TMPFS in kernels

[George Rosamond]

Ian Lepore:
> On Thu, 2014-03-06 at 13:03 +0800, Jia-Shiun Li wrote:
>> On Tue, Mar 4, 2014 at 10:48 PM, Warner Losh <imp at bsdimp.com> wrote:
>>>
>>> On Mar 4, 2014, at 3:30 AM, Jia-Shiun Li <jiashiun at gmail.com> wrote:
>>>
>>>> I remember hacking it a while ago to adopt tmpfs instead on my pxeboot
>>>> test environment. It only requires changing the line mdmfs mounting md to
>>>> 'mount -t tmpfs' (plus mount options), and everything else will work as usual.
>>>
>>> I’ll have to give it a spin on NanoBSD then, at least as an option…
>>>
>>
>> The actual patch & result pasted below to save you some time.
>> Only tested on x86 pxeboot though.
>>
>> -----8<----------8<----------8<-----
>>
>> % diff -bu /usr/src/etc/rc.initdiskless
>> /b/tftpboot/FreeBSD/install/etc/rc.initdiskless
>> --- /usr/src/etc/rc.initdiskless        2013-04-11 21:03:31.000000000 +0800
>> +++ /b/tftpboot/FreeBSD/install/etc/rc.initdiskless     2014-03-06
>> 12:43:47.000000000 +0800
>> @@ -198,7 +198,10 @@
>>  # Create a generic memory disk
>>  #
>>  mount_md() {
>> -    /sbin/mdmfs -S -i 4096 -s $1 -M md $2
>> +#    /sbin/mdmfs -S -i 4096 -s $1 -M md $2
>> +    local tmpfs_size
>> +    tmpfs_size=$(($1 * 1024))
>> +    /sbin/mount -t tmpfs -osize=$tmpfs_size tmpfs $2
>>  }
>>
>>  # Create the memory filesystem if it has not already been created
>>
>> % cat df
>> Filesystem                                    Size    Used   Avail
>> Capacity  Mounted on
>> 192.168.233.1:/b/tftpboot/FreeBSD/install/     29G     17G    9.8G    63%    /
>> devfs                                         1.0K    1.0K      0B
>> 100%    /dev
>> tmpfs                                          10M    2.6M    7.4M
>> 26%    /etc
>> tmpfs                                          10M    180K    9.8M
>> 2%    /var
>> /dev/md0                                       19M     24K     17M
>> 0%    /tmp
>> % cat mount
>> 192.168.233.1:/b/tftpboot/FreeBSD/install/ on / (nfs, read-only)
>> devfs on /dev (devfs, local, multilabel)
>> tmpfs on /etc (tmpfs, local)
>> tmpfs on /var (tmpfs, local)
>> /dev/md0 on /tmp (ufs, local)
>>
>>
>> -Jia-Shiun.
> 
> FYI, I just posted a patchset to freebsd-arch@ and freebsd-rc@ to
> address this in a slightly different way. 
> 
> http://lists.freebsd.org/pipermail/freebsd-arch/2014-March/015141.html
> 
> Basically I updated the mdmfs program to automatically use tmpfs if it's
> available in the kernel and the device name is "auto", along with
> changes to rc.initdiskless and defaults/rc.conf to set the device name
> to "auto" by default.
> 

Cool.  So assume it would then be added to the (new) RPI-B and ALIX
kernels.  Am I correct?

g