[arch-releng] [PATCH 1/1] allow to grow devices

[Gerardo Exequiel Pozzi]

On 08/29/2013 07:31 PM, Gerardo Exequiel Pozzi wrote:
> On 08/29/2013 10:55 AM, Christian Hesse wrote:
>> From: Christian Hesse <mail at eworm.de>
>>
>> actually cowfile_size is limited to values smaller or equal to 100. That
>> way you have to decide at iso build time what size your filesystems should
>> have.
>>
>> I have added a feature to allow values bigger than 100: In this case the
>> read only device is linearly assembled with a sparse file (we do not have
>> to care about size on disk as no write go to this file), this device is
>> used for read only device then. After chroot (or when the system has
>> bootet up) you can grow your filesystem to the new size.
>>
>> Growing the filesystem in initramfs would be possible, but we would have
>> to add userspace utilities (resize2fs, xfs_growfs, ...) there...
>> ---
>>  archiso/initcpio/hooks/archiso | 17 ++++++++++++++++-
>>  1 file changed, 16 insertions(+), 1 deletion(-)
>>
>> diff --git a/archiso/initcpio/hooks/archiso b/archiso/initcpio/hooks/archiso
>> index 66a6273..94d5a99 100644
>> --- a/archiso/initcpio/hooks/archiso
>> +++ b/archiso/initcpio/hooks/archiso
>> @@ -6,13 +6,28 @@ _mnt_fs() {
>>      local img_fullname="${img##*/}";
>>      local img_name="${img_fullname%%.*}"
>>      local dm_snap_name="${dm_snap_prefix}_${img_name}"
>> -    local ro_dev ro_dev_size rw_dev
>> +    local ro_dev ro_dev_size rw_dev rw_dev_size pad_dev pad_dev_size
>>  
>>      ro_dev=$(losetup --find --show --read-only "${img}")
>>      echo ${ro_dev} >> /run/archiso/used_block_devices
>>      ro_dev_size=$(blockdev --getsz ${ro_dev})
>> +
>>      if [[ "${cowfile_size}" == "100" ]]; then
>>          rw_dev_size=${ro_dev_size}
>> +    elif [[ "${cowfile_size}" -gt 100 ]]; then
>> +        pad_dev_size=$((ro_dev_size/100*cowfile_size - ro_dev_size))
>> +        dd of="/run/archiso/cowspace/${cow_directory}/${img_name}.pad" count=0 seek=${pad_dev_size} &> /dev/null
>> +        pad_dev=$(losetup --find --show --read-only "/run/archiso/cowspace/${cow_directory}/${img_name}.pad")
>> +        echo ${pad_dev} >> /run/archiso/used_block_devices
>> +        # this is just a sparse file that never gets written to, so just delete it
>> +        rm "/run/archiso/cowspace/${cow_directory}/${img_name}.pad"
>> +        echo -e "0 ${ro_dev_size} linear ${ro_dev} 0\n${ro_dev_size} ${pad_dev_size} linear ${pad_dev} 0" | dmsetup create "ro_${dm_snap_name}"
>> +
>> +        ro_dev="/dev/mapper/ro_${dm_snap_name}"
>> +        ro_dev_size="$((ro_dev_size + pad_dev_size))"
>> +        rw_dev_size="${ro_dev_size}"
>> +
>> +        msg ":: Device ${dm_snap_name} has been grown, remember to grow your filesystem!"
>>      else
>>          # size calculation done in this way to avoid integer overflow when ro_dev_size is > 10.2G
>>          rw_dev_size=$((ro_dev_size/100*cowfile_size))
>>
> 
> Too much complex, and some sematics broken (for example, you are mixing
> terms for setting non-cowdevices or storing non-cow file inside
> cowspace, missing proper device shutdown, ...)
> 
> Why not just use a value above 100%? ;)
> 
> Thanks for your interest on improving archiso :)
> 

Ignore me, was a bad smart answer, since you want to increse the size of
the device!

In any case, the semantics of cowfile_size should not be changed. You
can add another parameter like grow_ro_dev_size=, also should be ensure
the proper device shutdown and persistence.

We are reaching 3.11 and still no "overlayfs" :( (was promised for 3.10,
3.2, ...)

But before adding this I want an opinion from Thomas.

-- 
Gerardo Exequiel Pozzi
\cos^2\alpha + \sin^2\alpha = 1

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 555 bytes
Desc: OpenPGP digital signature
URL: <http://mailman.archlinux.org/pipermail/arch-releng/attachments/20130829/a4121eb9/attachment-0001.asc>