrfs-show can be used to find the correct device number for a give=
n
> > disk. =A0We don't use the device name because the scan might have f=
ound a
> > different device name to tie into the FS.
> >
> > Thanks,
> > Chris
>=20
> Before comments this issues. I first explain why this feature impleme=
nted.
>=20
> As you know, we implement the build image from some specific
> directory. the size is maybe small than designed devices. e.g., build
> image got the 400MiB but real device size has more the 8GiB.
> after program the btrfs image, then it will be expanded at first boot=
 only.

Yes, and this makes a lot of sense to me.  I can see how the patch fits
your usage and that you don't need the extra flag to pick a device on
mounting.

>=20
> Initial draft design is that add the some flag at build image. then i=
t
> checks it at first mount time. and expand to device size.
> But after some study we know that btrfs supports resize feature. So w=
e
> implement it as patch.
> Anyway that's our requirement.
>=20
> as you provided usage, can you use the ioctl to achieve this
> requirement? if not, we need to another method.

Yes, the ioctl can currently pick a device to resize.  In your case,
there will only be one device and this isn't an issue.  But, I'd like t=
o
see parity between what the mount option can do and what the ioctl can
do, just so we are a little more consistent.

-chris

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